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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130408 91177308-0d34-0410-b5e6-96231b3b80d8
1085 lines
42 KiB
C++
1085 lines
42 KiB
C++
//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
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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 simpler forms suitable for subsequent
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// analysis and transformation.
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//
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// This transformation makes the following changes to each loop with an
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// identifiable induction variable:
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// 1. All loops are transformed to have a SINGLE canonical induction variable
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// which starts at zero and steps by one.
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// 2. The canonical induction variable is guaranteed to be the first PHI node
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// in the loop header block.
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// 3. The canonical induction variable is guaranteed to be in a wide enough
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// type so that IV expressions need not be (directly) zero-extended or
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// sign-extended.
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// 4. Any pointer arithmetic recurrences are raised to use array subscripts.
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//
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// If the trip count of a loop is computable, this pass also makes the following
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// changes:
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// 1. The exit condition for the loop is canonicalized to compare the
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// induction value against the exit value. This turns loops like:
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// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
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// 2. Any use outside of the loop of an expression derived from the indvar
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// is changed to compute the derived value outside of the loop, eliminating
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// the dependence on the exit value of the induction variable. If the only
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// purpose of the loop is to compute the exit value of some derived
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// expression, this transformation will make the loop dead.
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//
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// This transformation should be followed by strength reduction after all of the
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// desired loop transformations have been performed.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "indvars"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/BasicBlock.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/LLVMContext.h"
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#include "llvm/Type.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/IVUsers.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/STLExtras.h"
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using namespace llvm;
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STATISTIC(NumRemoved , "Number of aux indvars removed");
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STATISTIC(NumInserted, "Number of canonical indvars added");
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STATISTIC(NumReplaced, "Number of exit values replaced");
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STATISTIC(NumLFTR , "Number of loop exit tests replaced");
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namespace {
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class IndVarSimplify : public LoopPass {
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IVUsers *IU;
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LoopInfo *LI;
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ScalarEvolution *SE;
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DominatorTree *DT;
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SmallVector<WeakVH, 16> DeadInsts;
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bool Changed;
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public:
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static char ID; // Pass identification, replacement for typeid
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IndVarSimplify() : LoopPass(ID) {
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initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
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}
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virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<DominatorTree>();
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AU.addRequired<LoopInfo>();
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AU.addRequired<ScalarEvolution>();
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AU.addRequiredID(LoopSimplifyID);
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AU.addRequiredID(LCSSAID);
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AU.addRequired<IVUsers>();
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AU.addPreserved<ScalarEvolution>();
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AU.addPreservedID(LoopSimplifyID);
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AU.addPreservedID(LCSSAID);
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AU.addPreserved<IVUsers>();
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AU.setPreservesCFG();
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}
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private:
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bool isValidRewrite(Value *FromVal, Value *ToVal);
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void EliminateIVComparisons();
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void EliminateIVRemainders();
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void RewriteNonIntegerIVs(Loop *L);
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ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
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PHINode *IndVar,
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BasicBlock *ExitingBlock,
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BranchInst *BI,
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SCEVExpander &Rewriter);
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void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
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void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter);
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void SinkUnusedInvariants(Loop *L);
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void HandleFloatingPointIV(Loop *L, PHINode *PH);
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};
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}
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char IndVarSimplify::ID = 0;
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INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
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"Canonicalize Induction Variables", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTree)
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INITIALIZE_PASS_DEPENDENCY(LoopInfo)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
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INITIALIZE_PASS_DEPENDENCY(LCSSA)
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INITIALIZE_PASS_DEPENDENCY(IVUsers)
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INITIALIZE_PASS_END(IndVarSimplify, "indvars",
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"Canonicalize Induction Variables", false, false)
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Pass *llvm::createIndVarSimplifyPass() {
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return new IndVarSimplify();
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}
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/// isValidRewrite - Return true if the SCEV expansion generated by the
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/// rewriter can replace the original value. SCEV guarantees that it
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/// produces the same value, but the way it is produced may be illegal IR.
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/// Ideally, this function will only be called for verification.
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bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
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// If an SCEV expression subsumed multiple pointers, its expansion could
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// reassociate the GEP changing the base pointer. This is illegal because the
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// final address produced by a GEP chain must be inbounds relative to its
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// underlying object. Otherwise basic alias analysis, among other things,
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// could fail in a dangerous way. Ultimately, SCEV will be improved to avoid
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// producing an expression involving multiple pointers. Until then, we must
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// bail out here.
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//
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// Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject
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// because it understands lcssa phis while SCEV does not.
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Value *FromPtr = FromVal;
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Value *ToPtr = ToVal;
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if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) {
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FromPtr = GEP->getPointerOperand();
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}
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if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) {
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ToPtr = GEP->getPointerOperand();
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}
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if (FromPtr != FromVal || ToPtr != ToVal) {
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// Quickly check the common case
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if (FromPtr == ToPtr)
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return true;
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// SCEV may have rewritten an expression that produces the GEP's pointer
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// operand. That's ok as long as the pointer operand has the same base
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// pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the
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// base of a recurrence. This handles the case in which SCEV expansion
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// converts a pointer type recurrence into a nonrecurrent pointer base
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// indexed by an integer recurrence.
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const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
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const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
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if (FromBase == ToBase)
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return true;
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DEBUG(dbgs() << "INDVARS: GEP rewrite bail out "
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<< *FromBase << " != " << *ToBase << "\n");
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return false;
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}
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return true;
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}
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/// LinearFunctionTestReplace - This method rewrites the exit condition of the
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/// loop to be a canonical != comparison against the incremented loop induction
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/// variable. This pass is able to rewrite the exit tests of any loop where the
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/// SCEV analysis can determine a loop-invariant trip count of the loop, which
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/// is actually a much broader range than just linear tests.
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ICmpInst *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
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const SCEV *BackedgeTakenCount,
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PHINode *IndVar,
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BasicBlock *ExitingBlock,
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BranchInst *BI,
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SCEVExpander &Rewriter) {
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// Special case: If the backedge-taken count is a UDiv, it's very likely a
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// UDiv that ScalarEvolution produced in order to compute a precise
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// expression, rather than a UDiv from the user's code. If we can't find a
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// UDiv in the code with some simple searching, assume the former and forego
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// rewriting the loop.
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if (isa<SCEVUDivExpr>(BackedgeTakenCount)) {
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ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition());
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if (!OrigCond) return 0;
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const SCEV *R = SE->getSCEV(OrigCond->getOperand(1));
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R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1));
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if (R != BackedgeTakenCount) {
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const SCEV *L = SE->getSCEV(OrigCond->getOperand(0));
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L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1));
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if (L != BackedgeTakenCount)
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return 0;
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}
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}
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// If the exiting block is not the same as the backedge block, we must compare
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// against the preincremented value, otherwise we prefer to compare against
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// the post-incremented value.
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Value *CmpIndVar;
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const SCEV *RHS = BackedgeTakenCount;
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if (ExitingBlock == L->getLoopLatch()) {
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// Add one to the "backedge-taken" count to get the trip count.
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// If this addition may overflow, we have to be more pessimistic and
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// cast the induction variable before doing the add.
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const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0);
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const SCEV *N =
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SE->getAddExpr(BackedgeTakenCount,
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SE->getConstant(BackedgeTakenCount->getType(), 1));
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if ((isa<SCEVConstant>(N) && !N->isZero()) ||
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SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
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// No overflow. Cast the sum.
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RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
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} else {
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// Potential overflow. Cast before doing the add.
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RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
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IndVar->getType());
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RHS = SE->getAddExpr(RHS,
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SE->getConstant(IndVar->getType(), 1));
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}
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// The BackedgeTaken expression contains the number of times that the
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// backedge branches to the loop header. This is one less than the
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// number of times the loop executes, so use the incremented indvar.
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CmpIndVar = IndVar->getIncomingValueForBlock(ExitingBlock);
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} else {
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// We have to use the preincremented value...
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RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
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IndVar->getType());
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CmpIndVar = IndVar;
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}
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// Expand the code for the iteration count.
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assert(SE->isLoopInvariant(RHS, L) &&
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"Computed iteration count is not loop invariant!");
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Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI);
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// Insert a new icmp_ne or icmp_eq instruction before the branch.
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ICmpInst::Predicate Opcode;
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if (L->contains(BI->getSuccessor(0)))
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Opcode = ICmpInst::ICMP_NE;
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else
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Opcode = ICmpInst::ICMP_EQ;
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DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
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<< " LHS:" << *CmpIndVar << '\n'
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<< " op:\t"
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<< (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
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<< " RHS:\t" << *RHS << "\n");
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ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond");
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Value *OrigCond = BI->getCondition();
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// It's tempting to use replaceAllUsesWith here to fully replace the old
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// comparison, but that's not immediately safe, since users of the old
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// comparison may not be dominated by the new comparison. Instead, just
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// update the branch to use the new comparison; in the common case this
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// will make old comparison dead.
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BI->setCondition(Cond);
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DeadInsts.push_back(OrigCond);
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++NumLFTR;
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Changed = true;
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return Cond;
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}
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/// RewriteLoopExitValues - Check to see if this loop has a computable
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/// loop-invariant execution count. If so, this means that we can compute the
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/// final value of any expressions that are recurrent in the loop, and
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/// substitute the exit values from the loop into any instructions outside of
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/// the loop that use the final values of the current expressions.
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///
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/// This is mostly redundant with the regular IndVarSimplify activities that
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/// happen later, except that it's more powerful in some cases, because it's
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/// able to brute-force evaluate arbitrary instructions as long as they have
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/// constant operands at the beginning of the loop.
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void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
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// Verify the input to the pass in already in LCSSA form.
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assert(L->isLCSSAForm(*DT));
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SmallVector<BasicBlock*, 8> ExitBlocks;
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L->getUniqueExitBlocks(ExitBlocks);
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// Find all values that are computed inside the loop, but used outside of it.
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// Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
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// the exit blocks of the loop to find them.
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for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
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BasicBlock *ExitBB = ExitBlocks[i];
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// If there are no PHI nodes in this exit block, then no values defined
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// inside the loop are used on this path, skip it.
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PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
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if (!PN) continue;
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unsigned NumPreds = PN->getNumIncomingValues();
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// Iterate over all of the PHI nodes.
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BasicBlock::iterator BBI = ExitBB->begin();
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while ((PN = dyn_cast<PHINode>(BBI++))) {
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if (PN->use_empty())
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continue; // dead use, don't replace it
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// SCEV only supports integer expressions for now.
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if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
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continue;
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// It's necessary to tell ScalarEvolution about this explicitly so that
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// it can walk the def-use list and forget all SCEVs, as it may not be
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// watching the PHI itself. Once the new exit value is in place, there
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// may not be a def-use connection between the loop and every instruction
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// which got a SCEVAddRecExpr for that loop.
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SE->forgetValue(PN);
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// Iterate over all of the values in all the PHI nodes.
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for (unsigned i = 0; i != NumPreds; ++i) {
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// If the value being merged in is not integer or is not defined
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// in the loop, skip it.
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Value *InVal = PN->getIncomingValue(i);
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if (!isa<Instruction>(InVal))
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continue;
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// If this pred is for a subloop, not L itself, skip it.
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if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
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continue; // The Block is in a subloop, skip it.
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// Check that InVal is defined in the loop.
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Instruction *Inst = cast<Instruction>(InVal);
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if (!L->contains(Inst))
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continue;
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// Okay, this instruction has a user outside of the current loop
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// and varies predictably *inside* the loop. Evaluate the value it
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// contains when the loop exits, if possible.
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const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
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if (!SE->isLoopInvariant(ExitValue, L))
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continue;
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Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
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DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
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<< " LoopVal = " << *Inst << "\n");
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if (!isValidRewrite(Inst, ExitVal)) {
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DeadInsts.push_back(ExitVal);
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continue;
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}
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Changed = true;
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++NumReplaced;
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PN->setIncomingValue(i, ExitVal);
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// If this instruction is dead now, delete it.
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RecursivelyDeleteTriviallyDeadInstructions(Inst);
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if (NumPreds == 1) {
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// Completely replace a single-pred PHI. This is safe, because the
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// NewVal won't be variant in the loop, so we don't need an LCSSA phi
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// node anymore.
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PN->replaceAllUsesWith(ExitVal);
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RecursivelyDeleteTriviallyDeadInstructions(PN);
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}
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}
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if (NumPreds != 1) {
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// Clone the PHI and delete the original one. This lets IVUsers and
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// any other maps purge the original user from their records.
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PHINode *NewPN = cast<PHINode>(PN->clone());
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NewPN->takeName(PN);
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NewPN->insertBefore(PN);
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PN->replaceAllUsesWith(NewPN);
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PN->eraseFromParent();
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}
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}
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}
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// The insertion point instruction may have been deleted; clear it out
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// so that the rewriter doesn't trip over it later.
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Rewriter.clearInsertPoint();
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}
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void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
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// First step. Check to see if there are any floating-point recurrences.
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// If there are, change them into integer recurrences, permitting analysis by
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// the SCEV routines.
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//
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BasicBlock *Header = L->getHeader();
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SmallVector<WeakVH, 8> PHIs;
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for (BasicBlock::iterator I = Header->begin();
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PHINode *PN = dyn_cast<PHINode>(I); ++I)
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PHIs.push_back(PN);
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for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
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if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i]))
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HandleFloatingPointIV(L, PN);
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// If the loop previously had floating-point IV, ScalarEvolution
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// may not have been able to compute a trip count. Now that we've done some
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// re-writing, the trip count may be computable.
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if (Changed)
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SE->forgetLoop(L);
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}
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void IndVarSimplify::EliminateIVComparisons() {
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// Look for ICmp users.
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for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
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IVStrideUse &UI = *I;
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ICmpInst *ICmp = dyn_cast<ICmpInst>(UI.getUser());
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if (!ICmp) continue;
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bool Swapped = UI.getOperandValToReplace() == ICmp->getOperand(1);
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ICmpInst::Predicate Pred = ICmp->getPredicate();
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if (Swapped) Pred = ICmpInst::getSwappedPredicate(Pred);
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// Get the SCEVs for the ICmp operands.
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const SCEV *S = IU->getReplacementExpr(UI);
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const SCEV *X = SE->getSCEV(ICmp->getOperand(!Swapped));
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// Simplify unnecessary loops away.
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const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
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S = SE->getSCEVAtScope(S, ICmpLoop);
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X = SE->getSCEVAtScope(X, ICmpLoop);
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// If the condition is always true or always false, replace it with
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// a constant value.
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if (SE->isKnownPredicate(Pred, S, X))
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ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
|
|
else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
|
|
ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
|
|
else
|
|
continue;
|
|
|
|
DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
|
|
DeadInsts.push_back(ICmp);
|
|
}
|
|
}
|
|
|
|
void IndVarSimplify::EliminateIVRemainders() {
|
|
// Look for SRem and URem users.
|
|
for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
|
|
IVStrideUse &UI = *I;
|
|
BinaryOperator *Rem = dyn_cast<BinaryOperator>(UI.getUser());
|
|
if (!Rem) continue;
|
|
|
|
bool isSigned = Rem->getOpcode() == Instruction::SRem;
|
|
if (!isSigned && Rem->getOpcode() != Instruction::URem)
|
|
continue;
|
|
|
|
// We're only interested in the case where we know something about
|
|
// the numerator.
|
|
if (UI.getOperandValToReplace() != Rem->getOperand(0))
|
|
continue;
|
|
|
|
// Get the SCEVs for the ICmp operands.
|
|
const SCEV *S = SE->getSCEV(Rem->getOperand(0));
|
|
const SCEV *X = SE->getSCEV(Rem->getOperand(1));
|
|
|
|
// Simplify unnecessary loops away.
|
|
const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
|
|
S = SE->getSCEVAtScope(S, ICmpLoop);
|
|
X = SE->getSCEVAtScope(X, ICmpLoop);
|
|
|
|
// i % n --> i if i is in [0,n).
|
|
if ((!isSigned || SE->isKnownNonNegative(S)) &&
|
|
SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
|
|
S, X))
|
|
Rem->replaceAllUsesWith(Rem->getOperand(0));
|
|
else {
|
|
// (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
|
|
const SCEV *LessOne =
|
|
SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1));
|
|
if ((!isSigned || SE->isKnownNonNegative(LessOne)) &&
|
|
SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
|
|
LessOne, X)) {
|
|
ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ,
|
|
Rem->getOperand(0), Rem->getOperand(1),
|
|
"tmp");
|
|
SelectInst *Sel =
|
|
SelectInst::Create(ICmp,
|
|
ConstantInt::get(Rem->getType(), 0),
|
|
Rem->getOperand(0), "tmp", Rem);
|
|
Rem->replaceAllUsesWith(Sel);
|
|
} else
|
|
continue;
|
|
}
|
|
|
|
// Inform IVUsers about the new users.
|
|
if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0)))
|
|
IU->AddUsersIfInteresting(I);
|
|
|
|
DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
|
|
DeadInsts.push_back(Rem);
|
|
}
|
|
}
|
|
|
|
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
// If LoopSimplify form is not available, stay out of trouble. Some notes:
|
|
// - LSR currently only supports LoopSimplify-form loops. Indvars'
|
|
// canonicalization can be a pessimization without LSR to "clean up"
|
|
// afterwards.
|
|
// - We depend on having a preheader; in particular,
|
|
// Loop::getCanonicalInductionVariable only supports loops with preheaders,
|
|
// and we're in trouble if we can't find the induction variable even when
|
|
// we've manually inserted one.
|
|
if (!L->isLoopSimplifyForm())
|
|
return false;
|
|
|
|
IU = &getAnalysis<IVUsers>();
|
|
LI = &getAnalysis<LoopInfo>();
|
|
SE = &getAnalysis<ScalarEvolution>();
|
|
DT = &getAnalysis<DominatorTree>();
|
|
DeadInsts.clear();
|
|
Changed = false;
|
|
|
|
// If there are any floating-point recurrences, attempt to
|
|
// transform them to use integer recurrences.
|
|
RewriteNonIntegerIVs(L);
|
|
|
|
BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null
|
|
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
|
|
|
|
// Create a rewriter object which we'll use to transform the code with.
|
|
SCEVExpander Rewriter(*SE);
|
|
|
|
// Check to see if this loop has a computable loop-invariant execution count.
|
|
// If so, this means that we can compute the final value of any expressions
|
|
// that are recurrent in the loop, and substitute the exit values from the
|
|
// loop into any instructions outside of the loop that use the final values of
|
|
// the current expressions.
|
|
//
|
|
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
|
|
RewriteLoopExitValues(L, Rewriter);
|
|
|
|
// Simplify ICmp IV users.
|
|
EliminateIVComparisons();
|
|
|
|
// Simplify SRem and URem IV users.
|
|
EliminateIVRemainders();
|
|
|
|
// Compute the type of the largest recurrence expression, and decide whether
|
|
// a canonical induction variable should be inserted.
|
|
const Type *LargestType = 0;
|
|
bool NeedCannIV = false;
|
|
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
|
|
LargestType = BackedgeTakenCount->getType();
|
|
LargestType = SE->getEffectiveSCEVType(LargestType);
|
|
// If we have a known trip count and a single exit block, we'll be
|
|
// rewriting the loop exit test condition below, which requires a
|
|
// canonical induction variable.
|
|
if (ExitingBlock)
|
|
NeedCannIV = true;
|
|
}
|
|
for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
|
|
const Type *Ty =
|
|
SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType());
|
|
if (!LargestType ||
|
|
SE->getTypeSizeInBits(Ty) >
|
|
SE->getTypeSizeInBits(LargestType))
|
|
LargestType = Ty;
|
|
NeedCannIV = true;
|
|
}
|
|
|
|
// Now that we know the largest of the induction variable expressions
|
|
// in this loop, insert a canonical induction variable of the largest size.
|
|
PHINode *IndVar = 0;
|
|
if (NeedCannIV) {
|
|
// Check to see if the loop already has any canonical-looking induction
|
|
// variables. If any are present and wider than the planned canonical
|
|
// induction variable, temporarily remove them, so that the Rewriter
|
|
// doesn't attempt to reuse them.
|
|
SmallVector<PHINode *, 2> OldCannIVs;
|
|
while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) {
|
|
if (SE->getTypeSizeInBits(OldCannIV->getType()) >
|
|
SE->getTypeSizeInBits(LargestType))
|
|
OldCannIV->removeFromParent();
|
|
else
|
|
break;
|
|
OldCannIVs.push_back(OldCannIV);
|
|
}
|
|
|
|
IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType);
|
|
|
|
++NumInserted;
|
|
Changed = true;
|
|
DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n');
|
|
|
|
// Now that the official induction variable is established, reinsert
|
|
// any old canonical-looking variables after it so that the IR remains
|
|
// consistent. They will be deleted as part of the dead-PHI deletion at
|
|
// the end of the pass.
|
|
while (!OldCannIVs.empty()) {
|
|
PHINode *OldCannIV = OldCannIVs.pop_back_val();
|
|
OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI());
|
|
}
|
|
}
|
|
|
|
// If we have a trip count expression, rewrite the loop's exit condition
|
|
// using it. We can currently only handle loops with a single exit.
|
|
ICmpInst *NewICmp = 0;
|
|
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
|
|
!BackedgeTakenCount->isZero() &&
|
|
ExitingBlock) {
|
|
assert(NeedCannIV &&
|
|
"LinearFunctionTestReplace requires a canonical induction variable");
|
|
// Can't rewrite non-branch yet.
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()))
|
|
NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
|
|
ExitingBlock, BI, Rewriter);
|
|
}
|
|
|
|
// Rewrite IV-derived expressions.
|
|
RewriteIVExpressions(L, Rewriter);
|
|
|
|
// Clear the rewriter cache, because values that are in the rewriter's cache
|
|
// can be deleted in the loop below, causing the AssertingVH in the cache to
|
|
// trigger.
|
|
Rewriter.clear();
|
|
|
|
// Now that we're done iterating through lists, clean up any instructions
|
|
// which are now dead.
|
|
while (!DeadInsts.empty())
|
|
if (Instruction *Inst =
|
|
dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
|
|
RecursivelyDeleteTriviallyDeadInstructions(Inst);
|
|
|
|
// The Rewriter may not be used from this point on.
|
|
|
|
// Loop-invariant instructions in the preheader that aren't used in the
|
|
// loop may be sunk below the loop to reduce register pressure.
|
|
SinkUnusedInvariants(L);
|
|
|
|
// For completeness, inform IVUsers of the IV use in the newly-created
|
|
// loop exit test instruction.
|
|
if (NewICmp)
|
|
IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)));
|
|
|
|
// Clean up dead instructions.
|
|
Changed |= DeleteDeadPHIs(L->getHeader());
|
|
// Check a post-condition.
|
|
assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!");
|
|
return Changed;
|
|
}
|
|
|
|
// FIXME: It is an extremely bad idea to indvar substitute anything more
|
|
// complex than affine induction variables. Doing so will put expensive
|
|
// polynomial evaluations inside of the loop, and the str reduction pass
|
|
// currently can only reduce affine polynomials. For now just disable
|
|
// indvar subst on anything more complex than an affine addrec, unless
|
|
// it can be expanded to a trivial value.
|
|
static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) {
|
|
// Loop-invariant values are safe.
|
|
if (SE->isLoopInvariant(S, L)) return true;
|
|
|
|
// Affine addrecs are safe. Non-affine are not, because LSR doesn't know how
|
|
// to transform them into efficient code.
|
|
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
|
|
return AR->isAffine();
|
|
|
|
// An add is safe it all its operands are safe.
|
|
if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) {
|
|
for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(),
|
|
E = Commutative->op_end(); I != E; ++I)
|
|
if (!isSafe(*I, L, SE)) return false;
|
|
return true;
|
|
}
|
|
|
|
// A cast is safe if its operand is.
|
|
if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
|
|
return isSafe(C->getOperand(), L, SE);
|
|
|
|
// A udiv is safe if its operands are.
|
|
if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S))
|
|
return isSafe(UD->getLHS(), L, SE) &&
|
|
isSafe(UD->getRHS(), L, SE);
|
|
|
|
// SCEVUnknown is always safe.
|
|
if (isa<SCEVUnknown>(S))
|
|
return true;
|
|
|
|
// Nothing else is safe.
|
|
return false;
|
|
}
|
|
|
|
void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
|
|
// Rewrite all induction variable expressions in terms of the canonical
|
|
// induction variable.
|
|
//
|
|
// If there were induction variables of other sizes or offsets, manually
|
|
// add the offsets to the primary induction variable and cast, avoiding
|
|
// the need for the code evaluation methods to insert induction variables
|
|
// of different sizes.
|
|
for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) {
|
|
Value *Op = UI->getOperandValToReplace();
|
|
const Type *UseTy = Op->getType();
|
|
Instruction *User = UI->getUser();
|
|
|
|
// Compute the final addrec to expand into code.
|
|
const SCEV *AR = IU->getReplacementExpr(*UI);
|
|
|
|
// Evaluate the expression out of the loop, if possible.
|
|
if (!L->contains(UI->getUser())) {
|
|
const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop());
|
|
if (SE->isLoopInvariant(ExitVal, L))
|
|
AR = ExitVal;
|
|
}
|
|
|
|
// FIXME: It is an extremely bad idea to indvar substitute anything more
|
|
// complex than affine induction variables. Doing so will put expensive
|
|
// polynomial evaluations inside of the loop, and the str reduction pass
|
|
// currently can only reduce affine polynomials. For now just disable
|
|
// indvar subst on anything more complex than an affine addrec, unless
|
|
// it can be expanded to a trivial value.
|
|
if (!isSafe(AR, L, SE))
|
|
continue;
|
|
|
|
// Determine the insertion point for this user. By default, insert
|
|
// immediately before the user. The SCEVExpander class will automatically
|
|
// hoist loop invariants out of the loop. For PHI nodes, there may be
|
|
// multiple uses, so compute the nearest common dominator for the
|
|
// incoming blocks.
|
|
Instruction *InsertPt = User;
|
|
if (PHINode *PHI = dyn_cast<PHINode>(InsertPt))
|
|
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
|
|
if (PHI->getIncomingValue(i) == Op) {
|
|
if (InsertPt == User)
|
|
InsertPt = PHI->getIncomingBlock(i)->getTerminator();
|
|
else
|
|
InsertPt =
|
|
DT->findNearestCommonDominator(InsertPt->getParent(),
|
|
PHI->getIncomingBlock(i))
|
|
->getTerminator();
|
|
}
|
|
|
|
// Now expand it into actual Instructions and patch it into place.
|
|
Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt);
|
|
|
|
DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
|
|
<< " into = " << *NewVal << "\n");
|
|
|
|
if (!isValidRewrite(Op, NewVal)) {
|
|
DeadInsts.push_back(NewVal);
|
|
continue;
|
|
}
|
|
// Inform ScalarEvolution that this value is changing. The change doesn't
|
|
// affect its value, but it does potentially affect which use lists the
|
|
// value will be on after the replacement, which affects ScalarEvolution's
|
|
// ability to walk use lists and drop dangling pointers when a value is
|
|
// deleted.
|
|
SE->forgetValue(User);
|
|
|
|
// Patch the new value into place.
|
|
if (Op->hasName())
|
|
NewVal->takeName(Op);
|
|
User->replaceUsesOfWith(Op, NewVal);
|
|
UI->setOperandValToReplace(NewVal);
|
|
|
|
++NumRemoved;
|
|
Changed = true;
|
|
|
|
// The old value may be dead now.
|
|
DeadInsts.push_back(Op);
|
|
}
|
|
}
|
|
|
|
/// If there's a single exit block, sink any loop-invariant values that
|
|
/// were defined in the preheader but not used inside the loop into the
|
|
/// exit block to reduce register pressure in the loop.
|
|
void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
|
|
BasicBlock *ExitBlock = L->getExitBlock();
|
|
if (!ExitBlock) return;
|
|
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
if (!Preheader) return;
|
|
|
|
Instruction *InsertPt = ExitBlock->getFirstNonPHI();
|
|
BasicBlock::iterator I = Preheader->getTerminator();
|
|
while (I != Preheader->begin()) {
|
|
--I;
|
|
// New instructions were inserted at the end of the preheader.
|
|
if (isa<PHINode>(I))
|
|
break;
|
|
|
|
// Don't move instructions which might have side effects, since the side
|
|
// effects need to complete before instructions inside the loop. Also don't
|
|
// move instructions which might read memory, since the loop may modify
|
|
// memory. Note that it's okay if the instruction might have undefined
|
|
// behavior: LoopSimplify guarantees that the preheader dominates the exit
|
|
// block.
|
|
if (I->mayHaveSideEffects() || I->mayReadFromMemory())
|
|
continue;
|
|
|
|
// Skip debug info intrinsics.
|
|
if (isa<DbgInfoIntrinsic>(I))
|
|
continue;
|
|
|
|
// Don't sink static AllocaInsts out of the entry block, which would
|
|
// turn them into dynamic allocas!
|
|
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
|
|
if (AI->isStaticAlloca())
|
|
continue;
|
|
|
|
// Determine if there is a use in or before the loop (direct or
|
|
// otherwise).
|
|
bool UsedInLoop = false;
|
|
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
|
|
UI != UE; ++UI) {
|
|
User *U = *UI;
|
|
BasicBlock *UseBB = cast<Instruction>(U)->getParent();
|
|
if (PHINode *P = dyn_cast<PHINode>(U)) {
|
|
unsigned i =
|
|
PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
|
|
UseBB = P->getIncomingBlock(i);
|
|
}
|
|
if (UseBB == Preheader || L->contains(UseBB)) {
|
|
UsedInLoop = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If there is, the def must remain in the preheader.
|
|
if (UsedInLoop)
|
|
continue;
|
|
|
|
// Otherwise, sink it to the exit block.
|
|
Instruction *ToMove = I;
|
|
bool Done = false;
|
|
|
|
if (I != Preheader->begin()) {
|
|
// Skip debug info intrinsics.
|
|
do {
|
|
--I;
|
|
} while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
|
|
|
|
if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
|
|
Done = true;
|
|
} else {
|
|
Done = true;
|
|
}
|
|
|
|
ToMove->moveBefore(InsertPt);
|
|
if (Done) break;
|
|
InsertPt = ToMove;
|
|
}
|
|
}
|
|
|
|
/// ConvertToSInt - Convert APF to an integer, if possible.
|
|
static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
|
|
bool isExact = false;
|
|
if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
|
|
return false;
|
|
// See if we can convert this to an int64_t
|
|
uint64_t UIntVal;
|
|
if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
|
|
&isExact) != APFloat::opOK || !isExact)
|
|
return false;
|
|
IntVal = UIntVal;
|
|
return true;
|
|
}
|
|
|
|
/// HandleFloatingPointIV - If the loop has floating induction variable
|
|
/// then insert corresponding integer induction variable if possible.
|
|
/// For example,
|
|
/// for(double i = 0; i < 10000; ++i)
|
|
/// bar(i)
|
|
/// is converted into
|
|
/// for(int i = 0; i < 10000; ++i)
|
|
/// bar((double)i);
|
|
///
|
|
void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
|
|
unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
|
|
unsigned BackEdge = IncomingEdge^1;
|
|
|
|
// Check incoming value.
|
|
ConstantFP *InitValueVal =
|
|
dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
|
|
|
|
int64_t InitValue;
|
|
if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
|
|
return;
|
|
|
|
// Check IV increment. Reject this PN if increment operation is not
|
|
// an add or increment value can not be represented by an integer.
|
|
BinaryOperator *Incr =
|
|
dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
|
|
if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
|
|
|
|
// If this is not an add of the PHI with a constantfp, or if the constant fp
|
|
// is not an integer, bail out.
|
|
ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
|
|
int64_t IncValue;
|
|
if (IncValueVal == 0 || Incr->getOperand(0) != PN ||
|
|
!ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
|
|
return;
|
|
|
|
// Check Incr uses. One user is PN and the other user is an exit condition
|
|
// used by the conditional terminator.
|
|
Value::use_iterator IncrUse = Incr->use_begin();
|
|
Instruction *U1 = cast<Instruction>(*IncrUse++);
|
|
if (IncrUse == Incr->use_end()) return;
|
|
Instruction *U2 = cast<Instruction>(*IncrUse++);
|
|
if (IncrUse != Incr->use_end()) return;
|
|
|
|
// Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
|
|
// only used by a branch, we can't transform it.
|
|
FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
|
|
if (!Compare)
|
|
Compare = dyn_cast<FCmpInst>(U2);
|
|
if (Compare == 0 || !Compare->hasOneUse() ||
|
|
!isa<BranchInst>(Compare->use_back()))
|
|
return;
|
|
|
|
BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
|
|
|
|
// We need to verify that the branch actually controls the iteration count
|
|
// of the loop. If not, the new IV can overflow and no one will notice.
|
|
// The branch block must be in the loop and one of the successors must be out
|
|
// of the loop.
|
|
assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
|
|
if (!L->contains(TheBr->getParent()) ||
|
|
(L->contains(TheBr->getSuccessor(0)) &&
|
|
L->contains(TheBr->getSuccessor(1))))
|
|
return;
|
|
|
|
|
|
// If it isn't a comparison with an integer-as-fp (the exit value), we can't
|
|
// transform it.
|
|
ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
|
|
int64_t ExitValue;
|
|
if (ExitValueVal == 0 ||
|
|
!ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
|
|
return;
|
|
|
|
// Find new predicate for integer comparison.
|
|
CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
|
|
switch (Compare->getPredicate()) {
|
|
default: return; // Unknown comparison.
|
|
case CmpInst::FCMP_OEQ:
|
|
case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
|
|
case CmpInst::FCMP_ONE:
|
|
case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
|
|
case CmpInst::FCMP_OGT:
|
|
case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
|
|
case CmpInst::FCMP_OGE:
|
|
case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
|
|
case CmpInst::FCMP_OLT:
|
|
case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
|
|
case CmpInst::FCMP_OLE:
|
|
case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
|
|
}
|
|
|
|
// We convert the floating point induction variable to a signed i32 value if
|
|
// we can. This is only safe if the comparison will not overflow in a way
|
|
// that won't be trapped by the integer equivalent operations. Check for this
|
|
// now.
|
|
// TODO: We could use i64 if it is native and the range requires it.
|
|
|
|
// The start/stride/exit values must all fit in signed i32.
|
|
if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
|
|
return;
|
|
|
|
// If not actually striding (add x, 0.0), avoid touching the code.
|
|
if (IncValue == 0)
|
|
return;
|
|
|
|
// Positive and negative strides have different safety conditions.
|
|
if (IncValue > 0) {
|
|
// If we have a positive stride, we require the init to be less than the
|
|
// exit value and an equality or less than comparison.
|
|
if (InitValue >= ExitValue ||
|
|
NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE)
|
|
return;
|
|
|
|
uint32_t Range = uint32_t(ExitValue-InitValue);
|
|
if (NewPred == CmpInst::ICMP_SLE) {
|
|
// Normalize SLE -> SLT, check for infinite loop.
|
|
if (++Range == 0) return; // Range overflows.
|
|
}
|
|
|
|
unsigned Leftover = Range % uint32_t(IncValue);
|
|
|
|
// If this is an equality comparison, we require that the strided value
|
|
// exactly land on the exit value, otherwise the IV condition will wrap
|
|
// around and do things the fp IV wouldn't.
|
|
if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
|
|
Leftover != 0)
|
|
return;
|
|
|
|
// If the stride would wrap around the i32 before exiting, we can't
|
|
// transform the IV.
|
|
if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
|
|
return;
|
|
|
|
} else {
|
|
// If we have a negative stride, we require the init to be greater than the
|
|
// exit value and an equality or greater than comparison.
|
|
if (InitValue >= ExitValue ||
|
|
NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE)
|
|
return;
|
|
|
|
uint32_t Range = uint32_t(InitValue-ExitValue);
|
|
if (NewPred == CmpInst::ICMP_SGE) {
|
|
// Normalize SGE -> SGT, check for infinite loop.
|
|
if (++Range == 0) return; // Range overflows.
|
|
}
|
|
|
|
unsigned Leftover = Range % uint32_t(-IncValue);
|
|
|
|
// If this is an equality comparison, we require that the strided value
|
|
// exactly land on the exit value, otherwise the IV condition will wrap
|
|
// around and do things the fp IV wouldn't.
|
|
if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
|
|
Leftover != 0)
|
|
return;
|
|
|
|
// If the stride would wrap around the i32 before exiting, we can't
|
|
// transform the IV.
|
|
if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
|
|
return;
|
|
}
|
|
|
|
const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
|
|
|
|
// Insert new integer induction variable.
|
|
PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
|
|
NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
|
|
PN->getIncomingBlock(IncomingEdge));
|
|
|
|
Value *NewAdd =
|
|
BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
|
|
Incr->getName()+".int", Incr);
|
|
NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
|
|
|
|
ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
|
|
ConstantInt::get(Int32Ty, ExitValue),
|
|
Compare->getName());
|
|
|
|
// In the following deletions, PN may become dead and may be deleted.
|
|
// Use a WeakVH to observe whether this happens.
|
|
WeakVH WeakPH = PN;
|
|
|
|
// Delete the old floating point exit comparison. The branch starts using the
|
|
// new comparison.
|
|
NewCompare->takeName(Compare);
|
|
Compare->replaceAllUsesWith(NewCompare);
|
|
RecursivelyDeleteTriviallyDeadInstructions(Compare);
|
|
|
|
// Delete the old floating point increment.
|
|
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
|
|
RecursivelyDeleteTriviallyDeadInstructions(Incr);
|
|
|
|
// If the FP induction variable still has uses, this is because something else
|
|
// in the loop uses its value. In order to canonicalize the induction
|
|
// variable, we chose to eliminate the IV and rewrite it in terms of an
|
|
// int->fp cast.
|
|
//
|
|
// We give preference to sitofp over uitofp because it is faster on most
|
|
// platforms.
|
|
if (WeakPH) {
|
|
Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
|
|
PN->getParent()->getFirstNonPHI());
|
|
PN->replaceAllUsesWith(Conv);
|
|
RecursivelyDeleteTriviallyDeadInstructions(PN);
|
|
}
|
|
|
|
// Add a new IVUsers entry for the newly-created integer PHI.
|
|
IU->AddUsersIfInteresting(NewPHI);
|
|
}
|