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llvm-6502/lib/Transforms/Scalar/LoopStrengthReduce.cpp
Dan Gohman 40a5a1b39e Extend ScalarEvolution's multiple-exit support to compute exact 
trip counts in more cases.

Generalize ScalarEvolution's isLoopGuardedByCond code to recognize
And and Or conditions, splitting the code out into an
isNecessaryCond helper function so that it can evaluate Ands and Ors
recursively, and make SCEVExpander be much more aggressive about
hoisting instructions out of loops.

test/CodeGen/X86/pr3495.ll has an additional instruction now, but
it appears to be due to an arbitrary register allocation difference.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74048 91177308-0d34-0410-b5e6-96231b3b80d8
2009-06-24 01:18:18 +00:00

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//===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transformation analyzes and transforms the induction variables (and
// computations derived from them) into forms suitable for efficient execution
// on the target.
//
// This pass performs a strength reduction on array references inside loops that
// have as one or more of their components the loop induction variable, it
// rewrites expressions to take advantage of scaled-index addressing modes
// available on the target, and it performs a variety of other optimizations
// related to loop induction variables.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loop-reduce"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Type.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/IVUsers.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Transforms/Utils/AddrModeMatcher.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Target/TargetLowering.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumReduced , "Number of IV uses strength reduced");
STATISTIC(NumInserted, "Number of PHIs inserted");
STATISTIC(NumVariable, "Number of PHIs with variable strides");
STATISTIC(NumEliminated, "Number of strides eliminated");
STATISTIC(NumShadow, "Number of Shadow IVs optimized");
STATISTIC(NumImmSunk, "Number of common expr immediates sunk into uses");
STATISTIC(NumLoopCond, "Number of loop terminating conds optimized");
static cl::opt<bool> EnableFullLSRMode("enable-full-lsr",
cl::init(false),
cl::Hidden);
namespace {
struct BasedUser;
/// IVInfo - This structure keeps track of one IV expression inserted during
/// StrengthReduceStridedIVUsers. It contains the stride, the common base, as
/// well as the PHI node and increment value created for rewrite.
struct VISIBILITY_HIDDEN IVExpr {
const SCEV* Stride;
const SCEV* Base;
PHINode *PHI;
IVExpr(const SCEV* const stride, const SCEV* const base, PHINode *phi)
: Stride(stride), Base(base), PHI(phi) {}
};
/// IVsOfOneStride - This structure keeps track of all IV expression inserted
/// during StrengthReduceStridedIVUsers for a particular stride of the IV.
struct VISIBILITY_HIDDEN IVsOfOneStride {
std::vector<IVExpr> IVs;
void addIV(const SCEV* const Stride, const SCEV* const Base, PHINode *PHI) {
IVs.push_back(IVExpr(Stride, Base, PHI));
}
};
class VISIBILITY_HIDDEN LoopStrengthReduce : public LoopPass {
IVUsers *IU;
LoopInfo *LI;
DominatorTree *DT;
ScalarEvolution *SE;
bool Changed;
/// IVsByStride - Keep track of all IVs that have been inserted for a
/// particular stride.
std::map<const SCEV*, IVsOfOneStride> IVsByStride;
/// StrideNoReuse - Keep track of all the strides whose ivs cannot be
/// reused (nor should they be rewritten to reuse other strides).
SmallSet<const SCEV*, 4> StrideNoReuse;
/// DeadInsts - Keep track of instructions we may have made dead, so that
/// we can remove them after we are done working.
SmallVector<WeakVH, 16> DeadInsts;
/// TLI - Keep a pointer of a TargetLowering to consult for determining
/// transformation profitability.
const TargetLowering *TLI;
public:
static char ID; // Pass ID, replacement for typeid
explicit LoopStrengthReduce(const TargetLowering *tli = NULL) :
LoopPass(&ID), TLI(tli) {
}
bool runOnLoop(Loop *L, LPPassManager &LPM);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
// We split critical edges, so we change the CFG. However, we do update
// many analyses if they are around.
AU.addPreservedID(LoopSimplifyID);
AU.addPreserved<LoopInfo>();
AU.addPreserved<DominanceFrontier>();
AU.addPreserved<DominatorTree>();
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfo>();
AU.addRequired<DominatorTree>();
AU.addRequired<ScalarEvolution>();
AU.addPreserved<ScalarEvolution>();
AU.addRequired<IVUsers>();
AU.addPreserved<IVUsers>();
}
private:
ICmpInst *ChangeCompareStride(Loop *L, ICmpInst *Cond,
IVStrideUse* &CondUse,
const SCEV* const * &CondStride);
void OptimizeIndvars(Loop *L);
void OptimizeLoopCountIV(Loop *L);
void OptimizeLoopTermCond(Loop *L);
/// OptimizeShadowIV - If IV is used in a int-to-float cast
/// inside the loop then try to eliminate the cast opeation.
void OptimizeShadowIV(Loop *L);
/// OptimizeMax - Rewrite the loop's terminating condition
/// if it uses a max computation.
ICmpInst *OptimizeMax(Loop *L, ICmpInst *Cond,
IVStrideUse* &CondUse);
bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse,
const SCEV* const * &CondStride);
bool RequiresTypeConversion(const Type *Ty, const Type *NewTy);
const SCEV* CheckForIVReuse(bool, bool, bool, const SCEV* const&,
IVExpr&, const Type*,
const std::vector<BasedUser>& UsersToProcess);
bool ValidScale(bool, int64_t,
const std::vector<BasedUser>& UsersToProcess);
bool ValidOffset(bool, int64_t, int64_t,
const std::vector<BasedUser>& UsersToProcess);
const SCEV* CollectIVUsers(const SCEV* const &Stride,
IVUsersOfOneStride &Uses,
Loop *L,
bool &AllUsesAreAddresses,
bool &AllUsesAreOutsideLoop,
std::vector<BasedUser> &UsersToProcess);
bool ShouldUseFullStrengthReductionMode(
const std::vector<BasedUser> &UsersToProcess,
const Loop *L,
bool AllUsesAreAddresses,
const SCEV* Stride);
void PrepareToStrengthReduceFully(
std::vector<BasedUser> &UsersToProcess,
const SCEV* Stride,
const SCEV* CommonExprs,
const Loop *L,
SCEVExpander &PreheaderRewriter);
void PrepareToStrengthReduceFromSmallerStride(
std::vector<BasedUser> &UsersToProcess,
Value *CommonBaseV,
const IVExpr &ReuseIV,
Instruction *PreInsertPt);
void PrepareToStrengthReduceWithNewPhi(
std::vector<BasedUser> &UsersToProcess,
const SCEV* Stride,
const SCEV* CommonExprs,
Value *CommonBaseV,
Instruction *IVIncInsertPt,
const Loop *L,
SCEVExpander &PreheaderRewriter);
void StrengthReduceStridedIVUsers(const SCEV* const &Stride,
IVUsersOfOneStride &Uses,
Loop *L);
void DeleteTriviallyDeadInstructions();
};
}
char LoopStrengthReduce::ID = 0;
static RegisterPass<LoopStrengthReduce>
X("loop-reduce", "Loop Strength Reduction");
Pass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) {
return new LoopStrengthReduce(TLI);
}
/// DeleteTriviallyDeadInstructions - If any of the instructions is the
/// specified set are trivially dead, delete them and see if this makes any of
/// their operands subsequently dead.
void LoopStrengthReduce::DeleteTriviallyDeadInstructions() {
if (DeadInsts.empty()) return;
while (!DeadInsts.empty()) {
Instruction *I = dyn_cast_or_null<Instruction>(DeadInsts.back());
DeadInsts.pop_back();
if (I == 0 || !isInstructionTriviallyDead(I))
continue;
for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) {
if (Instruction *U = dyn_cast<Instruction>(*OI)) {
*OI = 0;
if (U->use_empty())
DeadInsts.push_back(U);
}
}
I->eraseFromParent();
Changed = true;
}
}
/// containsAddRecFromDifferentLoop - Determine whether expression S involves a
/// subexpression that is an AddRec from a loop other than L. An outer loop
/// of L is OK, but not an inner loop nor a disjoint loop.
static bool containsAddRecFromDifferentLoop(const SCEV* S, Loop *L) {
// This is very common, put it first.
if (isa<SCEVConstant>(S))
return false;
if (const SCEVCommutativeExpr *AE = dyn_cast<SCEVCommutativeExpr>(S)) {
for (unsigned int i=0; i< AE->getNumOperands(); i++)
if (containsAddRecFromDifferentLoop(AE->getOperand(i), L))
return true;
return false;
}
if (const SCEVAddRecExpr *AE = dyn_cast<SCEVAddRecExpr>(S)) {
if (const Loop *newLoop = AE->getLoop()) {
if (newLoop == L)
return false;
// if newLoop is an outer loop of L, this is OK.
if (!LoopInfoBase<BasicBlock>::isNotAlreadyContainedIn(L, newLoop))
return false;
}
return true;
}
if (const SCEVUDivExpr *DE = dyn_cast<SCEVUDivExpr>(S))
return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
containsAddRecFromDifferentLoop(DE->getRHS(), L);
#if 0
// SCEVSDivExpr has been backed out temporarily, but will be back; we'll
// need this when it is.
if (const SCEVSDivExpr *DE = dyn_cast<SCEVSDivExpr>(S))
return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
containsAddRecFromDifferentLoop(DE->getRHS(), L);
#endif
if (const SCEVCastExpr *CE = dyn_cast<SCEVCastExpr>(S))
return containsAddRecFromDifferentLoop(CE->getOperand(), L);
return false;
}
/// isAddressUse - Returns true if the specified instruction is using the
/// specified value as an address.
static bool isAddressUse(Instruction *Inst, Value *OperandVal) {
bool isAddress = isa<LoadInst>(Inst);
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (SI->getOperand(1) == OperandVal)
isAddress = true;
} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
// Addressing modes can also be folded into prefetches and a variety
// of intrinsics.
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::prefetch:
case Intrinsic::x86_sse2_loadu_dq:
case Intrinsic::x86_sse2_loadu_pd:
case Intrinsic::x86_sse_loadu_ps:
case Intrinsic::x86_sse_storeu_ps:
case Intrinsic::x86_sse2_storeu_pd:
case Intrinsic::x86_sse2_storeu_dq:
case Intrinsic::x86_sse2_storel_dq:
if (II->getOperand(1) == OperandVal)
isAddress = true;
break;
}
}
return isAddress;
}
/// getAccessType - Return the type of the memory being accessed.
static const Type *getAccessType(const Instruction *Inst) {
const Type *AccessTy = Inst->getType();
if (const StoreInst *SI = dyn_cast<StoreInst>(Inst))
AccessTy = SI->getOperand(0)->getType();
else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
// Addressing modes can also be folded into prefetches and a variety
// of intrinsics.
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::x86_sse_storeu_ps:
case Intrinsic::x86_sse2_storeu_pd:
case Intrinsic::x86_sse2_storeu_dq:
case Intrinsic::x86_sse2_storel_dq:
AccessTy = II->getOperand(1)->getType();
break;
}
}
return AccessTy;
}
namespace {
/// BasedUser - For a particular base value, keep information about how we've
/// partitioned the expression so far.
struct BasedUser {
/// SE - The current ScalarEvolution object.
ScalarEvolution *SE;
/// Base - The Base value for the PHI node that needs to be inserted for
/// this use. As the use is processed, information gets moved from this
/// field to the Imm field (below). BasedUser values are sorted by this
/// field.
const SCEV* Base;
/// Inst - The instruction using the induction variable.
Instruction *Inst;
/// OperandValToReplace - The operand value of Inst to replace with the
/// EmittedBase.
Value *OperandValToReplace;
/// Imm - The immediate value that should be added to the base immediately
/// before Inst, because it will be folded into the imm field of the
/// instruction. This is also sometimes used for loop-variant values that
/// must be added inside the loop.
const SCEV* Imm;
/// Phi - The induction variable that performs the striding that
/// should be used for this user.
PHINode *Phi;
// isUseOfPostIncrementedValue - True if this should use the
// post-incremented version of this IV, not the preincremented version.
// This can only be set in special cases, such as the terminating setcc
// instruction for a loop and uses outside the loop that are dominated by
// the loop.
bool isUseOfPostIncrementedValue;
BasedUser(IVStrideUse &IVSU, ScalarEvolution *se)
: SE(se), Base(IVSU.getOffset()), Inst(IVSU.getUser()),
OperandValToReplace(IVSU.getOperandValToReplace()),
Imm(SE->getIntegerSCEV(0, Base->getType())),
isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue()) {}
// Once we rewrite the code to insert the new IVs we want, update the
// operands of Inst to use the new expression 'NewBase', with 'Imm' added
// to it.
void RewriteInstructionToUseNewBase(const SCEV* const &NewBase,
Instruction *InsertPt,
SCEVExpander &Rewriter, Loop *L, Pass *P,
LoopInfo &LI,
SmallVectorImpl<WeakVH> &DeadInsts);
Value *InsertCodeForBaseAtPosition(const SCEV* const &NewBase,
const Type *Ty,
SCEVExpander &Rewriter,
Instruction *IP, Loop *L,
LoopInfo &LI);
void dump() const;
};
}
void BasedUser::dump() const {
cerr << " Base=" << *Base;
cerr << " Imm=" << *Imm;
cerr << " Inst: " << *Inst;
}
Value *BasedUser::InsertCodeForBaseAtPosition(const SCEV* const &NewBase,
const Type *Ty,
SCEVExpander &Rewriter,
Instruction *IP, Loop *L,
LoopInfo &LI) {
// Figure out where we *really* want to insert this code. In particular, if
// the user is inside of a loop that is nested inside of L, we really don't
// want to insert this expression before the user, we'd rather pull it out as
// many loops as possible.
Instruction *BaseInsertPt = IP;
// Figure out the most-nested loop that IP is in.
Loop *InsertLoop = LI.getLoopFor(IP->getParent());
// If InsertLoop is not L, and InsertLoop is nested inside of L, figure out
// the preheader of the outer-most loop where NewBase is not loop invariant.
if (L->contains(IP->getParent()))
while (InsertLoop && NewBase->isLoopInvariant(InsertLoop)) {
BaseInsertPt = InsertLoop->getLoopPreheader()->getTerminator();
InsertLoop = InsertLoop->getParentLoop();
}
Value *Base = Rewriter.expandCodeFor(NewBase, 0, BaseInsertPt);
const SCEV* NewValSCEV = SE->getUnknown(Base);
// Always emit the immediate into the same block as the user.
NewValSCEV = SE->getAddExpr(NewValSCEV, Imm);
return Rewriter.expandCodeFor(NewValSCEV, Ty, IP);
}
// Once we rewrite the code to insert the new IVs we want, update the
// operands of Inst to use the new expression 'NewBase', with 'Imm' added
// to it. NewBasePt is the last instruction which contributes to the
// value of NewBase in the case that it's a diffferent instruction from
// the PHI that NewBase is computed from, or null otherwise.
//
void BasedUser::RewriteInstructionToUseNewBase(const SCEV* const &NewBase,
Instruction *NewBasePt,
SCEVExpander &Rewriter, Loop *L, Pass *P,
LoopInfo &LI,
SmallVectorImpl<WeakVH> &DeadInsts) {
if (!isa<PHINode>(Inst)) {
// By default, insert code at the user instruction.
BasicBlock::iterator InsertPt = Inst;
// However, if the Operand is itself an instruction, the (potentially
// complex) inserted code may be shared by many users. Because of this, we
// want to emit code for the computation of the operand right before its old
// computation. This is usually safe, because we obviously used to use the
// computation when it was computed in its current block. However, in some
// cases (e.g. use of a post-incremented induction variable) the NewBase
// value will be pinned to live somewhere after the original computation.
// In this case, we have to back off.
//
// If this is a use outside the loop (which means after, since it is based
// on a loop indvar) we use the post-incremented value, so that we don't
// artificially make the preinc value live out the bottom of the loop.
if (!isUseOfPostIncrementedValue && L->contains(Inst->getParent())) {
if (NewBasePt && isa<PHINode>(OperandValToReplace)) {
InsertPt = NewBasePt;
++InsertPt;
} else if (Instruction *OpInst
= dyn_cast<Instruction>(OperandValToReplace)) {
InsertPt = OpInst;
while (isa<PHINode>(InsertPt)) ++InsertPt;
}
}
Value *NewVal = InsertCodeForBaseAtPosition(NewBase,
OperandValToReplace->getType(),
Rewriter, InsertPt, L, LI);
// Replace the use of the operand Value with the new Phi we just created.
Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
DOUT << " Replacing with ";
DEBUG(WriteAsOperand(*DOUT, NewVal, /*PrintType=*/false));
DOUT << ", which has value " << *NewBase << " plus IMM " << *Imm << "\n";
return;
}
// PHI nodes are more complex. We have to insert one copy of the NewBase+Imm
// expression into each operand block that uses it. Note that PHI nodes can
// have multiple entries for the same predecessor. We use a map to make sure
// that a PHI node only has a single Value* for each predecessor (which also
// prevents us from inserting duplicate code in some blocks).
DenseMap<BasicBlock*, Value*> InsertedCode;
PHINode *PN = cast<PHINode>(Inst);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
if (PN->getIncomingValue(i) == OperandValToReplace) {
// If the original expression is outside the loop, put the replacement
// code in the same place as the original expression,
// which need not be an immediate predecessor of this PHI. This way we
// need only one copy of it even if it is referenced multiple times in
// the PHI. We don't do this when the original expression is inside the
// loop because multiple copies sometimes do useful sinking of code in
// that case(?).
Instruction *OldLoc = dyn_cast<Instruction>(OperandValToReplace);
if (L->contains(OldLoc->getParent())) {
// If this is a critical edge, split the edge so that we do not insert
// the code on all predecessor/successor paths. We do this unless this
// is the canonical backedge for this loop, as this can make some
// inserted code be in an illegal position.
BasicBlock *PHIPred = PN->getIncomingBlock(i);
if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 &&
(PN->getParent() != L->getHeader() || !L->contains(PHIPred))) {
// First step, split the critical edge.
SplitCriticalEdge(PHIPred, PN->getParent(), P, false);
// Next step: move the basic block. In particular, if the PHI node
// is outside of the loop, and PredTI is in the loop, we want to
// move the block to be immediately before the PHI block, not
// immediately after PredTI.
if (L->contains(PHIPred) && !L->contains(PN->getParent())) {
BasicBlock *NewBB = PN->getIncomingBlock(i);
NewBB->moveBefore(PN->getParent());
}
// Splitting the edge can reduce the number of PHI entries we have.
e = PN->getNumIncomingValues();
}
}
Value *&Code = InsertedCode[PN->getIncomingBlock(i)];
if (!Code) {
// Insert the code into the end of the predecessor block.
Instruction *InsertPt = (L->contains(OldLoc->getParent())) ?
PN->getIncomingBlock(i)->getTerminator() :
OldLoc->getParent()->getTerminator();
Code = InsertCodeForBaseAtPosition(NewBase, PN->getType(),
Rewriter, InsertPt, L, LI);
DOUT << " Changing PHI use to ";
DEBUG(WriteAsOperand(*DOUT, Code, /*PrintType=*/false));
DOUT << ", 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* const &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->getParent()))
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->getParent()))
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->getParent()))
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->getParent())) {
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::VoidTy;
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::VoidTy;
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* const &Stride,
IVExpr &IV, const Type *Ty,
const std::vector<BasedUser>& UsersToProcess) {
if (StrideNoReuse.count(Stride))
return SE->getIntegerSCEV(0, Stride->getType());
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) ||
StrideNoReuse.count(SI->first))
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* const &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* const &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->getParent())) {
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) {
DOUT << " 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->getParent()))
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) {
DOUT << " 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;
DOUT << " IV=";
DEBUG(WriteAsOperand(*DOUT, Phi, /*PrintType=*/false));
DOUT << "\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) {
DOUT << " 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;
}
/// StrengthReduceStridedIVUsers - 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::StrengthReduceStridedIVUsers(const SCEV* const &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::VoidTy, 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::VoidTy,
UsersToProcess, TLI);
if (DoSink) {
DOUT << " 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.
//
DOUT << "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::Int32Ty),
SE->getIntegerSCEV(0, Type::Int32Ty),
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);
DOUT << " INSERTING code for BASE = " << *Base << ":";
if (BaseV->hasName())
DOUT << " Result value name = %" << BaseV->getNameStr();
DOUT << "\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<Instruction>(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();
DOUT << " Examining ";
if (User.isUseOfPostIncrementedValue)
DOUT << "postinc";
else
DOUT << "preinc";
DOUT << " use ";
DEBUG(WriteAsOperand(*DOUT, UsersToProcess.back().OperandValToReplace,
/*PrintType=*/false));
DOUT << " 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->getParent()) && 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->getParent()))
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, *LI,
DeadInsts);
// 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.
}
/// 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* const * &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* const &LHS, const SCEV* const &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* const* &CondStride) {
// 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() ||
I->second->Users.size() != 1)
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 stride constant and the comparision constant signs to detect
// overflow.
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))
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;
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::isSignedPredicate(Predicate) &&
(CmpVal & SignBit) != (NewCmpVal & SignBit))
continue;
if (NewCmpVal == CmpVal)
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(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::isSignedPredicate(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;
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(Predicate, NewCmpLHS, NewCmpRHS,
L->getHeader()->getName() + ".termcond",
OldCond);
// 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(Pred, Cond->getOperand(0), NewRHS, "scmp", Cond);
// 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.
MVT 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;
/* 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);
}
/// OptimizeLoopTermCond - Change loop terminating condition to use the
/// postinc iv when possible.
void LoopStrengthReduce::OptimizeLoopTermCond(Loop *L) {
// 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.
BasicBlock *LatchBlock = L->getLoopLatch();
BasicBlock *ExitingBlock = L->getExitingBlock();
if (!ExitingBlock)
// Multiple exits, just look at the exit in the latch block if there is one.
ExitingBlock = LatchBlock;
BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
if (!TermBr)
return;
if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition()))
return;
// Search IVUsesByStride to find Cond's IVUse if there is one.
IVStrideUse *CondUse = 0;
const SCEV* const *CondStride = 0;
ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
if (!FindIVUserForCond(Cond, CondUse, CondStride))
return; // setcc doesn't use the IV.
if (ExitingBlock != LatchBlock) {
if (!Cond->hasOneUse())
// See below, we don't want the condition to be cloned.
return;
// 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())
return;
}
// FIXME: This is expensive, and worse still ChangeCompareStride does a
// similar check. Can we perform all the icmp related transformations after
// StrengthReduceStridedIVUsers?
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(*CondStride)) {
int64_t SInt = SC->getValue()->getSExtValue();
for (unsigned NewStride = 0, ee = IU->StrideOrder.size(); NewStride != ee;
++NewStride) {
std::map<const SCEV*, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(IU->StrideOrder[NewStride]);
if (!isa<SCEVConstant>(SI->first) || SI->first == *CondStride)
continue;
int64_t SSInt =
cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
if (SSInt == SInt)
return; // 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);
// 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))
return;
}
}
StrideNoReuse.insert(*CondStride);
}
// 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.
if (ExitingBlock == LatchBlock)
Cond = ChangeCompareStride(L, Cond, CondUse, CondStride);
// 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 latch 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");
LatchBlock->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;
}
/// 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.
void LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) {
// If the number of times the loop is executed isn't computable, give up.
const SCEV* BackedgeTakenCount = SE->getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
return;
// Get the terminating condition for the loop if possible (this isn't
// necessarily in the latch, or a block that's a predecessor of the header).
if (!L->getExitBlock())
return; // More than one loop exit blocks.
// Okay, there is one exit block. Try to find the condition that causes the
// loop to be exited.
BasicBlock *ExitingBlock = L->getExitingBlock();
if (!ExitingBlock)
return; // More than one block exiting!
// Okay, we've computed the exiting block. See what condition causes us to
// exit.
//
// FIXME: we should be able to handle switch instructions (with a single exit)
BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
if (TermBr == 0) return;
assert(TermBr->isConditional() && "If unconditional, it can't be in loop!");
if (!isa<ICmpInst>(TermBr->getCondition()))
return;
ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
// Handle only tests for equality for the moment, and only stride 1.
if (Cond->getPredicate() != CmpInst::ICMP_EQ)
return;
const SCEV* IV = SE->getSCEV(Cond->getOperand(0));
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
const SCEV* One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType());
if (!AR || !AR->isAffine() || AR->getStepRecurrence(*SE) != One)
return;
// If the RHS of the comparison is defined inside the loop, the rewrite
// cannot be done.
if (Instruction *CR = dyn_cast<Instruction>(Cond->getOperand(1)))
if (L->contains(CR->getParent()))
return;
// Make sure the IV is only used for counting. Value may be preinc or
// postinc; 2 uses in either case.
if (!Cond->getOperand(0)->hasNUses(2))
return;
PHINode *phi = dyn_cast<PHINode>(Cond->getOperand(0));
Instruction *incr;
if (phi && phi->getParent()==L->getHeader()) {
// value tested is preinc. Find the increment.
// A CmpInst is not a BinaryOperator; we depend on this.
Instruction::use_iterator UI = phi->use_begin();
incr = dyn_cast<BinaryOperator>(UI);
if (!incr)
incr = dyn_cast<BinaryOperator>(++UI);
// 1 use for postinc value, the phi. Unnecessarily conservative?
if (!incr || !incr->hasOneUse() || incr->getOpcode()!=Instruction::Add)
return;
} else {
// Value tested is postinc. Find the phi node.
incr = dyn_cast<BinaryOperator>(Cond->getOperand(0));
if (!incr || incr->getOpcode()!=Instruction::Add)
return;
Instruction::use_iterator UI = Cond->getOperand(0)->use_begin();
phi = dyn_cast<PHINode>(UI);
if (!phi)
phi = dyn_cast<PHINode>(++UI);
// 1 use for preinc value, the increment.
if (!phi || phi->getParent()!=L->getHeader() || !phi->hasOneUse())
return;
}
// Replace the increment with a decrement.
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();
int inBlock = L->contains(phi->getIncomingBlock(0)) ? 1 : 0;
Value *startVal = phi->getIncomingValue(inBlock);
Value *endVal = Cond->getOperand(1);
// 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);
phi->setIncomingValue(inBlock, NewStartVal);
Cond->setOperand(1, Zero);
Changed = true;
}
bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
IU = &getAnalysis<IVUsers>();
LI = &getAnalysis<LoopInfo>();
DT = &getAnalysis<DominatorTree>();
SE = &getAnalysis<ScalarEvolution>();
Changed = false;
if (!IU->IVUsesByStride.empty()) {
#ifndef NDEBUG
DOUT << "\nLSR on \"" << L->getHeader()->getParent()->getNameStart()
<< "\" ";
DEBUG(L->dump());
#endif
// 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
// StrengthReduceStridedIVUsers?
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?");
// Note: this processes each stride/type pair individually. All users
// passed into StrengthReduceStridedIVUsers 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;
StrengthReduceStridedIVUsers(SI->first, *SI->second, 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();
StrideNoReuse.clear();
// Clean up after ourselves
if (!DeadInsts.empty())
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;
}
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