1 //===-- LoopPredication.cpp - Guard based loop predication pass -----------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // The LoopPredication pass tries to convert loop variant range checks to loop
10 // invariant by widening checks across loop iterations. For example, it will
13 // for (i = 0; i < n; i++) {
20 // for (i = 0; i < n; i++) {
21 // guard(n - 1 < len);
25 // After this transformation the condition of the guard is loop invariant, so
26 // loop-unswitch can later unswitch the loop by this condition which basically
27 // predicates the loop by the widened condition:
30 // for (i = 0; i < n; i++) {
36 // It's tempting to rely on SCEV here, but it has proven to be problematic.
37 // Generally the facts SCEV provides about the increment step of add
38 // recurrences are true if the backedge of the loop is taken, which implicitly
39 // assumes that the guard doesn't fail. Using these facts to optimize the
40 // guard results in a circular logic where the guard is optimized under the
41 // assumption that it never fails.
43 // For example, in the loop below the induction variable will be marked as nuw
44 // basing on the guard. Basing on nuw the guard predicate will be considered
45 // monotonic. Given a monotonic condition it's tempting to replace the induction
46 // variable in the condition with its value on the last iteration. But this
47 // transformation is not correct, e.g. e = 4, b = 5 breaks the loop.
49 // for (int i = b; i != e; i++)
52 // One of the ways to reason about this problem is to use an inductive proof
53 // approach. Given the loop:
63 // where B(x) and G(x) are predicates that map integers to booleans, we want a
64 // loop invariant expression M such the following program has the same semantics
75 // One solution for M is M = forall X . (G(X) && B(X)) => G(X + Step)
77 // Informal proof that the transformation above is correct:
79 // By the definition of guards we can rewrite the guard condition to:
82 // Let's prove that for each iteration of the loop:
84 // And the condition above can be simplified to G(Start) && M.
89 // Induction step. Assuming G(0) && M => G(I) on the subsequent
92 // B(I) is true because it's the backedge condition.
93 // G(I) is true because the backedge is guarded by this condition.
95 // So M = forall X . (G(X) && B(X)) => G(X + Step) implies G(I + Step).
97 // Note that we can use anything stronger than M, i.e. any condition which
100 // When S = 1 (i.e. forward iterating loop), the transformation is supported
102 // * The loop has a single latch with the condition of the form:
103 // B(X) = latchStart + X <pred> latchLimit,
104 // where <pred> is u<, u<=, s<, or s<=.
105 // * The guard condition is of the form
106 // G(X) = guardStart + X u< guardLimit
108 // For the ult latch comparison case M is:
109 // forall X . guardStart + X u< guardLimit && latchStart + X <u latchLimit =>
110 // guardStart + X + 1 u< guardLimit
112 // The only way the antecedent can be true and the consequent can be false is
114 // X == guardLimit - 1 - guardStart
115 // (and guardLimit is non-zero, but we won't use this latter fact).
116 // If X == guardLimit - 1 - guardStart then the second half of the antecedent is
117 // latchStart + guardLimit - 1 - guardStart u< latchLimit
118 // and its negation is
119 // latchStart + guardLimit - 1 - guardStart u>= latchLimit
121 // In other words, if
122 // latchLimit u<= latchStart + guardLimit - 1 - guardStart
124 // (the ranges below are written in ConstantRange notation, where [A, B) is the
125 // set for (I = A; I != B; I++ /*maywrap*/) yield(I);)
127 // forall X . guardStart + X u< guardLimit &&
128 // latchStart + X u< latchLimit =>
129 // guardStart + X + 1 u< guardLimit
130 // == forall X . guardStart + X u< guardLimit &&
131 // latchStart + X u< latchStart + guardLimit - 1 - guardStart =>
132 // guardStart + X + 1 u< guardLimit
133 // == forall X . (guardStart + X) in [0, guardLimit) &&
134 // (latchStart + X) in [0, latchStart + guardLimit - 1 - guardStart) =>
135 // (guardStart + X + 1) in [0, guardLimit)
136 // == forall X . X in [-guardStart, guardLimit - guardStart) &&
137 // X in [-latchStart, guardLimit - 1 - guardStart) =>
138 // X in [-guardStart - 1, guardLimit - guardStart - 1)
141 // So the widened condition is:
142 // guardStart u< guardLimit &&
143 // latchStart + guardLimit - 1 - guardStart u>= latchLimit
144 // Similarly for ule condition the widened condition is:
145 // guardStart u< guardLimit &&
146 // latchStart + guardLimit - 1 - guardStart u> latchLimit
147 // For slt condition the widened condition is:
148 // guardStart u< guardLimit &&
149 // latchStart + guardLimit - 1 - guardStart s>= latchLimit
150 // For sle condition the widened condition is:
151 // guardStart u< guardLimit &&
152 // latchStart + guardLimit - 1 - guardStart s> latchLimit
154 // When S = -1 (i.e. reverse iterating loop), the transformation is supported
156 // * The loop has a single latch with the condition of the form:
157 // B(X) = X <pred> latchLimit, where <pred> is u>, u>=, s>, or s>=.
158 // * The guard condition is of the form
159 // G(X) = X - 1 u< guardLimit
161 // For the ugt latch comparison case M is:
162 // forall X. X-1 u< guardLimit and X u> latchLimit => X-2 u< guardLimit
164 // The only way the antecedent can be true and the consequent can be false is if
166 // If X == 1 then the second half of the antecedent is
167 // 1 u> latchLimit, and its negation is latchLimit u>= 1.
169 // So the widened condition is:
170 // guardStart u< guardLimit && latchLimit u>= 1.
171 // Similarly for sgt condition the widened condition is:
172 // guardStart u< guardLimit && latchLimit s>= 1.
173 // For uge condition the widened condition is:
174 // guardStart u< guardLimit && latchLimit u> 1.
175 // For sge condition the widened condition is:
176 // guardStart u< guardLimit && latchLimit s> 1.
177 //===----------------------------------------------------------------------===//
179 #include "llvm/Transforms/Scalar/LoopPredication.h"
180 #include "llvm/ADT/Statistic.h"
181 #include "llvm/Analysis/AliasAnalysis.h"
182 #include "llvm/Analysis/BranchProbabilityInfo.h"
183 #include "llvm/Analysis/GuardUtils.h"
184 #include "llvm/Analysis/LoopInfo.h"
185 #include "llvm/Analysis/LoopPass.h"
186 #include "llvm/Analysis/ScalarEvolution.h"
187 #include "llvm/Analysis/ScalarEvolutionExpander.h"
188 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
189 #include "llvm/IR/Function.h"
190 #include "llvm/IR/GlobalValue.h"
191 #include "llvm/IR/IntrinsicInst.h"
192 #include "llvm/IR/Module.h"
193 #include "llvm/IR/PatternMatch.h"
194 #include "llvm/InitializePasses.h"
195 #include "llvm/Pass.h"
196 #include "llvm/Support/CommandLine.h"
197 #include "llvm/Support/Debug.h"
198 #include "llvm/Transforms/Scalar.h"
199 #include "llvm/Transforms/Utils/GuardUtils.h"
200 #include "llvm/Transforms/Utils/Local.h"
201 #include "llvm/Transforms/Utils/LoopUtils.h"
203 #define DEBUG_TYPE "loop-predication"
205 STATISTIC(TotalConsidered, "Number of guards considered");
206 STATISTIC(TotalWidened, "Number of checks widened");
208 using namespace llvm;
210 static cl::opt<bool> EnableIVTruncation("loop-predication-enable-iv-truncation",
211 cl::Hidden, cl::init(true));
213 static cl::opt<bool> EnableCountDownLoop("loop-predication-enable-count-down-loop",
214 cl::Hidden, cl::init(true));
217 SkipProfitabilityChecks("loop-predication-skip-profitability-checks",
218 cl::Hidden, cl::init(false));
220 // This is the scale factor for the latch probability. We use this during
221 // profitability analysis to find other exiting blocks that have a much higher
222 // probability of exiting the loop instead of loop exiting via latch.
223 // This value should be greater than 1 for a sane profitability check.
224 static cl::opt<float> LatchExitProbabilityScale(
225 "loop-predication-latch-probability-scale", cl::Hidden, cl::init(2.0),
226 cl::desc("scale factor for the latch probability. Value should be greater "
227 "than 1. Lower values are ignored"));
229 static cl::opt<bool> PredicateWidenableBranchGuards(
230 "loop-predication-predicate-widenable-branches-to-deopt", cl::Hidden,
231 cl::desc("Whether or not we should predicate guards "
232 "expressed as widenable branches to deoptimize blocks"),
236 /// Represents an induction variable check:
237 /// icmp Pred, <induction variable>, <loop invariant limit>
239 ICmpInst::Predicate Pred;
240 const SCEVAddRecExpr *IV;
242 LoopICmp(ICmpInst::Predicate Pred, const SCEVAddRecExpr *IV,
244 : Pred(Pred), IV(IV), Limit(Limit) {}
247 dbgs() << "LoopICmp Pred = " << Pred << ", IV = " << *IV
248 << ", Limit = " << *Limit << "\n";
252 class LoopPredication {
257 BranchProbabilityInfo *BPI;
260 const DataLayout *DL;
261 BasicBlock *Preheader;
264 bool isSupportedStep(const SCEV* Step);
265 Optional<LoopICmp> parseLoopICmp(ICmpInst *ICI);
266 Optional<LoopICmp> parseLoopLatchICmp();
268 /// Return an insertion point suitable for inserting a safe to speculate
269 /// instruction whose only user will be 'User' which has operands 'Ops'. A
270 /// trivial result would be the at the User itself, but we try to return a
271 /// loop invariant location if possible.
272 Instruction *findInsertPt(Instruction *User, ArrayRef<Value*> Ops);
273 /// Same as above, *except* that this uses the SCEV definition of invariant
274 /// which is that an expression *can be made* invariant via SCEVExpander.
275 /// Thus, this version is only suitable for finding an insert point to be be
276 /// passed to SCEVExpander!
277 Instruction *findInsertPt(Instruction *User, ArrayRef<const SCEV*> Ops);
279 /// Return true if the value is known to produce a single fixed value across
280 /// all iterations on which it executes. Note that this does not imply
281 /// speculation safety. That must be established seperately.
282 bool isLoopInvariantValue(const SCEV* S);
284 Value *expandCheck(SCEVExpander &Expander, Instruction *Guard,
285 ICmpInst::Predicate Pred, const SCEV *LHS,
288 Optional<Value *> widenICmpRangeCheck(ICmpInst *ICI, SCEVExpander &Expander,
290 Optional<Value *> widenICmpRangeCheckIncrementingLoop(LoopICmp LatchCheck,
292 SCEVExpander &Expander,
294 Optional<Value *> widenICmpRangeCheckDecrementingLoop(LoopICmp LatchCheck,
296 SCEVExpander &Expander,
298 unsigned collectChecks(SmallVectorImpl<Value *> &Checks, Value *Condition,
299 SCEVExpander &Expander, Instruction *Guard);
300 bool widenGuardConditions(IntrinsicInst *II, SCEVExpander &Expander);
301 bool widenWidenableBranchGuardConditions(BranchInst *Guard, SCEVExpander &Expander);
302 // If the loop always exits through another block in the loop, we should not
303 // predicate based on the latch check. For example, the latch check can be a
304 // very coarse grained check and there can be more fine grained exit checks
305 // within the loop. We identify such unprofitable loops through BPI.
306 bool isLoopProfitableToPredicate();
308 bool predicateLoopExits(Loop *L, SCEVExpander &Rewriter);
311 LoopPredication(AliasAnalysis *AA, DominatorTree *DT,
312 ScalarEvolution *SE, LoopInfo *LI,
313 BranchProbabilityInfo *BPI)
314 : AA(AA), DT(DT), SE(SE), LI(LI), BPI(BPI) {};
315 bool runOnLoop(Loop *L);
318 class LoopPredicationLegacyPass : public LoopPass {
321 LoopPredicationLegacyPass() : LoopPass(ID) {
322 initializeLoopPredicationLegacyPassPass(*PassRegistry::getPassRegistry());
325 void getAnalysisUsage(AnalysisUsage &AU) const override {
326 AU.addRequired<BranchProbabilityInfoWrapperPass>();
327 getLoopAnalysisUsage(AU);
330 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
333 auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
334 auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
335 auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
336 BranchProbabilityInfo &BPI =
337 getAnalysis<BranchProbabilityInfoWrapperPass>().getBPI();
338 auto *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
339 LoopPredication LP(AA, DT, SE, LI, &BPI);
340 return LP.runOnLoop(L);
344 char LoopPredicationLegacyPass::ID = 0;
345 } // end namespace llvm
347 INITIALIZE_PASS_BEGIN(LoopPredicationLegacyPass, "loop-predication",
348 "Loop predication", false, false)
349 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
350 INITIALIZE_PASS_DEPENDENCY(LoopPass)
351 INITIALIZE_PASS_END(LoopPredicationLegacyPass, "loop-predication",
352 "Loop predication", false, false)
354 Pass *llvm::createLoopPredicationPass() {
355 return new LoopPredicationLegacyPass();
358 PreservedAnalyses LoopPredicationPass::run(Loop &L, LoopAnalysisManager &AM,
359 LoopStandardAnalysisResults &AR,
362 AM.getResult<FunctionAnalysisManagerLoopProxy>(L, AR).getManager();
363 Function *F = L.getHeader()->getParent();
364 auto *BPI = FAM.getCachedResult<BranchProbabilityAnalysis>(*F);
365 LoopPredication LP(&AR.AA, &AR.DT, &AR.SE, &AR.LI, BPI);
366 if (!LP.runOnLoop(&L))
367 return PreservedAnalyses::all();
369 return getLoopPassPreservedAnalyses();
373 LoopPredication::parseLoopICmp(ICmpInst *ICI) {
374 auto Pred = ICI->getPredicate();
375 auto *LHS = ICI->getOperand(0);
376 auto *RHS = ICI->getOperand(1);
378 const SCEV *LHSS = SE->getSCEV(LHS);
379 if (isa<SCEVCouldNotCompute>(LHSS))
381 const SCEV *RHSS = SE->getSCEV(RHS);
382 if (isa<SCEVCouldNotCompute>(RHSS))
385 // Canonicalize RHS to be loop invariant bound, LHS - a loop computable IV
386 if (SE->isLoopInvariant(LHSS, L)) {
388 std::swap(LHSS, RHSS);
389 Pred = ICmpInst::getSwappedPredicate(Pred);
392 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHSS);
393 if (!AR || AR->getLoop() != L)
396 return LoopICmp(Pred, AR, RHSS);
399 Value *LoopPredication::expandCheck(SCEVExpander &Expander,
401 ICmpInst::Predicate Pred, const SCEV *LHS,
403 Type *Ty = LHS->getType();
404 assert(Ty == RHS->getType() && "expandCheck operands have different types?");
406 if (SE->isLoopInvariant(LHS, L) && SE->isLoopInvariant(RHS, L)) {
407 IRBuilder<> Builder(Guard);
408 if (SE->isLoopEntryGuardedByCond(L, Pred, LHS, RHS))
409 return Builder.getTrue();
410 if (SE->isLoopEntryGuardedByCond(L, ICmpInst::getInversePredicate(Pred),
412 return Builder.getFalse();
415 Value *LHSV = Expander.expandCodeFor(LHS, Ty, findInsertPt(Guard, {LHS}));
416 Value *RHSV = Expander.expandCodeFor(RHS, Ty, findInsertPt(Guard, {RHS}));
417 IRBuilder<> Builder(findInsertPt(Guard, {LHSV, RHSV}));
418 return Builder.CreateICmp(Pred, LHSV, RHSV);
422 // Returns true if its safe to truncate the IV to RangeCheckType.
423 // When the IV type is wider than the range operand type, we can still do loop
424 // predication, by generating SCEVs for the range and latch that are of the
425 // same type. We achieve this by generating a SCEV truncate expression for the
426 // latch IV. This is done iff truncation of the IV is a safe operation,
427 // without loss of information.
428 // Another way to achieve this is by generating a wider type SCEV for the
429 // range check operand, however, this needs a more involved check that
430 // operands do not overflow. This can lead to loss of information when the
431 // range operand is of the form: add i32 %offset, %iv. We need to prove that
432 // sext(x + y) is same as sext(x) + sext(y).
433 // This function returns true if we can safely represent the IV type in
434 // the RangeCheckType without loss of information.
435 static bool isSafeToTruncateWideIVType(const DataLayout &DL,
437 const LoopICmp LatchCheck,
438 Type *RangeCheckType) {
439 if (!EnableIVTruncation)
441 assert(DL.getTypeSizeInBits(LatchCheck.IV->getType()) >
442 DL.getTypeSizeInBits(RangeCheckType) &&
443 "Expected latch check IV type to be larger than range check operand "
445 // The start and end values of the IV should be known. This is to guarantee
446 // that truncating the wide type will not lose information.
447 auto *Limit = dyn_cast<SCEVConstant>(LatchCheck.Limit);
448 auto *Start = dyn_cast<SCEVConstant>(LatchCheck.IV->getStart());
449 if (!Limit || !Start)
451 // This check makes sure that the IV does not change sign during loop
452 // iterations. Consider latchType = i64, LatchStart = 5, Pred = ICMP_SGE,
453 // LatchEnd = 2, rangeCheckType = i32. If it's not a monotonic predicate, the
454 // IV wraps around, and the truncation of the IV would lose the range of
455 // iterations between 2^32 and 2^64.
457 if (!SE.isMonotonicPredicate(LatchCheck.IV, LatchCheck.Pred, Increasing))
459 // The active bits should be less than the bits in the RangeCheckType. This
460 // guarantees that truncating the latch check to RangeCheckType is a safe
462 auto RangeCheckTypeBitSize = DL.getTypeSizeInBits(RangeCheckType);
463 return Start->getAPInt().getActiveBits() < RangeCheckTypeBitSize &&
464 Limit->getAPInt().getActiveBits() < RangeCheckTypeBitSize;
468 // Return an LoopICmp describing a latch check equivlent to LatchCheck but with
469 // the requested type if safe to do so. May involve the use of a new IV.
470 static Optional<LoopICmp> generateLoopLatchCheck(const DataLayout &DL,
472 const LoopICmp LatchCheck,
473 Type *RangeCheckType) {
475 auto *LatchType = LatchCheck.IV->getType();
476 if (RangeCheckType == LatchType)
478 // For now, bail out if latch type is narrower than range type.
479 if (DL.getTypeSizeInBits(LatchType) < DL.getTypeSizeInBits(RangeCheckType))
481 if (!isSafeToTruncateWideIVType(DL, SE, LatchCheck, RangeCheckType))
483 // We can now safely identify the truncated version of the IV and limit for
485 LoopICmp NewLatchCheck;
486 NewLatchCheck.Pred = LatchCheck.Pred;
487 NewLatchCheck.IV = dyn_cast<SCEVAddRecExpr>(
488 SE.getTruncateExpr(LatchCheck.IV, RangeCheckType));
489 if (!NewLatchCheck.IV)
491 NewLatchCheck.Limit = SE.getTruncateExpr(LatchCheck.Limit, RangeCheckType);
492 LLVM_DEBUG(dbgs() << "IV of type: " << *LatchType
493 << "can be represented as range check type:"
494 << *RangeCheckType << "\n");
495 LLVM_DEBUG(dbgs() << "LatchCheck.IV: " << *NewLatchCheck.IV << "\n");
496 LLVM_DEBUG(dbgs() << "LatchCheck.Limit: " << *NewLatchCheck.Limit << "\n");
497 return NewLatchCheck;
500 bool LoopPredication::isSupportedStep(const SCEV* Step) {
501 return Step->isOne() || (Step->isAllOnesValue() && EnableCountDownLoop);
504 Instruction *LoopPredication::findInsertPt(Instruction *Use,
505 ArrayRef<Value*> Ops) {
506 for (Value *Op : Ops)
507 if (!L->isLoopInvariant(Op))
509 return Preheader->getTerminator();
512 Instruction *LoopPredication::findInsertPt(Instruction *Use,
513 ArrayRef<const SCEV*> Ops) {
514 // Subtlety: SCEV considers things to be invariant if the value produced is
515 // the same across iterations. This is not the same as being able to
516 // evaluate outside the loop, which is what we actually need here.
517 for (const SCEV *Op : Ops)
518 if (!SE->isLoopInvariant(Op, L) ||
519 !isSafeToExpandAt(Op, Preheader->getTerminator(), *SE))
521 return Preheader->getTerminator();
524 bool LoopPredication::isLoopInvariantValue(const SCEV* S) {
525 // Handling expressions which produce invariant results, but *haven't* yet
526 // been removed from the loop serves two important purposes.
527 // 1) Most importantly, it resolves a pass ordering cycle which would
528 // otherwise need us to iteration licm, loop-predication, and either
529 // loop-unswitch or loop-peeling to make progress on examples with lots of
530 // predicable range checks in a row. (Since, in the general case, we can't
531 // hoist the length checks until the dominating checks have been discharged
532 // as we can't prove doing so is safe.)
533 // 2) As a nice side effect, this exposes the value of peeling or unswitching
534 // much more obviously in the IR. Otherwise, the cost modeling for other
535 // transforms would end up needing to duplicate all of this logic to model a
536 // check which becomes predictable based on a modeled peel or unswitch.
538 // The cost of doing so in the worst case is an extra fill from the stack in
539 // the loop to materialize the loop invariant test value instead of checking
540 // against the original IV which is presumable in a register inside the loop.
541 // Such cases are presumably rare, and hint at missing oppurtunities for
544 if (SE->isLoopInvariant(S, L))
545 // Note: This the SCEV variant, so the original Value* may be within the
546 // loop even though SCEV has proven it is loop invariant.
549 // Handle a particular important case which SCEV doesn't yet know about which
550 // shows up in range checks on arrays with immutable lengths.
551 // TODO: This should be sunk inside SCEV.
552 if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S))
553 if (const auto *LI = dyn_cast<LoadInst>(U->getValue()))
554 if (LI->isUnordered() && L->hasLoopInvariantOperands(LI))
555 if (AA->pointsToConstantMemory(LI->getOperand(0)) ||
556 LI->hasMetadata(LLVMContext::MD_invariant_load))
561 Optional<Value *> LoopPredication::widenICmpRangeCheckIncrementingLoop(
562 LoopICmp LatchCheck, LoopICmp RangeCheck,
563 SCEVExpander &Expander, Instruction *Guard) {
564 auto *Ty = RangeCheck.IV->getType();
565 // Generate the widened condition for the forward loop:
566 // guardStart u< guardLimit &&
567 // latchLimit <pred> guardLimit - 1 - guardStart + latchStart
568 // where <pred> depends on the latch condition predicate. See the file
569 // header comment for the reasoning.
570 // guardLimit - guardStart + latchStart - 1
571 const SCEV *GuardStart = RangeCheck.IV->getStart();
572 const SCEV *GuardLimit = RangeCheck.Limit;
573 const SCEV *LatchStart = LatchCheck.IV->getStart();
574 const SCEV *LatchLimit = LatchCheck.Limit;
575 // Subtlety: We need all the values to be *invariant* across all iterations,
576 // but we only need to check expansion safety for those which *aren't*
577 // already guaranteed to dominate the guard.
578 if (!isLoopInvariantValue(GuardStart) ||
579 !isLoopInvariantValue(GuardLimit) ||
580 !isLoopInvariantValue(LatchStart) ||
581 !isLoopInvariantValue(LatchLimit)) {
582 LLVM_DEBUG(dbgs() << "Can't expand limit check!\n");
585 if (!isSafeToExpandAt(LatchStart, Guard, *SE) ||
586 !isSafeToExpandAt(LatchLimit, Guard, *SE)) {
587 LLVM_DEBUG(dbgs() << "Can't expand limit check!\n");
591 // guardLimit - guardStart + latchStart - 1
593 SE->getAddExpr(SE->getMinusSCEV(GuardLimit, GuardStart),
594 SE->getMinusSCEV(LatchStart, SE->getOne(Ty)));
595 auto LimitCheckPred =
596 ICmpInst::getFlippedStrictnessPredicate(LatchCheck.Pred);
598 LLVM_DEBUG(dbgs() << "LHS: " << *LatchLimit << "\n");
599 LLVM_DEBUG(dbgs() << "RHS: " << *RHS << "\n");
600 LLVM_DEBUG(dbgs() << "Pred: " << LimitCheckPred << "\n");
603 expandCheck(Expander, Guard, LimitCheckPred, LatchLimit, RHS);
604 auto *FirstIterationCheck = expandCheck(Expander, Guard, RangeCheck.Pred,
605 GuardStart, GuardLimit);
606 IRBuilder<> Builder(findInsertPt(Guard, {FirstIterationCheck, LimitCheck}));
607 return Builder.CreateAnd(FirstIterationCheck, LimitCheck);
610 Optional<Value *> LoopPredication::widenICmpRangeCheckDecrementingLoop(
611 LoopICmp LatchCheck, LoopICmp RangeCheck,
612 SCEVExpander &Expander, Instruction *Guard) {
613 auto *Ty = RangeCheck.IV->getType();
614 const SCEV *GuardStart = RangeCheck.IV->getStart();
615 const SCEV *GuardLimit = RangeCheck.Limit;
616 const SCEV *LatchStart = LatchCheck.IV->getStart();
617 const SCEV *LatchLimit = LatchCheck.Limit;
618 // Subtlety: We need all the values to be *invariant* across all iterations,
619 // but we only need to check expansion safety for those which *aren't*
620 // already guaranteed to dominate the guard.
621 if (!isLoopInvariantValue(GuardStart) ||
622 !isLoopInvariantValue(GuardLimit) ||
623 !isLoopInvariantValue(LatchStart) ||
624 !isLoopInvariantValue(LatchLimit)) {
625 LLVM_DEBUG(dbgs() << "Can't expand limit check!\n");
628 if (!isSafeToExpandAt(LatchStart, Guard, *SE) ||
629 !isSafeToExpandAt(LatchLimit, Guard, *SE)) {
630 LLVM_DEBUG(dbgs() << "Can't expand limit check!\n");
633 // The decrement of the latch check IV should be the same as the
635 auto *PostDecLatchCheckIV = LatchCheck.IV->getPostIncExpr(*SE);
636 if (RangeCheck.IV != PostDecLatchCheckIV) {
637 LLVM_DEBUG(dbgs() << "Not the same. PostDecLatchCheckIV: "
638 << *PostDecLatchCheckIV
639 << " and RangeCheckIV: " << *RangeCheck.IV << "\n");
643 // Generate the widened condition for CountDownLoop:
644 // guardStart u< guardLimit &&
645 // latchLimit <pred> 1.
646 // See the header comment for reasoning of the checks.
647 auto LimitCheckPred =
648 ICmpInst::getFlippedStrictnessPredicate(LatchCheck.Pred);
649 auto *FirstIterationCheck = expandCheck(Expander, Guard,
651 GuardStart, GuardLimit);
652 auto *LimitCheck = expandCheck(Expander, Guard, LimitCheckPred, LatchLimit,
654 IRBuilder<> Builder(findInsertPt(Guard, {FirstIterationCheck, LimitCheck}));
655 return Builder.CreateAnd(FirstIterationCheck, LimitCheck);
658 static void normalizePredicate(ScalarEvolution *SE, Loop *L,
660 // LFTR canonicalizes checks to the ICMP_NE/EQ form; normalize back to the
661 // ULT/UGE form for ease of handling by our caller.
662 if (ICmpInst::isEquality(RC.Pred) &&
663 RC.IV->getStepRecurrence(*SE)->isOne() &&
664 SE->isKnownPredicate(ICmpInst::ICMP_ULE, RC.IV->getStart(), RC.Limit))
665 RC.Pred = RC.Pred == ICmpInst::ICMP_NE ?
666 ICmpInst::ICMP_ULT : ICmpInst::ICMP_UGE;
670 /// If ICI can be widened to a loop invariant condition emits the loop
671 /// invariant condition in the loop preheader and return it, otherwise
673 Optional<Value *> LoopPredication::widenICmpRangeCheck(ICmpInst *ICI,
674 SCEVExpander &Expander,
675 Instruction *Guard) {
676 LLVM_DEBUG(dbgs() << "Analyzing ICmpInst condition:\n");
677 LLVM_DEBUG(ICI->dump());
679 // parseLoopStructure guarantees that the latch condition is:
680 // ++i <pred> latchLimit, where <pred> is u<, u<=, s<, or s<=.
681 // We are looking for the range checks of the form:
683 auto RangeCheck = parseLoopICmp(ICI);
685 LLVM_DEBUG(dbgs() << "Failed to parse the loop latch condition!\n");
688 LLVM_DEBUG(dbgs() << "Guard check:\n");
689 LLVM_DEBUG(RangeCheck->dump());
690 if (RangeCheck->Pred != ICmpInst::ICMP_ULT) {
691 LLVM_DEBUG(dbgs() << "Unsupported range check predicate("
692 << RangeCheck->Pred << ")!\n");
695 auto *RangeCheckIV = RangeCheck->IV;
696 if (!RangeCheckIV->isAffine()) {
697 LLVM_DEBUG(dbgs() << "Range check IV is not affine!\n");
700 auto *Step = RangeCheckIV->getStepRecurrence(*SE);
701 // We cannot just compare with latch IV step because the latch and range IVs
702 // may have different types.
703 if (!isSupportedStep(Step)) {
704 LLVM_DEBUG(dbgs() << "Range check and latch have IVs different steps!\n");
707 auto *Ty = RangeCheckIV->getType();
708 auto CurrLatchCheckOpt = generateLoopLatchCheck(*DL, *SE, LatchCheck, Ty);
709 if (!CurrLatchCheckOpt) {
710 LLVM_DEBUG(dbgs() << "Failed to generate a loop latch check "
711 "corresponding to range type: "
716 LoopICmp CurrLatchCheck = *CurrLatchCheckOpt;
717 // At this point, the range and latch step should have the same type, but need
718 // not have the same value (we support both 1 and -1 steps).
719 assert(Step->getType() ==
720 CurrLatchCheck.IV->getStepRecurrence(*SE)->getType() &&
721 "Range and latch steps should be of same type!");
722 if (Step != CurrLatchCheck.IV->getStepRecurrence(*SE)) {
723 LLVM_DEBUG(dbgs() << "Range and latch have different step values!\n");
728 return widenICmpRangeCheckIncrementingLoop(CurrLatchCheck, *RangeCheck,
731 assert(Step->isAllOnesValue() && "Step should be -1!");
732 return widenICmpRangeCheckDecrementingLoop(CurrLatchCheck, *RangeCheck,
737 unsigned LoopPredication::collectChecks(SmallVectorImpl<Value *> &Checks,
739 SCEVExpander &Expander,
740 Instruction *Guard) {
741 unsigned NumWidened = 0;
742 // The guard condition is expected to be in form of:
743 // cond1 && cond2 && cond3 ...
744 // Iterate over subconditions looking for icmp conditions which can be
745 // widened across loop iterations. Widening these conditions remember the
746 // resulting list of subconditions in Checks vector.
747 SmallVector<Value *, 4> Worklist(1, Condition);
748 SmallPtrSet<Value *, 4> Visited;
749 Value *WideableCond = nullptr;
751 Value *Condition = Worklist.pop_back_val();
752 if (!Visited.insert(Condition).second)
756 using namespace llvm::PatternMatch;
757 if (match(Condition, m_And(m_Value(LHS), m_Value(RHS)))) {
758 Worklist.push_back(LHS);
759 Worklist.push_back(RHS);
764 m_Intrinsic<Intrinsic::experimental_widenable_condition>())) {
765 // Pick any, we don't care which
766 WideableCond = Condition;
770 if (ICmpInst *ICI = dyn_cast<ICmpInst>(Condition)) {
771 if (auto NewRangeCheck = widenICmpRangeCheck(ICI, Expander,
773 Checks.push_back(NewRangeCheck.getValue());
779 // Save the condition as is if we can't widen it
780 Checks.push_back(Condition);
781 } while (!Worklist.empty());
782 // At the moment, our matching logic for wideable conditions implicitly
783 // assumes we preserve the form: (br (and Cond, WC())). FIXME
784 // Note that if there were multiple calls to wideable condition in the
785 // traversal, we only need to keep one, and which one is arbitrary.
787 Checks.push_back(WideableCond);
791 bool LoopPredication::widenGuardConditions(IntrinsicInst *Guard,
792 SCEVExpander &Expander) {
793 LLVM_DEBUG(dbgs() << "Processing guard:\n");
794 LLVM_DEBUG(Guard->dump());
797 SmallVector<Value *, 4> Checks;
798 unsigned NumWidened = collectChecks(Checks, Guard->getOperand(0), Expander,
803 TotalWidened += NumWidened;
805 // Emit the new guard condition
806 IRBuilder<> Builder(findInsertPt(Guard, Checks));
807 Value *AllChecks = Builder.CreateAnd(Checks);
808 auto *OldCond = Guard->getOperand(0);
809 Guard->setOperand(0, AllChecks);
810 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
812 LLVM_DEBUG(dbgs() << "Widened checks = " << NumWidened << "\n");
816 bool LoopPredication::widenWidenableBranchGuardConditions(
817 BranchInst *BI, SCEVExpander &Expander) {
818 assert(isGuardAsWidenableBranch(BI) && "Must be!");
819 LLVM_DEBUG(dbgs() << "Processing guard:\n");
820 LLVM_DEBUG(BI->dump());
823 SmallVector<Value *, 4> Checks;
824 unsigned NumWidened = collectChecks(Checks, BI->getCondition(),
829 TotalWidened += NumWidened;
831 // Emit the new guard condition
832 IRBuilder<> Builder(findInsertPt(BI, Checks));
833 Value *AllChecks = Builder.CreateAnd(Checks);
834 auto *OldCond = BI->getCondition();
835 BI->setCondition(AllChecks);
836 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
837 assert(isGuardAsWidenableBranch(BI) &&
838 "Stopped being a guard after transform?");
840 LLVM_DEBUG(dbgs() << "Widened checks = " << NumWidened << "\n");
844 Optional<LoopICmp> LoopPredication::parseLoopLatchICmp() {
845 using namespace PatternMatch;
847 BasicBlock *LoopLatch = L->getLoopLatch();
849 LLVM_DEBUG(dbgs() << "The loop doesn't have a single latch!\n");
853 auto *BI = dyn_cast<BranchInst>(LoopLatch->getTerminator());
854 if (!BI || !BI->isConditional()) {
855 LLVM_DEBUG(dbgs() << "Failed to match the latch terminator!\n");
858 BasicBlock *TrueDest = BI->getSuccessor(0);
860 (TrueDest == L->getHeader() || BI->getSuccessor(1) == L->getHeader()) &&
861 "One of the latch's destinations must be the header");
863 auto *ICI = dyn_cast<ICmpInst>(BI->getCondition());
865 LLVM_DEBUG(dbgs() << "Failed to match the latch condition!\n");
868 auto Result = parseLoopICmp(ICI);
870 LLVM_DEBUG(dbgs() << "Failed to parse the loop latch condition!\n");
874 if (TrueDest != L->getHeader())
875 Result->Pred = ICmpInst::getInversePredicate(Result->Pred);
877 // Check affine first, so if it's not we don't try to compute the step
879 if (!Result->IV->isAffine()) {
880 LLVM_DEBUG(dbgs() << "The induction variable is not affine!\n");
884 auto *Step = Result->IV->getStepRecurrence(*SE);
885 if (!isSupportedStep(Step)) {
886 LLVM_DEBUG(dbgs() << "Unsupported loop stride(" << *Step << ")!\n");
890 auto IsUnsupportedPredicate = [](const SCEV *Step, ICmpInst::Predicate Pred) {
892 return Pred != ICmpInst::ICMP_ULT && Pred != ICmpInst::ICMP_SLT &&
893 Pred != ICmpInst::ICMP_ULE && Pred != ICmpInst::ICMP_SLE;
895 assert(Step->isAllOnesValue() && "Step should be -1!");
896 return Pred != ICmpInst::ICMP_UGT && Pred != ICmpInst::ICMP_SGT &&
897 Pred != ICmpInst::ICMP_UGE && Pred != ICmpInst::ICMP_SGE;
901 normalizePredicate(SE, L, *Result);
902 if (IsUnsupportedPredicate(Step, Result->Pred)) {
903 LLVM_DEBUG(dbgs() << "Unsupported loop latch predicate(" << Result->Pred
912 bool LoopPredication::isLoopProfitableToPredicate() {
913 if (SkipProfitabilityChecks || !BPI)
916 SmallVector<std::pair<BasicBlock *, BasicBlock *>, 8> ExitEdges;
917 L->getExitEdges(ExitEdges);
918 // If there is only one exiting edge in the loop, it is always profitable to
919 // predicate the loop.
920 if (ExitEdges.size() == 1)
923 // Calculate the exiting probabilities of all exiting edges from the loop,
924 // starting with the LatchExitProbability.
925 // Heuristic for profitability: If any of the exiting blocks' probability of
926 // exiting the loop is larger than exiting through the latch block, it's not
927 // profitable to predicate the loop.
928 auto *LatchBlock = L->getLoopLatch();
929 assert(LatchBlock && "Should have a single latch at this point!");
930 auto *LatchTerm = LatchBlock->getTerminator();
931 assert(LatchTerm->getNumSuccessors() == 2 &&
932 "expected to be an exiting block with 2 succs!");
933 unsigned LatchBrExitIdx =
934 LatchTerm->getSuccessor(0) == L->getHeader() ? 1 : 0;
935 BranchProbability LatchExitProbability =
936 BPI->getEdgeProbability(LatchBlock, LatchBrExitIdx);
938 // Protect against degenerate inputs provided by the user. Providing a value
939 // less than one, can invert the definition of profitable loop predication.
940 float ScaleFactor = LatchExitProbabilityScale;
941 if (ScaleFactor < 1) {
944 << "Ignored user setting for loop-predication-latch-probability-scale: "
945 << LatchExitProbabilityScale << "\n");
946 LLVM_DEBUG(dbgs() << "The value is set to 1.0\n");
949 const auto LatchProbabilityThreshold =
950 LatchExitProbability * ScaleFactor;
952 for (const auto &ExitEdge : ExitEdges) {
953 BranchProbability ExitingBlockProbability =
954 BPI->getEdgeProbability(ExitEdge.first, ExitEdge.second);
955 // Some exiting edge has higher probability than the latch exiting edge.
956 // No longer profitable to predicate.
957 if (ExitingBlockProbability > LatchProbabilityThreshold)
960 // Using BPI, we have concluded that the most probable way to exit from the
961 // loop is through the latch (or there's no profile information and all
962 // exits are equally likely).
966 /// If we can (cheaply) find a widenable branch which controls entry into the
968 static BranchInst *FindWidenableTerminatorAboveLoop(Loop *L, LoopInfo &LI) {
969 // Walk back through any unconditional executed blocks and see if we can find
970 // a widenable condition which seems to control execution of this loop. Note
971 // that we predict that maythrow calls are likely untaken and thus that it's
972 // profitable to widen a branch before a maythrow call with a condition
973 // afterwards even though that may cause the slow path to run in a case where
974 // it wouldn't have otherwise.
975 BasicBlock *BB = L->getLoopPreheader();
979 if (BasicBlock *Pred = BB->getSinglePredecessor())
980 if (BB == Pred->getSingleSuccessor()) {
987 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
988 auto *Term = Pred->getTerminator();
991 BasicBlock *IfTrueBB, *IfFalseBB;
992 if (parseWidenableBranch(Term, Cond, WC, IfTrueBB, IfFalseBB) &&
994 return cast<BranchInst>(Term);
999 /// Return the minimum of all analyzeable exit counts. This is an upper bound
1000 /// on the actual exit count. If there are not at least two analyzeable exits,
1001 /// returns SCEVCouldNotCompute.
1002 static const SCEV *getMinAnalyzeableBackedgeTakenCount(ScalarEvolution &SE,
1005 SmallVector<BasicBlock *, 16> ExitingBlocks;
1006 L->getExitingBlocks(ExitingBlocks);
1008 SmallVector<const SCEV *, 4> ExitCounts;
1009 for (BasicBlock *ExitingBB : ExitingBlocks) {
1010 const SCEV *ExitCount = SE.getExitCount(L, ExitingBB);
1011 if (isa<SCEVCouldNotCompute>(ExitCount))
1013 assert(DT.dominates(ExitingBB, L->getLoopLatch()) &&
1014 "We should only have known counts for exiting blocks that "
1016 ExitCounts.push_back(ExitCount);
1018 if (ExitCounts.size() < 2)
1019 return SE.getCouldNotCompute();
1020 return SE.getUMinFromMismatchedTypes(ExitCounts);
1023 /// Return true if we can be fairly sure that executing block BB will probably
1024 /// lead to executing an __llvm_deoptimize. This is a profitability heuristic,
1025 /// not a legality constraint.
1026 static bool isVeryLikelyToDeopt(BasicBlock *BB) {
1027 while (BB->getUniqueSuccessor())
1028 // Will skip side effects, that's okay
1029 BB = BB->getUniqueSuccessor();
1031 return BB->getTerminatingDeoptimizeCall();
1034 /// This implements an analogous, but entirely distinct transform from the main
1035 /// loop predication transform. This one is phrased in terms of using a
1036 /// widenable branch *outside* the loop to allow us to simplify loop exits in a
1037 /// following loop. This is close in spirit to the IndVarSimplify transform
1038 /// of the same name, but is materially different widening loosens legality
1040 bool LoopPredication::predicateLoopExits(Loop *L, SCEVExpander &Rewriter) {
1041 // The transformation performed here aims to widen a widenable condition
1042 // above the loop such that all analyzeable exit leading to deopt are dead.
1043 // It assumes that the latch is the dominant exit for profitability and that
1044 // exits branching to deoptimizing blocks are rarely taken. It relies on the
1045 // semantics of widenable expressions for legality. (i.e. being able to fall
1046 // down the widenable path spuriously allows us to ignore exit order,
1047 // unanalyzeable exits, side effects, exceptional exits, and other challenges
1048 // which restrict the applicability of the non-WC based version of this
1049 // transform in IndVarSimplify.)
1051 // NOTE ON POISON/UNDEF - We're hoisting an expression above guards which may
1052 // imply flags on the expression being hoisted and inserting new uses (flags
1053 // are only correct for current uses). The result is that we may be
1054 // inserting a branch on the value which can be either poison or undef. In
1055 // this case, the branch can legally go either way; we just need to avoid
1056 // introducing UB. This is achieved through the use of the freeze
1059 SmallVector<BasicBlock *, 16> ExitingBlocks;
1060 L->getExitingBlocks(ExitingBlocks);
1062 if (ExitingBlocks.empty())
1063 return false; // Nothing to do.
1065 auto *Latch = L->getLoopLatch();
1069 auto *WidenableBR = FindWidenableTerminatorAboveLoop(L, *LI);
1073 const SCEV *LatchEC = SE->getExitCount(L, Latch);
1074 if (isa<SCEVCouldNotCompute>(LatchEC))
1075 return false; // profitability - want hot exit in analyzeable set
1077 // At this point, we have found an analyzeable latch, and a widenable
1078 // condition above the loop. If we have a widenable exit within the loop
1079 // (for which we can't compute exit counts), drop the ability to further
1080 // widen so that we gain ability to analyze it's exit count and perform this
1081 // transform. TODO: It'd be nice to know for sure the exit became
1082 // analyzeable after dropping widenability.
1084 bool Invalidate = false;
1086 for (auto *ExitingBB : ExitingBlocks) {
1087 if (LI->getLoopFor(ExitingBB) != L)
1090 auto *BI = dyn_cast<BranchInst>(ExitingBB->getTerminator());
1095 BasicBlock *IfTrueBB, *IfFalseBB;
1096 if (parseWidenableBranch(BI, Cond, WC, IfTrueBB, IfFalseBB) &&
1097 L->contains(IfTrueBB)) {
1098 WC->set(ConstantInt::getTrue(IfTrueBB->getContext()));
1106 // The use of umin(all analyzeable exits) instead of latch is subtle, but
1107 // important for profitability. We may have a loop which hasn't been fully
1108 // canonicalized just yet. If the exit we chose to widen is provably never
1109 // taken, we want the widened form to *also* be provably never taken. We
1110 // can't guarantee this as a current unanalyzeable exit may later become
1111 // analyzeable, but we can at least avoid the obvious cases.
1112 const SCEV *MinEC = getMinAnalyzeableBackedgeTakenCount(*SE, *DT, L);
1113 if (isa<SCEVCouldNotCompute>(MinEC) || MinEC->getType()->isPointerTy() ||
1114 !SE->isLoopInvariant(MinEC, L) ||
1115 !isSafeToExpandAt(MinEC, WidenableBR, *SE))
1118 // Subtlety: We need to avoid inserting additional uses of the WC. We know
1119 // that it can only have one transitive use at the moment, and thus moving
1120 // that use to just before the branch and inserting code before it and then
1121 // modifying the operand is legal.
1122 auto *IP = cast<Instruction>(WidenableBR->getCondition());
1123 IP->moveBefore(WidenableBR);
1124 Rewriter.setInsertPoint(IP);
1127 bool Changed = false;
1128 Value *MinECV = nullptr; // lazily generated if needed
1129 for (BasicBlock *ExitingBB : ExitingBlocks) {
1130 // If our exiting block exits multiple loops, we can only rewrite the
1131 // innermost one. Otherwise, we're changing how many times the innermost
1132 // loop runs before it exits.
1133 if (LI->getLoopFor(ExitingBB) != L)
1136 // Can't rewrite non-branch yet.
1137 auto *BI = dyn_cast<BranchInst>(ExitingBB->getTerminator());
1141 // If already constant, nothing to do.
1142 if (isa<Constant>(BI->getCondition()))
1145 const SCEV *ExitCount = SE->getExitCount(L, ExitingBB);
1146 if (isa<SCEVCouldNotCompute>(ExitCount) ||
1147 ExitCount->getType()->isPointerTy() ||
1148 !isSafeToExpandAt(ExitCount, WidenableBR, *SE))
1151 const bool ExitIfTrue = !L->contains(*succ_begin(ExitingBB));
1152 BasicBlock *ExitBB = BI->getSuccessor(ExitIfTrue ? 0 : 1);
1153 if (!isVeryLikelyToDeopt(ExitBB))
1154 // Profitability: indicator of rarely/never taken exit
1157 // If we found a widenable exit condition, do two things:
1158 // 1) fold the widened exit test into the widenable condition
1159 // 2) fold the branch to untaken - avoids infinite looping
1161 Value *ECV = Rewriter.expandCodeFor(ExitCount);
1163 MinECV = Rewriter.expandCodeFor(MinEC);
1164 Value *RHS = MinECV;
1165 if (ECV->getType() != RHS->getType()) {
1166 Type *WiderTy = SE->getWiderType(ECV->getType(), RHS->getType());
1167 ECV = B.CreateZExt(ECV, WiderTy);
1168 RHS = B.CreateZExt(RHS, WiderTy);
1170 assert(!Latch || DT->dominates(ExitingBB, Latch));
1171 Value *NewCond = B.CreateICmp(ICmpInst::ICMP_UGT, ECV, RHS);
1172 // Freeze poison or undef to an arbitrary bit pattern to ensure we can
1173 // branch without introducing UB. See NOTE ON POISON/UNDEF above for
1175 NewCond = B.CreateFreeze(NewCond);
1177 widenWidenableBranch(WidenableBR, NewCond);
1179 Value *OldCond = BI->getCondition();
1180 BI->setCondition(ConstantInt::get(OldCond->getType(), !ExitIfTrue));
1185 // We just mutated a bunch of loop exits changing there exit counts
1186 // widely. We need to force recomputation of the exit counts given these
1187 // changes. Note that all of the inserted exits are never taken, and
1188 // should be removed next time the CFG is modified.
1193 bool LoopPredication::runOnLoop(Loop *Loop) {
1196 LLVM_DEBUG(dbgs() << "Analyzing ");
1197 LLVM_DEBUG(L->dump());
1199 Module *M = L->getHeader()->getModule();
1201 // There is nothing to do if the module doesn't use guards
1203 M->getFunction(Intrinsic::getName(Intrinsic::experimental_guard));
1204 bool HasIntrinsicGuards = GuardDecl && !GuardDecl->use_empty();
1205 auto *WCDecl = M->getFunction(
1206 Intrinsic::getName(Intrinsic::experimental_widenable_condition));
1207 bool HasWidenableConditions =
1208 PredicateWidenableBranchGuards && WCDecl && !WCDecl->use_empty();
1209 if (!HasIntrinsicGuards && !HasWidenableConditions)
1212 DL = &M->getDataLayout();
1214 Preheader = L->getLoopPreheader();
1218 auto LatchCheckOpt = parseLoopLatchICmp();
1221 LatchCheck = *LatchCheckOpt;
1223 LLVM_DEBUG(dbgs() << "Latch check:\n");
1224 LLVM_DEBUG(LatchCheck.dump());
1226 if (!isLoopProfitableToPredicate()) {
1227 LLVM_DEBUG(dbgs() << "Loop not profitable to predicate!\n");
1230 // Collect all the guards into a vector and process later, so as not
1231 // to invalidate the instruction iterator.
1232 SmallVector<IntrinsicInst *, 4> Guards;
1233 SmallVector<BranchInst *, 4> GuardsAsWidenableBranches;
1234 for (const auto BB : L->blocks()) {
1237 Guards.push_back(cast<IntrinsicInst>(&I));
1238 if (PredicateWidenableBranchGuards &&
1239 isGuardAsWidenableBranch(BB->getTerminator()))
1240 GuardsAsWidenableBranches.push_back(
1241 cast<BranchInst>(BB->getTerminator()));
1244 SCEVExpander Expander(*SE, *DL, "loop-predication");
1245 bool Changed = false;
1246 for (auto *Guard : Guards)
1247 Changed |= widenGuardConditions(Guard, Expander);
1248 for (auto *Guard : GuardsAsWidenableBranches)
1249 Changed |= widenWidenableBranchGuardConditions(Guard, Expander);
1250 Changed |= predicateLoopExits(L, Expander);