1 //===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This transformation analyzes and transforms the induction variables (and
11 // computations derived from them) into forms suitable for efficient execution
14 // This pass performs a strength reduction on array references inside loops that
15 // have as one or more of their components the loop induction variable, it
16 // rewrites expressions to take advantage of scaled-index addressing modes
17 // available on the target, and it performs a variety of other optimizations
18 // related to loop induction variables.
20 //===----------------------------------------------------------------------===//
22 #define DEBUG_TYPE "loop-reduce"
23 #include "llvm/Transforms/Scalar.h"
24 #include "llvm/Constants.h"
25 #include "llvm/Instructions.h"
26 #include "llvm/IntrinsicInst.h"
27 #include "llvm/Type.h"
28 #include "llvm/DerivedTypes.h"
29 #include "llvm/Analysis/Dominators.h"
30 #include "llvm/Analysis/IVUsers.h"
31 #include "llvm/Analysis/LoopInfo.h"
32 #include "llvm/Analysis/LoopPass.h"
33 #include "llvm/Analysis/ScalarEvolutionExpander.h"
34 #include "llvm/Transforms/Utils/AddrModeMatcher.h"
35 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
36 #include "llvm/Transforms/Utils/Local.h"
37 #include "llvm/ADT/Statistic.h"
38 #include "llvm/Support/CFG.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/Compiler.h"
41 #include "llvm/Support/CommandLine.h"
42 #include "llvm/Support/ValueHandle.h"
43 #include "llvm/Target/TargetLowering.h"
47 STATISTIC(NumReduced , "Number of IV uses strength reduced");
48 STATISTIC(NumInserted, "Number of PHIs inserted");
49 STATISTIC(NumVariable, "Number of PHIs with variable strides");
50 STATISTIC(NumEliminated, "Number of strides eliminated");
51 STATISTIC(NumShadow, "Number of Shadow IVs optimized");
52 STATISTIC(NumImmSunk, "Number of common expr immediates sunk into uses");
53 STATISTIC(NumLoopCond, "Number of loop terminating conds optimized");
55 static cl::opt<bool> EnableFullLSRMode("enable-full-lsr",
63 /// IVInfo - This structure keeps track of one IV expression inserted during
64 /// StrengthReduceStridedIVUsers. It contains the stride, the common base, as
65 /// well as the PHI node and increment value created for rewrite.
66 struct VISIBILITY_HIDDEN IVExpr {
71 IVExpr(const SCEVHandle &stride, const SCEVHandle &base, PHINode *phi)
72 : Stride(stride), Base(base), PHI(phi) {}
75 /// IVsOfOneStride - This structure keeps track of all IV expression inserted
76 /// during StrengthReduceStridedIVUsers for a particular stride of the IV.
77 struct VISIBILITY_HIDDEN IVsOfOneStride {
78 std::vector<IVExpr> IVs;
80 void addIV(const SCEVHandle &Stride, const SCEVHandle &Base, PHINode *PHI) {
81 IVs.push_back(IVExpr(Stride, Base, PHI));
85 class VISIBILITY_HIDDEN LoopStrengthReduce : public LoopPass {
92 /// IVsByStride - Keep track of all IVs that have been inserted for a
93 /// particular stride.
94 std::map<SCEVHandle, IVsOfOneStride> IVsByStride;
96 /// StrideNoReuse - Keep track of all the strides whose ivs cannot be
97 /// reused (nor should they be rewritten to reuse other strides).
98 SmallSet<SCEVHandle, 4> StrideNoReuse;
100 /// DeadInsts - Keep track of instructions we may have made dead, so that
101 /// we can remove them after we are done working.
102 SmallVector<WeakVH, 16> DeadInsts;
104 /// TLI - Keep a pointer of a TargetLowering to consult for determining
105 /// transformation profitability.
106 const TargetLowering *TLI;
109 static char ID; // Pass ID, replacement for typeid
110 explicit LoopStrengthReduce(const TargetLowering *tli = NULL) :
111 LoopPass(&ID), TLI(tli) {
114 bool runOnLoop(Loop *L, LPPassManager &LPM);
116 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
117 // We split critical edges, so we change the CFG. However, we do update
118 // many analyses if they are around.
119 AU.addPreservedID(LoopSimplifyID);
120 AU.addPreserved<LoopInfo>();
121 AU.addPreserved<DominanceFrontier>();
122 AU.addPreserved<DominatorTree>();
124 AU.addRequiredID(LoopSimplifyID);
125 AU.addRequired<LoopInfo>();
126 AU.addRequired<DominatorTree>();
127 AU.addRequired<ScalarEvolution>();
128 AU.addPreserved<ScalarEvolution>();
129 AU.addRequired<IVUsers>();
130 AU.addPreserved<IVUsers>();
134 ICmpInst *ChangeCompareStride(Loop *L, ICmpInst *Cond,
135 IVStrideUse* &CondUse,
136 const SCEVHandle* &CondStride);
138 void OptimizeIndvars(Loop *L);
139 void OptimizeLoopCountIV(Loop *L);
140 void OptimizeLoopTermCond(Loop *L);
142 /// OptimizeShadowIV - If IV is used in a int-to-float cast
143 /// inside the loop then try to eliminate the cast opeation.
144 void OptimizeShadowIV(Loop *L);
146 /// OptimizeMax - Rewrite the loop's terminating condition
147 /// if it uses a max computation.
148 ICmpInst *OptimizeMax(Loop *L, ICmpInst *Cond,
149 IVStrideUse* &CondUse);
151 bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse,
152 const SCEVHandle *&CondStride);
153 bool RequiresTypeConversion(const Type *Ty, const Type *NewTy);
154 SCEVHandle CheckForIVReuse(bool, bool, bool, const SCEVHandle&,
155 IVExpr&, const Type*,
156 const std::vector<BasedUser>& UsersToProcess);
157 bool ValidScale(bool, int64_t,
158 const std::vector<BasedUser>& UsersToProcess);
159 bool ValidOffset(bool, int64_t, int64_t,
160 const std::vector<BasedUser>& UsersToProcess);
161 SCEVHandle CollectIVUsers(const SCEVHandle &Stride,
162 IVUsersOfOneStride &Uses,
164 bool &AllUsesAreAddresses,
165 bool &AllUsesAreOutsideLoop,
166 std::vector<BasedUser> &UsersToProcess);
167 bool ShouldUseFullStrengthReductionMode(
168 const std::vector<BasedUser> &UsersToProcess,
170 bool AllUsesAreAddresses,
172 void PrepareToStrengthReduceFully(
173 std::vector<BasedUser> &UsersToProcess,
175 SCEVHandle CommonExprs,
177 SCEVExpander &PreheaderRewriter);
178 void PrepareToStrengthReduceFromSmallerStride(
179 std::vector<BasedUser> &UsersToProcess,
181 const IVExpr &ReuseIV,
182 Instruction *PreInsertPt);
183 void PrepareToStrengthReduceWithNewPhi(
184 std::vector<BasedUser> &UsersToProcess,
186 SCEVHandle CommonExprs,
188 Instruction *IVIncInsertPt,
190 SCEVExpander &PreheaderRewriter);
191 void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
192 IVUsersOfOneStride &Uses,
194 void DeleteTriviallyDeadInstructions();
198 char LoopStrengthReduce::ID = 0;
199 static RegisterPass<LoopStrengthReduce>
200 X("loop-reduce", "Loop Strength Reduction");
202 Pass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) {
203 return new LoopStrengthReduce(TLI);
206 /// DeleteTriviallyDeadInstructions - If any of the instructions is the
207 /// specified set are trivially dead, delete them and see if this makes any of
208 /// their operands subsequently dead.
209 void LoopStrengthReduce::DeleteTriviallyDeadInstructions() {
210 if (DeadInsts.empty()) return;
212 while (!DeadInsts.empty()) {
213 Instruction *I = dyn_cast_or_null<Instruction>(DeadInsts.back());
214 DeadInsts.pop_back();
216 if (I == 0 || !isInstructionTriviallyDead(I))
219 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) {
220 if (Instruction *U = dyn_cast<Instruction>(*OI)) {
223 DeadInsts.push_back(U);
227 I->eraseFromParent();
232 /// containsAddRecFromDifferentLoop - Determine whether expression S involves a
233 /// subexpression that is an AddRec from a loop other than L. An outer loop
234 /// of L is OK, but not an inner loop nor a disjoint loop.
235 static bool containsAddRecFromDifferentLoop(SCEVHandle S, Loop *L) {
236 // This is very common, put it first.
237 if (isa<SCEVConstant>(S))
239 if (const SCEVCommutativeExpr *AE = dyn_cast<SCEVCommutativeExpr>(S)) {
240 for (unsigned int i=0; i< AE->getNumOperands(); i++)
241 if (containsAddRecFromDifferentLoop(AE->getOperand(i), L))
245 if (const SCEVAddRecExpr *AE = dyn_cast<SCEVAddRecExpr>(S)) {
246 if (const Loop *newLoop = AE->getLoop()) {
249 // if newLoop is an outer loop of L, this is OK.
250 if (!LoopInfoBase<BasicBlock>::isNotAlreadyContainedIn(L, newLoop))
255 if (const SCEVUDivExpr *DE = dyn_cast<SCEVUDivExpr>(S))
256 return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
257 containsAddRecFromDifferentLoop(DE->getRHS(), L);
259 // SCEVSDivExpr has been backed out temporarily, but will be back; we'll
260 // need this when it is.
261 if (const SCEVSDivExpr *DE = dyn_cast<SCEVSDivExpr>(S))
262 return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
263 containsAddRecFromDifferentLoop(DE->getRHS(), L);
265 if (const SCEVCastExpr *CE = dyn_cast<SCEVCastExpr>(S))
266 return containsAddRecFromDifferentLoop(CE->getOperand(), L);
270 /// isAddressUse - Returns true if the specified instruction is using the
271 /// specified value as an address.
272 static bool isAddressUse(Instruction *Inst, Value *OperandVal) {
273 bool isAddress = isa<LoadInst>(Inst);
274 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
275 if (SI->getOperand(1) == OperandVal)
277 } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
278 // Addressing modes can also be folded into prefetches and a variety
280 switch (II->getIntrinsicID()) {
282 case Intrinsic::prefetch:
283 case Intrinsic::x86_sse2_loadu_dq:
284 case Intrinsic::x86_sse2_loadu_pd:
285 case Intrinsic::x86_sse_loadu_ps:
286 case Intrinsic::x86_sse_storeu_ps:
287 case Intrinsic::x86_sse2_storeu_pd:
288 case Intrinsic::x86_sse2_storeu_dq:
289 case Intrinsic::x86_sse2_storel_dq:
290 if (II->getOperand(1) == OperandVal)
298 /// getAccessType - Return the type of the memory being accessed.
299 static const Type *getAccessType(const Instruction *Inst) {
300 const Type *AccessTy = Inst->getType();
301 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst))
302 AccessTy = SI->getOperand(0)->getType();
303 else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
304 // Addressing modes can also be folded into prefetches and a variety
306 switch (II->getIntrinsicID()) {
308 case Intrinsic::x86_sse_storeu_ps:
309 case Intrinsic::x86_sse2_storeu_pd:
310 case Intrinsic::x86_sse2_storeu_dq:
311 case Intrinsic::x86_sse2_storel_dq:
312 AccessTy = II->getOperand(1)->getType();
320 /// BasedUser - For a particular base value, keep information about how we've
321 /// partitioned the expression so far.
323 /// SE - The current ScalarEvolution object.
326 /// Base - The Base value for the PHI node that needs to be inserted for
327 /// this use. As the use is processed, information gets moved from this
328 /// field to the Imm field (below). BasedUser values are sorted by this
332 /// Inst - The instruction using the induction variable.
335 /// OperandValToReplace - The operand value of Inst to replace with the
337 Value *OperandValToReplace;
339 /// Imm - The immediate value that should be added to the base immediately
340 /// before Inst, because it will be folded into the imm field of the
341 /// instruction. This is also sometimes used for loop-variant values that
342 /// must be added inside the loop.
345 /// Phi - The induction variable that performs the striding that
346 /// should be used for this user.
349 // isUseOfPostIncrementedValue - True if this should use the
350 // post-incremented version of this IV, not the preincremented version.
351 // This can only be set in special cases, such as the terminating setcc
352 // instruction for a loop and uses outside the loop that are dominated by
354 bool isUseOfPostIncrementedValue;
356 BasedUser(IVStrideUse &IVSU, ScalarEvolution *se)
357 : SE(se), Base(IVSU.getOffset()), Inst(IVSU.getUser()),
358 OperandValToReplace(IVSU.getOperandValToReplace()),
359 Imm(SE->getIntegerSCEV(0, Base->getType())),
360 isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue()) {}
362 // Once we rewrite the code to insert the new IVs we want, update the
363 // operands of Inst to use the new expression 'NewBase', with 'Imm' added
365 void RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
366 Instruction *InsertPt,
367 SCEVExpander &Rewriter, Loop *L, Pass *P,
369 SmallVectorImpl<WeakVH> &DeadInsts);
371 Value *InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
373 SCEVExpander &Rewriter,
374 Instruction *IP, Loop *L,
380 void BasedUser::dump() const {
381 cerr << " Base=" << *Base;
382 cerr << " Imm=" << *Imm;
383 cerr << " Inst: " << *Inst;
386 Value *BasedUser::InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
388 SCEVExpander &Rewriter,
389 Instruction *IP, Loop *L,
391 // Figure out where we *really* want to insert this code. In particular, if
392 // the user is inside of a loop that is nested inside of L, we really don't
393 // want to insert this expression before the user, we'd rather pull it out as
394 // many loops as possible.
395 Instruction *BaseInsertPt = IP;
397 // Figure out the most-nested loop that IP is in.
398 Loop *InsertLoop = LI.getLoopFor(IP->getParent());
400 // If InsertLoop is not L, and InsertLoop is nested inside of L, figure out
401 // the preheader of the outer-most loop where NewBase is not loop invariant.
402 if (L->contains(IP->getParent()))
403 while (InsertLoop && NewBase->isLoopInvariant(InsertLoop)) {
404 BaseInsertPt = InsertLoop->getLoopPreheader()->getTerminator();
405 InsertLoop = InsertLoop->getParentLoop();
408 Value *Base = Rewriter.expandCodeFor(NewBase, 0, BaseInsertPt);
410 SCEVHandle NewValSCEV = SE->getUnknown(Base);
412 // If there is no immediate value, skip the next part.
413 if (!Imm->isZero()) {
414 // If we are inserting the base and imm values in the same block, make sure
415 // to adjust the IP position if insertion reused a result.
416 if (IP == BaseInsertPt)
417 IP = Rewriter.getInsertionPoint();
419 // Always emit the immediate (if non-zero) into the same block as the user.
420 NewValSCEV = SE->getAddExpr(NewValSCEV, Imm);
423 return Rewriter.expandCodeFor(NewValSCEV, Ty, IP);
427 // Once we rewrite the code to insert the new IVs we want, update the
428 // operands of Inst to use the new expression 'NewBase', with 'Imm' added
429 // to it. NewBasePt is the last instruction which contributes to the
430 // value of NewBase in the case that it's a diffferent instruction from
431 // the PHI that NewBase is computed from, or null otherwise.
433 void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
434 Instruction *NewBasePt,
435 SCEVExpander &Rewriter, Loop *L, Pass *P,
437 SmallVectorImpl<WeakVH> &DeadInsts) {
438 if (!isa<PHINode>(Inst)) {
439 // By default, insert code at the user instruction.
440 BasicBlock::iterator InsertPt = Inst;
442 // However, if the Operand is itself an instruction, the (potentially
443 // complex) inserted code may be shared by many users. Because of this, we
444 // want to emit code for the computation of the operand right before its old
445 // computation. This is usually safe, because we obviously used to use the
446 // computation when it was computed in its current block. However, in some
447 // cases (e.g. use of a post-incremented induction variable) the NewBase
448 // value will be pinned to live somewhere after the original computation.
449 // In this case, we have to back off.
451 // If this is a use outside the loop (which means after, since it is based
452 // on a loop indvar) we use the post-incremented value, so that we don't
453 // artificially make the preinc value live out the bottom of the loop.
454 if (!isUseOfPostIncrementedValue && L->contains(Inst->getParent())) {
455 if (NewBasePt && isa<PHINode>(OperandValToReplace)) {
456 InsertPt = NewBasePt;
458 } else if (Instruction *OpInst
459 = dyn_cast<Instruction>(OperandValToReplace)) {
461 while (isa<PHINode>(InsertPt)) ++InsertPt;
464 Value *NewVal = InsertCodeForBaseAtPosition(NewBase,
465 OperandValToReplace->getType(),
466 Rewriter, InsertPt, L, LI);
467 // Replace the use of the operand Value with the new Phi we just created.
468 Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
470 DOUT << " Replacing with ";
471 DEBUG(WriteAsOperand(*DOUT, NewVal, /*PrintType=*/false));
472 DOUT << ", which has value " << *NewBase << " plus IMM " << *Imm << "\n";
476 // PHI nodes are more complex. We have to insert one copy of the NewBase+Imm
477 // expression into each operand block that uses it. Note that PHI nodes can
478 // have multiple entries for the same predecessor. We use a map to make sure
479 // that a PHI node only has a single Value* for each predecessor (which also
480 // prevents us from inserting duplicate code in some blocks).
481 DenseMap<BasicBlock*, Value*> InsertedCode;
482 PHINode *PN = cast<PHINode>(Inst);
483 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
484 if (PN->getIncomingValue(i) == OperandValToReplace) {
485 // If the original expression is outside the loop, put the replacement
486 // code in the same place as the original expression,
487 // which need not be an immediate predecessor of this PHI. This way we
488 // need only one copy of it even if it is referenced multiple times in
489 // the PHI. We don't do this when the original expression is inside the
490 // loop because multiple copies sometimes do useful sinking of code in
492 Instruction *OldLoc = dyn_cast<Instruction>(OperandValToReplace);
493 if (L->contains(OldLoc->getParent())) {
494 // If this is a critical edge, split the edge so that we do not insert
495 // the code on all predecessor/successor paths. We do this unless this
496 // is the canonical backedge for this loop, as this can make some
497 // inserted code be in an illegal position.
498 BasicBlock *PHIPred = PN->getIncomingBlock(i);
499 if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 &&
500 (PN->getParent() != L->getHeader() || !L->contains(PHIPred))) {
502 // First step, split the critical edge.
503 SplitCriticalEdge(PHIPred, PN->getParent(), P, false);
505 // Next step: move the basic block. In particular, if the PHI node
506 // is outside of the loop, and PredTI is in the loop, we want to
507 // move the block to be immediately before the PHI block, not
508 // immediately after PredTI.
509 if (L->contains(PHIPred) && !L->contains(PN->getParent())) {
510 BasicBlock *NewBB = PN->getIncomingBlock(i);
511 NewBB->moveBefore(PN->getParent());
514 // Splitting the edge can reduce the number of PHI entries we have.
515 e = PN->getNumIncomingValues();
518 Value *&Code = InsertedCode[PN->getIncomingBlock(i)];
520 // Insert the code into the end of the predecessor block.
521 Instruction *InsertPt = (L->contains(OldLoc->getParent())) ?
522 PN->getIncomingBlock(i)->getTerminator() :
523 OldLoc->getParent()->getTerminator();
524 Code = InsertCodeForBaseAtPosition(NewBase, PN->getType(),
525 Rewriter, InsertPt, L, LI);
527 DOUT << " Changing PHI use to ";
528 DEBUG(WriteAsOperand(*DOUT, Code, /*PrintType=*/false));
529 DOUT << ", which has value " << *NewBase << " plus IMM " << *Imm << "\n";
532 // Replace the use of the operand Value with the new Phi we just created.
533 PN->setIncomingValue(i, Code);
538 // PHI node might have become a constant value after SplitCriticalEdge.
539 DeadInsts.push_back(Inst);
543 /// fitsInAddressMode - Return true if V can be subsumed within an addressing
544 /// mode, and does not need to be put in a register first.
545 static bool fitsInAddressMode(const SCEVHandle &V, const Type *AccessTy,
546 const TargetLowering *TLI, bool HasBaseReg) {
547 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) {
548 int64_t VC = SC->getValue()->getSExtValue();
550 TargetLowering::AddrMode AM;
552 AM.HasBaseReg = HasBaseReg;
553 return TLI->isLegalAddressingMode(AM, AccessTy);
555 // Defaults to PPC. PPC allows a sign-extended 16-bit immediate field.
556 return (VC > -(1 << 16) && VC < (1 << 16)-1);
560 if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V))
561 if (GlobalValue *GV = dyn_cast<GlobalValue>(SU->getValue())) {
563 TargetLowering::AddrMode AM;
565 AM.HasBaseReg = HasBaseReg;
566 return TLI->isLegalAddressingMode(AM, AccessTy);
568 // Default: assume global addresses are not legal.
575 /// MoveLoopVariantsToImmediateField - Move any subexpressions from Val that are
576 /// loop varying to the Imm operand.
577 static void MoveLoopVariantsToImmediateField(SCEVHandle &Val, SCEVHandle &Imm,
578 Loop *L, ScalarEvolution *SE) {
579 if (Val->isLoopInvariant(L)) return; // Nothing to do.
581 if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
582 SmallVector<SCEVHandle, 4> NewOps;
583 NewOps.reserve(SAE->getNumOperands());
585 for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
586 if (!SAE->getOperand(i)->isLoopInvariant(L)) {
587 // If this is a loop-variant expression, it must stay in the immediate
588 // field of the expression.
589 Imm = SE->getAddExpr(Imm, SAE->getOperand(i));
591 NewOps.push_back(SAE->getOperand(i));
595 Val = SE->getIntegerSCEV(0, Val->getType());
597 Val = SE->getAddExpr(NewOps);
598 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
599 // Try to pull immediates out of the start value of nested addrec's.
600 SCEVHandle Start = SARE->getStart();
601 MoveLoopVariantsToImmediateField(Start, Imm, L, SE);
603 SmallVector<SCEVHandle, 4> Ops(SARE->op_begin(), SARE->op_end());
605 Val = SE->getAddRecExpr(Ops, SARE->getLoop());
607 // Otherwise, all of Val is variant, move the whole thing over.
608 Imm = SE->getAddExpr(Imm, Val);
609 Val = SE->getIntegerSCEV(0, Val->getType());
614 /// MoveImmediateValues - Look at Val, and pull out any additions of constants
615 /// that can fit into the immediate field of instructions in the target.
616 /// Accumulate these immediate values into the Imm value.
617 static void MoveImmediateValues(const TargetLowering *TLI,
618 const Type *AccessTy,
619 SCEVHandle &Val, SCEVHandle &Imm,
620 bool isAddress, Loop *L,
621 ScalarEvolution *SE) {
622 if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
623 SmallVector<SCEVHandle, 4> NewOps;
624 NewOps.reserve(SAE->getNumOperands());
626 for (unsigned i = 0; i != SAE->getNumOperands(); ++i) {
627 SCEVHandle NewOp = SAE->getOperand(i);
628 MoveImmediateValues(TLI, AccessTy, NewOp, Imm, isAddress, L, SE);
630 if (!NewOp->isLoopInvariant(L)) {
631 // If this is a loop-variant expression, it must stay in the immediate
632 // field of the expression.
633 Imm = SE->getAddExpr(Imm, NewOp);
635 NewOps.push_back(NewOp);
640 Val = SE->getIntegerSCEV(0, Val->getType());
642 Val = SE->getAddExpr(NewOps);
644 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
645 // Try to pull immediates out of the start value of nested addrec's.
646 SCEVHandle Start = SARE->getStart();
647 MoveImmediateValues(TLI, AccessTy, Start, Imm, isAddress, L, SE);
649 if (Start != SARE->getStart()) {
650 SmallVector<SCEVHandle, 4> Ops(SARE->op_begin(), SARE->op_end());
652 Val = SE->getAddRecExpr(Ops, SARE->getLoop());
655 } else if (const SCEVMulExpr *SME = dyn_cast<SCEVMulExpr>(Val)) {
656 // Transform "8 * (4 + v)" -> "32 + 8*V" if "32" fits in the immed field.
658 fitsInAddressMode(SME->getOperand(0), AccessTy, TLI, false) &&
659 SME->getNumOperands() == 2 && SME->isLoopInvariant(L)) {
661 SCEVHandle SubImm = SE->getIntegerSCEV(0, Val->getType());
662 SCEVHandle NewOp = SME->getOperand(1);
663 MoveImmediateValues(TLI, AccessTy, NewOp, SubImm, isAddress, L, SE);
665 // If we extracted something out of the subexpressions, see if we can
667 if (NewOp != SME->getOperand(1)) {
668 // Scale SubImm up by "8". If the result is a target constant, we are
670 SubImm = SE->getMulExpr(SubImm, SME->getOperand(0));
671 if (fitsInAddressMode(SubImm, AccessTy, TLI, false)) {
672 // Accumulate the immediate.
673 Imm = SE->getAddExpr(Imm, SubImm);
675 // Update what is left of 'Val'.
676 Val = SE->getMulExpr(SME->getOperand(0), NewOp);
683 // Loop-variant expressions must stay in the immediate field of the
685 if ((isAddress && fitsInAddressMode(Val, AccessTy, TLI, false)) ||
686 !Val->isLoopInvariant(L)) {
687 Imm = SE->getAddExpr(Imm, Val);
688 Val = SE->getIntegerSCEV(0, Val->getType());
692 // Otherwise, no immediates to move.
695 static void MoveImmediateValues(const TargetLowering *TLI,
697 SCEVHandle &Val, SCEVHandle &Imm,
698 bool isAddress, Loop *L,
699 ScalarEvolution *SE) {
700 const Type *AccessTy = getAccessType(User);
701 MoveImmediateValues(TLI, AccessTy, Val, Imm, isAddress, L, SE);
704 /// SeparateSubExprs - Decompose Expr into all of the subexpressions that are
705 /// added together. This is used to reassociate common addition subexprs
706 /// together for maximal sharing when rewriting bases.
707 static void SeparateSubExprs(SmallVector<SCEVHandle, 16> &SubExprs,
709 ScalarEvolution *SE) {
710 if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) {
711 for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
712 SeparateSubExprs(SubExprs, AE->getOperand(j), SE);
713 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) {
714 SCEVHandle Zero = SE->getIntegerSCEV(0, Expr->getType());
715 if (SARE->getOperand(0) == Zero) {
716 SubExprs.push_back(Expr);
718 // Compute the addrec with zero as its base.
719 SmallVector<SCEVHandle, 4> Ops(SARE->op_begin(), SARE->op_end());
720 Ops[0] = Zero; // Start with zero base.
721 SubExprs.push_back(SE->getAddRecExpr(Ops, SARE->getLoop()));
724 SeparateSubExprs(SubExprs, SARE->getOperand(0), SE);
726 } else if (!Expr->isZero()) {
728 SubExprs.push_back(Expr);
732 // This is logically local to the following function, but C++ says we have
733 // to make it file scope.
734 struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; };
736 /// RemoveCommonExpressionsFromUseBases - Look through all of the Bases of all
737 /// the Uses, removing any common subexpressions, except that if all such
738 /// subexpressions can be folded into an addressing mode for all uses inside
739 /// the loop (this case is referred to as "free" in comments herein) we do
740 /// not remove anything. This looks for things like (a+b+c) and
741 /// (a+c+d) and computes the common (a+c) subexpression. The common expression
742 /// is *removed* from the Bases and returned.
744 RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses,
745 ScalarEvolution *SE, Loop *L,
746 const TargetLowering *TLI) {
747 unsigned NumUses = Uses.size();
749 // Only one use? This is a very common case, so we handle it specially and
751 SCEVHandle Zero = SE->getIntegerSCEV(0, Uses[0].Base->getType());
752 SCEVHandle Result = Zero;
753 SCEVHandle FreeResult = Zero;
755 // If the use is inside the loop, use its base, regardless of what it is:
756 // it is clearly shared across all the IV's. If the use is outside the loop
757 // (which means after it) we don't want to factor anything *into* the loop,
758 // so just use 0 as the base.
759 if (L->contains(Uses[0].Inst->getParent()))
760 std::swap(Result, Uses[0].Base);
764 // To find common subexpressions, count how many of Uses use each expression.
765 // If any subexpressions are used Uses.size() times, they are common.
766 // Also track whether all uses of each expression can be moved into an
767 // an addressing mode "for free"; such expressions are left within the loop.
768 // struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; };
769 std::map<SCEVHandle, SubExprUseData> SubExpressionUseData;
771 // UniqueSubExprs - Keep track of all of the subexpressions we see in the
772 // order we see them.
773 SmallVector<SCEVHandle, 16> UniqueSubExprs;
775 SmallVector<SCEVHandle, 16> SubExprs;
776 unsigned NumUsesInsideLoop = 0;
777 for (unsigned i = 0; i != NumUses; ++i) {
778 // If the user is outside the loop, just ignore it for base computation.
779 // Since the user is outside the loop, it must be *after* the loop (if it
780 // were before, it could not be based on the loop IV). We don't want users
781 // after the loop to affect base computation of values *inside* the loop,
782 // because we can always add their offsets to the result IV after the loop
783 // is done, ensuring we get good code inside the loop.
784 if (!L->contains(Uses[i].Inst->getParent()))
788 // If the base is zero (which is common), return zero now, there are no
790 if (Uses[i].Base == Zero) return Zero;
792 // If this use is as an address we may be able to put CSEs in the addressing
793 // mode rather than hoisting them.
794 bool isAddrUse = isAddressUse(Uses[i].Inst, Uses[i].OperandValToReplace);
795 // We may need the AccessTy below, but only when isAddrUse, so compute it
796 // only in that case.
797 const Type *AccessTy = 0;
799 AccessTy = getAccessType(Uses[i].Inst);
801 // Split the expression into subexprs.
802 SeparateSubExprs(SubExprs, Uses[i].Base, SE);
803 // Add one to SubExpressionUseData.Count for each subexpr present, and
804 // if the subexpr is not a valid immediate within an addressing mode use,
805 // set SubExpressionUseData.notAllUsesAreFree. We definitely want to
806 // hoist these out of the loop (if they are common to all uses).
807 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) {
808 if (++SubExpressionUseData[SubExprs[j]].Count == 1)
809 UniqueSubExprs.push_back(SubExprs[j]);
810 if (!isAddrUse || !fitsInAddressMode(SubExprs[j], AccessTy, TLI, false))
811 SubExpressionUseData[SubExprs[j]].notAllUsesAreFree = true;
816 // Now that we know how many times each is used, build Result. Iterate over
817 // UniqueSubexprs so that we have a stable ordering.
818 for (unsigned i = 0, e = UniqueSubExprs.size(); i != e; ++i) {
819 std::map<SCEVHandle, SubExprUseData>::iterator I =
820 SubExpressionUseData.find(UniqueSubExprs[i]);
821 assert(I != SubExpressionUseData.end() && "Entry not found?");
822 if (I->second.Count == NumUsesInsideLoop) { // Found CSE!
823 if (I->second.notAllUsesAreFree)
824 Result = SE->getAddExpr(Result, I->first);
826 FreeResult = SE->getAddExpr(FreeResult, I->first);
828 // Remove non-cse's from SubExpressionUseData.
829 SubExpressionUseData.erase(I);
832 if (FreeResult != Zero) {
833 // We have some subexpressions that can be subsumed into addressing
834 // modes in every use inside the loop. However, it's possible that
835 // there are so many of them that the combined FreeResult cannot
836 // be subsumed, or that the target cannot handle both a FreeResult
837 // and a Result in the same instruction (for example because it would
838 // require too many registers). Check this.
839 for (unsigned i=0; i<NumUses; ++i) {
840 if (!L->contains(Uses[i].Inst->getParent()))
842 // We know this is an addressing mode use; if there are any uses that
843 // are not, FreeResult would be Zero.
844 const Type *AccessTy = getAccessType(Uses[i].Inst);
845 if (!fitsInAddressMode(FreeResult, AccessTy, TLI, Result!=Zero)) {
846 // FIXME: could split up FreeResult into pieces here, some hoisted
847 // and some not. There is no obvious advantage to this.
848 Result = SE->getAddExpr(Result, FreeResult);
855 // If we found no CSE's, return now.
856 if (Result == Zero) return Result;
858 // If we still have a FreeResult, remove its subexpressions from
859 // SubExpressionUseData. This means they will remain in the use Bases.
860 if (FreeResult != Zero) {
861 SeparateSubExprs(SubExprs, FreeResult, SE);
862 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) {
863 std::map<SCEVHandle, SubExprUseData>::iterator I =
864 SubExpressionUseData.find(SubExprs[j]);
865 SubExpressionUseData.erase(I);
870 // Otherwise, remove all of the CSE's we found from each of the base values.
871 for (unsigned i = 0; i != NumUses; ++i) {
872 // Uses outside the loop don't necessarily include the common base, but
873 // the final IV value coming into those uses does. Instead of trying to
874 // remove the pieces of the common base, which might not be there,
875 // subtract off the base to compensate for this.
876 if (!L->contains(Uses[i].Inst->getParent())) {
877 Uses[i].Base = SE->getMinusSCEV(Uses[i].Base, Result);
881 // Split the expression into subexprs.
882 SeparateSubExprs(SubExprs, Uses[i].Base, SE);
884 // Remove any common subexpressions.
885 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j)
886 if (SubExpressionUseData.count(SubExprs[j])) {
887 SubExprs.erase(SubExprs.begin()+j);
891 // Finally, add the non-shared expressions together.
892 if (SubExprs.empty())
895 Uses[i].Base = SE->getAddExpr(SubExprs);
902 /// ValidScale - Check whether the given Scale is valid for all loads and
903 /// stores in UsersToProcess.
905 bool LoopStrengthReduce::ValidScale(bool HasBaseReg, int64_t Scale,
906 const std::vector<BasedUser>& UsersToProcess) {
910 for (unsigned i = 0, e = UsersToProcess.size(); i!=e; ++i) {
911 // If this is a load or other access, pass the type of the access in.
912 const Type *AccessTy = Type::VoidTy;
913 if (isAddressUse(UsersToProcess[i].Inst,
914 UsersToProcess[i].OperandValToReplace))
915 AccessTy = getAccessType(UsersToProcess[i].Inst);
916 else if (isa<PHINode>(UsersToProcess[i].Inst))
919 TargetLowering::AddrMode AM;
920 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm))
921 AM.BaseOffs = SC->getValue()->getSExtValue();
922 AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero();
925 // If load[imm+r*scale] is illegal, bail out.
926 if (!TLI->isLegalAddressingMode(AM, AccessTy))
932 /// ValidOffset - Check whether the given Offset is valid for all loads and
933 /// stores in UsersToProcess.
935 bool LoopStrengthReduce::ValidOffset(bool HasBaseReg,
938 const std::vector<BasedUser>& UsersToProcess) {
942 for (unsigned i=0, e = UsersToProcess.size(); i!=e; ++i) {
943 // If this is a load or other access, pass the type of the access in.
944 const Type *AccessTy = Type::VoidTy;
945 if (isAddressUse(UsersToProcess[i].Inst,
946 UsersToProcess[i].OperandValToReplace))
947 AccessTy = getAccessType(UsersToProcess[i].Inst);
948 else if (isa<PHINode>(UsersToProcess[i].Inst))
951 TargetLowering::AddrMode AM;
952 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm))
953 AM.BaseOffs = SC->getValue()->getSExtValue();
954 AM.BaseOffs = (uint64_t)AM.BaseOffs + (uint64_t)Offset;
955 AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero();
958 // If load[imm+r*scale] is illegal, bail out.
959 if (!TLI->isLegalAddressingMode(AM, AccessTy))
965 /// RequiresTypeConversion - Returns true if converting Ty1 to Ty2 is not
967 bool LoopStrengthReduce::RequiresTypeConversion(const Type *Ty1,
971 Ty1 = SE->getEffectiveSCEVType(Ty1);
972 Ty2 = SE->getEffectiveSCEVType(Ty2);
975 if (Ty1->canLosslesslyBitCastTo(Ty2))
977 if (TLI && TLI->isTruncateFree(Ty1, Ty2))
982 /// CheckForIVReuse - Returns the multiple if the stride is the multiple
983 /// of a previous stride and it is a legal value for the target addressing
984 /// mode scale component and optional base reg. This allows the users of
985 /// this stride to be rewritten as prev iv * factor. It returns 0 if no
986 /// reuse is possible. Factors can be negative on same targets, e.g. ARM.
988 /// If all uses are outside the loop, we don't require that all multiplies
989 /// be folded into the addressing mode, nor even that the factor be constant;
990 /// a multiply (executed once) outside the loop is better than another IV
991 /// within. Well, usually.
992 SCEVHandle LoopStrengthReduce::CheckForIVReuse(bool HasBaseReg,
993 bool AllUsesAreAddresses,
994 bool AllUsesAreOutsideLoop,
995 const SCEVHandle &Stride,
996 IVExpr &IV, const Type *Ty,
997 const std::vector<BasedUser>& UsersToProcess) {
998 if (StrideNoReuse.count(Stride))
999 return SE->getIntegerSCEV(0, Stride->getType());
1001 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
1002 int64_t SInt = SC->getValue()->getSExtValue();
1003 for (unsigned NewStride = 0, e = IU->StrideOrder.size();
1004 NewStride != e; ++NewStride) {
1005 std::map<SCEVHandle, IVsOfOneStride>::iterator SI =
1006 IVsByStride.find(IU->StrideOrder[NewStride]);
1007 if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first) ||
1008 StrideNoReuse.count(SI->first))
1010 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
1011 if (SI->first != Stride &&
1012 (unsigned(abs64(SInt)) < SSInt || (SInt % SSInt) != 0))
1014 int64_t Scale = SInt / SSInt;
1015 // Check that this stride is valid for all the types used for loads and
1016 // stores; if it can be used for some and not others, we might as well use
1017 // the original stride everywhere, since we have to create the IV for it
1018 // anyway. If the scale is 1, then we don't need to worry about folding
1021 (AllUsesAreAddresses &&
1022 ValidScale(HasBaseReg, Scale, UsersToProcess))) {
1023 // Prefer to reuse an IV with a base of zero.
1024 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
1025 IE = SI->second.IVs.end(); II != IE; ++II)
1026 // Only reuse previous IV if it would not require a type conversion
1027 // and if the base difference can be folded.
1028 if (II->Base->isZero() &&
1029 !RequiresTypeConversion(II->Base->getType(), Ty)) {
1031 return SE->getIntegerSCEV(Scale, Stride->getType());
1033 // Otherwise, settle for an IV with a foldable base.
1034 if (AllUsesAreAddresses)
1035 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
1036 IE = SI->second.IVs.end(); II != IE; ++II)
1037 // Only reuse previous IV if it would not require a type conversion
1038 // and if the base difference can be folded.
1039 if (SE->getEffectiveSCEVType(II->Base->getType()) ==
1040 SE->getEffectiveSCEVType(Ty) &&
1041 isa<SCEVConstant>(II->Base)) {
1043 cast<SCEVConstant>(II->Base)->getValue()->getSExtValue();
1044 if (Base > INT32_MIN && Base <= INT32_MAX &&
1045 ValidOffset(HasBaseReg, -Base * Scale,
1046 Scale, UsersToProcess)) {
1048 return SE->getIntegerSCEV(Scale, Stride->getType());
1053 } else if (AllUsesAreOutsideLoop) {
1054 // Accept nonconstant strides here; it is really really right to substitute
1055 // an existing IV if we can.
1056 for (unsigned NewStride = 0, e = IU->StrideOrder.size();
1057 NewStride != e; ++NewStride) {
1058 std::map<SCEVHandle, IVsOfOneStride>::iterator SI =
1059 IVsByStride.find(IU->StrideOrder[NewStride]);
1060 if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first))
1062 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
1063 if (SI->first != Stride && SSInt != 1)
1065 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
1066 IE = SI->second.IVs.end(); II != IE; ++II)
1067 // Accept nonzero base here.
1068 // Only reuse previous IV if it would not require a type conversion.
1069 if (!RequiresTypeConversion(II->Base->getType(), Ty)) {
1074 // Special case, old IV is -1*x and this one is x. Can treat this one as
1076 for (unsigned NewStride = 0, e = IU->StrideOrder.size();
1077 NewStride != e; ++NewStride) {
1078 std::map<SCEVHandle, IVsOfOneStride>::iterator SI =
1079 IVsByStride.find(IU->StrideOrder[NewStride]);
1080 if (SI == IVsByStride.end())
1082 if (const SCEVMulExpr *ME = dyn_cast<SCEVMulExpr>(SI->first))
1083 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(ME->getOperand(0)))
1084 if (Stride == ME->getOperand(1) &&
1085 SC->getValue()->getSExtValue() == -1LL)
1086 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
1087 IE = SI->second.IVs.end(); II != IE; ++II)
1088 // Accept nonzero base here.
1089 // Only reuse previous IV if it would not require type conversion.
1090 if (!RequiresTypeConversion(II->Base->getType(), Ty)) {
1092 return SE->getIntegerSCEV(-1LL, Stride->getType());
1096 return SE->getIntegerSCEV(0, Stride->getType());
1099 /// PartitionByIsUseOfPostIncrementedValue - Simple boolean predicate that
1100 /// returns true if Val's isUseOfPostIncrementedValue is true.
1101 static bool PartitionByIsUseOfPostIncrementedValue(const BasedUser &Val) {
1102 return Val.isUseOfPostIncrementedValue;
1105 /// isNonConstantNegative - Return true if the specified scev is negated, but
1107 static bool isNonConstantNegative(const SCEVHandle &Expr) {
1108 const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Expr);
1109 if (!Mul) return false;
1111 // If there is a constant factor, it will be first.
1112 const SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0));
1113 if (!SC) return false;
1115 // Return true if the value is negative, this matches things like (-42 * V).
1116 return SC->getValue()->getValue().isNegative();
1119 /// CollectIVUsers - Transform our list of users and offsets to a bit more
1120 /// complex table. In this new vector, each 'BasedUser' contains 'Base', the base
1121 /// of the strided accesses, as well as the old information from Uses. We
1122 /// progressively move information from the Base field to the Imm field, until
1123 /// we eventually have the full access expression to rewrite the use.
1124 SCEVHandle LoopStrengthReduce::CollectIVUsers(const SCEVHandle &Stride,
1125 IVUsersOfOneStride &Uses,
1127 bool &AllUsesAreAddresses,
1128 bool &AllUsesAreOutsideLoop,
1129 std::vector<BasedUser> &UsersToProcess) {
1130 // FIXME: Generalize to non-affine IV's.
1131 if (!Stride->isLoopInvariant(L))
1132 return SE->getIntegerSCEV(0, Stride->getType());
1134 UsersToProcess.reserve(Uses.Users.size());
1135 for (ilist<IVStrideUse>::iterator I = Uses.Users.begin(),
1136 E = Uses.Users.end(); I != E; ++I) {
1137 UsersToProcess.push_back(BasedUser(*I, SE));
1139 // Move any loop variant operands from the offset field to the immediate
1140 // field of the use, so that we don't try to use something before it is
1142 MoveLoopVariantsToImmediateField(UsersToProcess.back().Base,
1143 UsersToProcess.back().Imm, L, SE);
1144 assert(UsersToProcess.back().Base->isLoopInvariant(L) &&
1145 "Base value is not loop invariant!");
1148 // We now have a whole bunch of uses of like-strided induction variables, but
1149 // they might all have different bases. We want to emit one PHI node for this
1150 // stride which we fold as many common expressions (between the IVs) into as
1151 // possible. Start by identifying the common expressions in the base values
1152 // for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
1153 // "A+B"), emit it to the preheader, then remove the expression from the
1154 // UsersToProcess base values.
1155 SCEVHandle CommonExprs =
1156 RemoveCommonExpressionsFromUseBases(UsersToProcess, SE, L, TLI);
1158 // Next, figure out what we can represent in the immediate fields of
1159 // instructions. If we can represent anything there, move it to the imm
1160 // fields of the BasedUsers. We do this so that it increases the commonality
1161 // of the remaining uses.
1162 unsigned NumPHI = 0;
1163 bool HasAddress = false;
1164 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
1165 // If the user is not in the current loop, this means it is using the exit
1166 // value of the IV. Do not put anything in the base, make sure it's all in
1167 // the immediate field to allow as much factoring as possible.
1168 if (!L->contains(UsersToProcess[i].Inst->getParent())) {
1169 UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm,
1170 UsersToProcess[i].Base);
1171 UsersToProcess[i].Base =
1172 SE->getIntegerSCEV(0, UsersToProcess[i].Base->getType());
1174 // Not all uses are outside the loop.
1175 AllUsesAreOutsideLoop = false;
1177 // Addressing modes can be folded into loads and stores. Be careful that
1178 // the store is through the expression, not of the expression though.
1180 bool isAddress = isAddressUse(UsersToProcess[i].Inst,
1181 UsersToProcess[i].OperandValToReplace);
1182 if (isa<PHINode>(UsersToProcess[i].Inst)) {
1190 // If this use isn't an address, then not all uses are addresses.
1191 if (!isAddress && !isPHI)
1192 AllUsesAreAddresses = false;
1194 MoveImmediateValues(TLI, UsersToProcess[i].Inst, UsersToProcess[i].Base,
1195 UsersToProcess[i].Imm, isAddress, L, SE);
1199 // If one of the use is a PHI node and all other uses are addresses, still
1200 // allow iv reuse. Essentially we are trading one constant multiplication
1201 // for one fewer iv.
1203 AllUsesAreAddresses = false;
1205 // There are no in-loop address uses.
1206 if (AllUsesAreAddresses && (!HasAddress && !AllUsesAreOutsideLoop))
1207 AllUsesAreAddresses = false;
1212 /// ShouldUseFullStrengthReductionMode - Test whether full strength-reduction
1213 /// is valid and profitable for the given set of users of a stride. In
1214 /// full strength-reduction mode, all addresses at the current stride are
1215 /// strength-reduced all the way down to pointer arithmetic.
1217 bool LoopStrengthReduce::ShouldUseFullStrengthReductionMode(
1218 const std::vector<BasedUser> &UsersToProcess,
1220 bool AllUsesAreAddresses,
1221 SCEVHandle Stride) {
1222 if (!EnableFullLSRMode)
1225 // The heuristics below aim to avoid increasing register pressure, but
1226 // fully strength-reducing all the addresses increases the number of
1227 // add instructions, so don't do this when optimizing for size.
1228 // TODO: If the loop is large, the savings due to simpler addresses
1229 // may oughtweight the costs of the extra increment instructions.
1230 if (L->getHeader()->getParent()->hasFnAttr(Attribute::OptimizeForSize))
1233 // TODO: For now, don't do full strength reduction if there could
1234 // potentially be greater-stride multiples of the current stride
1235 // which could reuse the current stride IV.
1236 if (IU->StrideOrder.back() != Stride)
1239 // Iterate through the uses to find conditions that automatically rule out
1241 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) {
1242 const SCEV *Base = UsersToProcess[i].Base;
1243 const SCEV *Imm = UsersToProcess[i].Imm;
1244 // If any users have a loop-variant component, they can't be fully
1245 // strength-reduced.
1246 if (Imm && !Imm->isLoopInvariant(L))
1248 // If there are to users with the same base and the difference between
1249 // the two Imm values can't be folded into the address, full
1250 // strength reduction would increase register pressure.
1252 const SCEV *CurImm = UsersToProcess[i].Imm;
1253 if ((CurImm || Imm) && CurImm != Imm) {
1254 if (!CurImm) CurImm = SE->getIntegerSCEV(0, Stride->getType());
1255 if (!Imm) Imm = SE->getIntegerSCEV(0, Stride->getType());
1256 const Instruction *Inst = UsersToProcess[i].Inst;
1257 const Type *AccessTy = getAccessType(Inst);
1258 SCEVHandle Diff = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm);
1259 if (!Diff->isZero() &&
1260 (!AllUsesAreAddresses ||
1261 !fitsInAddressMode(Diff, AccessTy, TLI, /*HasBaseReg=*/true)))
1264 } while (++i != e && Base == UsersToProcess[i].Base);
1267 // If there's exactly one user in this stride, fully strength-reducing it
1268 // won't increase register pressure. If it's starting from a non-zero base,
1269 // it'll be simpler this way.
1270 if (UsersToProcess.size() == 1 && !UsersToProcess[0].Base->isZero())
1273 // Otherwise, if there are any users in this stride that don't require
1274 // a register for their base, full strength-reduction will increase
1275 // register pressure.
1276 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
1277 if (UsersToProcess[i].Base->isZero())
1280 // Otherwise, go for it.
1284 /// InsertAffinePhi Create and insert a PHI node for an induction variable
1285 /// with the specified start and step values in the specified loop.
1287 /// If NegateStride is true, the stride should be negated by using a
1288 /// subtract instead of an add.
1290 /// Return the created phi node.
1292 static PHINode *InsertAffinePhi(SCEVHandle Start, SCEVHandle Step,
1293 Instruction *IVIncInsertPt,
1295 SCEVExpander &Rewriter) {
1296 assert(Start->isLoopInvariant(L) && "New PHI start is not loop invariant!");
1297 assert(Step->isLoopInvariant(L) && "New PHI stride is not loop invariant!");
1299 BasicBlock *Header = L->getHeader();
1300 BasicBlock *Preheader = L->getLoopPreheader();
1301 BasicBlock *LatchBlock = L->getLoopLatch();
1302 const Type *Ty = Start->getType();
1303 Ty = Rewriter.SE.getEffectiveSCEVType(Ty);
1305 PHINode *PN = PHINode::Create(Ty, "lsr.iv", Header->begin());
1306 PN->addIncoming(Rewriter.expandCodeFor(Start, Ty, Preheader->getTerminator()),
1309 // If the stride is negative, insert a sub instead of an add for the
1311 bool isNegative = isNonConstantNegative(Step);
1312 SCEVHandle IncAmount = Step;
1314 IncAmount = Rewriter.SE.getNegativeSCEV(Step);
1316 // Insert an add instruction right before the terminator corresponding
1317 // to the back-edge or just before the only use. The location is determined
1318 // by the caller and passed in as IVIncInsertPt.
1319 Value *StepV = Rewriter.expandCodeFor(IncAmount, Ty,
1320 Preheader->getTerminator());
1323 IncV = BinaryOperator::CreateSub(PN, StepV, "lsr.iv.next",
1326 IncV = BinaryOperator::CreateAdd(PN, StepV, "lsr.iv.next",
1329 if (!isa<ConstantInt>(StepV)) ++NumVariable;
1331 PN->addIncoming(IncV, LatchBlock);
1337 static void SortUsersToProcess(std::vector<BasedUser> &UsersToProcess) {
1338 // We want to emit code for users inside the loop first. To do this, we
1339 // rearrange BasedUser so that the entries at the end have
1340 // isUseOfPostIncrementedValue = false, because we pop off the end of the
1341 // vector (so we handle them first).
1342 std::partition(UsersToProcess.begin(), UsersToProcess.end(),
1343 PartitionByIsUseOfPostIncrementedValue);
1345 // Sort this by base, so that things with the same base are handled
1346 // together. By partitioning first and stable-sorting later, we are
1347 // guaranteed that within each base we will pop off users from within the
1348 // loop before users outside of the loop with a particular base.
1350 // We would like to use stable_sort here, but we can't. The problem is that
1351 // SCEVHandle's don't have a deterministic ordering w.r.t to each other, so
1352 // we don't have anything to do a '<' comparison on. Because we think the
1353 // number of uses is small, do a horrible bubble sort which just relies on
1355 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
1356 // Get a base value.
1357 SCEVHandle Base = UsersToProcess[i].Base;
1359 // Compact everything with this base to be consecutive with this one.
1360 for (unsigned j = i+1; j != e; ++j) {
1361 if (UsersToProcess[j].Base == Base) {
1362 std::swap(UsersToProcess[i+1], UsersToProcess[j]);
1369 /// PrepareToStrengthReduceFully - Prepare to fully strength-reduce
1370 /// UsersToProcess, meaning lowering addresses all the way down to direct
1371 /// pointer arithmetic.
1374 LoopStrengthReduce::PrepareToStrengthReduceFully(
1375 std::vector<BasedUser> &UsersToProcess,
1377 SCEVHandle CommonExprs,
1379 SCEVExpander &PreheaderRewriter) {
1380 DOUT << " Fully reducing all users\n";
1382 // Rewrite the UsersToProcess records, creating a separate PHI for each
1383 // unique Base value.
1384 Instruction *IVIncInsertPt = L->getLoopLatch()->getTerminator();
1385 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) {
1386 // TODO: The uses are grouped by base, but not sorted. We arbitrarily
1387 // pick the first Imm value here to start with, and adjust it for the
1389 SCEVHandle Imm = UsersToProcess[i].Imm;
1390 SCEVHandle Base = UsersToProcess[i].Base;
1391 SCEVHandle Start = SE->getAddExpr(CommonExprs, Base, Imm);
1392 PHINode *Phi = InsertAffinePhi(Start, Stride, IVIncInsertPt, L,
1394 // Loop over all the users with the same base.
1396 UsersToProcess[i].Base = SE->getIntegerSCEV(0, Stride->getType());
1397 UsersToProcess[i].Imm = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm);
1398 UsersToProcess[i].Phi = Phi;
1399 assert(UsersToProcess[i].Imm->isLoopInvariant(L) &&
1400 "ShouldUseFullStrengthReductionMode should reject this!");
1401 } while (++i != e && Base == UsersToProcess[i].Base);
1405 /// FindIVIncInsertPt - Return the location to insert the increment instruction.
1406 /// If the only use if a use of postinc value, (must be the loop termination
1407 /// condition), then insert it just before the use.
1408 static Instruction *FindIVIncInsertPt(std::vector<BasedUser> &UsersToProcess,
1410 if (UsersToProcess.size() == 1 &&
1411 UsersToProcess[0].isUseOfPostIncrementedValue &&
1412 L->contains(UsersToProcess[0].Inst->getParent()))
1413 return UsersToProcess[0].Inst;
1414 return L->getLoopLatch()->getTerminator();
1417 /// PrepareToStrengthReduceWithNewPhi - Insert a new induction variable for the
1418 /// given users to share.
1421 LoopStrengthReduce::PrepareToStrengthReduceWithNewPhi(
1422 std::vector<BasedUser> &UsersToProcess,
1424 SCEVHandle CommonExprs,
1426 Instruction *IVIncInsertPt,
1428 SCEVExpander &PreheaderRewriter) {
1429 DOUT << " Inserting new PHI:\n";
1431 PHINode *Phi = InsertAffinePhi(SE->getUnknown(CommonBaseV),
1432 Stride, IVIncInsertPt, L,
1435 // Remember this in case a later stride is multiple of this.
1436 IVsByStride[Stride].addIV(Stride, CommonExprs, Phi);
1438 // All the users will share this new IV.
1439 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
1440 UsersToProcess[i].Phi = Phi;
1443 DEBUG(WriteAsOperand(*DOUT, Phi, /*PrintType=*/false));
1447 /// PrepareToStrengthReduceFromSmallerStride - Prepare for the given users to
1448 /// reuse an induction variable with a stride that is a factor of the current
1449 /// induction variable.
1452 LoopStrengthReduce::PrepareToStrengthReduceFromSmallerStride(
1453 std::vector<BasedUser> &UsersToProcess,
1455 const IVExpr &ReuseIV,
1456 Instruction *PreInsertPt) {
1457 DOUT << " Rewriting in terms of existing IV of STRIDE " << *ReuseIV.Stride
1458 << " and BASE " << *ReuseIV.Base << "\n";
1460 // All the users will share the reused IV.
1461 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
1462 UsersToProcess[i].Phi = ReuseIV.PHI;
1464 Constant *C = dyn_cast<Constant>(CommonBaseV);
1466 (!C->isNullValue() &&
1467 !fitsInAddressMode(SE->getUnknown(CommonBaseV), CommonBaseV->getType(),
1469 // We want the common base emitted into the preheader! This is just
1470 // using cast as a copy so BitCast (no-op cast) is appropriate
1471 CommonBaseV = new BitCastInst(CommonBaseV, CommonBaseV->getType(),
1472 "commonbase", PreInsertPt);
1475 static bool IsImmFoldedIntoAddrMode(GlobalValue *GV, int64_t Offset,
1476 const Type *AccessTy,
1477 std::vector<BasedUser> &UsersToProcess,
1478 const TargetLowering *TLI) {
1479 SmallVector<Instruction*, 16> AddrModeInsts;
1480 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
1481 if (UsersToProcess[i].isUseOfPostIncrementedValue)
1483 ExtAddrMode AddrMode =
1484 AddressingModeMatcher::Match(UsersToProcess[i].OperandValToReplace,
1485 AccessTy, UsersToProcess[i].Inst,
1486 AddrModeInsts, *TLI);
1487 if (GV && GV != AddrMode.BaseGV)
1489 if (Offset && !AddrMode.BaseOffs)
1490 // FIXME: How to accurate check it's immediate offset is folded.
1492 AddrModeInsts.clear();
1497 /// StrengthReduceStridedIVUsers - Strength reduce all of the users of a single
1498 /// stride of IV. All of the users may have different starting values, and this
1499 /// may not be the only stride.
1500 void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
1501 IVUsersOfOneStride &Uses,
1503 // If all the users are moved to another stride, then there is nothing to do.
1504 if (Uses.Users.empty())
1507 // Keep track if every use in UsersToProcess is an address. If they all are,
1508 // we may be able to rewrite the entire collection of them in terms of a
1509 // smaller-stride IV.
1510 bool AllUsesAreAddresses = true;
1512 // Keep track if every use of a single stride is outside the loop. If so,
1513 // we want to be more aggressive about reusing a smaller-stride IV; a
1514 // multiply outside the loop is better than another IV inside. Well, usually.
1515 bool AllUsesAreOutsideLoop = true;
1517 // Transform our list of users and offsets to a bit more complex table. In
1518 // this new vector, each 'BasedUser' contains 'Base' the base of the
1519 // strided accessas well as the old information from Uses. We progressively
1520 // move information from the Base field to the Imm field, until we eventually
1521 // have the full access expression to rewrite the use.
1522 std::vector<BasedUser> UsersToProcess;
1523 SCEVHandle CommonExprs = CollectIVUsers(Stride, Uses, L, AllUsesAreAddresses,
1524 AllUsesAreOutsideLoop,
1527 // Sort the UsersToProcess array so that users with common bases are
1528 // next to each other.
1529 SortUsersToProcess(UsersToProcess);
1531 // If we managed to find some expressions in common, we'll need to carry
1532 // their value in a register and add it in for each use. This will take up
1533 // a register operand, which potentially restricts what stride values are
1535 bool HaveCommonExprs = !CommonExprs->isZero();
1536 const Type *ReplacedTy = CommonExprs->getType();
1538 // If all uses are addresses, consider sinking the immediate part of the
1539 // common expression back into uses if they can fit in the immediate fields.
1540 if (TLI && HaveCommonExprs && AllUsesAreAddresses) {
1541 SCEVHandle NewCommon = CommonExprs;
1542 SCEVHandle Imm = SE->getIntegerSCEV(0, ReplacedTy);
1543 MoveImmediateValues(TLI, Type::VoidTy, NewCommon, Imm, true, L, SE);
1544 if (!Imm->isZero()) {
1547 // If the immediate part of the common expression is a GV, check if it's
1548 // possible to fold it into the target addressing mode.
1549 GlobalValue *GV = 0;
1550 if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(Imm))
1551 GV = dyn_cast<GlobalValue>(SU->getValue());
1553 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Imm))
1554 Offset = SC->getValue()->getSExtValue();
1556 // Pass VoidTy as the AccessTy to be conservative, because
1557 // there could be multiple access types among all the uses.
1558 DoSink = IsImmFoldedIntoAddrMode(GV, Offset, Type::VoidTy,
1559 UsersToProcess, TLI);
1562 DOUT << " Sinking " << *Imm << " back down into uses\n";
1563 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
1564 UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm, Imm);
1565 CommonExprs = NewCommon;
1566 HaveCommonExprs = !CommonExprs->isZero();
1572 // Now that we know what we need to do, insert the PHI node itself.
1574 DOUT << "LSR: Examining IVs of TYPE " << *ReplacedTy << " of STRIDE "
1576 << " Common base: " << *CommonExprs << "\n";
1578 SCEVExpander Rewriter(*SE);
1579 SCEVExpander PreheaderRewriter(*SE);
1581 BasicBlock *Preheader = L->getLoopPreheader();
1582 Instruction *PreInsertPt = Preheader->getTerminator();
1583 BasicBlock *LatchBlock = L->getLoopLatch();
1584 Instruction *IVIncInsertPt = LatchBlock->getTerminator();
1586 Value *CommonBaseV = Constant::getNullValue(ReplacedTy);
1588 SCEVHandle RewriteFactor = SE->getIntegerSCEV(0, ReplacedTy);
1589 IVExpr ReuseIV(SE->getIntegerSCEV(0, Type::Int32Ty),
1590 SE->getIntegerSCEV(0, Type::Int32Ty),
1593 /// Choose a strength-reduction strategy and prepare for it by creating
1594 /// the necessary PHIs and adjusting the bookkeeping.
1595 if (ShouldUseFullStrengthReductionMode(UsersToProcess, L,
1596 AllUsesAreAddresses, Stride)) {
1597 PrepareToStrengthReduceFully(UsersToProcess, Stride, CommonExprs, L,
1600 // Emit the initial base value into the loop preheader.
1601 CommonBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, ReplacedTy,
1604 // If all uses are addresses, check if it is possible to reuse an IV. The
1605 // new IV must have a stride that is a multiple of the old stride; the
1606 // multiple must be a number that can be encoded in the scale field of the
1607 // target addressing mode; and we must have a valid instruction after this
1608 // substitution, including the immediate field, if any.
1609 RewriteFactor = CheckForIVReuse(HaveCommonExprs, AllUsesAreAddresses,
1610 AllUsesAreOutsideLoop,
1611 Stride, ReuseIV, ReplacedTy,
1613 if (!RewriteFactor->isZero())
1614 PrepareToStrengthReduceFromSmallerStride(UsersToProcess, CommonBaseV,
1615 ReuseIV, PreInsertPt);
1617 IVIncInsertPt = FindIVIncInsertPt(UsersToProcess, L);
1618 PrepareToStrengthReduceWithNewPhi(UsersToProcess, Stride, CommonExprs,
1619 CommonBaseV, IVIncInsertPt,
1620 L, PreheaderRewriter);
1624 // Process all the users now, replacing their strided uses with
1625 // strength-reduced forms. This outer loop handles all bases, the inner
1626 // loop handles all users of a particular base.
1627 while (!UsersToProcess.empty()) {
1628 SCEVHandle Base = UsersToProcess.back().Base;
1629 Instruction *Inst = UsersToProcess.back().Inst;
1631 // Emit the code for Base into the preheader.
1633 if (!Base->isZero()) {
1634 BaseV = PreheaderRewriter.expandCodeFor(Base, 0, PreInsertPt);
1636 DOUT << " INSERTING code for BASE = " << *Base << ":";
1637 if (BaseV->hasName())
1638 DOUT << " Result value name = %" << BaseV->getNameStr();
1641 // If BaseV is a non-zero constant, make sure that it gets inserted into
1642 // the preheader, instead of being forward substituted into the uses. We
1643 // do this by forcing a BitCast (noop cast) to be inserted into the
1644 // preheader in this case.
1645 if (!fitsInAddressMode(Base, getAccessType(Inst), TLI, false)) {
1646 // We want this constant emitted into the preheader! This is just
1647 // using cast as a copy so BitCast (no-op cast) is appropriate
1648 BaseV = new BitCastInst(BaseV, BaseV->getType(), "preheaderinsert",
1653 // Emit the code to add the immediate offset to the Phi value, just before
1654 // the instructions that we identified as using this stride and base.
1656 // FIXME: Use emitted users to emit other users.
1657 BasedUser &User = UsersToProcess.back();
1659 DOUT << " Examining ";
1660 if (User.isUseOfPostIncrementedValue)
1665 DEBUG(WriteAsOperand(*DOUT, UsersToProcess.back().OperandValToReplace,
1666 /*PrintType=*/false));
1667 DOUT << " in Inst: " << *(User.Inst);
1669 // If this instruction wants to use the post-incremented value, move it
1670 // after the post-inc and use its value instead of the PHI.
1671 Value *RewriteOp = User.Phi;
1672 if (User.isUseOfPostIncrementedValue) {
1673 RewriteOp = User.Phi->getIncomingValueForBlock(LatchBlock);
1674 // If this user is in the loop, make sure it is the last thing in the
1675 // loop to ensure it is dominated by the increment. In case it's the
1676 // only use of the iv, the increment instruction is already before the
1678 if (L->contains(User.Inst->getParent()) && User.Inst != IVIncInsertPt)
1679 User.Inst->moveBefore(IVIncInsertPt);
1682 SCEVHandle RewriteExpr = SE->getUnknown(RewriteOp);
1684 if (SE->getEffectiveSCEVType(RewriteOp->getType()) !=
1685 SE->getEffectiveSCEVType(ReplacedTy)) {
1686 assert(SE->getTypeSizeInBits(RewriteOp->getType()) >
1687 SE->getTypeSizeInBits(ReplacedTy) &&
1688 "Unexpected widening cast!");
1689 RewriteExpr = SE->getTruncateExpr(RewriteExpr, ReplacedTy);
1692 // If we had to insert new instructions for RewriteOp, we have to
1693 // consider that they may not have been able to end up immediately
1694 // next to RewriteOp, because non-PHI instructions may never precede
1695 // PHI instructions in a block. In this case, remember where the last
1696 // instruction was inserted so that if we're replacing a different
1697 // PHI node, we can use the later point to expand the final
1699 Instruction *NewBasePt = dyn_cast<Instruction>(RewriteOp);
1700 if (RewriteOp == User.Phi) NewBasePt = 0;
1702 // Clear the SCEVExpander's expression map so that we are guaranteed
1703 // to have the code emitted where we expect it.
1706 // If we are reusing the iv, then it must be multiplied by a constant
1707 // factor to take advantage of the addressing mode scale component.
1708 if (!RewriteFactor->isZero()) {
1709 // If we're reusing an IV with a nonzero base (currently this happens
1710 // only when all reuses are outside the loop) subtract that base here.
1711 // The base has been used to initialize the PHI node but we don't want
1713 if (!ReuseIV.Base->isZero()) {
1714 SCEVHandle typedBase = ReuseIV.Base;
1715 if (SE->getEffectiveSCEVType(RewriteExpr->getType()) !=
1716 SE->getEffectiveSCEVType(ReuseIV.Base->getType())) {
1717 // It's possible the original IV is a larger type than the new IV,
1718 // in which case we have to truncate the Base. We checked in
1719 // RequiresTypeConversion that this is valid.
1720 assert(SE->getTypeSizeInBits(RewriteExpr->getType()) <
1721 SE->getTypeSizeInBits(ReuseIV.Base->getType()) &&
1722 "Unexpected lengthening conversion!");
1723 typedBase = SE->getTruncateExpr(ReuseIV.Base,
1724 RewriteExpr->getType());
1726 RewriteExpr = SE->getMinusSCEV(RewriteExpr, typedBase);
1729 // Multiply old variable, with base removed, by new scale factor.
1730 RewriteExpr = SE->getMulExpr(RewriteFactor,
1733 // The common base is emitted in the loop preheader. But since we
1734 // are reusing an IV, it has not been used to initialize the PHI node.
1735 // Add it to the expression used to rewrite the uses.
1736 // When this use is outside the loop, we earlier subtracted the
1737 // common base, and are adding it back here. Use the same expression
1738 // as before, rather than CommonBaseV, so DAGCombiner will zap it.
1739 if (!CommonExprs->isZero()) {
1740 if (L->contains(User.Inst->getParent()))
1741 RewriteExpr = SE->getAddExpr(RewriteExpr,
1742 SE->getUnknown(CommonBaseV));
1744 RewriteExpr = SE->getAddExpr(RewriteExpr, CommonExprs);
1748 // Now that we know what we need to do, insert code before User for the
1749 // immediate and any loop-variant expressions.
1751 // Add BaseV to the PHI value if needed.
1752 RewriteExpr = SE->getAddExpr(RewriteExpr, SE->getUnknown(BaseV));
1754 User.RewriteInstructionToUseNewBase(RewriteExpr, NewBasePt,
1755 Rewriter, L, this, *LI,
1758 // Mark old value we replaced as possibly dead, so that it is eliminated
1759 // if we just replaced the last use of that value.
1760 DeadInsts.push_back(User.OperandValToReplace);
1762 UsersToProcess.pop_back();
1765 // If there are any more users to process with the same base, process them
1766 // now. We sorted by base above, so we just have to check the last elt.
1767 } while (!UsersToProcess.empty() && UsersToProcess.back().Base == Base);
1768 // TODO: Next, find out which base index is the most common, pull it out.
1771 // IMPORTANT TODO: Figure out how to partition the IV's with this stride, but
1772 // different starting values, into different PHIs.
1775 /// FindIVUserForCond - If Cond has an operand that is an expression of an IV,
1776 /// set the IV user and stride information and return true, otherwise return
1778 bool LoopStrengthReduce::FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse,
1779 const SCEVHandle *&CondStride) {
1780 for (unsigned Stride = 0, e = IU->StrideOrder.size();
1781 Stride != e && !CondUse; ++Stride) {
1782 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
1783 IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
1784 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
1786 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
1787 E = SI->second->Users.end(); UI != E; ++UI)
1788 if (UI->getUser() == Cond) {
1789 // NOTE: we could handle setcc instructions with multiple uses here, but
1790 // InstCombine does it as well for simple uses, it's not clear that it
1791 // occurs enough in real life to handle.
1793 CondStride = &SI->first;
1801 // Constant strides come first which in turns are sorted by their absolute
1802 // values. If absolute values are the same, then positive strides comes first.
1804 // 4, -1, X, 1, 2 ==> 1, -1, 2, 4, X
1805 struct StrideCompare {
1806 const ScalarEvolution *SE;
1807 explicit StrideCompare(const ScalarEvolution *se) : SE(se) {}
1809 bool operator()(const SCEVHandle &LHS, const SCEVHandle &RHS) {
1810 const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS);
1811 const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
1813 int64_t LV = LHSC->getValue()->getSExtValue();
1814 int64_t RV = RHSC->getValue()->getSExtValue();
1815 uint64_t ALV = (LV < 0) ? -LV : LV;
1816 uint64_t ARV = (RV < 0) ? -RV : RV;
1824 // If it's the same value but different type, sort by bit width so
1825 // that we emit larger induction variables before smaller
1826 // ones, letting the smaller be re-written in terms of larger ones.
1827 return SE->getTypeSizeInBits(RHS->getType()) <
1828 SE->getTypeSizeInBits(LHS->getType());
1830 return LHSC && !RHSC;
1835 /// ChangeCompareStride - If a loop termination compare instruction is the
1836 /// only use of its stride, and the compaison is against a constant value,
1837 /// try eliminate the stride by moving the compare instruction to another
1838 /// stride and change its constant operand accordingly. e.g.
1844 /// if (v2 < 10) goto loop
1849 /// if (v1 < 30) goto loop
1850 ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
1851 IVStrideUse* &CondUse,
1852 const SCEVHandle* &CondStride) {
1853 // If there's only one stride in the loop, there's nothing to do here.
1854 if (IU->StrideOrder.size() < 2)
1856 // If there are other users of the condition's stride, don't bother
1857 // trying to change the condition because the stride will still
1859 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator I =
1860 IU->IVUsesByStride.find(*CondStride);
1861 if (I == IU->IVUsesByStride.end() ||
1862 I->second->Users.size() != 1)
1864 // Only handle constant strides for now.
1865 const SCEVConstant *SC = dyn_cast<SCEVConstant>(*CondStride);
1866 if (!SC) return Cond;
1868 ICmpInst::Predicate Predicate = Cond->getPredicate();
1869 int64_t CmpSSInt = SC->getValue()->getSExtValue();
1870 unsigned BitWidth = SE->getTypeSizeInBits((*CondStride)->getType());
1871 uint64_t SignBit = 1ULL << (BitWidth-1);
1872 const Type *CmpTy = Cond->getOperand(0)->getType();
1873 const Type *NewCmpTy = NULL;
1874 unsigned TyBits = SE->getTypeSizeInBits(CmpTy);
1875 unsigned NewTyBits = 0;
1876 SCEVHandle *NewStride = NULL;
1877 Value *NewCmpLHS = NULL;
1878 Value *NewCmpRHS = NULL;
1880 SCEVHandle NewOffset = SE->getIntegerSCEV(0, CmpTy);
1882 if (ConstantInt *C = dyn_cast<ConstantInt>(Cond->getOperand(1))) {
1883 int64_t CmpVal = C->getValue().getSExtValue();
1885 // Check stride constant and the comparision constant signs to detect
1887 if ((CmpVal & SignBit) != (CmpSSInt & SignBit))
1890 // Look for a suitable stride / iv as replacement.
1891 for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
1892 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
1893 IU->IVUsesByStride.find(IU->StrideOrder[i]);
1894 if (!isa<SCEVConstant>(SI->first))
1896 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
1897 if (SSInt == CmpSSInt ||
1898 abs64(SSInt) < abs64(CmpSSInt) ||
1899 (SSInt % CmpSSInt) != 0)
1902 Scale = SSInt / CmpSSInt;
1903 int64_t NewCmpVal = CmpVal * Scale;
1904 APInt Mul = APInt(BitWidth*2, CmpVal, true);
1905 Mul = Mul * APInt(BitWidth*2, Scale, true);
1906 // Check for overflow.
1907 if (!Mul.isSignedIntN(BitWidth))
1909 // Check for overflow in the stride's type too.
1910 if (!Mul.isSignedIntN(SE->getTypeSizeInBits(SI->first->getType())))
1913 // Watch out for overflow.
1914 if (ICmpInst::isSignedPredicate(Predicate) &&
1915 (CmpVal & SignBit) != (NewCmpVal & SignBit))
1918 if (NewCmpVal == CmpVal)
1920 // Pick the best iv to use trying to avoid a cast.
1922 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
1923 E = SI->second->Users.end(); UI != E; ++UI) {
1924 Value *Op = UI->getOperandValToReplace();
1926 // If the IVStrideUse implies a cast, check for an actual cast which
1927 // can be used to find the original IV expression.
1928 if (SE->getEffectiveSCEVType(Op->getType()) !=
1929 SE->getEffectiveSCEVType(SI->first->getType())) {
1930 CastInst *CI = dyn_cast<CastInst>(Op);
1931 // If it's not a simple cast, it's complicated.
1934 // If it's a cast from a type other than the stride type,
1935 // it's complicated.
1936 if (CI->getOperand(0)->getType() != SI->first->getType())
1938 // Ok, we found the IV expression in the stride's type.
1939 Op = CI->getOperand(0);
1943 if (NewCmpLHS->getType() == CmpTy)
1949 NewCmpTy = NewCmpLHS->getType();
1950 NewTyBits = SE->getTypeSizeInBits(NewCmpTy);
1951 const Type *NewCmpIntTy = IntegerType::get(NewTyBits);
1952 if (RequiresTypeConversion(NewCmpTy, CmpTy)) {
1953 // Check if it is possible to rewrite it using
1954 // an iv / stride of a smaller integer type.
1955 unsigned Bits = NewTyBits;
1956 if (ICmpInst::isSignedPredicate(Predicate))
1958 uint64_t Mask = (1ULL << Bits) - 1;
1959 if (((uint64_t)NewCmpVal & Mask) != (uint64_t)NewCmpVal)
1963 // Don't rewrite if use offset is non-constant and the new type is
1964 // of a different type.
1965 // FIXME: too conservative?
1966 if (NewTyBits != TyBits && !isa<SCEVConstant>(CondUse->getOffset()))
1969 bool AllUsesAreAddresses = true;
1970 bool AllUsesAreOutsideLoop = true;
1971 std::vector<BasedUser> UsersToProcess;
1972 SCEVHandle CommonExprs = CollectIVUsers(SI->first, *SI->second, L,
1973 AllUsesAreAddresses,
1974 AllUsesAreOutsideLoop,
1976 // Avoid rewriting the compare instruction with an iv of new stride
1977 // if it's likely the new stride uses will be rewritten using the
1978 // stride of the compare instruction.
1979 if (AllUsesAreAddresses &&
1980 ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess))
1983 // Avoid rewriting the compare instruction with an iv which has
1984 // implicit extension or truncation built into it.
1985 // TODO: This is over-conservative.
1986 if (SE->getTypeSizeInBits(CondUse->getOffset()->getType()) != TyBits)
1989 // If scale is negative, use swapped predicate unless it's testing
1991 if (Scale < 0 && !Cond->isEquality())
1992 Predicate = ICmpInst::getSwappedPredicate(Predicate);
1994 NewStride = &IU->StrideOrder[i];
1995 if (!isa<PointerType>(NewCmpTy))
1996 NewCmpRHS = ConstantInt::get(NewCmpTy, NewCmpVal);
1998 Constant *CI = ConstantInt::get(NewCmpIntTy, NewCmpVal);
1999 NewCmpRHS = ConstantExpr::getIntToPtr(CI, NewCmpTy);
2001 NewOffset = TyBits == NewTyBits
2002 ? SE->getMulExpr(CondUse->getOffset(),
2003 SE->getConstant(CmpTy, Scale))
2004 : SE->getConstant(NewCmpIntTy,
2005 cast<SCEVConstant>(CondUse->getOffset())->getValue()
2006 ->getSExtValue()*Scale);
2011 // Forgo this transformation if it the increment happens to be
2012 // unfortunately positioned after the condition, and the condition
2013 // has multiple uses which prevent it from being moved immediately
2014 // before the branch. See
2015 // test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-*.ll
2016 // for an example of this situation.
2017 if (!Cond->hasOneUse()) {
2018 for (BasicBlock::iterator I = Cond, E = Cond->getParent()->end();
2025 // Create a new compare instruction using new stride / iv.
2026 ICmpInst *OldCond = Cond;
2027 // Insert new compare instruction.
2028 Cond = new ICmpInst(Predicate, NewCmpLHS, NewCmpRHS,
2029 L->getHeader()->getName() + ".termcond",
2032 // Remove the old compare instruction. The old indvar is probably dead too.
2033 DeadInsts.push_back(CondUse->getOperandValToReplace());
2034 OldCond->replaceAllUsesWith(Cond);
2035 OldCond->eraseFromParent();
2037 IU->IVUsesByStride[*NewStride]->addUser(NewOffset, Cond, NewCmpLHS);
2038 CondUse = &IU->IVUsesByStride[*NewStride]->Users.back();
2039 CondStride = NewStride;
2047 /// OptimizeMax - Rewrite the loop's terminating condition if it uses
2048 /// a max computation.
2050 /// This is a narrow solution to a specific, but acute, problem. For loops
2056 /// } while (++i < n);
2058 /// the trip count isn't just 'n', because 'n' might not be positive. And
2059 /// unfortunately this can come up even for loops where the user didn't use
2060 /// a C do-while loop. For example, seemingly well-behaved top-test loops
2061 /// will commonly be lowered like this:
2067 /// } while (++i < n);
2070 /// and then it's possible for subsequent optimization to obscure the if
2071 /// test in such a way that indvars can't find it.
2073 /// When indvars can't find the if test in loops like this, it creates a
2074 /// max expression, which allows it to give the loop a canonical
2075 /// induction variable:
2078 /// max = n < 1 ? 1 : n;
2081 /// } while (++i != max);
2083 /// Canonical induction variables are necessary because the loop passes
2084 /// are designed around them. The most obvious example of this is the
2085 /// LoopInfo analysis, which doesn't remember trip count values. It
2086 /// expects to be able to rediscover the trip count each time it is
2087 /// needed, and it does this using a simple analyis that only succeeds if
2088 /// the loop has a canonical induction variable.
2090 /// However, when it comes time to generate code, the maximum operation
2091 /// can be quite costly, especially if it's inside of an outer loop.
2093 /// This function solves this problem by detecting this type of loop and
2094 /// rewriting their conditions from ICMP_NE back to ICMP_SLT, and deleting
2095 /// the instructions for the maximum computation.
2097 ICmpInst *LoopStrengthReduce::OptimizeMax(Loop *L, ICmpInst *Cond,
2098 IVStrideUse* &CondUse) {
2099 // Check that the loop matches the pattern we're looking for.
2100 if (Cond->getPredicate() != CmpInst::ICMP_EQ &&
2101 Cond->getPredicate() != CmpInst::ICMP_NE)
2104 SelectInst *Sel = dyn_cast<SelectInst>(Cond->getOperand(1));
2105 if (!Sel || !Sel->hasOneUse()) return Cond;
2107 SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L);
2108 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
2110 SCEVHandle One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType());
2112 // Add one to the backedge-taken count to get the trip count.
2113 SCEVHandle IterationCount = SE->getAddExpr(BackedgeTakenCount, One);
2115 // Check for a max calculation that matches the pattern.
2116 if (!isa<SCEVSMaxExpr>(IterationCount) && !isa<SCEVUMaxExpr>(IterationCount))
2118 const SCEVNAryExpr *Max = cast<SCEVNAryExpr>(IterationCount);
2119 if (Max != SE->getSCEV(Sel)) return Cond;
2121 SCEVHandle MaxLHS = Max->getOperand(0);
2122 SCEVHandle MaxRHS = Max->getOperand(1);
2123 if (!MaxLHS || MaxLHS != One) return Cond;
2125 // Check the relevant induction variable for conformance to
2127 SCEVHandle IV = SE->getSCEV(Cond->getOperand(0));
2128 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
2129 if (!AR || !AR->isAffine() ||
2130 AR->getStart() != One ||
2131 AR->getStepRecurrence(*SE) != One)
2134 assert(AR->getLoop() == L &&
2135 "Loop condition operand is an addrec in a different loop!");
2137 // Check the right operand of the select, and remember it, as it will
2138 // be used in the new comparison instruction.
2140 if (SE->getSCEV(Sel->getOperand(1)) == MaxRHS)
2141 NewRHS = Sel->getOperand(1);
2142 else if (SE->getSCEV(Sel->getOperand(2)) == MaxRHS)
2143 NewRHS = Sel->getOperand(2);
2144 if (!NewRHS) return Cond;
2146 // Determine the new comparison opcode. It may be signed or unsigned,
2147 // and the original comparison may be either equality or inequality.
2148 CmpInst::Predicate Pred =
2149 isa<SCEVSMaxExpr>(Max) ? CmpInst::ICMP_SLT : CmpInst::ICMP_ULT;
2150 if (Cond->getPredicate() == CmpInst::ICMP_EQ)
2151 Pred = CmpInst::getInversePredicate(Pred);
2153 // Ok, everything looks ok to change the condition into an SLT or SGE and
2154 // delete the max calculation.
2156 new ICmpInst(Pred, Cond->getOperand(0), NewRHS, "scmp", Cond);
2158 // Delete the max calculation instructions.
2159 Cond->replaceAllUsesWith(NewCond);
2160 CondUse->setUser(NewCond);
2161 Instruction *Cmp = cast<Instruction>(Sel->getOperand(0));
2162 Cond->eraseFromParent();
2163 Sel->eraseFromParent();
2164 if (Cmp->use_empty())
2165 Cmp->eraseFromParent();
2169 /// OptimizeShadowIV - If IV is used in a int-to-float cast
2170 /// inside the loop then try to eliminate the cast opeation.
2171 void LoopStrengthReduce::OptimizeShadowIV(Loop *L) {
2173 SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L);
2174 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
2177 for (unsigned Stride = 0, e = IU->StrideOrder.size(); Stride != e;
2179 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
2180 IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
2181 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
2182 if (!isa<SCEVConstant>(SI->first))
2185 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
2186 E = SI->second->Users.end(); UI != E; /* empty */) {
2187 ilist<IVStrideUse>::iterator CandidateUI = UI;
2189 Instruction *ShadowUse = CandidateUI->getUser();
2190 const Type *DestTy = NULL;
2192 /* If shadow use is a int->float cast then insert a second IV
2193 to eliminate this cast.
2195 for (unsigned i = 0; i < n; ++i)
2201 for (unsigned i = 0; i < n; ++i, ++d)
2204 if (UIToFPInst *UCast = dyn_cast<UIToFPInst>(CandidateUI->getUser()))
2205 DestTy = UCast->getDestTy();
2206 else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->getUser()))
2207 DestTy = SCast->getDestTy();
2208 if (!DestTy) continue;
2211 // If target does not support DestTy natively then do not apply
2212 // this transformation.
2213 MVT DVT = TLI->getValueType(DestTy);
2214 if (!TLI->isTypeLegal(DVT)) continue;
2217 PHINode *PH = dyn_cast<PHINode>(ShadowUse->getOperand(0));
2219 if (PH->getNumIncomingValues() != 2) continue;
2221 const Type *SrcTy = PH->getType();
2222 int Mantissa = DestTy->getFPMantissaWidth();
2223 if (Mantissa == -1) continue;
2224 if ((int)SE->getTypeSizeInBits(SrcTy) > Mantissa)
2227 unsigned Entry, Latch;
2228 if (PH->getIncomingBlock(0) == L->getLoopPreheader()) {
2236 ConstantInt *Init = dyn_cast<ConstantInt>(PH->getIncomingValue(Entry));
2237 if (!Init) continue;
2238 Constant *NewInit = ConstantFP::get(DestTy, Init->getZExtValue());
2240 BinaryOperator *Incr =
2241 dyn_cast<BinaryOperator>(PH->getIncomingValue(Latch));
2242 if (!Incr) continue;
2243 if (Incr->getOpcode() != Instruction::Add
2244 && Incr->getOpcode() != Instruction::Sub)
2247 /* Initialize new IV, double d = 0.0 in above example. */
2248 ConstantInt *C = NULL;
2249 if (Incr->getOperand(0) == PH)
2250 C = dyn_cast<ConstantInt>(Incr->getOperand(1));
2251 else if (Incr->getOperand(1) == PH)
2252 C = dyn_cast<ConstantInt>(Incr->getOperand(0));
2258 /* Add new PHINode. */
2259 PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH);
2261 /* create new increment. '++d' in above example. */
2262 Constant *CFP = ConstantFP::get(DestTy, C->getZExtValue());
2263 BinaryOperator *NewIncr =
2264 BinaryOperator::Create(Incr->getOpcode() == Instruction::Add ?
2265 Instruction::FAdd : Instruction::FSub,
2266 NewPH, CFP, "IV.S.next.", Incr);
2268 NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry));
2269 NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch));
2271 /* Remove cast operation */
2272 ShadowUse->replaceAllUsesWith(NewPH);
2273 ShadowUse->eraseFromParent();
2280 /// OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar
2281 /// uses in the loop, look to see if we can eliminate some, in favor of using
2282 /// common indvars for the different uses.
2283 void LoopStrengthReduce::OptimizeIndvars(Loop *L) {
2284 // TODO: implement optzns here.
2286 OptimizeShadowIV(L);
2289 /// OptimizeLoopTermCond - Change loop terminating condition to use the
2290 /// postinc iv when possible.
2291 void LoopStrengthReduce::OptimizeLoopTermCond(Loop *L) {
2292 // Finally, get the terminating condition for the loop if possible. If we
2293 // can, we want to change it to use a post-incremented version of its
2294 // induction variable, to allow coalescing the live ranges for the IV into
2295 // one register value.
2296 BasicBlock *LatchBlock = L->getLoopLatch();
2297 BasicBlock *ExitBlock = L->getExitingBlock();
2299 // Multiple exits, just look at the exit in the latch block if there is one.
2300 ExitBlock = LatchBlock;
2301 BranchInst *TermBr = dyn_cast<BranchInst>(ExitBlock->getTerminator());
2304 if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition()))
2307 // Search IVUsesByStride to find Cond's IVUse if there is one.
2308 IVStrideUse *CondUse = 0;
2309 const SCEVHandle *CondStride = 0;
2310 ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
2311 if (!FindIVUserForCond(Cond, CondUse, CondStride))
2312 return; // setcc doesn't use the IV.
2314 if (ExitBlock != LatchBlock) {
2315 if (!Cond->hasOneUse())
2316 // See below, we don't want the condition to be cloned.
2319 // If exiting block is the latch block, we know it's safe and profitable to
2320 // transform the icmp to use post-inc iv. Otherwise do so only if it would
2321 // not reuse another iv and its iv would be reused by other uses. We are
2322 // optimizing for the case where the icmp is the only use of the iv.
2323 IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[*CondStride];
2324 for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(),
2325 E = StrideUses.Users.end(); I != E; ++I) {
2326 if (I->getUser() == Cond)
2328 if (!I->isUseOfPostIncrementedValue())
2332 // FIXME: This is expensive, and worse still ChangeCompareStride does a
2333 // similar check. Can we perform all the icmp related transformations after
2334 // StrengthReduceStridedIVUsers?
2335 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(*CondStride)) {
2336 int64_t SInt = SC->getValue()->getSExtValue();
2337 for (unsigned NewStride = 0, ee = IU->StrideOrder.size(); NewStride != ee;
2339 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
2340 IU->IVUsesByStride.find(IU->StrideOrder[NewStride]);
2341 if (!isa<SCEVConstant>(SI->first) || SI->first == *CondStride)
2344 cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
2346 return; // This can definitely be reused.
2347 if (unsigned(abs64(SSInt)) < SInt || (SSInt % SInt) != 0)
2349 int64_t Scale = SSInt / SInt;
2350 bool AllUsesAreAddresses = true;
2351 bool AllUsesAreOutsideLoop = true;
2352 std::vector<BasedUser> UsersToProcess;
2353 SCEVHandle CommonExprs = CollectIVUsers(SI->first, *SI->second, L,
2354 AllUsesAreAddresses,
2355 AllUsesAreOutsideLoop,
2357 // Avoid rewriting the compare instruction with an iv of new stride
2358 // if it's likely the new stride uses will be rewritten using the
2359 // stride of the compare instruction.
2360 if (AllUsesAreAddresses &&
2361 ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess))
2366 StrideNoReuse.insert(*CondStride);
2369 // If the trip count is computed in terms of a max (due to ScalarEvolution
2370 // being unable to find a sufficient guard, for example), change the loop
2371 // comparison to use SLT or ULT instead of NE.
2372 Cond = OptimizeMax(L, Cond, CondUse);
2374 // If possible, change stride and operands of the compare instruction to
2375 // eliminate one stride.
2376 if (ExitBlock == LatchBlock)
2377 Cond = ChangeCompareStride(L, Cond, CondUse, CondStride);
2379 // It's possible for the setcc instruction to be anywhere in the loop, and
2380 // possible for it to have multiple users. If it is not immediately before
2381 // the latch block branch, move it.
2382 if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) {
2383 if (Cond->hasOneUse()) { // Condition has a single use, just move it.
2384 Cond->moveBefore(TermBr);
2386 // Otherwise, clone the terminating condition and insert into the loopend.
2387 Cond = cast<ICmpInst>(Cond->clone());
2388 Cond->setName(L->getHeader()->getName() + ".termcond");
2389 LatchBlock->getInstList().insert(TermBr, Cond);
2391 // Clone the IVUse, as the old use still exists!
2392 IU->IVUsesByStride[*CondStride]->addUser(CondUse->getOffset(), Cond,
2393 CondUse->getOperandValToReplace());
2394 CondUse = &IU->IVUsesByStride[*CondStride]->Users.back();
2398 // If we get to here, we know that we can transform the setcc instruction to
2399 // use the post-incremented version of the IV, allowing us to coalesce the
2400 // live ranges for the IV correctly.
2401 CondUse->setOffset(SE->getMinusSCEV(CondUse->getOffset(), *CondStride));
2402 CondUse->setIsUseOfPostIncrementedValue(true);
2408 /// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for deciding
2409 /// when to exit the loop is used only for that purpose, try to rearrange things
2410 /// so it counts down to a test against zero.
2411 void LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) {
2413 // If the number of times the loop is executed isn't computable, give up.
2414 SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L);
2415 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
2418 // Get the terminating condition for the loop if possible (this isn't
2419 // necessarily in the latch, or a block that's a predecessor of the header).
2420 if (!L->getExitBlock())
2421 return; // More than one loop exit blocks.
2423 // Okay, there is one exit block. Try to find the condition that causes the
2424 // loop to be exited.
2425 BasicBlock *ExitingBlock = L->getExitingBlock();
2427 return; // More than one block exiting!
2429 // Okay, we've computed the exiting block. See what condition causes us to
2432 // FIXME: we should be able to handle switch instructions (with a single exit)
2433 BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
2434 if (TermBr == 0) return;
2435 assert(TermBr->isConditional() && "If unconditional, it can't be in loop!");
2436 if (!isa<ICmpInst>(TermBr->getCondition()))
2438 ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
2440 // Handle only tests for equality for the moment, and only stride 1.
2441 if (Cond->getPredicate() != CmpInst::ICMP_EQ)
2443 SCEVHandle IV = SE->getSCEV(Cond->getOperand(0));
2444 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
2445 SCEVHandle One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType());
2446 if (!AR || !AR->isAffine() || AR->getStepRecurrence(*SE) != One)
2448 // If the RHS of the comparison is defined inside the loop, the rewrite
2450 if (Instruction *CR = dyn_cast<Instruction>(Cond->getOperand(1)))
2451 if (L->contains(CR->getParent()))
2454 // Make sure the IV is only used for counting. Value may be preinc or
2455 // postinc; 2 uses in either case.
2456 if (!Cond->getOperand(0)->hasNUses(2))
2458 PHINode *phi = dyn_cast<PHINode>(Cond->getOperand(0));
2460 if (phi && phi->getParent()==L->getHeader()) {
2461 // value tested is preinc. Find the increment.
2462 // A CmpInst is not a BinaryOperator; we depend on this.
2463 Instruction::use_iterator UI = phi->use_begin();
2464 incr = dyn_cast<BinaryOperator>(UI);
2466 incr = dyn_cast<BinaryOperator>(++UI);
2467 // 1 use for postinc value, the phi. Unnecessarily conservative?
2468 if (!incr || !incr->hasOneUse() || incr->getOpcode()!=Instruction::Add)
2471 // Value tested is postinc. Find the phi node.
2472 incr = dyn_cast<BinaryOperator>(Cond->getOperand(0));
2473 if (!incr || incr->getOpcode()!=Instruction::Add)
2476 Instruction::use_iterator UI = Cond->getOperand(0)->use_begin();
2477 phi = dyn_cast<PHINode>(UI);
2479 phi = dyn_cast<PHINode>(++UI);
2480 // 1 use for preinc value, the increment.
2481 if (!phi || phi->getParent()!=L->getHeader() || !phi->hasOneUse())
2485 // Replace the increment with a decrement.
2486 BinaryOperator *decr =
2487 BinaryOperator::Create(Instruction::Sub, incr->getOperand(0),
2488 incr->getOperand(1), "tmp", incr);
2489 incr->replaceAllUsesWith(decr);
2490 incr->eraseFromParent();
2492 // Substitute endval-startval for the original startval, and 0 for the
2493 // original endval. Since we're only testing for equality this is OK even
2494 // if the computation wraps around.
2495 BasicBlock *Preheader = L->getLoopPreheader();
2496 Instruction *PreInsertPt = Preheader->getTerminator();
2497 int inBlock = L->contains(phi->getIncomingBlock(0)) ? 1 : 0;
2498 Value *startVal = phi->getIncomingValue(inBlock);
2499 Value *endVal = Cond->getOperand(1);
2500 // FIXME check for case where both are constant
2501 Constant* Zero = ConstantInt::get(Cond->getOperand(1)->getType(), 0);
2502 BinaryOperator *NewStartVal =
2503 BinaryOperator::Create(Instruction::Sub, endVal, startVal,
2504 "tmp", PreInsertPt);
2505 phi->setIncomingValue(inBlock, NewStartVal);
2506 Cond->setOperand(1, Zero);
2511 bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
2513 IU = &getAnalysis<IVUsers>();
2514 LI = &getAnalysis<LoopInfo>();
2515 DT = &getAnalysis<DominatorTree>();
2516 SE = &getAnalysis<ScalarEvolution>();
2519 if (!IU->IVUsesByStride.empty()) {
2521 DOUT << "\nLSR on \"" << L->getHeader()->getParent()->getNameStart()
2526 // Sort the StrideOrder so we process larger strides first.
2527 std::stable_sort(IU->StrideOrder.begin(), IU->StrideOrder.end(),
2530 // Optimize induction variables. Some indvar uses can be transformed to use
2531 // strides that will be needed for other purposes. A common example of this
2532 // is the exit test for the loop, which can often be rewritten to use the
2533 // computation of some other indvar to decide when to terminate the loop.
2536 // Change loop terminating condition to use the postinc iv when possible
2537 // and optimize loop terminating compare. FIXME: Move this after
2538 // StrengthReduceStridedIVUsers?
2539 OptimizeLoopTermCond(L);
2541 // FIXME: We can shrink overlarge IV's here. e.g. if the code has
2542 // computation in i64 values and the target doesn't support i64, demote
2543 // the computation to 32-bit if safe.
2545 // FIXME: Attempt to reuse values across multiple IV's. In particular, we
2546 // could have something like "for(i) { foo(i*8); bar(i*16) }", which should
2547 // be codegened as "for (j = 0;; j+=8) { foo(j); bar(j+j); }" on X86/PPC.
2548 // Need to be careful that IV's are all the same type. Only works for
2549 // intptr_t indvars.
2551 // IVsByStride keeps IVs for one particular loop.
2552 assert(IVsByStride.empty() && "Stale entries in IVsByStride?");
2554 // Note: this processes each stride/type pair individually. All users
2555 // passed into StrengthReduceStridedIVUsers have the same type AND stride.
2556 // Also, note that we iterate over IVUsesByStride indirectly by using
2557 // StrideOrder. This extra layer of indirection makes the ordering of
2558 // strides deterministic - not dependent on map order.
2559 for (unsigned Stride = 0, e = IU->StrideOrder.size();
2560 Stride != e; ++Stride) {
2561 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
2562 IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
2563 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
2564 // FIXME: Generalize to non-affine IV's.
2565 if (!SI->first->isLoopInvariant(L))
2567 StrengthReduceStridedIVUsers(SI->first, *SI->second, L);
2571 // After all sharing is done, see if we can adjust the loop to test against
2572 // zero instead of counting up to a maximum. This is usually faster.
2573 OptimizeLoopCountIV(L);
2575 // We're done analyzing this loop; release all the state we built up for it.
2576 IVsByStride.clear();
2577 StrideNoReuse.clear();
2579 // Clean up after ourselves
2580 if (!DeadInsts.empty())
2581 DeleteTriviallyDeadInstructions();
2583 // At this point, it is worth checking to see if any recurrence PHIs are also
2584 // dead, so that we can remove them as well.
2585 DeleteDeadPHIs(L->getHeader());