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Diffstat (limited to 'lib/Transforms/Scalar/LoopStrengthReduce.cpp')
| -rw-r--r-- | lib/Transforms/Scalar/LoopStrengthReduce.cpp | 2605 |
1 files changed, 2605 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp new file mode 100644 index 0000000..92270b5 --- /dev/null +++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp @@ -0,0 +1,2605 @@ +//===- 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 { + SCEVHandle Stride; + SCEVHandle Base; + PHINode *PHI; + + IVExpr(const SCEVHandle &stride, const SCEVHandle &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 SCEVHandle &Stride, const SCEVHandle &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<SCEVHandle, IVsOfOneStride> IVsByStride; + + /// StrideNoReuse - Keep track of all the strides whose ivs cannot be + /// reused (nor should they be rewritten to reuse other strides). + SmallSet<SCEVHandle, 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 SCEVHandle* &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); + + /// OptimizeSMax - Rewrite the loop's terminating condition + /// if it uses an smax computation. + ICmpInst *OptimizeSMax(Loop *L, ICmpInst *Cond, + IVStrideUse* &CondUse); + + bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse, + const SCEVHandle *&CondStride); + bool RequiresTypeConversion(const Type *Ty, const Type *NewTy); + SCEVHandle CheckForIVReuse(bool, bool, bool, const SCEVHandle&, + 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); + SCEVHandle CollectIVUsers(const SCEVHandle &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, + SCEVHandle Stride); + void PrepareToStrengthReduceFully( + std::vector<BasedUser> &UsersToProcess, + SCEVHandle Stride, + SCEVHandle 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, + SCEVHandle Stride, + SCEVHandle CommonExprs, + Value *CommonBaseV, + Instruction *IVIncInsertPt, + const Loop *L, + SCEVExpander &PreheaderRewriter); + void StrengthReduceStridedIVUsers(const SCEVHandle &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(SCEVHandle 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. + SCEVHandle Base; + + /// Inst - The instruction using the induction variable. + Instruction *Inst; + + /// OperandValToReplace - The operand value of Inst to replace with the + /// EmittedBase. + Value *OperandValToReplace; + + /// isSigned - The stride (and thus also the Base) of this use may be in + /// a narrower type than the use itself (OperandValToReplace->getType()). + /// When this is the case, the isSigned field indicates whether the + /// IV expression should be signed-extended instead of zero-extended to + /// fit the type of the use. + bool isSigned; + + /// 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. + SCEVHandle 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()), + isSigned(IVSU.isSigned()), + 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 SCEVHandle &NewBase, + Instruction *InsertPt, + SCEVExpander &Rewriter, Loop *L, Pass *P, + LoopInfo &LI, + SmallVectorImpl<WeakVH> &DeadInsts); + + Value *InsertCodeForBaseAtPosition(const SCEVHandle &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 SCEVHandle &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); + + SCEVHandle NewValSCEV = SE->getUnknown(Base); + + // If there is no immediate value, skip the next part. + if (!Imm->isZero()) { + // If we are inserting the base and imm values in the same block, make sure + // to adjust the IP position if insertion reused a result. + if (IP == BaseInsertPt) + IP = Rewriter.getInsertionPoint(); + + // Always emit the immediate (if non-zero) into the same block as the user. + NewValSCEV = SE->getAddExpr(NewValSCEV, Imm); + } + + if (isSigned) + NewValSCEV = SE->getTruncateOrSignExtend(NewValSCEV, Ty); + else + NewValSCEV = SE->getTruncateOrZeroExtend(NewValSCEV, Ty); + + 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 SCEVHandle &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 SCEVHandle &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(SCEVHandle &Val, SCEVHandle &Imm, + Loop *L, ScalarEvolution *SE) { + if (Val->isLoopInvariant(L)) return; // Nothing to do. + + if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) { + std::vector<SCEVHandle> 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. + SCEVHandle Start = SARE->getStart(); + MoveLoopVariantsToImmediateField(Start, Imm, L, SE); + + std::vector<SCEVHandle> 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, + SCEVHandle &Val, SCEVHandle &Imm, + bool isAddress, Loop *L, + ScalarEvolution *SE) { + if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) { + std::vector<SCEVHandle> NewOps; + NewOps.reserve(SAE->getNumOperands()); + + for (unsigned i = 0; i != SAE->getNumOperands(); ++i) { + SCEVHandle 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. + SCEVHandle Start = SARE->getStart(); + MoveImmediateValues(TLI, AccessTy, Start, Imm, isAddress, L, SE); + + if (Start != SARE->getStart()) { + std::vector<SCEVHandle> 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)) { + + SCEVHandle SubImm = SE->getIntegerSCEV(0, Val->getType()); + SCEVHandle 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, + SCEVHandle &Val, SCEVHandle &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(std::vector<SCEVHandle> &SubExprs, + SCEVHandle 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)) { + SCEVHandle Zero = SE->getIntegerSCEV(0, Expr->getType()); + if (SARE->getOperand(0) == Zero) { + SubExprs.push_back(Expr); + } else { + // Compute the addrec with zero as its base. + std::vector<SCEVHandle> 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 SCEVHandle +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. + SCEVHandle Zero = SE->getIntegerSCEV(0, Uses[0].Base->getType()); + SCEVHandle Result = Zero; + SCEVHandle 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<SCEVHandle, SubExprUseData> SubExpressionUseData; + + // UniqueSubExprs - Keep track of all of the subexpressions we see in the + // order we see them. + std::vector<SCEVHandle> UniqueSubExprs; + + std::vector<SCEVHandle> 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<SCEVHandle, 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<SCEVHandle, 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. +SCEVHandle LoopStrengthReduce::CheckForIVReuse(bool HasBaseReg, + bool AllUsesAreAddresses, + bool AllUsesAreOutsideLoop, + const SCEVHandle &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<SCEVHandle, 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<SCEVHandle, 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<SCEVHandle, 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 SCEVHandle &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. +SCEVHandle LoopStrengthReduce::CollectIVUsers(const SCEVHandle &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. + SCEVHandle 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, + SCEVHandle 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); + SCEVHandle 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(SCEVHandle Start, SCEVHandle 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); + SCEVHandle 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 + // SCEVHandle'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. + SCEVHandle 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, + SCEVHandle Stride, + SCEVHandle 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. + SCEVHandle Imm = UsersToProcess[i].Imm; + SCEVHandle Base = UsersToProcess[i].Base; + SCEVHandle 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, + SCEVHandle Stride, + SCEVHandle 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 SCEVHandle &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; + SCEVHandle 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) { + SCEVHandle NewCommon = CommonExprs; + SCEVHandle 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); + + SCEVHandle 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()) { + SCEVHandle 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)) { + // 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); + } + + SCEVHandle 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()) { + SCEVHandle 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 SCEVHandle *&CondStride) { + for (unsigned Stride = 0, e = IU->StrideOrder.size(); + Stride != e && !CondUse; ++Stride) { + std::map<SCEVHandle, 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 SCEVHandle &LHS, const SCEVHandle &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 SCEVHandle* &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<SCEVHandle, 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; + SCEVHandle *NewStride = NULL; + Value *NewCmpLHS = NULL; + Value *NewCmpRHS = NULL; + int64_t Scale = 1; + SCEVHandle 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<SCEVHandle, 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; + SCEVHandle 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 { + ConstantInt *CI = ConstantInt::get(NewCmpIntTy, NewCmpVal); + NewCmpRHS = ConstantExpr::getIntToPtr(CI, NewCmpTy); + } + NewOffset = TyBits == NewTyBits + ? SE->getMulExpr(CondUse->getOffset(), + SE->getConstant(ConstantInt::get(CmpTy, Scale))) + : SE->getConstant(ConstantInt::get(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, false); + CondUse = &IU->IVUsesByStride[*NewStride]->Users.back(); + CondStride = NewStride; + ++NumEliminated; + Changed = true; + } + + return Cond; +} + +/// OptimizeSMax - Rewrite the loop's terminating condition if it uses +/// an smax 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); +/// +/// where the comparison is signed, the trip count isn't just 'n', because +/// 'n' could be negative. 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 +/// signed-max expression, which allows it to give the loop a canonical +/// induction variable: +/// +/// i = 0; +/// smax = n < 1 ? 1 : n; +/// do { +/// p[i] = 0.0; +/// } while (++i != smax); +/// +/// 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::OptimizeSMax(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; + + SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L); + if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) + return Cond; + SCEVHandle One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType()); + + // Add one to the backedge-taken count to get the trip count. + SCEVHandle IterationCount = SE->getAddExpr(BackedgeTakenCount, One); + + // Check for a max calculation that matches the pattern. + const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(IterationCount); + if (!SMax || SMax != SE->getSCEV(Sel)) return Cond; + + SCEVHandle SMaxLHS = SMax->getOperand(0); + SCEVHandle SMaxRHS = SMax->getOperand(1); + if (!SMaxLHS || SMaxLHS != One) return Cond; + + // Check the relevant induction variable for conformance to + // the pattern. + SCEVHandle 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)) == SMaxRHS) + NewRHS = Sel->getOperand(1); + else if (SE->getSCEV(Sel->getOperand(2)) == SMaxRHS) + NewRHS = Sel->getOperand(2); + if (!NewRHS) return Cond; + + // Ok, everything looks ok to change the condition into an SLT or SGE and + // delete the max calculation. + ICmpInst *NewCond = + new ICmpInst(Cond->getPredicate() == CmpInst::ICMP_NE ? + CmpInst::ICMP_SLT : + CmpInst::ICMP_SGE, + 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) { + + SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L); + if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) + return; + + for (unsigned Stride = 0, e = IU->StrideOrder.size(); Stride != e; + ++Stride) { + std::map<SCEVHandle, 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; + ConstantFP *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. */ + ConstantFP *CFP = ConstantFP::get(DestTy, C->getZExtValue()); + BinaryOperator *NewIncr = + BinaryOperator::Create(Incr->getOpcode(), + 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 *ExitBlock = L->getExitingBlock(); + if (!ExitBlock) + // Multiple exits, just look at the exit in the latch block if there is one. + ExitBlock = LatchBlock; + BranchInst *TermBr = dyn_cast<BranchInst>(ExitBlock->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 SCEVHandle *CondStride = 0; + ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition()); + if (!FindIVUserForCond(Cond, CondUse, CondStride)) + return; // setcc doesn't use the IV. + + if (ExitBlock != 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<SCEVHandle, 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; + SCEVHandle 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 an smax (due to ScalarEvolution + // being unable to find a sufficient guard, for example), change the loop + // comparison to use SLT instead of NE. + Cond = OptimizeSMax(L, Cond, CondUse); + + // If possible, change stride and operands of the compare instruction to + // eliminate one stride. + if (ExitBlock == 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(), + false); + 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. + SCEVHandle 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). + SmallVector<BasicBlock*, 8> ExitBlocks; + L->getExitBlocks(ExitBlocks); + if (ExitBlocks.size() != 1) return; + + // Okay, there is one exit block. Try to find the condition that causes the + // loop to be exited. + BasicBlock *ExitBlock = ExitBlocks[0]; + + BasicBlock *ExitingBlock = 0; + for (pred_iterator PI = pred_begin(ExitBlock), E = pred_end(ExitBlock); + PI != E; ++PI) + if (L->contains(*PI)) { + if (ExitingBlock == 0) + ExitingBlock = *PI; + else + return; // More than one block exiting! + } + assert(ExitingBlock && "No exits from loop, something is broken!"); + + // 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; + SCEVHandle IV = SE->getSCEV(Cond->getOperand(0)); + const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV); + SCEVHandle 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 + ConstantInt* 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<SCEVHandle, 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; +} |
