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contains another loop, or an instruction. The loop form is substantially more efficient on large loops than the typical code it replaces. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91654 91177308-0d34-0410-b5e6-96231b3b80d8
2730 lines
112 KiB
C++
2730 lines
112 KiB
C++
//===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This transformation analyzes and transforms the induction variables (and
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// computations derived from them) into forms suitable for efficient execution
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// on the target.
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//
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// This pass performs a strength reduction on array references inside loops that
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// have as one or more of their components the loop induction variable, it
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// rewrites expressions to take advantage of scaled-index addressing modes
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// available on the target, and it performs a variety of other optimizations
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// related to loop induction variables.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loop-reduce"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Analysis/IVUsers.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Transforms/Utils/AddrModeMatcher.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/ValueHandle.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetLowering.h"
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#include <algorithm>
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using namespace llvm;
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STATISTIC(NumReduced , "Number of IV uses strength reduced");
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STATISTIC(NumInserted, "Number of PHIs inserted");
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STATISTIC(NumVariable, "Number of PHIs with variable strides");
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STATISTIC(NumEliminated, "Number of strides eliminated");
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STATISTIC(NumShadow, "Number of Shadow IVs optimized");
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STATISTIC(NumImmSunk, "Number of common expr immediates sunk into uses");
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STATISTIC(NumLoopCond, "Number of loop terminating conds optimized");
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STATISTIC(NumCountZero, "Number of count iv optimized to count toward zero");
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static cl::opt<bool> EnableFullLSRMode("enable-full-lsr",
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cl::init(false),
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cl::Hidden);
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namespace {
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struct BasedUser;
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/// IVInfo - This structure keeps track of one IV expression inserted during
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/// StrengthReduceStridedIVUsers. It contains the stride, the common base, as
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/// well as the PHI node and increment value created for rewrite.
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struct IVExpr {
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const SCEV *Stride;
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const SCEV *Base;
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PHINode *PHI;
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IVExpr(const SCEV *const stride, const SCEV *const base, PHINode *phi)
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: Stride(stride), Base(base), PHI(phi) {}
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};
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/// IVsOfOneStride - This structure keeps track of all IV expression inserted
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/// during StrengthReduceStridedIVUsers for a particular stride of the IV.
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struct IVsOfOneStride {
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std::vector<IVExpr> IVs;
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void addIV(const SCEV *const Stride, const SCEV *const Base, PHINode *PHI) {
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IVs.push_back(IVExpr(Stride, Base, PHI));
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}
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};
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class LoopStrengthReduce : public LoopPass {
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IVUsers *IU;
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ScalarEvolution *SE;
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bool Changed;
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/// IVsByStride - Keep track of all IVs that have been inserted for a
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/// particular stride.
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std::map<const SCEV *, IVsOfOneStride> IVsByStride;
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/// DeadInsts - Keep track of instructions we may have made dead, so that
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/// we can remove them after we are done working.
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SmallVector<WeakVH, 16> DeadInsts;
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/// TLI - Keep a pointer of a TargetLowering to consult for determining
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/// transformation profitability.
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const TargetLowering *TLI;
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public:
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static char ID; // Pass ID, replacement for typeid
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explicit LoopStrengthReduce(const TargetLowering *tli = NULL) :
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LoopPass(&ID), TLI(tli) {}
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bool runOnLoop(Loop *L, LPPassManager &LPM);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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// We split critical edges, so we change the CFG. However, we do update
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// many analyses if they are around.
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AU.addPreservedID(LoopSimplifyID);
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AU.addPreserved("loops");
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AU.addPreserved("domfrontier");
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AU.addPreserved("domtree");
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AU.addRequiredID(LoopSimplifyID);
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AU.addRequired<ScalarEvolution>();
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AU.addPreserved<ScalarEvolution>();
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AU.addRequired<IVUsers>();
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AU.addPreserved<IVUsers>();
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}
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private:
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void OptimizeIndvars(Loop *L);
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/// OptimizeLoopTermCond - Change loop terminating condition to use the
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/// postinc iv when possible.
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void OptimizeLoopTermCond(Loop *L);
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/// OptimizeShadowIV - If IV is used in a int-to-float cast
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/// inside the loop then try to eliminate the cast opeation.
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void OptimizeShadowIV(Loop *L);
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/// OptimizeMax - Rewrite the loop's terminating condition
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/// if it uses a max computation.
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ICmpInst *OptimizeMax(Loop *L, ICmpInst *Cond,
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IVStrideUse* &CondUse);
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/// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for
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/// deciding when to exit the loop is used only for that purpose, try to
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/// rearrange things so it counts down to a test against zero.
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bool OptimizeLoopCountIV(Loop *L);
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bool OptimizeLoopCountIVOfStride(const SCEV* &Stride,
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IVStrideUse* &CondUse, Loop *L);
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/// StrengthReduceIVUsersOfStride - Strength reduce all of the users of a
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/// single stride of IV. All of the users may have different starting
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/// values, and this may not be the only stride.
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void StrengthReduceIVUsersOfStride(const SCEV *Stride,
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IVUsersOfOneStride &Uses,
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Loop *L);
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void StrengthReduceIVUsers(Loop *L);
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ICmpInst *ChangeCompareStride(Loop *L, ICmpInst *Cond,
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IVStrideUse* &CondUse,
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const SCEV* &CondStride,
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bool PostPass = false);
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bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse,
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const SCEV* &CondStride);
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bool RequiresTypeConversion(const Type *Ty, const Type *NewTy);
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const SCEV *CheckForIVReuse(bool, bool, bool, const SCEV *,
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IVExpr&, const Type*,
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const std::vector<BasedUser>& UsersToProcess);
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bool ValidScale(bool, int64_t,
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const std::vector<BasedUser>& UsersToProcess);
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bool ValidOffset(bool, int64_t, int64_t,
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const std::vector<BasedUser>& UsersToProcess);
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const SCEV *CollectIVUsers(const SCEV *Stride,
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IVUsersOfOneStride &Uses,
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Loop *L,
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bool &AllUsesAreAddresses,
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bool &AllUsesAreOutsideLoop,
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std::vector<BasedUser> &UsersToProcess);
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bool StrideMightBeShared(const SCEV *Stride, Loop *L, bool CheckPreInc);
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bool ShouldUseFullStrengthReductionMode(
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const std::vector<BasedUser> &UsersToProcess,
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const Loop *L,
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bool AllUsesAreAddresses,
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const SCEV *Stride);
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void PrepareToStrengthReduceFully(
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std::vector<BasedUser> &UsersToProcess,
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const SCEV *Stride,
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const SCEV *CommonExprs,
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const Loop *L,
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SCEVExpander &PreheaderRewriter);
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void PrepareToStrengthReduceFromSmallerStride(
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std::vector<BasedUser> &UsersToProcess,
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Value *CommonBaseV,
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const IVExpr &ReuseIV,
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Instruction *PreInsertPt);
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void PrepareToStrengthReduceWithNewPhi(
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std::vector<BasedUser> &UsersToProcess,
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const SCEV *Stride,
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const SCEV *CommonExprs,
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Value *CommonBaseV,
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Instruction *IVIncInsertPt,
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const Loop *L,
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SCEVExpander &PreheaderRewriter);
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void DeleteTriviallyDeadInstructions();
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};
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}
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char LoopStrengthReduce::ID = 0;
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static RegisterPass<LoopStrengthReduce>
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X("loop-reduce", "Loop Strength Reduction");
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Pass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) {
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return new LoopStrengthReduce(TLI);
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}
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/// DeleteTriviallyDeadInstructions - If any of the instructions is the
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/// specified set are trivially dead, delete them and see if this makes any of
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/// their operands subsequently dead.
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void LoopStrengthReduce::DeleteTriviallyDeadInstructions() {
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while (!DeadInsts.empty()) {
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Instruction *I = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val());
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if (I == 0 || !isInstructionTriviallyDead(I))
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continue;
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for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
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if (Instruction *U = dyn_cast<Instruction>(*OI)) {
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*OI = 0;
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if (U->use_empty())
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DeadInsts.push_back(U);
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}
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I->eraseFromParent();
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Changed = true;
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}
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}
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/// isAddressUse - Returns true if the specified instruction is using the
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/// specified value as an address.
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static bool isAddressUse(Instruction *Inst, Value *OperandVal) {
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bool isAddress = isa<LoadInst>(Inst);
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if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
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if (SI->getOperand(1) == OperandVal)
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isAddress = true;
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} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
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// Addressing modes can also be folded into prefetches and a variety
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// of intrinsics.
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switch (II->getIntrinsicID()) {
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default: break;
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case Intrinsic::prefetch:
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case Intrinsic::x86_sse2_loadu_dq:
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case Intrinsic::x86_sse2_loadu_pd:
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case Intrinsic::x86_sse_loadu_ps:
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case Intrinsic::x86_sse_storeu_ps:
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case Intrinsic::x86_sse2_storeu_pd:
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case Intrinsic::x86_sse2_storeu_dq:
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case Intrinsic::x86_sse2_storel_dq:
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if (II->getOperand(1) == OperandVal)
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isAddress = true;
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break;
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}
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}
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return isAddress;
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}
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/// getAccessType - Return the type of the memory being accessed.
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static const Type *getAccessType(const Instruction *Inst) {
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const Type *AccessTy = Inst->getType();
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if (const StoreInst *SI = dyn_cast<StoreInst>(Inst))
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AccessTy = SI->getOperand(0)->getType();
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else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
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// Addressing modes can also be folded into prefetches and a variety
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// of intrinsics.
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switch (II->getIntrinsicID()) {
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default: break;
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case Intrinsic::x86_sse_storeu_ps:
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case Intrinsic::x86_sse2_storeu_pd:
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case Intrinsic::x86_sse2_storeu_dq:
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case Intrinsic::x86_sse2_storel_dq:
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AccessTy = II->getOperand(1)->getType();
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break;
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}
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}
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return AccessTy;
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}
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namespace {
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/// BasedUser - For a particular base value, keep information about how we've
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/// partitioned the expression so far.
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struct BasedUser {
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/// Base - The Base value for the PHI node that needs to be inserted for
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/// this use. As the use is processed, information gets moved from this
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/// field to the Imm field (below). BasedUser values are sorted by this
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/// field.
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const SCEV *Base;
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/// Inst - The instruction using the induction variable.
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Instruction *Inst;
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/// OperandValToReplace - The operand value of Inst to replace with the
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/// EmittedBase.
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Value *OperandValToReplace;
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/// Imm - The immediate value that should be added to the base immediately
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/// before Inst, because it will be folded into the imm field of the
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/// instruction. This is also sometimes used for loop-variant values that
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/// must be added inside the loop.
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const SCEV *Imm;
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/// Phi - The induction variable that performs the striding that
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/// should be used for this user.
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PHINode *Phi;
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// isUseOfPostIncrementedValue - True if this should use the
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// post-incremented version of this IV, not the preincremented version.
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// This can only be set in special cases, such as the terminating setcc
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// instruction for a loop and uses outside the loop that are dominated by
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// the loop.
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bool isUseOfPostIncrementedValue;
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BasedUser(IVStrideUse &IVSU, ScalarEvolution *se)
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: Base(IVSU.getOffset()), Inst(IVSU.getUser()),
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OperandValToReplace(IVSU.getOperandValToReplace()),
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Imm(se->getIntegerSCEV(0, Base->getType())),
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isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue()) {}
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// Once we rewrite the code to insert the new IVs we want, update the
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// operands of Inst to use the new expression 'NewBase', with 'Imm' added
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// to it.
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void RewriteInstructionToUseNewBase(const SCEV *NewBase,
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Instruction *InsertPt,
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SCEVExpander &Rewriter, Loop *L, Pass *P,
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SmallVectorImpl<WeakVH> &DeadInsts,
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ScalarEvolution *SE);
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Value *InsertCodeForBaseAtPosition(const SCEV *NewBase,
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const Type *Ty,
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SCEVExpander &Rewriter,
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Instruction *IP,
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ScalarEvolution *SE);
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void dump() const;
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};
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}
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void BasedUser::dump() const {
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errs() << " Base=" << *Base;
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errs() << " Imm=" << *Imm;
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errs() << " Inst: " << *Inst;
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}
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Value *BasedUser::InsertCodeForBaseAtPosition(const SCEV *NewBase,
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const Type *Ty,
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SCEVExpander &Rewriter,
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Instruction *IP,
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ScalarEvolution *SE) {
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Value *Base = Rewriter.expandCodeFor(NewBase, 0, IP);
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// Wrap the base in a SCEVUnknown so that ScalarEvolution doesn't try to
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// re-analyze it.
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const SCEV *NewValSCEV = SE->getUnknown(Base);
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// Always emit the immediate into the same block as the user.
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NewValSCEV = SE->getAddExpr(NewValSCEV, Imm);
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return Rewriter.expandCodeFor(NewValSCEV, Ty, IP);
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}
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// Once we rewrite the code to insert the new IVs we want, update the
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// operands of Inst to use the new expression 'NewBase', with 'Imm' added
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// to it. NewBasePt is the last instruction which contributes to the
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// value of NewBase in the case that it's a diffferent instruction from
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// the PHI that NewBase is computed from, or null otherwise.
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//
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void BasedUser::RewriteInstructionToUseNewBase(const SCEV *NewBase,
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Instruction *NewBasePt,
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SCEVExpander &Rewriter, Loop *L, Pass *P,
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SmallVectorImpl<WeakVH> &DeadInsts,
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ScalarEvolution *SE) {
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if (!isa<PHINode>(Inst)) {
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// By default, insert code at the user instruction.
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BasicBlock::iterator InsertPt = Inst;
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// However, if the Operand is itself an instruction, the (potentially
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// complex) inserted code may be shared by many users. Because of this, we
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// want to emit code for the computation of the operand right before its old
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// computation. This is usually safe, because we obviously used to use the
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// computation when it was computed in its current block. However, in some
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// cases (e.g. use of a post-incremented induction variable) the NewBase
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// value will be pinned to live somewhere after the original computation.
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// In this case, we have to back off.
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//
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// If this is a use outside the loop (which means after, since it is based
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// on a loop indvar) we use the post-incremented value, so that we don't
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// artificially make the preinc value live out the bottom of the loop.
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if (!isUseOfPostIncrementedValue && L->contains(Inst)) {
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if (NewBasePt && isa<PHINode>(OperandValToReplace)) {
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InsertPt = NewBasePt;
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++InsertPt;
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} else if (Instruction *OpInst
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= dyn_cast<Instruction>(OperandValToReplace)) {
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InsertPt = OpInst;
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while (isa<PHINode>(InsertPt)) ++InsertPt;
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}
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}
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Value *NewVal = InsertCodeForBaseAtPosition(NewBase,
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OperandValToReplace->getType(),
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Rewriter, InsertPt, SE);
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// Replace the use of the operand Value with the new Phi we just created.
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Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
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DEBUG(errs() << " Replacing with ");
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DEBUG(WriteAsOperand(errs(), NewVal, /*PrintType=*/false));
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DEBUG(errs() << ", which has value " << *NewBase << " plus IMM "
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<< *Imm << "\n");
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return;
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}
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// PHI nodes are more complex. We have to insert one copy of the NewBase+Imm
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// expression into each operand block that uses it. Note that PHI nodes can
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// have multiple entries for the same predecessor. We use a map to make sure
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// that a PHI node only has a single Value* for each predecessor (which also
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// prevents us from inserting duplicate code in some blocks).
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DenseMap<BasicBlock*, Value*> InsertedCode;
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PHINode *PN = cast<PHINode>(Inst);
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
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if (PN->getIncomingValue(i) == OperandValToReplace) {
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// If the original expression is outside the loop, put the replacement
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// code in the same place as the original expression,
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// which need not be an immediate predecessor of this PHI. This way we
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// need only one copy of it even if it is referenced multiple times in
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// the PHI. We don't do this when the original expression is inside the
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// loop because multiple copies sometimes do useful sinking of code in
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// that case(?).
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Instruction *OldLoc = dyn_cast<Instruction>(OperandValToReplace);
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BasicBlock *PHIPred = PN->getIncomingBlock(i);
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if (L->contains(OldLoc)) {
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// If this is a critical edge, split the edge so that we do not insert
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// the code on all predecessor/successor paths. We do this unless this
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// is the canonical backedge for this loop, as this can make some
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// inserted code be in an illegal position.
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if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 &&
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!isa<IndirectBrInst>(PHIPred->getTerminator()) &&
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(PN->getParent() != L->getHeader() || !L->contains(PHIPred))) {
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// First step, split the critical edge.
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BasicBlock *NewBB = SplitCriticalEdge(PHIPred, PN->getParent(),
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P, false);
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// Next step: move the basic block. In particular, if the PHI node
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// is outside of the loop, and PredTI is in the loop, we want to
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// move the block to be immediately before the PHI block, not
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// immediately after PredTI.
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if (L->contains(PHIPred) && !L->contains(PN))
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NewBB->moveBefore(PN->getParent());
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// Splitting the edge can reduce the number of PHI entries we have.
|
|
e = PN->getNumIncomingValues();
|
|
PHIPred = NewBB;
|
|
i = PN->getBasicBlockIndex(PHIPred);
|
|
}
|
|
}
|
|
Value *&Code = InsertedCode[PHIPred];
|
|
if (!Code) {
|
|
// Insert the code into the end of the predecessor block.
|
|
Instruction *InsertPt = (L->contains(OldLoc)) ?
|
|
PHIPred->getTerminator() :
|
|
OldLoc->getParent()->getTerminator();
|
|
Code = InsertCodeForBaseAtPosition(NewBase, PN->getType(),
|
|
Rewriter, InsertPt, SE);
|
|
|
|
DEBUG(errs() << " Changing PHI use to ");
|
|
DEBUG(WriteAsOperand(errs(), Code, /*PrintType=*/false));
|
|
DEBUG(errs() << ", which has value " << *NewBase << " plus IMM "
|
|
<< *Imm << "\n");
|
|
}
|
|
|
|
// Replace the use of the operand Value with the new Phi we just created.
|
|
PN->setIncomingValue(i, Code);
|
|
Rewriter.clear();
|
|
}
|
|
}
|
|
|
|
// PHI node might have become a constant value after SplitCriticalEdge.
|
|
DeadInsts.push_back(Inst);
|
|
}
|
|
|
|
|
|
/// fitsInAddressMode - Return true if V can be subsumed within an addressing
|
|
/// mode, and does not need to be put in a register first.
|
|
static bool fitsInAddressMode(const SCEV *V, const Type *AccessTy,
|
|
const TargetLowering *TLI, bool HasBaseReg) {
|
|
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) {
|
|
int64_t VC = SC->getValue()->getSExtValue();
|
|
if (TLI) {
|
|
TargetLowering::AddrMode AM;
|
|
AM.BaseOffs = VC;
|
|
AM.HasBaseReg = HasBaseReg;
|
|
return TLI->isLegalAddressingMode(AM, AccessTy);
|
|
} else {
|
|
// Defaults to PPC. PPC allows a sign-extended 16-bit immediate field.
|
|
return (VC > -(1 << 16) && VC < (1 << 16)-1);
|
|
}
|
|
}
|
|
|
|
if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V))
|
|
if (GlobalValue *GV = dyn_cast<GlobalValue>(SU->getValue())) {
|
|
if (TLI) {
|
|
TargetLowering::AddrMode AM;
|
|
AM.BaseGV = GV;
|
|
AM.HasBaseReg = HasBaseReg;
|
|
return TLI->isLegalAddressingMode(AM, AccessTy);
|
|
} else {
|
|
// Default: assume global addresses are not legal.
|
|
}
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// MoveLoopVariantsToImmediateField - Move any subexpressions from Val that are
|
|
/// loop varying to the Imm operand.
|
|
static void MoveLoopVariantsToImmediateField(const SCEV *&Val, const SCEV *&Imm,
|
|
Loop *L, ScalarEvolution *SE) {
|
|
if (Val->isLoopInvariant(L)) return; // Nothing to do.
|
|
|
|
if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
|
|
SmallVector<const SCEV *, 4> NewOps;
|
|
NewOps.reserve(SAE->getNumOperands());
|
|
|
|
for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
|
|
if (!SAE->getOperand(i)->isLoopInvariant(L)) {
|
|
// If this is a loop-variant expression, it must stay in the immediate
|
|
// field of the expression.
|
|
Imm = SE->getAddExpr(Imm, SAE->getOperand(i));
|
|
} else {
|
|
NewOps.push_back(SAE->getOperand(i));
|
|
}
|
|
|
|
if (NewOps.empty())
|
|
Val = SE->getIntegerSCEV(0, Val->getType());
|
|
else
|
|
Val = SE->getAddExpr(NewOps);
|
|
} else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
|
|
// Try to pull immediates out of the start value of nested addrec's.
|
|
const SCEV *Start = SARE->getStart();
|
|
MoveLoopVariantsToImmediateField(Start, Imm, L, SE);
|
|
|
|
SmallVector<const SCEV *, 4> Ops(SARE->op_begin(), SARE->op_end());
|
|
Ops[0] = Start;
|
|
Val = SE->getAddRecExpr(Ops, SARE->getLoop());
|
|
} else {
|
|
// Otherwise, all of Val is variant, move the whole thing over.
|
|
Imm = SE->getAddExpr(Imm, Val);
|
|
Val = SE->getIntegerSCEV(0, Val->getType());
|
|
}
|
|
}
|
|
|
|
|
|
/// MoveImmediateValues - Look at Val, and pull out any additions of constants
|
|
/// that can fit into the immediate field of instructions in the target.
|
|
/// Accumulate these immediate values into the Imm value.
|
|
static void MoveImmediateValues(const TargetLowering *TLI,
|
|
const Type *AccessTy,
|
|
const SCEV *&Val, const SCEV *&Imm,
|
|
bool isAddress, Loop *L,
|
|
ScalarEvolution *SE) {
|
|
if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
|
|
SmallVector<const SCEV *, 4> NewOps;
|
|
NewOps.reserve(SAE->getNumOperands());
|
|
|
|
for (unsigned i = 0; i != SAE->getNumOperands(); ++i) {
|
|
const SCEV *NewOp = SAE->getOperand(i);
|
|
MoveImmediateValues(TLI, AccessTy, NewOp, Imm, isAddress, L, SE);
|
|
|
|
if (!NewOp->isLoopInvariant(L)) {
|
|
// If this is a loop-variant expression, it must stay in the immediate
|
|
// field of the expression.
|
|
Imm = SE->getAddExpr(Imm, NewOp);
|
|
} else {
|
|
NewOps.push_back(NewOp);
|
|
}
|
|
}
|
|
|
|
if (NewOps.empty())
|
|
Val = SE->getIntegerSCEV(0, Val->getType());
|
|
else
|
|
Val = SE->getAddExpr(NewOps);
|
|
return;
|
|
} else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
|
|
// Try to pull immediates out of the start value of nested addrec's.
|
|
const SCEV *Start = SARE->getStart();
|
|
MoveImmediateValues(TLI, AccessTy, Start, Imm, isAddress, L, SE);
|
|
|
|
if (Start != SARE->getStart()) {
|
|
SmallVector<const SCEV *, 4> Ops(SARE->op_begin(), SARE->op_end());
|
|
Ops[0] = Start;
|
|
Val = SE->getAddRecExpr(Ops, SARE->getLoop());
|
|
}
|
|
return;
|
|
} else if (const SCEVMulExpr *SME = dyn_cast<SCEVMulExpr>(Val)) {
|
|
// Transform "8 * (4 + v)" -> "32 + 8*V" if "32" fits in the immed field.
|
|
if (isAddress &&
|
|
fitsInAddressMode(SME->getOperand(0), AccessTy, TLI, false) &&
|
|
SME->getNumOperands() == 2 && SME->isLoopInvariant(L)) {
|
|
|
|
const SCEV *SubImm = SE->getIntegerSCEV(0, Val->getType());
|
|
const SCEV *NewOp = SME->getOperand(1);
|
|
MoveImmediateValues(TLI, AccessTy, NewOp, SubImm, isAddress, L, SE);
|
|
|
|
// If we extracted something out of the subexpressions, see if we can
|
|
// simplify this!
|
|
if (NewOp != SME->getOperand(1)) {
|
|
// Scale SubImm up by "8". If the result is a target constant, we are
|
|
// good.
|
|
SubImm = SE->getMulExpr(SubImm, SME->getOperand(0));
|
|
if (fitsInAddressMode(SubImm, AccessTy, TLI, false)) {
|
|
// Accumulate the immediate.
|
|
Imm = SE->getAddExpr(Imm, SubImm);
|
|
|
|
// Update what is left of 'Val'.
|
|
Val = SE->getMulExpr(SME->getOperand(0), NewOp);
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Loop-variant expressions must stay in the immediate field of the
|
|
// expression.
|
|
if ((isAddress && fitsInAddressMode(Val, AccessTy, TLI, false)) ||
|
|
!Val->isLoopInvariant(L)) {
|
|
Imm = SE->getAddExpr(Imm, Val);
|
|
Val = SE->getIntegerSCEV(0, Val->getType());
|
|
return;
|
|
}
|
|
|
|
// Otherwise, no immediates to move.
|
|
}
|
|
|
|
static void MoveImmediateValues(const TargetLowering *TLI,
|
|
Instruction *User,
|
|
const SCEV *&Val, const SCEV *&Imm,
|
|
bool isAddress, Loop *L,
|
|
ScalarEvolution *SE) {
|
|
const Type *AccessTy = getAccessType(User);
|
|
MoveImmediateValues(TLI, AccessTy, Val, Imm, isAddress, L, SE);
|
|
}
|
|
|
|
/// SeparateSubExprs - Decompose Expr into all of the subexpressions that are
|
|
/// added together. This is used to reassociate common addition subexprs
|
|
/// together for maximal sharing when rewriting bases.
|
|
static void SeparateSubExprs(SmallVector<const SCEV *, 16> &SubExprs,
|
|
const SCEV *Expr,
|
|
ScalarEvolution *SE) {
|
|
if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) {
|
|
for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
|
|
SeparateSubExprs(SubExprs, AE->getOperand(j), SE);
|
|
} else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) {
|
|
const SCEV *Zero = SE->getIntegerSCEV(0, Expr->getType());
|
|
if (SARE->getOperand(0) == Zero) {
|
|
SubExprs.push_back(Expr);
|
|
} else {
|
|
// Compute the addrec with zero as its base.
|
|
SmallVector<const SCEV *, 4> Ops(SARE->op_begin(), SARE->op_end());
|
|
Ops[0] = Zero; // Start with zero base.
|
|
SubExprs.push_back(SE->getAddRecExpr(Ops, SARE->getLoop()));
|
|
|
|
|
|
SeparateSubExprs(SubExprs, SARE->getOperand(0), SE);
|
|
}
|
|
} else if (!Expr->isZero()) {
|
|
// Do not add zero.
|
|
SubExprs.push_back(Expr);
|
|
}
|
|
}
|
|
|
|
// This is logically local to the following function, but C++ says we have
|
|
// to make it file scope.
|
|
struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; };
|
|
|
|
/// RemoveCommonExpressionsFromUseBases - Look through all of the Bases of all
|
|
/// the Uses, removing any common subexpressions, except that if all such
|
|
/// subexpressions can be folded into an addressing mode for all uses inside
|
|
/// the loop (this case is referred to as "free" in comments herein) we do
|
|
/// not remove anything. This looks for things like (a+b+c) and
|
|
/// (a+c+d) and computes the common (a+c) subexpression. The common expression
|
|
/// is *removed* from the Bases and returned.
|
|
static const SCEV *
|
|
RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses,
|
|
ScalarEvolution *SE, Loop *L,
|
|
const TargetLowering *TLI) {
|
|
unsigned NumUses = Uses.size();
|
|
|
|
// Only one use? This is a very common case, so we handle it specially and
|
|
// cheaply.
|
|
const SCEV *Zero = SE->getIntegerSCEV(0, Uses[0].Base->getType());
|
|
const SCEV *Result = Zero;
|
|
const SCEV *FreeResult = Zero;
|
|
if (NumUses == 1) {
|
|
// If the use is inside the loop, use its base, regardless of what it is:
|
|
// it is clearly shared across all the IV's. If the use is outside the loop
|
|
// (which means after it) we don't want to factor anything *into* the loop,
|
|
// so just use 0 as the base.
|
|
if (L->contains(Uses[0].Inst))
|
|
std::swap(Result, Uses[0].Base);
|
|
return Result;
|
|
}
|
|
|
|
// To find common subexpressions, count how many of Uses use each expression.
|
|
// If any subexpressions are used Uses.size() times, they are common.
|
|
// Also track whether all uses of each expression can be moved into an
|
|
// an addressing mode "for free"; such expressions are left within the loop.
|
|
// struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; };
|
|
std::map<const SCEV *, SubExprUseData> SubExpressionUseData;
|
|
|
|
// UniqueSubExprs - Keep track of all of the subexpressions we see in the
|
|
// order we see them.
|
|
SmallVector<const SCEV *, 16> UniqueSubExprs;
|
|
|
|
SmallVector<const SCEV *, 16> SubExprs;
|
|
unsigned NumUsesInsideLoop = 0;
|
|
for (unsigned i = 0; i != NumUses; ++i) {
|
|
// If the user is outside the loop, just ignore it for base computation.
|
|
// Since the user is outside the loop, it must be *after* the loop (if it
|
|
// were before, it could not be based on the loop IV). We don't want users
|
|
// after the loop to affect base computation of values *inside* the loop,
|
|
// because we can always add their offsets to the result IV after the loop
|
|
// is done, ensuring we get good code inside the loop.
|
|
if (!L->contains(Uses[i].Inst))
|
|
continue;
|
|
NumUsesInsideLoop++;
|
|
|
|
// If the base is zero (which is common), return zero now, there are no
|
|
// CSEs we can find.
|
|
if (Uses[i].Base == Zero) return Zero;
|
|
|
|
// If this use is as an address we may be able to put CSEs in the addressing
|
|
// mode rather than hoisting them.
|
|
bool isAddrUse = isAddressUse(Uses[i].Inst, Uses[i].OperandValToReplace);
|
|
// We may need the AccessTy below, but only when isAddrUse, so compute it
|
|
// only in that case.
|
|
const Type *AccessTy = 0;
|
|
if (isAddrUse)
|
|
AccessTy = getAccessType(Uses[i].Inst);
|
|
|
|
// Split the expression into subexprs.
|
|
SeparateSubExprs(SubExprs, Uses[i].Base, SE);
|
|
// Add one to SubExpressionUseData.Count for each subexpr present, and
|
|
// if the subexpr is not a valid immediate within an addressing mode use,
|
|
// set SubExpressionUseData.notAllUsesAreFree. We definitely want to
|
|
// hoist these out of the loop (if they are common to all uses).
|
|
for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) {
|
|
if (++SubExpressionUseData[SubExprs[j]].Count == 1)
|
|
UniqueSubExprs.push_back(SubExprs[j]);
|
|
if (!isAddrUse || !fitsInAddressMode(SubExprs[j], AccessTy, TLI, false))
|
|
SubExpressionUseData[SubExprs[j]].notAllUsesAreFree = true;
|
|
}
|
|
SubExprs.clear();
|
|
}
|
|
|
|
// Now that we know how many times each is used, build Result. Iterate over
|
|
// UniqueSubexprs so that we have a stable ordering.
|
|
for (unsigned i = 0, e = UniqueSubExprs.size(); i != e; ++i) {
|
|
std::map<const SCEV *, SubExprUseData>::iterator I =
|
|
SubExpressionUseData.find(UniqueSubExprs[i]);
|
|
assert(I != SubExpressionUseData.end() && "Entry not found?");
|
|
if (I->second.Count == NumUsesInsideLoop) { // Found CSE!
|
|
if (I->second.notAllUsesAreFree)
|
|
Result = SE->getAddExpr(Result, I->first);
|
|
else
|
|
FreeResult = SE->getAddExpr(FreeResult, I->first);
|
|
} else
|
|
// Remove non-cse's from SubExpressionUseData.
|
|
SubExpressionUseData.erase(I);
|
|
}
|
|
|
|
if (FreeResult != Zero) {
|
|
// We have some subexpressions that can be subsumed into addressing
|
|
// modes in every use inside the loop. However, it's possible that
|
|
// there are so many of them that the combined FreeResult cannot
|
|
// be subsumed, or that the target cannot handle both a FreeResult
|
|
// and a Result in the same instruction (for example because it would
|
|
// require too many registers). Check this.
|
|
for (unsigned i=0; i<NumUses; ++i) {
|
|
if (!L->contains(Uses[i].Inst))
|
|
continue;
|
|
// We know this is an addressing mode use; if there are any uses that
|
|
// are not, FreeResult would be Zero.
|
|
const Type *AccessTy = getAccessType(Uses[i].Inst);
|
|
if (!fitsInAddressMode(FreeResult, AccessTy, TLI, Result!=Zero)) {
|
|
// FIXME: could split up FreeResult into pieces here, some hoisted
|
|
// and some not. There is no obvious advantage to this.
|
|
Result = SE->getAddExpr(Result, FreeResult);
|
|
FreeResult = Zero;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// If we found no CSE's, return now.
|
|
if (Result == Zero) return Result;
|
|
|
|
// If we still have a FreeResult, remove its subexpressions from
|
|
// SubExpressionUseData. This means they will remain in the use Bases.
|
|
if (FreeResult != Zero) {
|
|
SeparateSubExprs(SubExprs, FreeResult, SE);
|
|
for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) {
|
|
std::map<const SCEV *, SubExprUseData>::iterator I =
|
|
SubExpressionUseData.find(SubExprs[j]);
|
|
SubExpressionUseData.erase(I);
|
|
}
|
|
SubExprs.clear();
|
|
}
|
|
|
|
// Otherwise, remove all of the CSE's we found from each of the base values.
|
|
for (unsigned i = 0; i != NumUses; ++i) {
|
|
// Uses outside the loop don't necessarily include the common base, but
|
|
// the final IV value coming into those uses does. Instead of trying to
|
|
// remove the pieces of the common base, which might not be there,
|
|
// subtract off the base to compensate for this.
|
|
if (!L->contains(Uses[i].Inst)) {
|
|
Uses[i].Base = SE->getMinusSCEV(Uses[i].Base, Result);
|
|
continue;
|
|
}
|
|
|
|
// Split the expression into subexprs.
|
|
SeparateSubExprs(SubExprs, Uses[i].Base, SE);
|
|
|
|
// Remove any common subexpressions.
|
|
for (unsigned j = 0, e = SubExprs.size(); j != e; ++j)
|
|
if (SubExpressionUseData.count(SubExprs[j])) {
|
|
SubExprs.erase(SubExprs.begin()+j);
|
|
--j; --e;
|
|
}
|
|
|
|
// Finally, add the non-shared expressions together.
|
|
if (SubExprs.empty())
|
|
Uses[i].Base = Zero;
|
|
else
|
|
Uses[i].Base = SE->getAddExpr(SubExprs);
|
|
SubExprs.clear();
|
|
}
|
|
|
|
return Result;
|
|
}
|
|
|
|
/// ValidScale - Check whether the given Scale is valid for all loads and
|
|
/// stores in UsersToProcess.
|
|
///
|
|
bool LoopStrengthReduce::ValidScale(bool HasBaseReg, int64_t Scale,
|
|
const std::vector<BasedUser>& UsersToProcess) {
|
|
if (!TLI)
|
|
return true;
|
|
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i!=e; ++i) {
|
|
// If this is a load or other access, pass the type of the access in.
|
|
const Type *AccessTy =
|
|
Type::getVoidTy(UsersToProcess[i].Inst->getContext());
|
|
if (isAddressUse(UsersToProcess[i].Inst,
|
|
UsersToProcess[i].OperandValToReplace))
|
|
AccessTy = getAccessType(UsersToProcess[i].Inst);
|
|
else if (isa<PHINode>(UsersToProcess[i].Inst))
|
|
continue;
|
|
|
|
TargetLowering::AddrMode AM;
|
|
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm))
|
|
AM.BaseOffs = SC->getValue()->getSExtValue();
|
|
AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero();
|
|
AM.Scale = Scale;
|
|
|
|
// If load[imm+r*scale] is illegal, bail out.
|
|
if (!TLI->isLegalAddressingMode(AM, AccessTy))
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// ValidOffset - Check whether the given Offset is valid for all loads and
|
|
/// stores in UsersToProcess.
|
|
///
|
|
bool LoopStrengthReduce::ValidOffset(bool HasBaseReg,
|
|
int64_t Offset,
|
|
int64_t Scale,
|
|
const std::vector<BasedUser>& UsersToProcess) {
|
|
if (!TLI)
|
|
return true;
|
|
|
|
for (unsigned i=0, e = UsersToProcess.size(); i!=e; ++i) {
|
|
// If this is a load or other access, pass the type of the access in.
|
|
const Type *AccessTy =
|
|
Type::getVoidTy(UsersToProcess[i].Inst->getContext());
|
|
if (isAddressUse(UsersToProcess[i].Inst,
|
|
UsersToProcess[i].OperandValToReplace))
|
|
AccessTy = getAccessType(UsersToProcess[i].Inst);
|
|
else if (isa<PHINode>(UsersToProcess[i].Inst))
|
|
continue;
|
|
|
|
TargetLowering::AddrMode AM;
|
|
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm))
|
|
AM.BaseOffs = SC->getValue()->getSExtValue();
|
|
AM.BaseOffs = (uint64_t)AM.BaseOffs + (uint64_t)Offset;
|
|
AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero();
|
|
AM.Scale = Scale;
|
|
|
|
// If load[imm+r*scale] is illegal, bail out.
|
|
if (!TLI->isLegalAddressingMode(AM, AccessTy))
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// RequiresTypeConversion - Returns true if converting Ty1 to Ty2 is not
|
|
/// a nop.
|
|
bool LoopStrengthReduce::RequiresTypeConversion(const Type *Ty1,
|
|
const Type *Ty2) {
|
|
if (Ty1 == Ty2)
|
|
return false;
|
|
Ty1 = SE->getEffectiveSCEVType(Ty1);
|
|
Ty2 = SE->getEffectiveSCEVType(Ty2);
|
|
if (Ty1 == Ty2)
|
|
return false;
|
|
if (Ty1->canLosslesslyBitCastTo(Ty2))
|
|
return false;
|
|
if (TLI && TLI->isTruncateFree(Ty1, Ty2))
|
|
return false;
|
|
return true;
|
|
}
|
|
|
|
/// CheckForIVReuse - Returns the multiple if the stride is the multiple
|
|
/// of a previous stride and it is a legal value for the target addressing
|
|
/// mode scale component and optional base reg. This allows the users of
|
|
/// this stride to be rewritten as prev iv * factor. It returns 0 if no
|
|
/// reuse is possible. Factors can be negative on same targets, e.g. ARM.
|
|
///
|
|
/// If all uses are outside the loop, we don't require that all multiplies
|
|
/// be folded into the addressing mode, nor even that the factor be constant;
|
|
/// a multiply (executed once) outside the loop is better than another IV
|
|
/// within. Well, usually.
|
|
const SCEV *LoopStrengthReduce::CheckForIVReuse(bool HasBaseReg,
|
|
bool AllUsesAreAddresses,
|
|
bool AllUsesAreOutsideLoop,
|
|
const SCEV *Stride,
|
|
IVExpr &IV, const Type *Ty,
|
|
const std::vector<BasedUser>& UsersToProcess) {
|
|
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
|
|
int64_t SInt = SC->getValue()->getSExtValue();
|
|
for (unsigned NewStride = 0, e = IU->StrideOrder.size();
|
|
NewStride != e; ++NewStride) {
|
|
std::map<const SCEV *, IVsOfOneStride>::iterator SI =
|
|
IVsByStride.find(IU->StrideOrder[NewStride]);
|
|
if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first))
|
|
continue;
|
|
// The other stride has no uses, don't reuse it.
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator UI =
|
|
IU->IVUsesByStride.find(IU->StrideOrder[NewStride]);
|
|
if (UI->second->Users.empty())
|
|
continue;
|
|
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
|
|
if (SI->first != Stride &&
|
|
(unsigned(abs64(SInt)) < SSInt || (SInt % SSInt) != 0))
|
|
continue;
|
|
int64_t Scale = SInt / SSInt;
|
|
// Check that this stride is valid for all the types used for loads and
|
|
// stores; if it can be used for some and not others, we might as well use
|
|
// the original stride everywhere, since we have to create the IV for it
|
|
// anyway. If the scale is 1, then we don't need to worry about folding
|
|
// multiplications.
|
|
if (Scale == 1 ||
|
|
(AllUsesAreAddresses &&
|
|
ValidScale(HasBaseReg, Scale, UsersToProcess))) {
|
|
// Prefer to reuse an IV with a base of zero.
|
|
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
|
|
IE = SI->second.IVs.end(); II != IE; ++II)
|
|
// Only reuse previous IV if it would not require a type conversion
|
|
// and if the base difference can be folded.
|
|
if (II->Base->isZero() &&
|
|
!RequiresTypeConversion(II->Base->getType(), Ty)) {
|
|
IV = *II;
|
|
return SE->getIntegerSCEV(Scale, Stride->getType());
|
|
}
|
|
// Otherwise, settle for an IV with a foldable base.
|
|
if (AllUsesAreAddresses)
|
|
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
|
|
IE = SI->second.IVs.end(); II != IE; ++II)
|
|
// Only reuse previous IV if it would not require a type conversion
|
|
// and if the base difference can be folded.
|
|
if (SE->getEffectiveSCEVType(II->Base->getType()) ==
|
|
SE->getEffectiveSCEVType(Ty) &&
|
|
isa<SCEVConstant>(II->Base)) {
|
|
int64_t Base =
|
|
cast<SCEVConstant>(II->Base)->getValue()->getSExtValue();
|
|
if (Base > INT32_MIN && Base <= INT32_MAX &&
|
|
ValidOffset(HasBaseReg, -Base * Scale,
|
|
Scale, UsersToProcess)) {
|
|
IV = *II;
|
|
return SE->getIntegerSCEV(Scale, Stride->getType());
|
|
}
|
|
}
|
|
}
|
|
}
|
|
} else if (AllUsesAreOutsideLoop) {
|
|
// Accept nonconstant strides here; it is really really right to substitute
|
|
// an existing IV if we can.
|
|
for (unsigned NewStride = 0, e = IU->StrideOrder.size();
|
|
NewStride != e; ++NewStride) {
|
|
std::map<const SCEV *, IVsOfOneStride>::iterator SI =
|
|
IVsByStride.find(IU->StrideOrder[NewStride]);
|
|
if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first))
|
|
continue;
|
|
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
|
|
if (SI->first != Stride && SSInt != 1)
|
|
continue;
|
|
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
|
|
IE = SI->second.IVs.end(); II != IE; ++II)
|
|
// Accept nonzero base here.
|
|
// Only reuse previous IV if it would not require a type conversion.
|
|
if (!RequiresTypeConversion(II->Base->getType(), Ty)) {
|
|
IV = *II;
|
|
return Stride;
|
|
}
|
|
}
|
|
// Special case, old IV is -1*x and this one is x. Can treat this one as
|
|
// -1*old.
|
|
for (unsigned NewStride = 0, e = IU->StrideOrder.size();
|
|
NewStride != e; ++NewStride) {
|
|
std::map<const SCEV *, IVsOfOneStride>::iterator SI =
|
|
IVsByStride.find(IU->StrideOrder[NewStride]);
|
|
if (SI == IVsByStride.end())
|
|
continue;
|
|
if (const SCEVMulExpr *ME = dyn_cast<SCEVMulExpr>(SI->first))
|
|
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(ME->getOperand(0)))
|
|
if (Stride == ME->getOperand(1) &&
|
|
SC->getValue()->getSExtValue() == -1LL)
|
|
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
|
|
IE = SI->second.IVs.end(); II != IE; ++II)
|
|
// Accept nonzero base here.
|
|
// Only reuse previous IV if it would not require type conversion.
|
|
if (!RequiresTypeConversion(II->Base->getType(), Ty)) {
|
|
IV = *II;
|
|
return SE->getIntegerSCEV(-1LL, Stride->getType());
|
|
}
|
|
}
|
|
}
|
|
return SE->getIntegerSCEV(0, Stride->getType());
|
|
}
|
|
|
|
/// PartitionByIsUseOfPostIncrementedValue - Simple boolean predicate that
|
|
/// returns true if Val's isUseOfPostIncrementedValue is true.
|
|
static bool PartitionByIsUseOfPostIncrementedValue(const BasedUser &Val) {
|
|
return Val.isUseOfPostIncrementedValue;
|
|
}
|
|
|
|
/// isNonConstantNegative - Return true if the specified scev is negated, but
|
|
/// not a constant.
|
|
static bool isNonConstantNegative(const SCEV *Expr) {
|
|
const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Expr);
|
|
if (!Mul) return false;
|
|
|
|
// If there is a constant factor, it will be first.
|
|
const SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0));
|
|
if (!SC) return false;
|
|
|
|
// Return true if the value is negative, this matches things like (-42 * V).
|
|
return SC->getValue()->getValue().isNegative();
|
|
}
|
|
|
|
/// CollectIVUsers - Transform our list of users and offsets to a bit more
|
|
/// complex table. In this new vector, each 'BasedUser' contains 'Base', the
|
|
/// base of the strided accesses, as well as the old information from Uses. We
|
|
/// progressively move information from the Base field to the Imm field, until
|
|
/// we eventually have the full access expression to rewrite the use.
|
|
const SCEV *LoopStrengthReduce::CollectIVUsers(const SCEV *Stride,
|
|
IVUsersOfOneStride &Uses,
|
|
Loop *L,
|
|
bool &AllUsesAreAddresses,
|
|
bool &AllUsesAreOutsideLoop,
|
|
std::vector<BasedUser> &UsersToProcess) {
|
|
// FIXME: Generalize to non-affine IV's.
|
|
if (!Stride->isLoopInvariant(L))
|
|
return SE->getIntegerSCEV(0, Stride->getType());
|
|
|
|
UsersToProcess.reserve(Uses.Users.size());
|
|
for (ilist<IVStrideUse>::iterator I = Uses.Users.begin(),
|
|
E = Uses.Users.end(); I != E; ++I) {
|
|
UsersToProcess.push_back(BasedUser(*I, SE));
|
|
|
|
// Move any loop variant operands from the offset field to the immediate
|
|
// field of the use, so that we don't try to use something before it is
|
|
// computed.
|
|
MoveLoopVariantsToImmediateField(UsersToProcess.back().Base,
|
|
UsersToProcess.back().Imm, L, SE);
|
|
assert(UsersToProcess.back().Base->isLoopInvariant(L) &&
|
|
"Base value is not loop invariant!");
|
|
}
|
|
|
|
// We now have a whole bunch of uses of like-strided induction variables, but
|
|
// they might all have different bases. We want to emit one PHI node for this
|
|
// stride which we fold as many common expressions (between the IVs) into as
|
|
// possible. Start by identifying the common expressions in the base values
|
|
// for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
|
|
// "A+B"), emit it to the preheader, then remove the expression from the
|
|
// UsersToProcess base values.
|
|
const SCEV *CommonExprs =
|
|
RemoveCommonExpressionsFromUseBases(UsersToProcess, SE, L, TLI);
|
|
|
|
// Next, figure out what we can represent in the immediate fields of
|
|
// instructions. If we can represent anything there, move it to the imm
|
|
// fields of the BasedUsers. We do this so that it increases the commonality
|
|
// of the remaining uses.
|
|
unsigned NumPHI = 0;
|
|
bool HasAddress = false;
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
|
|
// If the user is not in the current loop, this means it is using the exit
|
|
// value of the IV. Do not put anything in the base, make sure it's all in
|
|
// the immediate field to allow as much factoring as possible.
|
|
if (!L->contains(UsersToProcess[i].Inst)) {
|
|
UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm,
|
|
UsersToProcess[i].Base);
|
|
UsersToProcess[i].Base =
|
|
SE->getIntegerSCEV(0, UsersToProcess[i].Base->getType());
|
|
} else {
|
|
// Not all uses are outside the loop.
|
|
AllUsesAreOutsideLoop = false;
|
|
|
|
// Addressing modes can be folded into loads and stores. Be careful that
|
|
// the store is through the expression, not of the expression though.
|
|
bool isPHI = false;
|
|
bool isAddress = isAddressUse(UsersToProcess[i].Inst,
|
|
UsersToProcess[i].OperandValToReplace);
|
|
if (isa<PHINode>(UsersToProcess[i].Inst)) {
|
|
isPHI = true;
|
|
++NumPHI;
|
|
}
|
|
|
|
if (isAddress)
|
|
HasAddress = true;
|
|
|
|
// If this use isn't an address, then not all uses are addresses.
|
|
if (!isAddress && !isPHI)
|
|
AllUsesAreAddresses = false;
|
|
|
|
MoveImmediateValues(TLI, UsersToProcess[i].Inst, UsersToProcess[i].Base,
|
|
UsersToProcess[i].Imm, isAddress, L, SE);
|
|
}
|
|
}
|
|
|
|
// If one of the use is a PHI node and all other uses are addresses, still
|
|
// allow iv reuse. Essentially we are trading one constant multiplication
|
|
// for one fewer iv.
|
|
if (NumPHI > 1)
|
|
AllUsesAreAddresses = false;
|
|
|
|
// There are no in-loop address uses.
|
|
if (AllUsesAreAddresses && (!HasAddress && !AllUsesAreOutsideLoop))
|
|
AllUsesAreAddresses = false;
|
|
|
|
return CommonExprs;
|
|
}
|
|
|
|
/// ShouldUseFullStrengthReductionMode - Test whether full strength-reduction
|
|
/// is valid and profitable for the given set of users of a stride. In
|
|
/// full strength-reduction mode, all addresses at the current stride are
|
|
/// strength-reduced all the way down to pointer arithmetic.
|
|
///
|
|
bool LoopStrengthReduce::ShouldUseFullStrengthReductionMode(
|
|
const std::vector<BasedUser> &UsersToProcess,
|
|
const Loop *L,
|
|
bool AllUsesAreAddresses,
|
|
const SCEV *Stride) {
|
|
if (!EnableFullLSRMode)
|
|
return false;
|
|
|
|
// The heuristics below aim to avoid increasing register pressure, but
|
|
// fully strength-reducing all the addresses increases the number of
|
|
// add instructions, so don't do this when optimizing for size.
|
|
// TODO: If the loop is large, the savings due to simpler addresses
|
|
// may oughtweight the costs of the extra increment instructions.
|
|
if (L->getHeader()->getParent()->hasFnAttr(Attribute::OptimizeForSize))
|
|
return false;
|
|
|
|
// TODO: For now, don't do full strength reduction if there could
|
|
// potentially be greater-stride multiples of the current stride
|
|
// which could reuse the current stride IV.
|
|
if (IU->StrideOrder.back() != Stride)
|
|
return false;
|
|
|
|
// Iterate through the uses to find conditions that automatically rule out
|
|
// full-lsr mode.
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) {
|
|
const SCEV *Base = UsersToProcess[i].Base;
|
|
const SCEV *Imm = UsersToProcess[i].Imm;
|
|
// If any users have a loop-variant component, they can't be fully
|
|
// strength-reduced.
|
|
if (Imm && !Imm->isLoopInvariant(L))
|
|
return false;
|
|
// If there are to users with the same base and the difference between
|
|
// the two Imm values can't be folded into the address, full
|
|
// strength reduction would increase register pressure.
|
|
do {
|
|
const SCEV *CurImm = UsersToProcess[i].Imm;
|
|
if ((CurImm || Imm) && CurImm != Imm) {
|
|
if (!CurImm) CurImm = SE->getIntegerSCEV(0, Stride->getType());
|
|
if (!Imm) Imm = SE->getIntegerSCEV(0, Stride->getType());
|
|
const Instruction *Inst = UsersToProcess[i].Inst;
|
|
const Type *AccessTy = getAccessType(Inst);
|
|
const SCEV *Diff = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm);
|
|
if (!Diff->isZero() &&
|
|
(!AllUsesAreAddresses ||
|
|
!fitsInAddressMode(Diff, AccessTy, TLI, /*HasBaseReg=*/true)))
|
|
return false;
|
|
}
|
|
} while (++i != e && Base == UsersToProcess[i].Base);
|
|
}
|
|
|
|
// If there's exactly one user in this stride, fully strength-reducing it
|
|
// won't increase register pressure. If it's starting from a non-zero base,
|
|
// it'll be simpler this way.
|
|
if (UsersToProcess.size() == 1 && !UsersToProcess[0].Base->isZero())
|
|
return true;
|
|
|
|
// Otherwise, if there are any users in this stride that don't require
|
|
// a register for their base, full strength-reduction will increase
|
|
// register pressure.
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
|
|
if (UsersToProcess[i].Base->isZero())
|
|
return false;
|
|
|
|
// Otherwise, go for it.
|
|
return true;
|
|
}
|
|
|
|
/// InsertAffinePhi Create and insert a PHI node for an induction variable
|
|
/// with the specified start and step values in the specified loop.
|
|
///
|
|
/// If NegateStride is true, the stride should be negated by using a
|
|
/// subtract instead of an add.
|
|
///
|
|
/// Return the created phi node.
|
|
///
|
|
static PHINode *InsertAffinePhi(const SCEV *Start, const SCEV *Step,
|
|
Instruction *IVIncInsertPt,
|
|
const Loop *L,
|
|
SCEVExpander &Rewriter) {
|
|
assert(Start->isLoopInvariant(L) && "New PHI start is not loop invariant!");
|
|
assert(Step->isLoopInvariant(L) && "New PHI stride is not loop invariant!");
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
BasicBlock *LatchBlock = L->getLoopLatch();
|
|
const Type *Ty = Start->getType();
|
|
Ty = Rewriter.SE.getEffectiveSCEVType(Ty);
|
|
|
|
PHINode *PN = PHINode::Create(Ty, "lsr.iv", Header->begin());
|
|
PN->addIncoming(Rewriter.expandCodeFor(Start, Ty, Preheader->getTerminator()),
|
|
Preheader);
|
|
|
|
// If the stride is negative, insert a sub instead of an add for the
|
|
// increment.
|
|
bool isNegative = isNonConstantNegative(Step);
|
|
const SCEV *IncAmount = Step;
|
|
if (isNegative)
|
|
IncAmount = Rewriter.SE.getNegativeSCEV(Step);
|
|
|
|
// Insert an add instruction right before the terminator corresponding
|
|
// to the back-edge or just before the only use. The location is determined
|
|
// by the caller and passed in as IVIncInsertPt.
|
|
Value *StepV = Rewriter.expandCodeFor(IncAmount, Ty,
|
|
Preheader->getTerminator());
|
|
Instruction *IncV;
|
|
if (isNegative) {
|
|
IncV = BinaryOperator::CreateSub(PN, StepV, "lsr.iv.next",
|
|
IVIncInsertPt);
|
|
} else {
|
|
IncV = BinaryOperator::CreateAdd(PN, StepV, "lsr.iv.next",
|
|
IVIncInsertPt);
|
|
}
|
|
if (!isa<ConstantInt>(StepV)) ++NumVariable;
|
|
|
|
PN->addIncoming(IncV, LatchBlock);
|
|
|
|
++NumInserted;
|
|
return PN;
|
|
}
|
|
|
|
static void SortUsersToProcess(std::vector<BasedUser> &UsersToProcess) {
|
|
// We want to emit code for users inside the loop first. To do this, we
|
|
// rearrange BasedUser so that the entries at the end have
|
|
// isUseOfPostIncrementedValue = false, because we pop off the end of the
|
|
// vector (so we handle them first).
|
|
std::partition(UsersToProcess.begin(), UsersToProcess.end(),
|
|
PartitionByIsUseOfPostIncrementedValue);
|
|
|
|
// Sort this by base, so that things with the same base are handled
|
|
// together. By partitioning first and stable-sorting later, we are
|
|
// guaranteed that within each base we will pop off users from within the
|
|
// loop before users outside of the loop with a particular base.
|
|
//
|
|
// We would like to use stable_sort here, but we can't. The problem is that
|
|
// const SCEV *'s don't have a deterministic ordering w.r.t to each other, so
|
|
// we don't have anything to do a '<' comparison on. Because we think the
|
|
// number of uses is small, do a horrible bubble sort which just relies on
|
|
// ==.
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
|
|
// Get a base value.
|
|
const SCEV *Base = UsersToProcess[i].Base;
|
|
|
|
// Compact everything with this base to be consecutive with this one.
|
|
for (unsigned j = i+1; j != e; ++j) {
|
|
if (UsersToProcess[j].Base == Base) {
|
|
std::swap(UsersToProcess[i+1], UsersToProcess[j]);
|
|
++i;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// PrepareToStrengthReduceFully - Prepare to fully strength-reduce
|
|
/// UsersToProcess, meaning lowering addresses all the way down to direct
|
|
/// pointer arithmetic.
|
|
///
|
|
void
|
|
LoopStrengthReduce::PrepareToStrengthReduceFully(
|
|
std::vector<BasedUser> &UsersToProcess,
|
|
const SCEV *Stride,
|
|
const SCEV *CommonExprs,
|
|
const Loop *L,
|
|
SCEVExpander &PreheaderRewriter) {
|
|
DEBUG(errs() << " Fully reducing all users\n");
|
|
|
|
// Rewrite the UsersToProcess records, creating a separate PHI for each
|
|
// unique Base value.
|
|
Instruction *IVIncInsertPt = L->getLoopLatch()->getTerminator();
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) {
|
|
// TODO: The uses are grouped by base, but not sorted. We arbitrarily
|
|
// pick the first Imm value here to start with, and adjust it for the
|
|
// other uses.
|
|
const SCEV *Imm = UsersToProcess[i].Imm;
|
|
const SCEV *Base = UsersToProcess[i].Base;
|
|
const SCEV *Start = SE->getAddExpr(CommonExprs, Base, Imm);
|
|
PHINode *Phi = InsertAffinePhi(Start, Stride, IVIncInsertPt, L,
|
|
PreheaderRewriter);
|
|
// Loop over all the users with the same base.
|
|
do {
|
|
UsersToProcess[i].Base = SE->getIntegerSCEV(0, Stride->getType());
|
|
UsersToProcess[i].Imm = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm);
|
|
UsersToProcess[i].Phi = Phi;
|
|
assert(UsersToProcess[i].Imm->isLoopInvariant(L) &&
|
|
"ShouldUseFullStrengthReductionMode should reject this!");
|
|
} while (++i != e && Base == UsersToProcess[i].Base);
|
|
}
|
|
}
|
|
|
|
/// FindIVIncInsertPt - Return the location to insert the increment instruction.
|
|
/// If the only use if a use of postinc value, (must be the loop termination
|
|
/// condition), then insert it just before the use.
|
|
static Instruction *FindIVIncInsertPt(std::vector<BasedUser> &UsersToProcess,
|
|
const Loop *L) {
|
|
if (UsersToProcess.size() == 1 &&
|
|
UsersToProcess[0].isUseOfPostIncrementedValue &&
|
|
L->contains(UsersToProcess[0].Inst))
|
|
return UsersToProcess[0].Inst;
|
|
return L->getLoopLatch()->getTerminator();
|
|
}
|
|
|
|
/// PrepareToStrengthReduceWithNewPhi - Insert a new induction variable for the
|
|
/// given users to share.
|
|
///
|
|
void
|
|
LoopStrengthReduce::PrepareToStrengthReduceWithNewPhi(
|
|
std::vector<BasedUser> &UsersToProcess,
|
|
const SCEV *Stride,
|
|
const SCEV *CommonExprs,
|
|
Value *CommonBaseV,
|
|
Instruction *IVIncInsertPt,
|
|
const Loop *L,
|
|
SCEVExpander &PreheaderRewriter) {
|
|
DEBUG(errs() << " Inserting new PHI:\n");
|
|
|
|
PHINode *Phi = InsertAffinePhi(SE->getUnknown(CommonBaseV),
|
|
Stride, IVIncInsertPt, L,
|
|
PreheaderRewriter);
|
|
|
|
// Remember this in case a later stride is multiple of this.
|
|
IVsByStride[Stride].addIV(Stride, CommonExprs, Phi);
|
|
|
|
// All the users will share this new IV.
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
|
|
UsersToProcess[i].Phi = Phi;
|
|
|
|
DEBUG(errs() << " IV=");
|
|
DEBUG(WriteAsOperand(errs(), Phi, /*PrintType=*/false));
|
|
DEBUG(errs() << "\n");
|
|
}
|
|
|
|
/// PrepareToStrengthReduceFromSmallerStride - Prepare for the given users to
|
|
/// reuse an induction variable with a stride that is a factor of the current
|
|
/// induction variable.
|
|
///
|
|
void
|
|
LoopStrengthReduce::PrepareToStrengthReduceFromSmallerStride(
|
|
std::vector<BasedUser> &UsersToProcess,
|
|
Value *CommonBaseV,
|
|
const IVExpr &ReuseIV,
|
|
Instruction *PreInsertPt) {
|
|
DEBUG(errs() << " Rewriting in terms of existing IV of STRIDE "
|
|
<< *ReuseIV.Stride << " and BASE " << *ReuseIV.Base << "\n");
|
|
|
|
// All the users will share the reused IV.
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
|
|
UsersToProcess[i].Phi = ReuseIV.PHI;
|
|
|
|
Constant *C = dyn_cast<Constant>(CommonBaseV);
|
|
if (C &&
|
|
(!C->isNullValue() &&
|
|
!fitsInAddressMode(SE->getUnknown(CommonBaseV), CommonBaseV->getType(),
|
|
TLI, false)))
|
|
// We want the common base emitted into the preheader! This is just
|
|
// using cast as a copy so BitCast (no-op cast) is appropriate
|
|
CommonBaseV = new BitCastInst(CommonBaseV, CommonBaseV->getType(),
|
|
"commonbase", PreInsertPt);
|
|
}
|
|
|
|
static bool IsImmFoldedIntoAddrMode(GlobalValue *GV, int64_t Offset,
|
|
const Type *AccessTy,
|
|
std::vector<BasedUser> &UsersToProcess,
|
|
const TargetLowering *TLI) {
|
|
SmallVector<Instruction*, 16> AddrModeInsts;
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
|
|
if (UsersToProcess[i].isUseOfPostIncrementedValue)
|
|
continue;
|
|
ExtAddrMode AddrMode =
|
|
AddressingModeMatcher::Match(UsersToProcess[i].OperandValToReplace,
|
|
AccessTy, UsersToProcess[i].Inst,
|
|
AddrModeInsts, *TLI);
|
|
if (GV && GV != AddrMode.BaseGV)
|
|
return false;
|
|
if (Offset && !AddrMode.BaseOffs)
|
|
// FIXME: How to accurate check it's immediate offset is folded.
|
|
return false;
|
|
AddrModeInsts.clear();
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// StrengthReduceIVUsersOfStride - Strength reduce all of the users of a single
|
|
/// stride of IV. All of the users may have different starting values, and this
|
|
/// may not be the only stride.
|
|
void
|
|
LoopStrengthReduce::StrengthReduceIVUsersOfStride(const SCEV *Stride,
|
|
IVUsersOfOneStride &Uses,
|
|
Loop *L) {
|
|
// If all the users are moved to another stride, then there is nothing to do.
|
|
if (Uses.Users.empty())
|
|
return;
|
|
|
|
// Keep track if every use in UsersToProcess is an address. If they all are,
|
|
// we may be able to rewrite the entire collection of them in terms of a
|
|
// smaller-stride IV.
|
|
bool AllUsesAreAddresses = true;
|
|
|
|
// Keep track if every use of a single stride is outside the loop. If so,
|
|
// we want to be more aggressive about reusing a smaller-stride IV; a
|
|
// multiply outside the loop is better than another IV inside. Well, usually.
|
|
bool AllUsesAreOutsideLoop = true;
|
|
|
|
// Transform our list of users and offsets to a bit more complex table. In
|
|
// this new vector, each 'BasedUser' contains 'Base' the base of the
|
|
// strided accessas well as the old information from Uses. We progressively
|
|
// move information from the Base field to the Imm field, until we eventually
|
|
// have the full access expression to rewrite the use.
|
|
std::vector<BasedUser> UsersToProcess;
|
|
const SCEV *CommonExprs = CollectIVUsers(Stride, Uses, L, AllUsesAreAddresses,
|
|
AllUsesAreOutsideLoop,
|
|
UsersToProcess);
|
|
|
|
// Sort the UsersToProcess array so that users with common bases are
|
|
// next to each other.
|
|
SortUsersToProcess(UsersToProcess);
|
|
|
|
// If we managed to find some expressions in common, we'll need to carry
|
|
// their value in a register and add it in for each use. This will take up
|
|
// a register operand, which potentially restricts what stride values are
|
|
// valid.
|
|
bool HaveCommonExprs = !CommonExprs->isZero();
|
|
const Type *ReplacedTy = CommonExprs->getType();
|
|
|
|
// If all uses are addresses, consider sinking the immediate part of the
|
|
// common expression back into uses if they can fit in the immediate fields.
|
|
if (TLI && HaveCommonExprs && AllUsesAreAddresses) {
|
|
const SCEV *NewCommon = CommonExprs;
|
|
const SCEV *Imm = SE->getIntegerSCEV(0, ReplacedTy);
|
|
MoveImmediateValues(TLI, Type::getVoidTy(
|
|
L->getLoopPreheader()->getContext()),
|
|
NewCommon, Imm, true, L, SE);
|
|
if (!Imm->isZero()) {
|
|
bool DoSink = true;
|
|
|
|
// If the immediate part of the common expression is a GV, check if it's
|
|
// possible to fold it into the target addressing mode.
|
|
GlobalValue *GV = 0;
|
|
if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(Imm))
|
|
GV = dyn_cast<GlobalValue>(SU->getValue());
|
|
int64_t Offset = 0;
|
|
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Imm))
|
|
Offset = SC->getValue()->getSExtValue();
|
|
if (GV || Offset)
|
|
// Pass VoidTy as the AccessTy to be conservative, because
|
|
// there could be multiple access types among all the uses.
|
|
DoSink = IsImmFoldedIntoAddrMode(GV, Offset,
|
|
Type::getVoidTy(L->getLoopPreheader()->getContext()),
|
|
UsersToProcess, TLI);
|
|
|
|
if (DoSink) {
|
|
DEBUG(errs() << " Sinking " << *Imm << " back down into uses\n");
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
|
|
UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm, Imm);
|
|
CommonExprs = NewCommon;
|
|
HaveCommonExprs = !CommonExprs->isZero();
|
|
++NumImmSunk;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Now that we know what we need to do, insert the PHI node itself.
|
|
//
|
|
DEBUG(errs() << "LSR: Examining IVs of TYPE " << *ReplacedTy << " of STRIDE "
|
|
<< *Stride << ":\n"
|
|
<< " Common base: " << *CommonExprs << "\n");
|
|
|
|
SCEVExpander Rewriter(*SE);
|
|
SCEVExpander PreheaderRewriter(*SE);
|
|
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
Instruction *PreInsertPt = Preheader->getTerminator();
|
|
BasicBlock *LatchBlock = L->getLoopLatch();
|
|
Instruction *IVIncInsertPt = LatchBlock->getTerminator();
|
|
|
|
Value *CommonBaseV = Constant::getNullValue(ReplacedTy);
|
|
|
|
const SCEV *RewriteFactor = SE->getIntegerSCEV(0, ReplacedTy);
|
|
IVExpr ReuseIV(SE->getIntegerSCEV(0,
|
|
Type::getInt32Ty(Preheader->getContext())),
|
|
SE->getIntegerSCEV(0,
|
|
Type::getInt32Ty(Preheader->getContext())),
|
|
0);
|
|
|
|
// Choose a strength-reduction strategy and prepare for it by creating
|
|
// the necessary PHIs and adjusting the bookkeeping.
|
|
if (ShouldUseFullStrengthReductionMode(UsersToProcess, L,
|
|
AllUsesAreAddresses, Stride)) {
|
|
PrepareToStrengthReduceFully(UsersToProcess, Stride, CommonExprs, L,
|
|
PreheaderRewriter);
|
|
} else {
|
|
// Emit the initial base value into the loop preheader.
|
|
CommonBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, ReplacedTy,
|
|
PreInsertPt);
|
|
|
|
// If all uses are addresses, check if it is possible to reuse an IV. The
|
|
// new IV must have a stride that is a multiple of the old stride; the
|
|
// multiple must be a number that can be encoded in the scale field of the
|
|
// target addressing mode; and we must have a valid instruction after this
|
|
// substitution, including the immediate field, if any.
|
|
RewriteFactor = CheckForIVReuse(HaveCommonExprs, AllUsesAreAddresses,
|
|
AllUsesAreOutsideLoop,
|
|
Stride, ReuseIV, ReplacedTy,
|
|
UsersToProcess);
|
|
if (!RewriteFactor->isZero())
|
|
PrepareToStrengthReduceFromSmallerStride(UsersToProcess, CommonBaseV,
|
|
ReuseIV, PreInsertPt);
|
|
else {
|
|
IVIncInsertPt = FindIVIncInsertPt(UsersToProcess, L);
|
|
PrepareToStrengthReduceWithNewPhi(UsersToProcess, Stride, CommonExprs,
|
|
CommonBaseV, IVIncInsertPt,
|
|
L, PreheaderRewriter);
|
|
}
|
|
}
|
|
|
|
// Process all the users now, replacing their strided uses with
|
|
// strength-reduced forms. This outer loop handles all bases, the inner
|
|
// loop handles all users of a particular base.
|
|
while (!UsersToProcess.empty()) {
|
|
const SCEV *Base = UsersToProcess.back().Base;
|
|
Instruction *Inst = UsersToProcess.back().Inst;
|
|
|
|
// Emit the code for Base into the preheader.
|
|
Value *BaseV = 0;
|
|
if (!Base->isZero()) {
|
|
BaseV = PreheaderRewriter.expandCodeFor(Base, 0, PreInsertPt);
|
|
|
|
DEBUG(errs() << " INSERTING code for BASE = " << *Base << ":");
|
|
if (BaseV->hasName())
|
|
DEBUG(errs() << " Result value name = %" << BaseV->getName());
|
|
DEBUG(errs() << "\n");
|
|
|
|
// If BaseV is a non-zero constant, make sure that it gets inserted into
|
|
// the preheader, instead of being forward substituted into the uses. We
|
|
// do this by forcing a BitCast (noop cast) to be inserted into the
|
|
// preheader in this case.
|
|
if (!fitsInAddressMode(Base, getAccessType(Inst), TLI, false) &&
|
|
isa<Constant>(BaseV)) {
|
|
// We want this constant emitted into the preheader! This is just
|
|
// using cast as a copy so BitCast (no-op cast) is appropriate
|
|
BaseV = new BitCastInst(BaseV, BaseV->getType(), "preheaderinsert",
|
|
PreInsertPt);
|
|
}
|
|
}
|
|
|
|
// Emit the code to add the immediate offset to the Phi value, just before
|
|
// the instructions that we identified as using this stride and base.
|
|
do {
|
|
// FIXME: Use emitted users to emit other users.
|
|
BasedUser &User = UsersToProcess.back();
|
|
|
|
DEBUG(errs() << " Examining ");
|
|
if (User.isUseOfPostIncrementedValue)
|
|
DEBUG(errs() << "postinc");
|
|
else
|
|
DEBUG(errs() << "preinc");
|
|
DEBUG(errs() << " use ");
|
|
DEBUG(WriteAsOperand(errs(), UsersToProcess.back().OperandValToReplace,
|
|
/*PrintType=*/false));
|
|
DEBUG(errs() << " in Inst: " << *User.Inst);
|
|
|
|
// If this instruction wants to use the post-incremented value, move it
|
|
// after the post-inc and use its value instead of the PHI.
|
|
Value *RewriteOp = User.Phi;
|
|
if (User.isUseOfPostIncrementedValue) {
|
|
RewriteOp = User.Phi->getIncomingValueForBlock(LatchBlock);
|
|
// If this user is in the loop, make sure it is the last thing in the
|
|
// loop to ensure it is dominated by the increment. In case it's the
|
|
// only use of the iv, the increment instruction is already before the
|
|
// use.
|
|
if (L->contains(User.Inst) && User.Inst != IVIncInsertPt)
|
|
User.Inst->moveBefore(IVIncInsertPt);
|
|
}
|
|
|
|
const SCEV *RewriteExpr = SE->getUnknown(RewriteOp);
|
|
|
|
if (SE->getEffectiveSCEVType(RewriteOp->getType()) !=
|
|
SE->getEffectiveSCEVType(ReplacedTy)) {
|
|
assert(SE->getTypeSizeInBits(RewriteOp->getType()) >
|
|
SE->getTypeSizeInBits(ReplacedTy) &&
|
|
"Unexpected widening cast!");
|
|
RewriteExpr = SE->getTruncateExpr(RewriteExpr, ReplacedTy);
|
|
}
|
|
|
|
// If we had to insert new instructions for RewriteOp, we have to
|
|
// consider that they may not have been able to end up immediately
|
|
// next to RewriteOp, because non-PHI instructions may never precede
|
|
// PHI instructions in a block. In this case, remember where the last
|
|
// instruction was inserted so that if we're replacing a different
|
|
// PHI node, we can use the later point to expand the final
|
|
// RewriteExpr.
|
|
Instruction *NewBasePt = dyn_cast<Instruction>(RewriteOp);
|
|
if (RewriteOp == User.Phi) NewBasePt = 0;
|
|
|
|
// Clear the SCEVExpander's expression map so that we are guaranteed
|
|
// to have the code emitted where we expect it.
|
|
Rewriter.clear();
|
|
|
|
// If we are reusing the iv, then it must be multiplied by a constant
|
|
// factor to take advantage of the addressing mode scale component.
|
|
if (!RewriteFactor->isZero()) {
|
|
// If we're reusing an IV with a nonzero base (currently this happens
|
|
// only when all reuses are outside the loop) subtract that base here.
|
|
// The base has been used to initialize the PHI node but we don't want
|
|
// it here.
|
|
if (!ReuseIV.Base->isZero()) {
|
|
const SCEV *typedBase = ReuseIV.Base;
|
|
if (SE->getEffectiveSCEVType(RewriteExpr->getType()) !=
|
|
SE->getEffectiveSCEVType(ReuseIV.Base->getType())) {
|
|
// It's possible the original IV is a larger type than the new IV,
|
|
// in which case we have to truncate the Base. We checked in
|
|
// RequiresTypeConversion that this is valid.
|
|
assert(SE->getTypeSizeInBits(RewriteExpr->getType()) <
|
|
SE->getTypeSizeInBits(ReuseIV.Base->getType()) &&
|
|
"Unexpected lengthening conversion!");
|
|
typedBase = SE->getTruncateExpr(ReuseIV.Base,
|
|
RewriteExpr->getType());
|
|
}
|
|
RewriteExpr = SE->getMinusSCEV(RewriteExpr, typedBase);
|
|
}
|
|
|
|
// Multiply old variable, with base removed, by new scale factor.
|
|
RewriteExpr = SE->getMulExpr(RewriteFactor,
|
|
RewriteExpr);
|
|
|
|
// The common base is emitted in the loop preheader. But since we
|
|
// are reusing an IV, it has not been used to initialize the PHI node.
|
|
// Add it to the expression used to rewrite the uses.
|
|
// When this use is outside the loop, we earlier subtracted the
|
|
// common base, and are adding it back here. Use the same expression
|
|
// as before, rather than CommonBaseV, so DAGCombiner will zap it.
|
|
if (!CommonExprs->isZero()) {
|
|
if (L->contains(User.Inst))
|
|
RewriteExpr = SE->getAddExpr(RewriteExpr,
|
|
SE->getUnknown(CommonBaseV));
|
|
else
|
|
RewriteExpr = SE->getAddExpr(RewriteExpr, CommonExprs);
|
|
}
|
|
}
|
|
|
|
// Now that we know what we need to do, insert code before User for the
|
|
// immediate and any loop-variant expressions.
|
|
if (BaseV)
|
|
// Add BaseV to the PHI value if needed.
|
|
RewriteExpr = SE->getAddExpr(RewriteExpr, SE->getUnknown(BaseV));
|
|
|
|
User.RewriteInstructionToUseNewBase(RewriteExpr, NewBasePt,
|
|
Rewriter, L, this,
|
|
DeadInsts, SE);
|
|
|
|
// Mark old value we replaced as possibly dead, so that it is eliminated
|
|
// if we just replaced the last use of that value.
|
|
DeadInsts.push_back(User.OperandValToReplace);
|
|
|
|
UsersToProcess.pop_back();
|
|
++NumReduced;
|
|
|
|
// If there are any more users to process with the same base, process them
|
|
// now. We sorted by base above, so we just have to check the last elt.
|
|
} while (!UsersToProcess.empty() && UsersToProcess.back().Base == Base);
|
|
// TODO: Next, find out which base index is the most common, pull it out.
|
|
}
|
|
|
|
// IMPORTANT TODO: Figure out how to partition the IV's with this stride, but
|
|
// different starting values, into different PHIs.
|
|
}
|
|
|
|
void LoopStrengthReduce::StrengthReduceIVUsers(Loop *L) {
|
|
// Note: this processes each stride/type pair individually. All users
|
|
// passed into StrengthReduceIVUsersOfStride have the same type AND stride.
|
|
// Also, note that we iterate over IVUsesByStride indirectly by using
|
|
// StrideOrder. This extra layer of indirection makes the ordering of
|
|
// strides deterministic - not dependent on map order.
|
|
for (unsigned Stride = 0, e = IU->StrideOrder.size(); Stride != e; ++Stride) {
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
|
|
IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
|
|
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
|
|
// FIXME: Generalize to non-affine IV's.
|
|
if (!SI->first->isLoopInvariant(L))
|
|
continue;
|
|
StrengthReduceIVUsersOfStride(SI->first, *SI->second, L);
|
|
}
|
|
}
|
|
|
|
/// FindIVUserForCond - If Cond has an operand that is an expression of an IV,
|
|
/// set the IV user and stride information and return true, otherwise return
|
|
/// false.
|
|
bool LoopStrengthReduce::FindIVUserForCond(ICmpInst *Cond,
|
|
IVStrideUse *&CondUse,
|
|
const SCEV* &CondStride) {
|
|
for (unsigned Stride = 0, e = IU->StrideOrder.size();
|
|
Stride != e && !CondUse; ++Stride) {
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
|
|
IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
|
|
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
|
|
|
|
for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
|
|
E = SI->second->Users.end(); UI != E; ++UI)
|
|
if (UI->getUser() == Cond) {
|
|
// NOTE: we could handle setcc instructions with multiple uses here, but
|
|
// InstCombine does it as well for simple uses, it's not clear that it
|
|
// occurs enough in real life to handle.
|
|
CondUse = UI;
|
|
CondStride = SI->first;
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
namespace {
|
|
// Constant strides come first which in turns are sorted by their absolute
|
|
// values. If absolute values are the same, then positive strides comes first.
|
|
// e.g.
|
|
// 4, -1, X, 1, 2 ==> 1, -1, 2, 4, X
|
|
struct StrideCompare {
|
|
const ScalarEvolution *SE;
|
|
explicit StrideCompare(const ScalarEvolution *se) : SE(se) {}
|
|
|
|
bool operator()(const SCEV *LHS, const SCEV *RHS) {
|
|
const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS);
|
|
const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
|
|
if (LHSC && RHSC) {
|
|
int64_t LV = LHSC->getValue()->getSExtValue();
|
|
int64_t RV = RHSC->getValue()->getSExtValue();
|
|
uint64_t ALV = (LV < 0) ? -LV : LV;
|
|
uint64_t ARV = (RV < 0) ? -RV : RV;
|
|
if (ALV == ARV) {
|
|
if (LV != RV)
|
|
return LV > RV;
|
|
} else {
|
|
return ALV < ARV;
|
|
}
|
|
|
|
// If it's the same value but different type, sort by bit width so
|
|
// that we emit larger induction variables before smaller
|
|
// ones, letting the smaller be re-written in terms of larger ones.
|
|
return SE->getTypeSizeInBits(RHS->getType()) <
|
|
SE->getTypeSizeInBits(LHS->getType());
|
|
}
|
|
return LHSC && !RHSC;
|
|
}
|
|
};
|
|
}
|
|
|
|
/// ChangeCompareStride - If a loop termination compare instruction is the
|
|
/// only use of its stride, and the compaison is against a constant value,
|
|
/// try eliminate the stride by moving the compare instruction to another
|
|
/// stride and change its constant operand accordingly. e.g.
|
|
///
|
|
/// loop:
|
|
/// ...
|
|
/// v1 = v1 + 3
|
|
/// v2 = v2 + 1
|
|
/// if (v2 < 10) goto loop
|
|
/// =>
|
|
/// loop:
|
|
/// ...
|
|
/// v1 = v1 + 3
|
|
/// if (v1 < 30) goto loop
|
|
ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
|
|
IVStrideUse* &CondUse,
|
|
const SCEV* &CondStride,
|
|
bool PostPass) {
|
|
// If there's only one stride in the loop, there's nothing to do here.
|
|
if (IU->StrideOrder.size() < 2)
|
|
return Cond;
|
|
// If there are other users of the condition's stride, don't bother
|
|
// trying to change the condition because the stride will still
|
|
// remain.
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator I =
|
|
IU->IVUsesByStride.find(CondStride);
|
|
if (I == IU->IVUsesByStride.end())
|
|
return Cond;
|
|
if (I->second->Users.size() > 1) {
|
|
for (ilist<IVStrideUse>::iterator II = I->second->Users.begin(),
|
|
EE = I->second->Users.end(); II != EE; ++II) {
|
|
if (II->getUser() == Cond)
|
|
continue;
|
|
if (!isInstructionTriviallyDead(II->getUser()))
|
|
return Cond;
|
|
}
|
|
}
|
|
// Only handle constant strides for now.
|
|
const SCEVConstant *SC = dyn_cast<SCEVConstant>(CondStride);
|
|
if (!SC) return Cond;
|
|
|
|
ICmpInst::Predicate Predicate = Cond->getPredicate();
|
|
int64_t CmpSSInt = SC->getValue()->getSExtValue();
|
|
unsigned BitWidth = SE->getTypeSizeInBits(CondStride->getType());
|
|
uint64_t SignBit = 1ULL << (BitWidth-1);
|
|
const Type *CmpTy = Cond->getOperand(0)->getType();
|
|
const Type *NewCmpTy = NULL;
|
|
unsigned TyBits = SE->getTypeSizeInBits(CmpTy);
|
|
unsigned NewTyBits = 0;
|
|
const SCEV *NewStride = NULL;
|
|
Value *NewCmpLHS = NULL;
|
|
Value *NewCmpRHS = NULL;
|
|
int64_t Scale = 1;
|
|
const SCEV *NewOffset = SE->getIntegerSCEV(0, CmpTy);
|
|
|
|
if (ConstantInt *C = dyn_cast<ConstantInt>(Cond->getOperand(1))) {
|
|
int64_t CmpVal = C->getValue().getSExtValue();
|
|
|
|
// Check the relevant induction variable for conformance to
|
|
// the pattern.
|
|
const SCEV *IV = SE->getSCEV(Cond->getOperand(0));
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
|
|
if (!AR || !AR->isAffine())
|
|
return Cond;
|
|
|
|
const SCEVConstant *StartC = dyn_cast<SCEVConstant>(AR->getStart());
|
|
// Check stride constant and the comparision constant signs to detect
|
|
// overflow.
|
|
if (StartC) {
|
|
if ((StartC->getValue()->getSExtValue() < CmpVal && CmpSSInt < 0) ||
|
|
(StartC->getValue()->getSExtValue() > CmpVal && CmpSSInt > 0))
|
|
return Cond;
|
|
} else {
|
|
// More restrictive check for the other cases.
|
|
if ((CmpVal & SignBit) != (CmpSSInt & SignBit))
|
|
return Cond;
|
|
}
|
|
|
|
// Look for a suitable stride / iv as replacement.
|
|
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
|
|
IU->IVUsesByStride.find(IU->StrideOrder[i]);
|
|
if (!isa<SCEVConstant>(SI->first) || SI->second->Users.empty())
|
|
continue;
|
|
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
|
|
if (SSInt == CmpSSInt ||
|
|
abs64(SSInt) < abs64(CmpSSInt) ||
|
|
(SSInt % CmpSSInt) != 0)
|
|
continue;
|
|
|
|
Scale = SSInt / CmpSSInt;
|
|
int64_t NewCmpVal = CmpVal * Scale;
|
|
|
|
// If old icmp value fits in icmp immediate field, but the new one doesn't
|
|
// try something else.
|
|
if (TLI &&
|
|
TLI->isLegalICmpImmediate(CmpVal) &&
|
|
!TLI->isLegalICmpImmediate(NewCmpVal))
|
|
continue;
|
|
|
|
APInt Mul = APInt(BitWidth*2, CmpVal, true);
|
|
Mul = Mul * APInt(BitWidth*2, Scale, true);
|
|
// Check for overflow.
|
|
if (!Mul.isSignedIntN(BitWidth))
|
|
continue;
|
|
// Check for overflow in the stride's type too.
|
|
if (!Mul.isSignedIntN(SE->getTypeSizeInBits(SI->first->getType())))
|
|
continue;
|
|
|
|
// Watch out for overflow.
|
|
if (ICmpInst::isSigned(Predicate) &&
|
|
(CmpVal & SignBit) != (NewCmpVal & SignBit))
|
|
continue;
|
|
|
|
// Pick the best iv to use trying to avoid a cast.
|
|
NewCmpLHS = NULL;
|
|
for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
|
|
E = SI->second->Users.end(); UI != E; ++UI) {
|
|
Value *Op = UI->getOperandValToReplace();
|
|
|
|
// If the IVStrideUse implies a cast, check for an actual cast which
|
|
// can be used to find the original IV expression.
|
|
if (SE->getEffectiveSCEVType(Op->getType()) !=
|
|
SE->getEffectiveSCEVType(SI->first->getType())) {
|
|
CastInst *CI = dyn_cast<CastInst>(Op);
|
|
// If it's not a simple cast, it's complicated.
|
|
if (!CI)
|
|
continue;
|
|
// If it's a cast from a type other than the stride type,
|
|
// it's complicated.
|
|
if (CI->getOperand(0)->getType() != SI->first->getType())
|
|
continue;
|
|
// Ok, we found the IV expression in the stride's type.
|
|
Op = CI->getOperand(0);
|
|
}
|
|
|
|
NewCmpLHS = Op;
|
|
if (NewCmpLHS->getType() == CmpTy)
|
|
break;
|
|
}
|
|
if (!NewCmpLHS)
|
|
continue;
|
|
|
|
NewCmpTy = NewCmpLHS->getType();
|
|
NewTyBits = SE->getTypeSizeInBits(NewCmpTy);
|
|
const Type *NewCmpIntTy = IntegerType::get(Cond->getContext(), NewTyBits);
|
|
if (RequiresTypeConversion(NewCmpTy, CmpTy)) {
|
|
// Check if it is possible to rewrite it using
|
|
// an iv / stride of a smaller integer type.
|
|
unsigned Bits = NewTyBits;
|
|
if (ICmpInst::isSigned(Predicate))
|
|
--Bits;
|
|
uint64_t Mask = (1ULL << Bits) - 1;
|
|
if (((uint64_t)NewCmpVal & Mask) != (uint64_t)NewCmpVal)
|
|
continue;
|
|
}
|
|
|
|
// Don't rewrite if use offset is non-constant and the new type is
|
|
// of a different type.
|
|
// FIXME: too conservative?
|
|
if (NewTyBits != TyBits && !isa<SCEVConstant>(CondUse->getOffset()))
|
|
continue;
|
|
|
|
if (!PostPass) {
|
|
bool AllUsesAreAddresses = true;
|
|
bool AllUsesAreOutsideLoop = true;
|
|
std::vector<BasedUser> UsersToProcess;
|
|
const SCEV *CommonExprs = CollectIVUsers(SI->first, *SI->second, L,
|
|
AllUsesAreAddresses,
|
|
AllUsesAreOutsideLoop,
|
|
UsersToProcess);
|
|
// Avoid rewriting the compare instruction with an iv of new stride
|
|
// if it's likely the new stride uses will be rewritten using the
|
|
// stride of the compare instruction.
|
|
if (AllUsesAreAddresses &&
|
|
ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess))
|
|
continue;
|
|
}
|
|
|
|
// Avoid rewriting the compare instruction with an iv which has
|
|
// implicit extension or truncation built into it.
|
|
// TODO: This is over-conservative.
|
|
if (SE->getTypeSizeInBits(CondUse->getOffset()->getType()) != TyBits)
|
|
continue;
|
|
|
|
// If scale is negative, use swapped predicate unless it's testing
|
|
// for equality.
|
|
if (Scale < 0 && !Cond->isEquality())
|
|
Predicate = ICmpInst::getSwappedPredicate(Predicate);
|
|
|
|
NewStride = IU->StrideOrder[i];
|
|
if (!isa<PointerType>(NewCmpTy))
|
|
NewCmpRHS = ConstantInt::get(NewCmpTy, NewCmpVal);
|
|
else {
|
|
Constant *CI = ConstantInt::get(NewCmpIntTy, NewCmpVal);
|
|
NewCmpRHS = ConstantExpr::getIntToPtr(CI, NewCmpTy);
|
|
}
|
|
NewOffset = TyBits == NewTyBits
|
|
? SE->getMulExpr(CondUse->getOffset(),
|
|
SE->getConstant(CmpTy, Scale))
|
|
: SE->getConstant(NewCmpIntTy,
|
|
cast<SCEVConstant>(CondUse->getOffset())->getValue()
|
|
->getSExtValue()*Scale);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Forgo this transformation if it the increment happens to be
|
|
// unfortunately positioned after the condition, and the condition
|
|
// has multiple uses which prevent it from being moved immediately
|
|
// before the branch. See
|
|
// test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-*.ll
|
|
// for an example of this situation.
|
|
if (!Cond->hasOneUse()) {
|
|
for (BasicBlock::iterator I = Cond, E = Cond->getParent()->end();
|
|
I != E; ++I)
|
|
if (I == NewCmpLHS)
|
|
return Cond;
|
|
}
|
|
|
|
if (NewCmpRHS) {
|
|
// Create a new compare instruction using new stride / iv.
|
|
ICmpInst *OldCond = Cond;
|
|
// Insert new compare instruction.
|
|
Cond = new ICmpInst(OldCond, Predicate, NewCmpLHS, NewCmpRHS,
|
|
L->getHeader()->getName() + ".termcond");
|
|
|
|
DEBUG(errs() << " Change compare stride in Inst " << *OldCond);
|
|
DEBUG(errs() << " to " << *Cond << '\n');
|
|
|
|
// Remove the old compare instruction. The old indvar is probably dead too.
|
|
DeadInsts.push_back(CondUse->getOperandValToReplace());
|
|
OldCond->replaceAllUsesWith(Cond);
|
|
OldCond->eraseFromParent();
|
|
|
|
IU->IVUsesByStride[NewStride]->addUser(NewOffset, Cond, NewCmpLHS);
|
|
CondUse = &IU->IVUsesByStride[NewStride]->Users.back();
|
|
CondStride = NewStride;
|
|
++NumEliminated;
|
|
Changed = true;
|
|
}
|
|
|
|
return Cond;
|
|
}
|
|
|
|
/// OptimizeMax - Rewrite the loop's terminating condition if it uses
|
|
/// a max computation.
|
|
///
|
|
/// This is a narrow solution to a specific, but acute, problem. For loops
|
|
/// like this:
|
|
///
|
|
/// i = 0;
|
|
/// do {
|
|
/// p[i] = 0.0;
|
|
/// } while (++i < n);
|
|
///
|
|
/// the trip count isn't just 'n', because 'n' might not be positive. And
|
|
/// unfortunately this can come up even for loops where the user didn't use
|
|
/// a C do-while loop. For example, seemingly well-behaved top-test loops
|
|
/// will commonly be lowered like this:
|
|
//
|
|
/// if (n > 0) {
|
|
/// i = 0;
|
|
/// do {
|
|
/// p[i] = 0.0;
|
|
/// } while (++i < n);
|
|
/// }
|
|
///
|
|
/// and then it's possible for subsequent optimization to obscure the if
|
|
/// test in such a way that indvars can't find it.
|
|
///
|
|
/// When indvars can't find the if test in loops like this, it creates a
|
|
/// max expression, which allows it to give the loop a canonical
|
|
/// induction variable:
|
|
///
|
|
/// i = 0;
|
|
/// max = n < 1 ? 1 : n;
|
|
/// do {
|
|
/// p[i] = 0.0;
|
|
/// } while (++i != max);
|
|
///
|
|
/// Canonical induction variables are necessary because the loop passes
|
|
/// are designed around them. The most obvious example of this is the
|
|
/// LoopInfo analysis, which doesn't remember trip count values. It
|
|
/// expects to be able to rediscover the trip count each time it is
|
|
/// needed, and it does this using a simple analyis that only succeeds if
|
|
/// the loop has a canonical induction variable.
|
|
///
|
|
/// However, when it comes time to generate code, the maximum operation
|
|
/// can be quite costly, especially if it's inside of an outer loop.
|
|
///
|
|
/// This function solves this problem by detecting this type of loop and
|
|
/// rewriting their conditions from ICMP_NE back to ICMP_SLT, and deleting
|
|
/// the instructions for the maximum computation.
|
|
///
|
|
ICmpInst *LoopStrengthReduce::OptimizeMax(Loop *L, ICmpInst *Cond,
|
|
IVStrideUse* &CondUse) {
|
|
// Check that the loop matches the pattern we're looking for.
|
|
if (Cond->getPredicate() != CmpInst::ICMP_EQ &&
|
|
Cond->getPredicate() != CmpInst::ICMP_NE)
|
|
return Cond;
|
|
|
|
SelectInst *Sel = dyn_cast<SelectInst>(Cond->getOperand(1));
|
|
if (!Sel || !Sel->hasOneUse()) return Cond;
|
|
|
|
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
|
|
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
|
|
return Cond;
|
|
const SCEV *One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType());
|
|
|
|
// Add one to the backedge-taken count to get the trip count.
|
|
const SCEV *IterationCount = SE->getAddExpr(BackedgeTakenCount, One);
|
|
|
|
// Check for a max calculation that matches the pattern.
|
|
if (!isa<SCEVSMaxExpr>(IterationCount) && !isa<SCEVUMaxExpr>(IterationCount))
|
|
return Cond;
|
|
const SCEVNAryExpr *Max = cast<SCEVNAryExpr>(IterationCount);
|
|
if (Max != SE->getSCEV(Sel)) return Cond;
|
|
|
|
// To handle a max with more than two operands, this optimization would
|
|
// require additional checking and setup.
|
|
if (Max->getNumOperands() != 2)
|
|
return Cond;
|
|
|
|
const SCEV *MaxLHS = Max->getOperand(0);
|
|
const SCEV *MaxRHS = Max->getOperand(1);
|
|
if (!MaxLHS || MaxLHS != One) return Cond;
|
|
|
|
// Check the relevant induction variable for conformance to
|
|
// the pattern.
|
|
const SCEV *IV = SE->getSCEV(Cond->getOperand(0));
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
|
|
if (!AR || !AR->isAffine() ||
|
|
AR->getStart() != One ||
|
|
AR->getStepRecurrence(*SE) != One)
|
|
return Cond;
|
|
|
|
assert(AR->getLoop() == L &&
|
|
"Loop condition operand is an addrec in a different loop!");
|
|
|
|
// Check the right operand of the select, and remember it, as it will
|
|
// be used in the new comparison instruction.
|
|
Value *NewRHS = 0;
|
|
if (SE->getSCEV(Sel->getOperand(1)) == MaxRHS)
|
|
NewRHS = Sel->getOperand(1);
|
|
else if (SE->getSCEV(Sel->getOperand(2)) == MaxRHS)
|
|
NewRHS = Sel->getOperand(2);
|
|
if (!NewRHS) return Cond;
|
|
|
|
// Determine the new comparison opcode. It may be signed or unsigned,
|
|
// and the original comparison may be either equality or inequality.
|
|
CmpInst::Predicate Pred =
|
|
isa<SCEVSMaxExpr>(Max) ? CmpInst::ICMP_SLT : CmpInst::ICMP_ULT;
|
|
if (Cond->getPredicate() == CmpInst::ICMP_EQ)
|
|
Pred = CmpInst::getInversePredicate(Pred);
|
|
|
|
// Ok, everything looks ok to change the condition into an SLT or SGE and
|
|
// delete the max calculation.
|
|
ICmpInst *NewCond =
|
|
new ICmpInst(Cond, Pred, Cond->getOperand(0), NewRHS, "scmp");
|
|
|
|
// Delete the max calculation instructions.
|
|
Cond->replaceAllUsesWith(NewCond);
|
|
CondUse->setUser(NewCond);
|
|
Instruction *Cmp = cast<Instruction>(Sel->getOperand(0));
|
|
Cond->eraseFromParent();
|
|
Sel->eraseFromParent();
|
|
if (Cmp->use_empty())
|
|
Cmp->eraseFromParent();
|
|
return NewCond;
|
|
}
|
|
|
|
/// OptimizeShadowIV - If IV is used in a int-to-float cast
|
|
/// inside the loop then try to eliminate the cast opeation.
|
|
void LoopStrengthReduce::OptimizeShadowIV(Loop *L) {
|
|
|
|
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
|
|
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
|
|
return;
|
|
|
|
for (unsigned Stride = 0, e = IU->StrideOrder.size(); Stride != e;
|
|
++Stride) {
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
|
|
IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
|
|
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
|
|
if (!isa<SCEVConstant>(SI->first))
|
|
continue;
|
|
|
|
for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
|
|
E = SI->second->Users.end(); UI != E; /* empty */) {
|
|
ilist<IVStrideUse>::iterator CandidateUI = UI;
|
|
++UI;
|
|
Instruction *ShadowUse = CandidateUI->getUser();
|
|
const Type *DestTy = NULL;
|
|
|
|
/* If shadow use is a int->float cast then insert a second IV
|
|
to eliminate this cast.
|
|
|
|
for (unsigned i = 0; i < n; ++i)
|
|
foo((double)i);
|
|
|
|
is transformed into
|
|
|
|
double d = 0.0;
|
|
for (unsigned i = 0; i < n; ++i, ++d)
|
|
foo(d);
|
|
*/
|
|
if (UIToFPInst *UCast = dyn_cast<UIToFPInst>(CandidateUI->getUser()))
|
|
DestTy = UCast->getDestTy();
|
|
else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->getUser()))
|
|
DestTy = SCast->getDestTy();
|
|
if (!DestTy) continue;
|
|
|
|
if (TLI) {
|
|
// If target does not support DestTy natively then do not apply
|
|
// this transformation.
|
|
EVT DVT = TLI->getValueType(DestTy);
|
|
if (!TLI->isTypeLegal(DVT)) continue;
|
|
}
|
|
|
|
PHINode *PH = dyn_cast<PHINode>(ShadowUse->getOperand(0));
|
|
if (!PH) continue;
|
|
if (PH->getNumIncomingValues() != 2) continue;
|
|
|
|
const Type *SrcTy = PH->getType();
|
|
int Mantissa = DestTy->getFPMantissaWidth();
|
|
if (Mantissa == -1) continue;
|
|
if ((int)SE->getTypeSizeInBits(SrcTy) > Mantissa)
|
|
continue;
|
|
|
|
unsigned Entry, Latch;
|
|
if (PH->getIncomingBlock(0) == L->getLoopPreheader()) {
|
|
Entry = 0;
|
|
Latch = 1;
|
|
} else {
|
|
Entry = 1;
|
|
Latch = 0;
|
|
}
|
|
|
|
ConstantInt *Init = dyn_cast<ConstantInt>(PH->getIncomingValue(Entry));
|
|
if (!Init) continue;
|
|
Constant *NewInit = ConstantFP::get(DestTy, Init->getZExtValue());
|
|
|
|
BinaryOperator *Incr =
|
|
dyn_cast<BinaryOperator>(PH->getIncomingValue(Latch));
|
|
if (!Incr) continue;
|
|
if (Incr->getOpcode() != Instruction::Add
|
|
&& Incr->getOpcode() != Instruction::Sub)
|
|
continue;
|
|
|
|
/* Initialize new IV, double d = 0.0 in above example. */
|
|
ConstantInt *C = NULL;
|
|
if (Incr->getOperand(0) == PH)
|
|
C = dyn_cast<ConstantInt>(Incr->getOperand(1));
|
|
else if (Incr->getOperand(1) == PH)
|
|
C = dyn_cast<ConstantInt>(Incr->getOperand(0));
|
|
else
|
|
continue;
|
|
|
|
if (!C) continue;
|
|
|
|
// Ignore negative constants, as the code below doesn't handle them
|
|
// correctly. TODO: Remove this restriction.
|
|
if (!C->getValue().isStrictlyPositive()) continue;
|
|
|
|
/* Add new PHINode. */
|
|
PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH);
|
|
|
|
/* create new increment. '++d' in above example. */
|
|
Constant *CFP = ConstantFP::get(DestTy, C->getZExtValue());
|
|
BinaryOperator *NewIncr =
|
|
BinaryOperator::Create(Incr->getOpcode() == Instruction::Add ?
|
|
Instruction::FAdd : Instruction::FSub,
|
|
NewPH, CFP, "IV.S.next.", Incr);
|
|
|
|
NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry));
|
|
NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch));
|
|
|
|
/* Remove cast operation */
|
|
ShadowUse->replaceAllUsesWith(NewPH);
|
|
ShadowUse->eraseFromParent();
|
|
NumShadow++;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/// OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar
|
|
/// uses in the loop, look to see if we can eliminate some, in favor of using
|
|
/// common indvars for the different uses.
|
|
void LoopStrengthReduce::OptimizeIndvars(Loop *L) {
|
|
// TODO: implement optzns here.
|
|
|
|
OptimizeShadowIV(L);
|
|
}
|
|
|
|
bool LoopStrengthReduce::StrideMightBeShared(const SCEV* Stride, Loop *L,
|
|
bool CheckPreInc) {
|
|
int64_t SInt = cast<SCEVConstant>(Stride)->getValue()->getSExtValue();
|
|
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
|
|
IU->IVUsesByStride.find(IU->StrideOrder[i]);
|
|
const SCEV *Share = SI->first;
|
|
if (!isa<SCEVConstant>(SI->first) || Share == Stride)
|
|
continue;
|
|
int64_t SSInt = cast<SCEVConstant>(Share)->getValue()->getSExtValue();
|
|
if (SSInt == SInt)
|
|
return true; // This can definitely be reused.
|
|
if (unsigned(abs64(SSInt)) < SInt || (SSInt % SInt) != 0)
|
|
continue;
|
|
int64_t Scale = SSInt / SInt;
|
|
bool AllUsesAreAddresses = true;
|
|
bool AllUsesAreOutsideLoop = true;
|
|
std::vector<BasedUser> UsersToProcess;
|
|
const SCEV *CommonExprs = CollectIVUsers(SI->first, *SI->second, L,
|
|
AllUsesAreAddresses,
|
|
AllUsesAreOutsideLoop,
|
|
UsersToProcess);
|
|
if (AllUsesAreAddresses &&
|
|
ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess)) {
|
|
if (!CheckPreInc)
|
|
return true;
|
|
// Any pre-inc iv use?
|
|
IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[Share];
|
|
for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(),
|
|
E = StrideUses.Users.end(); I != E; ++I) {
|
|
if (!I->isUseOfPostIncrementedValue())
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// isUsedByExitBranch - Return true if icmp is used by a loop terminating
|
|
/// conditional branch or it's and / or with other conditions before being used
|
|
/// as the condition.
|
|
static bool isUsedByExitBranch(ICmpInst *Cond, Loop *L) {
|
|
BasicBlock *CondBB = Cond->getParent();
|
|
if (!L->isLoopExiting(CondBB))
|
|
return false;
|
|
BranchInst *TermBr = dyn_cast<BranchInst>(CondBB->getTerminator());
|
|
if (!TermBr || !TermBr->isConditional())
|
|
return false;
|
|
|
|
Value *User = *Cond->use_begin();
|
|
Instruction *UserInst = dyn_cast<Instruction>(User);
|
|
while (UserInst &&
|
|
(UserInst->getOpcode() == Instruction::And ||
|
|
UserInst->getOpcode() == Instruction::Or)) {
|
|
if (!UserInst->hasOneUse() || UserInst->getParent() != CondBB)
|
|
return false;
|
|
User = *User->use_begin();
|
|
UserInst = dyn_cast<Instruction>(User);
|
|
}
|
|
return User == TermBr;
|
|
}
|
|
|
|
static bool ShouldCountToZero(ICmpInst *Cond, IVStrideUse* &CondUse,
|
|
ScalarEvolution *SE, Loop *L,
|
|
const TargetLowering *TLI = 0) {
|
|
if (!L->contains(Cond))
|
|
return false;
|
|
|
|
if (!isa<SCEVConstant>(CondUse->getOffset()))
|
|
return false;
|
|
|
|
// Handle only tests for equality for the moment.
|
|
if (!Cond->isEquality() || !Cond->hasOneUse())
|
|
return false;
|
|
if (!isUsedByExitBranch(Cond, L))
|
|
return false;
|
|
|
|
Value *CondOp0 = Cond->getOperand(0);
|
|
const SCEV *IV = SE->getSCEV(CondOp0);
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
|
|
if (!AR || !AR->isAffine())
|
|
return false;
|
|
|
|
const SCEVConstant *SC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
|
|
if (!SC || SC->getValue()->getSExtValue() < 0)
|
|
// If it's already counting down, don't do anything.
|
|
return false;
|
|
|
|
// If the RHS of the comparison is not an loop invariant, the rewrite
|
|
// cannot be done. Also bail out if it's already comparing against a zero.
|
|
// If we are checking this before cmp stride optimization, check if it's
|
|
// comparing against a already legal immediate.
|
|
Value *RHS = Cond->getOperand(1);
|
|
ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS);
|
|
if (!L->isLoopInvariant(RHS) ||
|
|
(RHSC && RHSC->isZero()) ||
|
|
(RHSC && TLI && TLI->isLegalICmpImmediate(RHSC->getSExtValue())))
|
|
return false;
|
|
|
|
// Make sure the IV is only used for counting. Value may be preinc or
|
|
// postinc; 2 uses in either case.
|
|
if (!CondOp0->hasNUses(2))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// OptimizeLoopTermCond - Change loop terminating condition to use the
|
|
/// postinc iv when possible.
|
|
void LoopStrengthReduce::OptimizeLoopTermCond(Loop *L) {
|
|
BasicBlock *LatchBlock = L->getLoopLatch();
|
|
bool LatchExit = L->isLoopExiting(LatchBlock);
|
|
SmallVector<BasicBlock*, 8> ExitingBlocks;
|
|
L->getExitingBlocks(ExitingBlocks);
|
|
|
|
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
|
|
BasicBlock *ExitingBlock = ExitingBlocks[i];
|
|
|
|
// Finally, get the terminating condition for the loop if possible. If we
|
|
// can, we want to change it to use a post-incremented version of its
|
|
// induction variable, to allow coalescing the live ranges for the IV into
|
|
// one register value.
|
|
|
|
BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
|
|
if (!TermBr)
|
|
continue;
|
|
// FIXME: Overly conservative, termination condition could be an 'or' etc..
|
|
if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition()))
|
|
continue;
|
|
|
|
// Search IVUsesByStride to find Cond's IVUse if there is one.
|
|
IVStrideUse *CondUse = 0;
|
|
const SCEV *CondStride = 0;
|
|
ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
|
|
if (!FindIVUserForCond(Cond, CondUse, CondStride))
|
|
continue;
|
|
|
|
// If the latch block is exiting and it's not a single block loop, it's
|
|
// not safe to use postinc iv in other exiting blocks. FIXME: overly
|
|
// conservative? How about icmp stride optimization?
|
|
bool UsePostInc = !(e > 1 && LatchExit && ExitingBlock != LatchBlock);
|
|
if (UsePostInc && ExitingBlock != LatchBlock) {
|
|
if (!Cond->hasOneUse())
|
|
// See below, we don't want the condition to be cloned.
|
|
UsePostInc = false;
|
|
else {
|
|
// If exiting block is the latch block, we know it's safe and profitable
|
|
// to transform the icmp to use post-inc iv. Otherwise do so only if it
|
|
// would not reuse another iv and its iv would be reused by other uses.
|
|
// We are optimizing for the case where the icmp is the only use of the
|
|
// iv.
|
|
IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[CondStride];
|
|
for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(),
|
|
E = StrideUses.Users.end(); I != E; ++I) {
|
|
if (I->getUser() == Cond)
|
|
continue;
|
|
if (!I->isUseOfPostIncrementedValue()) {
|
|
UsePostInc = false;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// If iv for the stride might be shared and any of the users use pre-inc
|
|
// iv might be used, then it's not safe to use post-inc iv.
|
|
if (UsePostInc &&
|
|
isa<SCEVConstant>(CondStride) &&
|
|
StrideMightBeShared(CondStride, L, true))
|
|
UsePostInc = false;
|
|
}
|
|
|
|
// If the trip count is computed in terms of a max (due to ScalarEvolution
|
|
// being unable to find a sufficient guard, for example), change the loop
|
|
// comparison to use SLT or ULT instead of NE.
|
|
Cond = OptimizeMax(L, Cond, CondUse);
|
|
|
|
// If possible, change stride and operands of the compare instruction to
|
|
// eliminate one stride. However, avoid rewriting the compare instruction
|
|
// with an iv of new stride if it's likely the new stride uses will be
|
|
// rewritten using the stride of the compare instruction.
|
|
if (ExitingBlock == LatchBlock && isa<SCEVConstant>(CondStride)) {
|
|
// If the condition stride is a constant and it's the only use, we might
|
|
// want to optimize it first by turning it to count toward zero.
|
|
if (!StrideMightBeShared(CondStride, L, false) &&
|
|
!ShouldCountToZero(Cond, CondUse, SE, L, TLI))
|
|
Cond = ChangeCompareStride(L, Cond, CondUse, CondStride);
|
|
}
|
|
|
|
if (!UsePostInc)
|
|
continue;
|
|
|
|
DEBUG(errs() << " Change loop exiting icmp to use postinc iv: "
|
|
<< *Cond << '\n');
|
|
|
|
// It's possible for the setcc instruction to be anywhere in the loop, and
|
|
// possible for it to have multiple users. If it is not immediately before
|
|
// the exiting block branch, move it.
|
|
if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) {
|
|
if (Cond->hasOneUse()) { // Condition has a single use, just move it.
|
|
Cond->moveBefore(TermBr);
|
|
} else {
|
|
// Otherwise, clone the terminating condition and insert into the
|
|
// loopend.
|
|
Cond = cast<ICmpInst>(Cond->clone());
|
|
Cond->setName(L->getHeader()->getName() + ".termcond");
|
|
ExitingBlock->getInstList().insert(TermBr, Cond);
|
|
|
|
// Clone the IVUse, as the old use still exists!
|
|
IU->IVUsesByStride[CondStride]->addUser(CondUse->getOffset(), Cond,
|
|
CondUse->getOperandValToReplace());
|
|
CondUse = &IU->IVUsesByStride[CondStride]->Users.back();
|
|
}
|
|
}
|
|
|
|
// If we get to here, we know that we can transform the setcc instruction to
|
|
// use the post-incremented version of the IV, allowing us to coalesce the
|
|
// live ranges for the IV correctly.
|
|
CondUse->setOffset(SE->getMinusSCEV(CondUse->getOffset(), CondStride));
|
|
CondUse->setIsUseOfPostIncrementedValue(true);
|
|
Changed = true;
|
|
|
|
++NumLoopCond;
|
|
}
|
|
}
|
|
|
|
bool LoopStrengthReduce::OptimizeLoopCountIVOfStride(const SCEV* &Stride,
|
|
IVStrideUse* &CondUse,
|
|
Loop *L) {
|
|
// If the only use is an icmp of a loop exiting conditional branch, then
|
|
// attempt the optimization.
|
|
BasedUser User = BasedUser(*CondUse, SE);
|
|
assert(isa<ICmpInst>(User.Inst) && "Expecting an ICMPInst!");
|
|
ICmpInst *Cond = cast<ICmpInst>(User.Inst);
|
|
|
|
// Less strict check now that compare stride optimization is done.
|
|
if (!ShouldCountToZero(Cond, CondUse, SE, L))
|
|
return false;
|
|
|
|
Value *CondOp0 = Cond->getOperand(0);
|
|
PHINode *PHIExpr = dyn_cast<PHINode>(CondOp0);
|
|
Instruction *Incr;
|
|
if (!PHIExpr) {
|
|
// Value tested is postinc. Find the phi node.
|
|
Incr = dyn_cast<BinaryOperator>(CondOp0);
|
|
// FIXME: Just use User.OperandValToReplace here?
|
|
if (!Incr || Incr->getOpcode() != Instruction::Add)
|
|
return false;
|
|
|
|
PHIExpr = dyn_cast<PHINode>(Incr->getOperand(0));
|
|
if (!PHIExpr)
|
|
return false;
|
|
// 1 use for preinc value, the increment.
|
|
if (!PHIExpr->hasOneUse())
|
|
return false;
|
|
} else {
|
|
assert(isa<PHINode>(CondOp0) &&
|
|
"Unexpected loop exiting counting instruction sequence!");
|
|
PHIExpr = cast<PHINode>(CondOp0);
|
|
// Value tested is preinc. Find the increment.
|
|
// A CmpInst is not a BinaryOperator; we depend on this.
|
|
Instruction::use_iterator UI = PHIExpr->use_begin();
|
|
Incr = dyn_cast<BinaryOperator>(UI);
|
|
if (!Incr)
|
|
Incr = dyn_cast<BinaryOperator>(++UI);
|
|
// One use for postinc value, the phi. Unnecessarily conservative?
|
|
if (!Incr || !Incr->hasOneUse() || Incr->getOpcode() != Instruction::Add)
|
|
return false;
|
|
}
|
|
|
|
// Replace the increment with a decrement.
|
|
DEBUG(errs() << "LSR: Examining use ");
|
|
DEBUG(WriteAsOperand(errs(), CondOp0, /*PrintType=*/false));
|
|
DEBUG(errs() << " in Inst: " << *Cond << '\n');
|
|
BinaryOperator *Decr = BinaryOperator::Create(Instruction::Sub,
|
|
Incr->getOperand(0), Incr->getOperand(1), "tmp", Incr);
|
|
Incr->replaceAllUsesWith(Decr);
|
|
Incr->eraseFromParent();
|
|
|
|
// Substitute endval-startval for the original startval, and 0 for the
|
|
// original endval. Since we're only testing for equality this is OK even
|
|
// if the computation wraps around.
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
Instruction *PreInsertPt = Preheader->getTerminator();
|
|
unsigned InBlock = L->contains(PHIExpr->getIncomingBlock(0)) ? 1 : 0;
|
|
Value *StartVal = PHIExpr->getIncomingValue(InBlock);
|
|
Value *EndVal = Cond->getOperand(1);
|
|
DEBUG(errs() << " Optimize loop counting iv to count down ["
|
|
<< *EndVal << " .. " << *StartVal << "]\n");
|
|
|
|
// FIXME: check for case where both are constant.
|
|
Constant* Zero = ConstantInt::get(Cond->getOperand(1)->getType(), 0);
|
|
BinaryOperator *NewStartVal = BinaryOperator::Create(Instruction::Sub,
|
|
EndVal, StartVal, "tmp", PreInsertPt);
|
|
PHIExpr->setIncomingValue(InBlock, NewStartVal);
|
|
Cond->setOperand(1, Zero);
|
|
DEBUG(errs() << " New icmp: " << *Cond << "\n");
|
|
|
|
int64_t SInt = cast<SCEVConstant>(Stride)->getValue()->getSExtValue();
|
|
const SCEV *NewStride = 0;
|
|
bool Found = false;
|
|
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
|
|
const SCEV *OldStride = IU->StrideOrder[i];
|
|
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(OldStride))
|
|
if (SC->getValue()->getSExtValue() == -SInt) {
|
|
Found = true;
|
|
NewStride = OldStride;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (!Found)
|
|
NewStride = SE->getIntegerSCEV(-SInt, Stride->getType());
|
|
IU->AddUser(NewStride, CondUse->getOffset(), Cond, Cond->getOperand(0));
|
|
IU->IVUsesByStride[Stride]->removeUser(CondUse);
|
|
|
|
CondUse = &IU->IVUsesByStride[NewStride]->Users.back();
|
|
Stride = NewStride;
|
|
|
|
++NumCountZero;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for deciding
|
|
/// when to exit the loop is used only for that purpose, try to rearrange things
|
|
/// so it counts down to a test against zero.
|
|
bool LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) {
|
|
bool ThisChanged = false;
|
|
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
|
|
const SCEV *Stride = IU->StrideOrder[i];
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
|
|
IU->IVUsesByStride.find(Stride);
|
|
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
|
|
// FIXME: Generalize to non-affine IV's.
|
|
if (!SI->first->isLoopInvariant(L))
|
|
continue;
|
|
// If stride is a constant and it has an icmpinst use, check if we can
|
|
// optimize the loop to count down.
|
|
if (isa<SCEVConstant>(Stride) && SI->second->Users.size() == 1) {
|
|
Instruction *User = SI->second->Users.begin()->getUser();
|
|
if (!isa<ICmpInst>(User))
|
|
continue;
|
|
const SCEV *CondStride = Stride;
|
|
IVStrideUse *Use = &*SI->second->Users.begin();
|
|
if (!OptimizeLoopCountIVOfStride(CondStride, Use, L))
|
|
continue;
|
|
ThisChanged = true;
|
|
|
|
// Now check if it's possible to reuse this iv for other stride uses.
|
|
for (unsigned j = 0, ee = IU->StrideOrder.size(); j != ee; ++j) {
|
|
const SCEV *SStride = IU->StrideOrder[j];
|
|
if (SStride == CondStride)
|
|
continue;
|
|
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SII =
|
|
IU->IVUsesByStride.find(SStride);
|
|
assert(SII != IU->IVUsesByStride.end() && "Stride doesn't exist!");
|
|
// FIXME: Generalize to non-affine IV's.
|
|
if (!SII->first->isLoopInvariant(L))
|
|
continue;
|
|
// FIXME: Rewrite other stride using CondStride.
|
|
}
|
|
}
|
|
}
|
|
|
|
Changed |= ThisChanged;
|
|
return ThisChanged;
|
|
}
|
|
|
|
bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
IU = &getAnalysis<IVUsers>();
|
|
SE = &getAnalysis<ScalarEvolution>();
|
|
Changed = false;
|
|
|
|
// If LoopSimplify form is not available, stay out of trouble.
|
|
if (!L->getLoopPreheader() || !L->getLoopLatch())
|
|
return false;
|
|
|
|
if (!IU->IVUsesByStride.empty()) {
|
|
DEBUG(errs() << "\nLSR on \"" << L->getHeader()->getParent()->getName()
|
|
<< "\" ";
|
|
L->dump());
|
|
|
|
// Sort the StrideOrder so we process larger strides first.
|
|
std::stable_sort(IU->StrideOrder.begin(), IU->StrideOrder.end(),
|
|
StrideCompare(SE));
|
|
|
|
// Optimize induction variables. Some indvar uses can be transformed to use
|
|
// strides that will be needed for other purposes. A common example of this
|
|
// is the exit test for the loop, which can often be rewritten to use the
|
|
// computation of some other indvar to decide when to terminate the loop.
|
|
OptimizeIndvars(L);
|
|
|
|
// Change loop terminating condition to use the postinc iv when possible
|
|
// and optimize loop terminating compare. FIXME: Move this after
|
|
// StrengthReduceIVUsersOfStride?
|
|
OptimizeLoopTermCond(L);
|
|
|
|
// FIXME: We can shrink overlarge IV's here. e.g. if the code has
|
|
// computation in i64 values and the target doesn't support i64, demote
|
|
// the computation to 32-bit if safe.
|
|
|
|
// FIXME: Attempt to reuse values across multiple IV's. In particular, we
|
|
// could have something like "for(i) { foo(i*8); bar(i*16) }", which should
|
|
// be codegened as "for (j = 0;; j+=8) { foo(j); bar(j+j); }" on X86/PPC.
|
|
// Need to be careful that IV's are all the same type. Only works for
|
|
// intptr_t indvars.
|
|
|
|
// IVsByStride keeps IVs for one particular loop.
|
|
assert(IVsByStride.empty() && "Stale entries in IVsByStride?");
|
|
|
|
StrengthReduceIVUsers(L);
|
|
|
|
// After all sharing is done, see if we can adjust the loop to test against
|
|
// zero instead of counting up to a maximum. This is usually faster.
|
|
OptimizeLoopCountIV(L);
|
|
|
|
// We're done analyzing this loop; release all the state we built up for it.
|
|
IVsByStride.clear();
|
|
|
|
// Clean up after ourselves
|
|
DeleteTriviallyDeadInstructions();
|
|
}
|
|
|
|
// At this point, it is worth checking to see if any recurrence PHIs are also
|
|
// dead, so that we can remove them as well.
|
|
DeleteDeadPHIs(L->getHeader());
|
|
|
|
return Changed;
|
|
}
|