1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
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 simpler forms suitable for subsequent
12 // analysis and transformation.
14 // This transformation makes the following changes to each loop with an
15 // identifiable induction variable:
16 // 1. All loops are transformed to have a SINGLE canonical induction variable
17 // which starts at zero and steps by one.
18 // 2. The canonical induction variable is guaranteed to be the first PHI node
19 // in the loop header block.
20 // 3. The canonical induction variable is guaranteed to be in a wide enough
21 // type so that IV expressions need not be (directly) zero-extended or
23 // 4. Any pointer arithmetic recurrences are raised to use array subscripts.
25 // If the trip count of a loop is computable, this pass also makes the following
27 // 1. The exit condition for the loop is canonicalized to compare the
28 // induction value against the exit value. This turns loops like:
29 // 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
30 // 2. Any use outside of the loop of an expression derived from the indvar
31 // is changed to compute the derived value outside of the loop, eliminating
32 // the dependence on the exit value of the induction variable. If the only
33 // purpose of the loop is to compute the exit value of some derived
34 // expression, this transformation will make the loop dead.
36 // This transformation should be followed by strength reduction after all of the
37 // desired loop transformations have been performed.
39 //===----------------------------------------------------------------------===//
41 #define DEBUG_TYPE "indvars"
42 #include "llvm/Transforms/Scalar.h"
43 #include "llvm/BasicBlock.h"
44 #include "llvm/Constants.h"
45 #include "llvm/Instructions.h"
46 #include "llvm/IntrinsicInst.h"
47 #include "llvm/LLVMContext.h"
48 #include "llvm/Type.h"
49 #include "llvm/Analysis/Dominators.h"
50 #include "llvm/Analysis/IVUsers.h"
51 #include "llvm/Analysis/ScalarEvolutionExpander.h"
52 #include "llvm/Analysis/LoopInfo.h"
53 #include "llvm/Analysis/LoopPass.h"
54 #include "llvm/Support/CFG.h"
55 #include "llvm/Support/CommandLine.h"
56 #include "llvm/Support/Debug.h"
57 #include "llvm/Support/raw_ostream.h"
58 #include "llvm/Transforms/Utils/Local.h"
59 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
60 #include "llvm/Target/TargetData.h"
61 #include "llvm/ADT/SmallVector.h"
62 #include "llvm/ADT/Statistic.h"
63 #include "llvm/ADT/STLExtras.h"
66 STATISTIC(NumRemoved , "Number of aux indvars removed");
67 STATISTIC(NumWidened , "Number of indvars widened");
68 STATISTIC(NumInserted , "Number of canonical indvars added");
69 STATISTIC(NumReplaced , "Number of exit values replaced");
70 STATISTIC(NumLFTR , "Number of loop exit tests replaced");
71 STATISTIC(NumElimIdentity, "Number of IV identities eliminated");
72 STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated");
73 STATISTIC(NumElimRem , "Number of IV remainder operations eliminated");
74 STATISTIC(NumElimCmp , "Number of IV comparisons eliminated");
76 static cl::opt<bool> DisableIVRewrite(
77 "disable-iv-rewrite", cl::Hidden,
78 cl::desc("Disable canonical induction variable rewriting"));
81 class IndVarSimplify : public LoopPass {
88 SmallVector<WeakVH, 16> DeadInsts;
92 static char ID; // Pass identification, replacement for typeid
93 IndVarSimplify() : LoopPass(ID), IU(0), LI(0), SE(0), DT(0), TD(0),
95 initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
98 virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
100 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
101 AU.addRequired<DominatorTree>();
102 AU.addRequired<LoopInfo>();
103 AU.addRequired<ScalarEvolution>();
104 AU.addRequiredID(LoopSimplifyID);
105 AU.addRequiredID(LCSSAID);
106 if (!DisableIVRewrite)
107 AU.addRequired<IVUsers>();
108 AU.addPreserved<ScalarEvolution>();
109 AU.addPreservedID(LoopSimplifyID);
110 AU.addPreservedID(LCSSAID);
111 if (!DisableIVRewrite)
112 AU.addPreserved<IVUsers>();
113 AU.setPreservesCFG();
117 bool isValidRewrite(Value *FromVal, Value *ToVal);
119 void SimplifyIVUsers(SCEVExpander &Rewriter);
120 void SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter);
122 bool EliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
123 void EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
124 void EliminateIVRemainder(BinaryOperator *Rem,
127 bool isSimpleIVUser(Instruction *I, const Loop *L);
128 void RewriteNonIntegerIVs(Loop *L);
130 ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
132 SCEVExpander &Rewriter);
134 void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
136 void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter);
138 void SinkUnusedInvariants(Loop *L);
140 void HandleFloatingPointIV(Loop *L, PHINode *PH);
144 char IndVarSimplify::ID = 0;
145 INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
146 "Induction Variable Simplification", false, false)
147 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
148 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
149 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
150 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
151 INITIALIZE_PASS_DEPENDENCY(LCSSA)
152 INITIALIZE_PASS_DEPENDENCY(IVUsers)
153 INITIALIZE_PASS_END(IndVarSimplify, "indvars",
154 "Induction Variable Simplification", false, false)
156 Pass *llvm::createIndVarSimplifyPass() {
157 return new IndVarSimplify();
160 /// isValidRewrite - Return true if the SCEV expansion generated by the
161 /// rewriter can replace the original value. SCEV guarantees that it
162 /// produces the same value, but the way it is produced may be illegal IR.
163 /// Ideally, this function will only be called for verification.
164 bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
165 // If an SCEV expression subsumed multiple pointers, its expansion could
166 // reassociate the GEP changing the base pointer. This is illegal because the
167 // final address produced by a GEP chain must be inbounds relative to its
168 // underlying object. Otherwise basic alias analysis, among other things,
169 // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid
170 // producing an expression involving multiple pointers. Until then, we must
173 // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject
174 // because it understands lcssa phis while SCEV does not.
175 Value *FromPtr = FromVal;
176 Value *ToPtr = ToVal;
177 if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) {
178 FromPtr = GEP->getPointerOperand();
180 if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) {
181 ToPtr = GEP->getPointerOperand();
183 if (FromPtr != FromVal || ToPtr != ToVal) {
184 // Quickly check the common case
185 if (FromPtr == ToPtr)
188 // SCEV may have rewritten an expression that produces the GEP's pointer
189 // operand. That's ok as long as the pointer operand has the same base
190 // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the
191 // base of a recurrence. This handles the case in which SCEV expansion
192 // converts a pointer type recurrence into a nonrecurrent pointer base
193 // indexed by an integer recurrence.
194 const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
195 const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
196 if (FromBase == ToBase)
199 DEBUG(dbgs() << "INDVARS: GEP rewrite bail out "
200 << *FromBase << " != " << *ToBase << "\n");
207 /// canExpandBackedgeTakenCount - Return true if this loop's backedge taken
208 /// count expression can be safely and cheaply expanded into an instruction
209 /// sequence that can be used by LinearFunctionTestReplace.
210 static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) {
211 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
212 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) ||
213 BackedgeTakenCount->isZero())
216 if (!L->getExitingBlock())
219 // Can't rewrite non-branch yet.
220 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
224 // Special case: If the backedge-taken count is a UDiv, it's very likely a
225 // UDiv that ScalarEvolution produced in order to compute a precise
226 // expression, rather than a UDiv from the user's code. If we can't find a
227 // UDiv in the code with some simple searching, assume the former and forego
228 // rewriting the loop.
229 if (isa<SCEVUDivExpr>(BackedgeTakenCount)) {
230 ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition());
231 if (!OrigCond) return false;
232 const SCEV *R = SE->getSCEV(OrigCond->getOperand(1));
233 R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1));
234 if (R != BackedgeTakenCount) {
235 const SCEV *L = SE->getSCEV(OrigCond->getOperand(0));
236 L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1));
237 if (L != BackedgeTakenCount)
244 /// getBackedgeIVType - Get the widest type used by the loop test after peeking
247 /// TODO: Unnecessary once LinearFunctionTestReplace is removed.
248 static const Type *getBackedgeIVType(Loop *L) {
249 if (!L->getExitingBlock())
252 // Can't rewrite non-branch yet.
253 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
257 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
262 for(User::op_iterator OI = Cond->op_begin(), OE = Cond->op_end();
264 assert((!Ty || Ty == (*OI)->getType()) && "bad icmp operand types");
265 TruncInst *Trunc = dyn_cast<TruncInst>(*OI);
269 return Trunc->getSrcTy();
274 /// LinearFunctionTestReplace - This method rewrites the exit condition of the
275 /// loop to be a canonical != comparison against the incremented loop induction
276 /// variable. This pass is able to rewrite the exit tests of any loop where the
277 /// SCEV analysis can determine a loop-invariant trip count of the loop, which
278 /// is actually a much broader range than just linear tests.
279 ICmpInst *IndVarSimplify::
280 LinearFunctionTestReplace(Loop *L,
281 const SCEV *BackedgeTakenCount,
283 SCEVExpander &Rewriter) {
284 assert(canExpandBackedgeTakenCount(L, SE) && "precondition");
285 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
287 // If the exiting block is not the same as the backedge block, we must compare
288 // against the preincremented value, otherwise we prefer to compare against
289 // the post-incremented value.
291 const SCEV *RHS = BackedgeTakenCount;
292 if (L->getExitingBlock() == L->getLoopLatch()) {
293 // Add one to the "backedge-taken" count to get the trip count.
294 // If this addition may overflow, we have to be more pessimistic and
295 // cast the induction variable before doing the add.
296 const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0);
298 SE->getAddExpr(BackedgeTakenCount,
299 SE->getConstant(BackedgeTakenCount->getType(), 1));
300 if ((isa<SCEVConstant>(N) && !N->isZero()) ||
301 SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
302 // No overflow. Cast the sum.
303 RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
305 // Potential overflow. Cast before doing the add.
306 RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
308 RHS = SE->getAddExpr(RHS,
309 SE->getConstant(IndVar->getType(), 1));
312 // The BackedgeTaken expression contains the number of times that the
313 // backedge branches to the loop header. This is one less than the
314 // number of times the loop executes, so use the incremented indvar.
315 CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
317 // We have to use the preincremented value...
318 RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
323 // Expand the code for the iteration count.
324 assert(SE->isLoopInvariant(RHS, L) &&
325 "Computed iteration count is not loop invariant!");
326 Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI);
328 // Insert a new icmp_ne or icmp_eq instruction before the branch.
329 ICmpInst::Predicate Opcode;
330 if (L->contains(BI->getSuccessor(0)))
331 Opcode = ICmpInst::ICMP_NE;
333 Opcode = ICmpInst::ICMP_EQ;
335 DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
336 << " LHS:" << *CmpIndVar << '\n'
338 << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
339 << " RHS:\t" << *RHS << "\n");
341 ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond");
343 Value *OrigCond = BI->getCondition();
344 // It's tempting to use replaceAllUsesWith here to fully replace the old
345 // comparison, but that's not immediately safe, since users of the old
346 // comparison may not be dominated by the new comparison. Instead, just
347 // update the branch to use the new comparison; in the common case this
348 // will make old comparison dead.
349 BI->setCondition(Cond);
350 DeadInsts.push_back(OrigCond);
357 /// RewriteLoopExitValues - Check to see if this loop has a computable
358 /// loop-invariant execution count. If so, this means that we can compute the
359 /// final value of any expressions that are recurrent in the loop, and
360 /// substitute the exit values from the loop into any instructions outside of
361 /// the loop that use the final values of the current expressions.
363 /// This is mostly redundant with the regular IndVarSimplify activities that
364 /// happen later, except that it's more powerful in some cases, because it's
365 /// able to brute-force evaluate arbitrary instructions as long as they have
366 /// constant operands at the beginning of the loop.
367 void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
368 // Verify the input to the pass in already in LCSSA form.
369 assert(L->isLCSSAForm(*DT));
371 SmallVector<BasicBlock*, 8> ExitBlocks;
372 L->getUniqueExitBlocks(ExitBlocks);
374 // Find all values that are computed inside the loop, but used outside of it.
375 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
376 // the exit blocks of the loop to find them.
377 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
378 BasicBlock *ExitBB = ExitBlocks[i];
380 // If there are no PHI nodes in this exit block, then no values defined
381 // inside the loop are used on this path, skip it.
382 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
385 unsigned NumPreds = PN->getNumIncomingValues();
387 // Iterate over all of the PHI nodes.
388 BasicBlock::iterator BBI = ExitBB->begin();
389 while ((PN = dyn_cast<PHINode>(BBI++))) {
391 continue; // dead use, don't replace it
393 // SCEV only supports integer expressions for now.
394 if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
397 // It's necessary to tell ScalarEvolution about this explicitly so that
398 // it can walk the def-use list and forget all SCEVs, as it may not be
399 // watching the PHI itself. Once the new exit value is in place, there
400 // may not be a def-use connection between the loop and every instruction
401 // which got a SCEVAddRecExpr for that loop.
404 // Iterate over all of the values in all the PHI nodes.
405 for (unsigned i = 0; i != NumPreds; ++i) {
406 // If the value being merged in is not integer or is not defined
407 // in the loop, skip it.
408 Value *InVal = PN->getIncomingValue(i);
409 if (!isa<Instruction>(InVal))
412 // If this pred is for a subloop, not L itself, skip it.
413 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
414 continue; // The Block is in a subloop, skip it.
416 // Check that InVal is defined in the loop.
417 Instruction *Inst = cast<Instruction>(InVal);
418 if (!L->contains(Inst))
421 // Okay, this instruction has a user outside of the current loop
422 // and varies predictably *inside* the loop. Evaluate the value it
423 // contains when the loop exits, if possible.
424 const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
425 if (!SE->isLoopInvariant(ExitValue, L))
428 Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
430 DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
431 << " LoopVal = " << *Inst << "\n");
433 if (!isValidRewrite(Inst, ExitVal)) {
434 DeadInsts.push_back(ExitVal);
440 PN->setIncomingValue(i, ExitVal);
442 // If this instruction is dead now, delete it.
443 RecursivelyDeleteTriviallyDeadInstructions(Inst);
446 // Completely replace a single-pred PHI. This is safe, because the
447 // NewVal won't be variant in the loop, so we don't need an LCSSA phi
449 PN->replaceAllUsesWith(ExitVal);
450 RecursivelyDeleteTriviallyDeadInstructions(PN);
454 // Clone the PHI and delete the original one. This lets IVUsers and
455 // any other maps purge the original user from their records.
456 PHINode *NewPN = cast<PHINode>(PN->clone());
458 NewPN->insertBefore(PN);
459 PN->replaceAllUsesWith(NewPN);
460 PN->eraseFromParent();
465 // The insertion point instruction may have been deleted; clear it out
466 // so that the rewriter doesn't trip over it later.
467 Rewriter.clearInsertPoint();
470 void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
471 // First step. Check to see if there are any floating-point recurrences.
472 // If there are, change them into integer recurrences, permitting analysis by
473 // the SCEV routines.
475 BasicBlock *Header = L->getHeader();
477 SmallVector<WeakVH, 8> PHIs;
478 for (BasicBlock::iterator I = Header->begin();
479 PHINode *PN = dyn_cast<PHINode>(I); ++I)
482 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
483 if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i]))
484 HandleFloatingPointIV(L, PN);
486 // If the loop previously had floating-point IV, ScalarEvolution
487 // may not have been able to compute a trip count. Now that we've done some
488 // re-writing, the trip count may be computable.
493 /// SimplifyIVUsers - Iteratively perform simplification on IVUsers within this
494 /// loop. IVUsers is treated as a worklist. Each successive simplification may
495 /// push more users which may themselves be candidates for simplification.
497 /// This is the old approach to IV simplification to be replaced by
498 /// SimplifyIVUsersNoRewrite.
500 void IndVarSimplify::SimplifyIVUsers(SCEVExpander &Rewriter) {
501 // Each round of simplification involves a round of eliminating operations
502 // followed by a round of widening IVs. A single IVUsers worklist is used
503 // across all rounds. The inner loop advances the user. If widening exposes
504 // more uses, then another pass through the outer loop is triggered.
505 for (IVUsers::iterator I = IU->begin(); I != IU->end(); ++I) {
506 Instruction *UseInst = I->getUser();
507 Value *IVOperand = I->getOperandValToReplace();
509 if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
510 EliminateIVComparison(ICmp, IVOperand);
513 if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) {
514 bool IsSigned = Rem->getOpcode() == Instruction::SRem;
515 if (IsSigned || Rem->getOpcode() == Instruction::URem) {
516 EliminateIVRemainder(Rem, IVOperand, IsSigned);
524 // Collect information about induction variables that are used by sign/zero
525 // extend operations. This information is recorded by CollectExtend and
526 // provides the input to WidenIV.
528 const Type *WidestNativeType; // Widest integer type created [sz]ext
529 bool IsSigned; // Was an sext user seen before a zext?
531 WideIVInfo() : WidestNativeType(0), IsSigned(false) {}
535 /// CollectExtend - Update information about the induction variable that is
536 /// extended by this sign or zero extend operation. This is used to determine
537 /// the final width of the IV before actually widening it.
538 static void CollectExtend(CastInst *Cast, bool IsSigned, WideIVInfo &WI,
539 ScalarEvolution *SE, const TargetData *TD) {
540 const Type *Ty = Cast->getType();
541 uint64_t Width = SE->getTypeSizeInBits(Ty);
542 if (TD && !TD->isLegalInteger(Width))
545 if (!WI.WidestNativeType) {
546 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
547 WI.IsSigned = IsSigned;
551 // We extend the IV to satisfy the sign of its first user, arbitrarily.
552 if (WI.IsSigned != IsSigned)
555 if (Width > SE->getTypeSizeInBits(WI.WidestNativeType))
556 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
560 /// WidenIV - The goal of this transform is to remove sign and zero extends
561 /// without creating any new induction variables. To do this, it creates a new
562 /// phi of the wider type and redirects all users, either removing extends or
563 /// inserting truncs whenever we stop propagating the type.
568 const Type *WideType;
579 Instruction *WideInc;
580 const SCEV *WideIncExpr;
581 SmallVectorImpl<WeakVH> &DeadInsts;
583 SmallPtrSet<Instruction*,16> Widened;
584 SmallVector<std::pair<Use *, Instruction *>, 8> NarrowIVUsers;
587 WidenIV(PHINode *PN, const WideIVInfo &WI, LoopInfo *LInfo,
588 ScalarEvolution *SEv, DominatorTree *DTree,
589 SmallVectorImpl<WeakVH> &DI) :
591 WideType(WI.WidestNativeType),
592 IsSigned(WI.IsSigned),
594 L(LI->getLoopFor(OrigPhi->getParent())),
601 assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV");
604 PHINode *CreateWideIV(SCEVExpander &Rewriter);
607 Instruction *CloneIVUser(Instruction *NarrowUse,
608 Instruction *NarrowDef,
609 Instruction *WideDef);
611 Instruction *WidenIVUse(Use &NarrowDefUse, Instruction *NarrowDef,
612 Instruction *WideDef);
614 void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
616 } // anonymous namespace
618 static Value *getExtend( Value *NarrowOper, const Type *WideType,
619 bool IsSigned, IRBuilder<> &Builder) {
620 return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) :
621 Builder.CreateZExt(NarrowOper, WideType);
624 /// CloneIVUser - Instantiate a wide operation to replace a narrow
625 /// operation. This only needs to handle operations that can evaluation to
626 /// SCEVAddRec. It can safely return 0 for any operation we decide not to clone.
627 Instruction *WidenIV::CloneIVUser(Instruction *NarrowUse,
628 Instruction *NarrowDef,
629 Instruction *WideDef) {
630 unsigned Opcode = NarrowUse->getOpcode();
634 case Instruction::Add:
635 case Instruction::Mul:
636 case Instruction::UDiv:
637 case Instruction::Sub:
638 case Instruction::And:
639 case Instruction::Or:
640 case Instruction::Xor:
641 case Instruction::Shl:
642 case Instruction::LShr:
643 case Instruction::AShr:
644 DEBUG(dbgs() << "Cloning IVUser: " << *NarrowUse << "\n");
646 IRBuilder<> Builder(NarrowUse);
648 // Replace NarrowDef operands with WideDef. Otherwise, we don't know
649 // anything about the narrow operand yet so must insert a [sz]ext. It is
650 // probably loop invariant and will be folded or hoisted. If it actually
651 // comes from a widened IV, it should be removed during a future call to
653 Value *LHS = (NarrowUse->getOperand(0) == NarrowDef) ? WideDef :
654 getExtend(NarrowUse->getOperand(0), WideType, IsSigned, Builder);
655 Value *RHS = (NarrowUse->getOperand(1) == NarrowDef) ? WideDef :
656 getExtend(NarrowUse->getOperand(1), WideType, IsSigned, Builder);
658 BinaryOperator *NarrowBO = cast<BinaryOperator>(NarrowUse);
659 BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(),
661 NarrowBO->getName());
662 Builder.Insert(WideBO);
663 if (const OverflowingBinaryOperator *OBO =
664 dyn_cast<OverflowingBinaryOperator>(NarrowBO)) {
665 if (OBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap();
666 if (OBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap();
673 /// HoistStep - Attempt to hoist an IV increment above a potential use.
675 /// To successfully hoist, two criteria must be met:
676 /// - IncV operands dominate InsertPos and
677 /// - InsertPos dominates IncV
679 /// Meeting the second condition means that we don't need to check all of IncV's
680 /// existing uses (it's moving up in the domtree).
682 /// This does not yet recursively hoist the operands, although that would
683 /// not be difficult.
684 static bool HoistStep(Instruction *IncV, Instruction *InsertPos,
685 const DominatorTree *DT)
687 if (DT->dominates(IncV, InsertPos))
690 if (!DT->dominates(InsertPos->getParent(), IncV->getParent()))
693 if (IncV->mayHaveSideEffects())
696 // Attempt to hoist IncV
697 for (User::op_iterator OI = IncV->op_begin(), OE = IncV->op_end();
699 Instruction *OInst = dyn_cast<Instruction>(OI);
700 if (OInst && !DT->dominates(OInst, InsertPos))
703 IncV->moveBefore(InsertPos);
707 /// WidenIVUse - Determine whether an individual user of the narrow IV can be
708 /// widened. If so, return the wide clone of the user.
709 Instruction *WidenIV::WidenIVUse(Use &NarrowDefUse, Instruction *NarrowDef,
710 Instruction *WideDef) {
711 Instruction *NarrowUse = cast<Instruction>(NarrowDefUse.getUser());
713 // Stop traversing the def-use chain at inner-loop phis or post-loop phis.
714 if (isa<PHINode>(NarrowUse) && LI->getLoopFor(NarrowUse->getParent()) != L)
717 // Our raison d'etre! Eliminate sign and zero extension.
718 if (IsSigned ? isa<SExtInst>(NarrowUse) : isa<ZExtInst>(NarrowUse)) {
719 Value *NewDef = WideDef;
720 if (NarrowUse->getType() != WideType) {
721 unsigned CastWidth = SE->getTypeSizeInBits(NarrowUse->getType());
722 unsigned IVWidth = SE->getTypeSizeInBits(WideType);
723 if (CastWidth < IVWidth) {
724 // The cast isn't as wide as the IV, so insert a Trunc.
725 IRBuilder<> Builder(NarrowDefUse);
726 NewDef = Builder.CreateTrunc(WideDef, NarrowUse->getType());
729 // A wider extend was hidden behind a narrower one. This may induce
730 // another round of IV widening in which the intermediate IV becomes
731 // dead. It should be very rare.
732 DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi
733 << " not wide enough to subsume " << *NarrowUse << "\n");
734 NarrowUse->replaceUsesOfWith(NarrowDef, WideDef);
738 if (NewDef != NarrowUse) {
739 DEBUG(dbgs() << "INDVARS: eliminating " << *NarrowUse
740 << " replaced by " << *WideDef << "\n");
742 NarrowUse->replaceAllUsesWith(NewDef);
743 DeadInsts.push_back(NarrowUse);
745 // Now that the extend is gone, we want to expose it's uses for potential
746 // further simplification. We don't need to directly inform SimplifyIVUsers
747 // of the new users, because their parent IV will be processed later as a
748 // new loop phi. If we preserved IVUsers analysis, we would also want to
749 // push the uses of WideDef here.
751 // No further widening is needed. The deceased [sz]ext had done it for us.
755 // Does this user itself evaluate to a recurrence after widening?
756 const SCEVAddRecExpr *WideAddRec = 0;
757 if (SE->isSCEVable(NarrowUse->getType())) {
758 const SCEV *NarrowExpr = SE->getSCEV(NarrowUse);
759 if (SE->getTypeSizeInBits(NarrowExpr->getType())
760 >= SE->getTypeSizeInBits(WideType)) {
761 // NarrowUse implicitly widens its operand. e.g. a gep with a narrow
762 // index. We have already extended the operand, so we're done.
765 const SCEV *WideExpr = IsSigned ?
766 SE->getSignExtendExpr(NarrowExpr, WideType) :
767 SE->getZeroExtendExpr(NarrowExpr, WideType);
769 // Only widen past values that evaluate to a recurrence in the same loop.
770 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr);
771 if (AddRec && AddRec->getLoop() == L)
775 // This user does not evaluate to a recurence after widening, so don't
776 // follow it. Instead insert a Trunc to kill off the original use,
777 // eventually isolating the original narrow IV so it can be removed.
778 IRBuilder<> Builder(NarrowDefUse);
779 Value *Trunc = Builder.CreateTrunc(WideDef, NarrowDef->getType());
780 NarrowUse->replaceUsesOfWith(NarrowDef, Trunc);
783 // We assume that block terminators are not SCEVable. We wouldn't want to
784 // insert a Trunc after a terminator if there happens to be a critical edge.
785 assert(NarrowUse != NarrowUse->getParent()->getTerminator() &&
786 "SCEV is not expected to evaluate a block terminator");
788 // Reuse the IV increment that SCEVExpander created as long as it dominates
790 Instruction *WideUse = 0;
791 if (WideAddRec == WideIncExpr && HoistStep(WideInc, NarrowUse, DT)) {
795 WideUse = CloneIVUser(NarrowUse, NarrowDef, WideDef);
799 // Evaluation of WideAddRec ensured that the narrow expression could be
800 // extended outside the loop without overflow. This suggests that the wide use
801 // evaluates to the same expression as the extended narrow use, but doesn't
802 // absolutely guarantee it. Hence the following failsafe check. In rare cases
803 // where it fails, we simply throw away the newly created wide use.
804 if (WideAddRec != SE->getSCEV(WideUse)) {
805 DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse
806 << ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n");
807 DeadInsts.push_back(WideUse);
811 // Returning WideUse pushes it on the worklist.
815 /// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers.
817 void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) {
818 for (Value::use_iterator UI = NarrowDef->use_begin(),
819 UE = NarrowDef->use_end(); UI != UE; ++UI) {
820 Use &U = UI.getUse();
822 // Handle data flow merges and bizarre phi cycles.
823 if (!Widened.insert(cast<Instruction>(U.getUser())))
826 NarrowIVUsers.push_back(std::make_pair(&UI.getUse(), WideDef));
830 /// CreateWideIV - Process a single induction variable. First use the
831 /// SCEVExpander to create a wide induction variable that evaluates to the same
832 /// recurrence as the original narrow IV. Then use a worklist to forward
833 /// traverse the narrow IV's def-use chain. After WidenIVUse has processed all
834 /// interesting IV users, the narrow IV will be isolated for removal by
837 /// It would be simpler to delete uses as they are processed, but we must avoid
838 /// invalidating SCEV expressions.
840 PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) {
841 // Is this phi an induction variable?
842 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi));
846 // Widen the induction variable expression.
847 const SCEV *WideIVExpr = IsSigned ?
848 SE->getSignExtendExpr(AddRec, WideType) :
849 SE->getZeroExtendExpr(AddRec, WideType);
851 assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType &&
852 "Expect the new IV expression to preserve its type");
854 // Can the IV be extended outside the loop without overflow?
855 AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr);
856 if (!AddRec || AddRec->getLoop() != L)
859 // An AddRec must have loop-invariant operands. Since this AddRec is
860 // materialized by a loop header phi, the expression cannot have any post-loop
861 // operands, so they must dominate the loop header.
862 assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) &&
863 SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader())
864 && "Loop header phi recurrence inputs do not dominate the loop");
866 // The rewriter provides a value for the desired IV expression. This may
867 // either find an existing phi or materialize a new one. Either way, we
868 // expect a well-formed cyclic phi-with-increments. i.e. any operand not part
869 // of the phi-SCC dominates the loop entry.
870 Instruction *InsertPt = L->getHeader()->begin();
871 WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt));
873 // Remembering the WideIV increment generated by SCEVExpander allows
874 // WidenIVUse to reuse it when widening the narrow IV's increment. We don't
875 // employ a general reuse mechanism because the call above is the only call to
876 // SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses.
877 if (BasicBlock *LatchBlock = L->getLoopLatch()) {
879 cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
880 WideIncExpr = SE->getSCEV(WideInc);
883 DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n");
886 // Traverse the def-use chain using a worklist starting at the original IV.
887 assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" );
889 Widened.insert(OrigPhi);
890 pushNarrowIVUsers(OrigPhi, WidePhi);
892 while (!NarrowIVUsers.empty()) {
894 Instruction *WideDef;
895 tie(UsePtr, WideDef) = NarrowIVUsers.pop_back_val();
896 Use &NarrowDefUse = *UsePtr;
898 // Process a def-use edge. This may replace the use, so don't hold a
899 // use_iterator across it.
900 Instruction *NarrowDef = cast<Instruction>(NarrowDefUse.get());
901 Instruction *WideUse = WidenIVUse(NarrowDefUse, NarrowDef, WideDef);
903 // Follow all def-use edges from the previous narrow use.
905 pushNarrowIVUsers(cast<Instruction>(NarrowDefUse.getUser()), WideUse);
907 // WidenIVUse may have removed the def-use edge.
908 if (NarrowDef->use_empty())
909 DeadInsts.push_back(NarrowDef);
914 void IndVarSimplify::EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
915 unsigned IVOperIdx = 0;
916 ICmpInst::Predicate Pred = ICmp->getPredicate();
917 if (IVOperand != ICmp->getOperand(0)) {
919 assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand");
921 Pred = ICmpInst::getSwappedPredicate(Pred);
924 // Get the SCEVs for the ICmp operands.
925 const SCEV *S = SE->getSCEV(ICmp->getOperand(IVOperIdx));
926 const SCEV *X = SE->getSCEV(ICmp->getOperand(1 - IVOperIdx));
928 // Simplify unnecessary loops away.
929 const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
930 S = SE->getSCEVAtScope(S, ICmpLoop);
931 X = SE->getSCEVAtScope(X, ICmpLoop);
933 // If the condition is always true or always false, replace it with
935 if (SE->isKnownPredicate(Pred, S, X))
936 ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
937 else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
938 ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
942 DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
945 DeadInsts.push_back(ICmp);
948 void IndVarSimplify::EliminateIVRemainder(BinaryOperator *Rem,
951 // We're only interested in the case where we know something about
953 if (IVOperand != Rem->getOperand(0))
956 // Get the SCEVs for the ICmp operands.
957 const SCEV *S = SE->getSCEV(Rem->getOperand(0));
958 const SCEV *X = SE->getSCEV(Rem->getOperand(1));
960 // Simplify unnecessary loops away.
961 const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
962 S = SE->getSCEVAtScope(S, ICmpLoop);
963 X = SE->getSCEVAtScope(X, ICmpLoop);
965 // i % n --> i if i is in [0,n).
966 if ((!IsSigned || SE->isKnownNonNegative(S)) &&
967 SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
969 Rem->replaceAllUsesWith(Rem->getOperand(0));
971 // (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
972 const SCEV *LessOne =
973 SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1));
974 if (IsSigned && !SE->isKnownNonNegative(LessOne))
977 if (!SE->isKnownPredicate(IsSigned ?
978 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
982 ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ,
983 Rem->getOperand(0), Rem->getOperand(1),
986 SelectInst::Create(ICmp,
987 ConstantInt::get(Rem->getType(), 0),
988 Rem->getOperand(0), "tmp", Rem);
989 Rem->replaceAllUsesWith(Sel);
992 // Inform IVUsers about the new users.
994 if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0)))
995 IU->AddUsersIfInteresting(I);
997 DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
1000 DeadInsts.push_back(Rem);
1003 /// EliminateIVUser - Eliminate an operation that consumes a simple IV and has
1004 /// no observable side-effect given the range of IV values.
1005 bool IndVarSimplify::EliminateIVUser(Instruction *UseInst,
1006 Instruction *IVOperand) {
1007 if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
1008 EliminateIVComparison(ICmp, IVOperand);
1011 if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) {
1012 bool IsSigned = Rem->getOpcode() == Instruction::SRem;
1013 if (IsSigned || Rem->getOpcode() == Instruction::URem) {
1014 EliminateIVRemainder(Rem, IVOperand, IsSigned);
1019 // Eliminate any operation that SCEV can prove is an identity function.
1020 if (!SE->isSCEVable(UseInst->getType()) ||
1021 (UseInst->getType() != IVOperand->getType()) ||
1022 (SE->getSCEV(UseInst) != SE->getSCEV(IVOperand)))
1025 DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n');
1027 UseInst->replaceAllUsesWith(IVOperand);
1030 DeadInsts.push_back(UseInst);
1034 /// pushIVUsers - Add all uses of Def to the current IV's worklist.
1036 static void pushIVUsers(
1038 SmallPtrSet<Instruction*,16> &Simplified,
1039 SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) {
1041 for (Value::use_iterator UI = Def->use_begin(), E = Def->use_end();
1043 Instruction *User = cast<Instruction>(*UI);
1045 // Avoid infinite or exponential worklist processing.
1046 // Also ensure unique worklist users.
1047 // If Def is a LoopPhi, it may not be in the Simplified set, so check for
1048 // self edges first.
1049 if (User != Def && Simplified.insert(User))
1050 SimpleIVUsers.push_back(std::make_pair(User, Def));
1054 /// isSimpleIVUser - Return true if this instruction generates a simple SCEV
1055 /// expression in terms of that IV.
1057 /// This is similar to IVUsers' isInsteresting() but processes each instruction
1058 /// non-recursively when the operand is already known to be a simpleIVUser.
1060 bool IndVarSimplify::isSimpleIVUser(Instruction *I, const Loop *L) {
1061 if (!SE->isSCEVable(I->getType()))
1064 // Get the symbolic expression for this instruction.
1065 const SCEV *S = SE->getSCEV(I);
1067 // We assume that terminators are not SCEVable.
1068 assert((!S || I != I->getParent()->getTerminator()) &&
1069 "can't fold terminators");
1071 // Only consider affine recurrences.
1072 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S);
1073 if (AR && AR->getLoop() == L)
1079 /// SimplifyIVUsersNoRewrite - Iteratively perform simplification on a worklist
1080 /// of IV users. Each successive simplification may push more users which may
1081 /// themselves be candidates for simplification.
1083 /// The "NoRewrite" algorithm does not require IVUsers analysis. Instead, it
1084 /// simplifies instructions in-place during analysis. Rather than rewriting
1085 /// induction variables bottom-up from their users, it transforms a chain of
1086 /// IVUsers top-down, updating the IR only when it encouters a clear
1087 /// optimization opportunitiy. A SCEVExpander "Rewriter" instance is still
1088 /// needed, but only used to generate a new IV (phi) of wider type for sign/zero
1089 /// extend elimination.
1091 /// Once DisableIVRewrite is default, LSR will be the only client of IVUsers.
1093 void IndVarSimplify::SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter) {
1094 std::map<PHINode *, WideIVInfo> WideIVMap;
1096 SmallVector<PHINode*, 8> LoopPhis;
1097 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
1098 LoopPhis.push_back(cast<PHINode>(I));
1100 // Each round of simplification iterates through the SimplifyIVUsers worklist
1101 // for all current phis, then determines whether any IVs can be
1102 // widened. Widening adds new phis to LoopPhis, inducing another round of
1103 // simplification on the wide IVs.
1104 while (!LoopPhis.empty()) {
1105 // Evaluate as many IV expressions as possible before widening any IVs. This
1106 // forces SCEV to set no-wrap flags before evaluating sign/zero
1107 // extension. The first time SCEV attempts to normalize sign/zero extension,
1108 // the result becomes final. So for the most predictable results, we delay
1109 // evaluation of sign/zero extend evaluation until needed, and avoid running
1110 // other SCEV based analysis prior to SimplifyIVUsersNoRewrite.
1112 PHINode *CurrIV = LoopPhis.pop_back_val();
1114 // Information about sign/zero extensions of CurrIV.
1117 // Instructions processed by SimplifyIVUsers for CurrIV.
1118 SmallPtrSet<Instruction*,16> Simplified;
1120 // Use-def pairs if IVUsers waiting to be processed for CurrIV.
1121 SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers;
1123 // Push users of the current LoopPhi. In rare cases, pushIVUsers may be
1124 // called multiple times for the same LoopPhi. This is the proper thing to
1125 // do for loop header phis that use each other.
1126 pushIVUsers(CurrIV, Simplified, SimpleIVUsers);
1128 while (!SimpleIVUsers.empty()) {
1129 Instruction *UseInst, *Operand;
1130 tie(UseInst, Operand) = SimpleIVUsers.pop_back_val();
1131 // Bypass back edges to avoid extra work.
1132 if (UseInst == CurrIV) continue;
1134 if (EliminateIVUser(UseInst, Operand)) {
1135 pushIVUsers(Operand, Simplified, SimpleIVUsers);
1138 if (CastInst *Cast = dyn_cast<CastInst>(UseInst)) {
1139 bool IsSigned = Cast->getOpcode() == Instruction::SExt;
1140 if (IsSigned || Cast->getOpcode() == Instruction::ZExt) {
1141 CollectExtend(Cast, IsSigned, WI, SE, TD);
1145 if (isSimpleIVUser(UseInst, L)) {
1146 pushIVUsers(UseInst, Simplified, SimpleIVUsers);
1149 if (WI.WidestNativeType) {
1150 WideIVMap[CurrIV] = WI;
1152 } while(!LoopPhis.empty());
1154 for (std::map<PHINode *, WideIVInfo>::const_iterator I = WideIVMap.begin(),
1155 E = WideIVMap.end(); I != E; ++I) {
1156 WidenIV Widener(I->first, I->second, LI, SE, DT, DeadInsts);
1157 if (PHINode *WidePhi = Widener.CreateWideIV(Rewriter)) {
1159 LoopPhis.push_back(WidePhi);
1166 bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
1167 // If LoopSimplify form is not available, stay out of trouble. Some notes:
1168 // - LSR currently only supports LoopSimplify-form loops. Indvars'
1169 // canonicalization can be a pessimization without LSR to "clean up"
1171 // - We depend on having a preheader; in particular,
1172 // Loop::getCanonicalInductionVariable only supports loops with preheaders,
1173 // and we're in trouble if we can't find the induction variable even when
1174 // we've manually inserted one.
1175 if (!L->isLoopSimplifyForm())
1178 if (!DisableIVRewrite)
1179 IU = &getAnalysis<IVUsers>();
1180 LI = &getAnalysis<LoopInfo>();
1181 SE = &getAnalysis<ScalarEvolution>();
1182 DT = &getAnalysis<DominatorTree>();
1183 TD = getAnalysisIfAvailable<TargetData>();
1188 // If there are any floating-point recurrences, attempt to
1189 // transform them to use integer recurrences.
1190 RewriteNonIntegerIVs(L);
1192 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
1194 // Create a rewriter object which we'll use to transform the code with.
1195 SCEVExpander Rewriter(*SE, "indvars");
1197 // Eliminate redundant IV users.
1199 // Simplification works best when run before other consumers of SCEV. We
1200 // attempt to avoid evaluating SCEVs for sign/zero extend operations until
1201 // other expressions involving loop IVs have been evaluated. This helps SCEV
1202 // set no-wrap flags before normalizing sign/zero extension.
1203 if (DisableIVRewrite) {
1204 Rewriter.disableCanonicalMode();
1205 SimplifyIVUsersNoRewrite(L, Rewriter);
1208 // Check to see if this loop has a computable loop-invariant execution count.
1209 // If so, this means that we can compute the final value of any expressions
1210 // that are recurrent in the loop, and substitute the exit values from the
1211 // loop into any instructions outside of the loop that use the final values of
1212 // the current expressions.
1214 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
1215 RewriteLoopExitValues(L, Rewriter);
1217 // Eliminate redundant IV users.
1218 if (!DisableIVRewrite)
1219 SimplifyIVUsers(Rewriter);
1221 // Compute the type of the largest recurrence expression, and decide whether
1222 // a canonical induction variable should be inserted.
1223 const Type *LargestType = 0;
1224 bool NeedCannIV = false;
1225 bool ExpandBECount = canExpandBackedgeTakenCount(L, SE);
1226 if (ExpandBECount) {
1227 // If we have a known trip count and a single exit block, we'll be
1228 // rewriting the loop exit test condition below, which requires a
1229 // canonical induction variable.
1231 const Type *Ty = BackedgeTakenCount->getType();
1232 if (DisableIVRewrite) {
1233 // In this mode, SimplifyIVUsers may have already widened the IV used by
1234 // the backedge test and inserted a Trunc on the compare's operand. Get
1235 // the wider type to avoid creating a redundant narrow IV only used by the
1237 LargestType = getBackedgeIVType(L);
1240 SE->getTypeSizeInBits(Ty) >
1241 SE->getTypeSizeInBits(LargestType))
1242 LargestType = SE->getEffectiveSCEVType(Ty);
1244 if (!DisableIVRewrite) {
1245 for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
1248 SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType());
1250 SE->getTypeSizeInBits(Ty) >
1251 SE->getTypeSizeInBits(LargestType))
1256 // Now that we know the largest of the induction variable expressions
1257 // in this loop, insert a canonical induction variable of the largest size.
1258 PHINode *IndVar = 0;
1260 // Check to see if the loop already has any canonical-looking induction
1261 // variables. If any are present and wider than the planned canonical
1262 // induction variable, temporarily remove them, so that the Rewriter
1263 // doesn't attempt to reuse them.
1264 SmallVector<PHINode *, 2> OldCannIVs;
1265 while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) {
1266 if (SE->getTypeSizeInBits(OldCannIV->getType()) >
1267 SE->getTypeSizeInBits(LargestType))
1268 OldCannIV->removeFromParent();
1271 OldCannIVs.push_back(OldCannIV);
1274 IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType);
1278 DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n');
1280 // Now that the official induction variable is established, reinsert
1281 // any old canonical-looking variables after it so that the IR remains
1282 // consistent. They will be deleted as part of the dead-PHI deletion at
1283 // the end of the pass.
1284 while (!OldCannIVs.empty()) {
1285 PHINode *OldCannIV = OldCannIVs.pop_back_val();
1286 OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI());
1290 // If we have a trip count expression, rewrite the loop's exit condition
1291 // using it. We can currently only handle loops with a single exit.
1292 ICmpInst *NewICmp = 0;
1293 if (ExpandBECount) {
1294 assert(canExpandBackedgeTakenCount(L, SE) &&
1295 "canonical IV disrupted BackedgeTaken expansion");
1296 assert(NeedCannIV &&
1297 "LinearFunctionTestReplace requires a canonical induction variable");
1298 NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
1301 // Rewrite IV-derived expressions.
1302 if (!DisableIVRewrite)
1303 RewriteIVExpressions(L, Rewriter);
1305 // Clear the rewriter cache, because values that are in the rewriter's cache
1306 // can be deleted in the loop below, causing the AssertingVH in the cache to
1310 // Now that we're done iterating through lists, clean up any instructions
1311 // which are now dead.
1312 while (!DeadInsts.empty())
1313 if (Instruction *Inst =
1314 dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
1315 RecursivelyDeleteTriviallyDeadInstructions(Inst);
1317 // The Rewriter may not be used from this point on.
1319 // Loop-invariant instructions in the preheader that aren't used in the
1320 // loop may be sunk below the loop to reduce register pressure.
1321 SinkUnusedInvariants(L);
1323 // For completeness, inform IVUsers of the IV use in the newly-created
1324 // loop exit test instruction.
1326 IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)));
1328 // Clean up dead instructions.
1329 Changed |= DeleteDeadPHIs(L->getHeader());
1330 // Check a post-condition.
1331 assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!");
1335 // FIXME: It is an extremely bad idea to indvar substitute anything more
1336 // complex than affine induction variables. Doing so will put expensive
1337 // polynomial evaluations inside of the loop, and the str reduction pass
1338 // currently can only reduce affine polynomials. For now just disable
1339 // indvar subst on anything more complex than an affine addrec, unless
1340 // it can be expanded to a trivial value.
1341 static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) {
1342 // Loop-invariant values are safe.
1343 if (SE->isLoopInvariant(S, L)) return true;
1345 // Affine addrecs are safe. Non-affine are not, because LSR doesn't know how
1346 // to transform them into efficient code.
1347 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
1348 return AR->isAffine();
1350 // An add is safe it all its operands are safe.
1351 if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) {
1352 for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(),
1353 E = Commutative->op_end(); I != E; ++I)
1354 if (!isSafe(*I, L, SE)) return false;
1358 // A cast is safe if its operand is.
1359 if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
1360 return isSafe(C->getOperand(), L, SE);
1362 // A udiv is safe if its operands are.
1363 if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S))
1364 return isSafe(UD->getLHS(), L, SE) &&
1365 isSafe(UD->getRHS(), L, SE);
1367 // SCEVUnknown is always safe.
1368 if (isa<SCEVUnknown>(S))
1371 // Nothing else is safe.
1375 void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
1376 // Rewrite all induction variable expressions in terms of the canonical
1377 // induction variable.
1379 // If there were induction variables of other sizes or offsets, manually
1380 // add the offsets to the primary induction variable and cast, avoiding
1381 // the need for the code evaluation methods to insert induction variables
1382 // of different sizes.
1383 for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) {
1384 Value *Op = UI->getOperandValToReplace();
1385 const Type *UseTy = Op->getType();
1386 Instruction *User = UI->getUser();
1388 // Compute the final addrec to expand into code.
1389 const SCEV *AR = IU->getReplacementExpr(*UI);
1391 // Evaluate the expression out of the loop, if possible.
1392 if (!L->contains(UI->getUser())) {
1393 const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop());
1394 if (SE->isLoopInvariant(ExitVal, L))
1398 // FIXME: It is an extremely bad idea to indvar substitute anything more
1399 // complex than affine induction variables. Doing so will put expensive
1400 // polynomial evaluations inside of the loop, and the str reduction pass
1401 // currently can only reduce affine polynomials. For now just disable
1402 // indvar subst on anything more complex than an affine addrec, unless
1403 // it can be expanded to a trivial value.
1404 if (!isSafe(AR, L, SE))
1407 // Determine the insertion point for this user. By default, insert
1408 // immediately before the user. The SCEVExpander class will automatically
1409 // hoist loop invariants out of the loop. For PHI nodes, there may be
1410 // multiple uses, so compute the nearest common dominator for the
1412 Instruction *InsertPt = User;
1413 if (PHINode *PHI = dyn_cast<PHINode>(InsertPt))
1414 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
1415 if (PHI->getIncomingValue(i) == Op) {
1416 if (InsertPt == User)
1417 InsertPt = PHI->getIncomingBlock(i)->getTerminator();
1420 DT->findNearestCommonDominator(InsertPt->getParent(),
1421 PHI->getIncomingBlock(i))
1425 // Now expand it into actual Instructions and patch it into place.
1426 Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt);
1428 DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
1429 << " into = " << *NewVal << "\n");
1431 if (!isValidRewrite(Op, NewVal)) {
1432 DeadInsts.push_back(NewVal);
1435 // Inform ScalarEvolution that this value is changing. The change doesn't
1436 // affect its value, but it does potentially affect which use lists the
1437 // value will be on after the replacement, which affects ScalarEvolution's
1438 // ability to walk use lists and drop dangling pointers when a value is
1440 SE->forgetValue(User);
1442 // Patch the new value into place.
1444 NewVal->takeName(Op);
1445 if (Instruction *NewValI = dyn_cast<Instruction>(NewVal))
1446 NewValI->setDebugLoc(User->getDebugLoc());
1447 User->replaceUsesOfWith(Op, NewVal);
1448 UI->setOperandValToReplace(NewVal);
1453 // The old value may be dead now.
1454 DeadInsts.push_back(Op);
1458 /// If there's a single exit block, sink any loop-invariant values that
1459 /// were defined in the preheader but not used inside the loop into the
1460 /// exit block to reduce register pressure in the loop.
1461 void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
1462 BasicBlock *ExitBlock = L->getExitBlock();
1463 if (!ExitBlock) return;
1465 BasicBlock *Preheader = L->getLoopPreheader();
1466 if (!Preheader) return;
1468 Instruction *InsertPt = ExitBlock->getFirstNonPHI();
1469 BasicBlock::iterator I = Preheader->getTerminator();
1470 while (I != Preheader->begin()) {
1472 // New instructions were inserted at the end of the preheader.
1473 if (isa<PHINode>(I))
1476 // Don't move instructions which might have side effects, since the side
1477 // effects need to complete before instructions inside the loop. Also don't
1478 // move instructions which might read memory, since the loop may modify
1479 // memory. Note that it's okay if the instruction might have undefined
1480 // behavior: LoopSimplify guarantees that the preheader dominates the exit
1482 if (I->mayHaveSideEffects() || I->mayReadFromMemory())
1485 // Skip debug info intrinsics.
1486 if (isa<DbgInfoIntrinsic>(I))
1489 // Don't sink static AllocaInsts out of the entry block, which would
1490 // turn them into dynamic allocas!
1491 if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
1492 if (AI->isStaticAlloca())
1495 // Determine if there is a use in or before the loop (direct or
1497 bool UsedInLoop = false;
1498 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
1501 BasicBlock *UseBB = cast<Instruction>(U)->getParent();
1502 if (PHINode *P = dyn_cast<PHINode>(U)) {
1504 PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
1505 UseBB = P->getIncomingBlock(i);
1507 if (UseBB == Preheader || L->contains(UseBB)) {
1513 // If there is, the def must remain in the preheader.
1517 // Otherwise, sink it to the exit block.
1518 Instruction *ToMove = I;
1521 if (I != Preheader->begin()) {
1522 // Skip debug info intrinsics.
1525 } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
1527 if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
1533 ToMove->moveBefore(InsertPt);
1539 /// ConvertToSInt - Convert APF to an integer, if possible.
1540 static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
1541 bool isExact = false;
1542 if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
1544 // See if we can convert this to an int64_t
1546 if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
1547 &isExact) != APFloat::opOK || !isExact)
1553 /// HandleFloatingPointIV - If the loop has floating induction variable
1554 /// then insert corresponding integer induction variable if possible.
1556 /// for(double i = 0; i < 10000; ++i)
1558 /// is converted into
1559 /// for(int i = 0; i < 10000; ++i)
1562 void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
1563 unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
1564 unsigned BackEdge = IncomingEdge^1;
1566 // Check incoming value.
1567 ConstantFP *InitValueVal =
1568 dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
1571 if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
1574 // Check IV increment. Reject this PN if increment operation is not
1575 // an add or increment value can not be represented by an integer.
1576 BinaryOperator *Incr =
1577 dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
1578 if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
1580 // If this is not an add of the PHI with a constantfp, or if the constant fp
1581 // is not an integer, bail out.
1582 ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
1584 if (IncValueVal == 0 || Incr->getOperand(0) != PN ||
1585 !ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
1588 // Check Incr uses. One user is PN and the other user is an exit condition
1589 // used by the conditional terminator.
1590 Value::use_iterator IncrUse = Incr->use_begin();
1591 Instruction *U1 = cast<Instruction>(*IncrUse++);
1592 if (IncrUse == Incr->use_end()) return;
1593 Instruction *U2 = cast<Instruction>(*IncrUse++);
1594 if (IncrUse != Incr->use_end()) return;
1596 // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
1597 // only used by a branch, we can't transform it.
1598 FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
1600 Compare = dyn_cast<FCmpInst>(U2);
1601 if (Compare == 0 || !Compare->hasOneUse() ||
1602 !isa<BranchInst>(Compare->use_back()))
1605 BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
1607 // We need to verify that the branch actually controls the iteration count
1608 // of the loop. If not, the new IV can overflow and no one will notice.
1609 // The branch block must be in the loop and one of the successors must be out
1611 assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
1612 if (!L->contains(TheBr->getParent()) ||
1613 (L->contains(TheBr->getSuccessor(0)) &&
1614 L->contains(TheBr->getSuccessor(1))))
1618 // If it isn't a comparison with an integer-as-fp (the exit value), we can't
1620 ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
1622 if (ExitValueVal == 0 ||
1623 !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
1626 // Find new predicate for integer comparison.
1627 CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
1628 switch (Compare->getPredicate()) {
1629 default: return; // Unknown comparison.
1630 case CmpInst::FCMP_OEQ:
1631 case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
1632 case CmpInst::FCMP_ONE:
1633 case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
1634 case CmpInst::FCMP_OGT:
1635 case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
1636 case CmpInst::FCMP_OGE:
1637 case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
1638 case CmpInst::FCMP_OLT:
1639 case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
1640 case CmpInst::FCMP_OLE:
1641 case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
1644 // We convert the floating point induction variable to a signed i32 value if
1645 // we can. This is only safe if the comparison will not overflow in a way
1646 // that won't be trapped by the integer equivalent operations. Check for this
1648 // TODO: We could use i64 if it is native and the range requires it.
1650 // The start/stride/exit values must all fit in signed i32.
1651 if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
1654 // If not actually striding (add x, 0.0), avoid touching the code.
1658 // Positive and negative strides have different safety conditions.
1660 // If we have a positive stride, we require the init to be less than the
1661 // exit value and an equality or less than comparison.
1662 if (InitValue >= ExitValue ||
1663 NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE)
1666 uint32_t Range = uint32_t(ExitValue-InitValue);
1667 if (NewPred == CmpInst::ICMP_SLE) {
1668 // Normalize SLE -> SLT, check for infinite loop.
1669 if (++Range == 0) return; // Range overflows.
1672 unsigned Leftover = Range % uint32_t(IncValue);
1674 // If this is an equality comparison, we require that the strided value
1675 // exactly land on the exit value, otherwise the IV condition will wrap
1676 // around and do things the fp IV wouldn't.
1677 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
1681 // If the stride would wrap around the i32 before exiting, we can't
1682 // transform the IV.
1683 if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
1687 // If we have a negative stride, we require the init to be greater than the
1688 // exit value and an equality or greater than comparison.
1689 if (InitValue >= ExitValue ||
1690 NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE)
1693 uint32_t Range = uint32_t(InitValue-ExitValue);
1694 if (NewPred == CmpInst::ICMP_SGE) {
1695 // Normalize SGE -> SGT, check for infinite loop.
1696 if (++Range == 0) return; // Range overflows.
1699 unsigned Leftover = Range % uint32_t(-IncValue);
1701 // If this is an equality comparison, we require that the strided value
1702 // exactly land on the exit value, otherwise the IV condition will wrap
1703 // around and do things the fp IV wouldn't.
1704 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
1708 // If the stride would wrap around the i32 before exiting, we can't
1709 // transform the IV.
1710 if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
1714 const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
1716 // Insert new integer induction variable.
1717 PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
1718 NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
1719 PN->getIncomingBlock(IncomingEdge));
1722 BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
1723 Incr->getName()+".int", Incr);
1724 NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
1726 ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
1727 ConstantInt::get(Int32Ty, ExitValue),
1728 Compare->getName());
1730 // In the following deletions, PN may become dead and may be deleted.
1731 // Use a WeakVH to observe whether this happens.
1734 // Delete the old floating point exit comparison. The branch starts using the
1736 NewCompare->takeName(Compare);
1737 Compare->replaceAllUsesWith(NewCompare);
1738 RecursivelyDeleteTriviallyDeadInstructions(Compare);
1740 // Delete the old floating point increment.
1741 Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
1742 RecursivelyDeleteTriviallyDeadInstructions(Incr);
1744 // If the FP induction variable still has uses, this is because something else
1745 // in the loop uses its value. In order to canonicalize the induction
1746 // variable, we chose to eliminate the IV and rewrite it in terms of an
1749 // We give preference to sitofp over uitofp because it is faster on most
1752 Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
1753 PN->getParent()->getFirstNonPHI());
1754 PN->replaceAllUsesWith(Conv);
1755 RecursivelyDeleteTriviallyDeadInstructions(PN);
1758 // Add a new IVUsers entry for the newly-created integer PHI.
1760 IU->AddUsersIfInteresting(NewPHI);