1 //===- CorrelatedValuePropagation.cpp - Propagate CFG-derived info --------===//
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 // This file implements the Correlated Value Propagation pass.
11 //===----------------------------------------------------------------------===//
13 #include "llvm/Transforms/Scalar/CorrelatedValuePropagation.h"
14 #include "llvm/ADT/DepthFirstIterator.h"
15 #include "llvm/ADT/Optional.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/Analysis/DomTreeUpdater.h"
19 #include "llvm/Analysis/GlobalsModRef.h"
20 #include "llvm/Analysis/InstructionSimplify.h"
21 #include "llvm/Analysis/LazyValueInfo.h"
22 #include "llvm/IR/Attributes.h"
23 #include "llvm/IR/BasicBlock.h"
24 #include "llvm/IR/CFG.h"
25 #include "llvm/IR/CallSite.h"
26 #include "llvm/IR/Constant.h"
27 #include "llvm/IR/ConstantRange.h"
28 #include "llvm/IR/Constants.h"
29 #include "llvm/IR/DerivedTypes.h"
30 #include "llvm/IR/Function.h"
31 #include "llvm/IR/IRBuilder.h"
32 #include "llvm/IR/InstrTypes.h"
33 #include "llvm/IR/Instruction.h"
34 #include "llvm/IR/Instructions.h"
35 #include "llvm/IR/IntrinsicInst.h"
36 #include "llvm/IR/Operator.h"
37 #include "llvm/IR/PassManager.h"
38 #include "llvm/IR/Type.h"
39 #include "llvm/IR/Value.h"
40 #include "llvm/InitializePasses.h"
41 #include "llvm/Pass.h"
42 #include "llvm/Support/Casting.h"
43 #include "llvm/Support/CommandLine.h"
44 #include "llvm/Support/Debug.h"
45 #include "llvm/Support/raw_ostream.h"
46 #include "llvm/Transforms/Scalar.h"
47 #include "llvm/Transforms/Utils/Local.h"
53 #define DEBUG_TYPE "correlated-value-propagation"
55 STATISTIC(NumPhis, "Number of phis propagated");
56 STATISTIC(NumPhiCommon, "Number of phis deleted via common incoming value");
57 STATISTIC(NumSelects, "Number of selects propagated");
58 STATISTIC(NumMemAccess, "Number of memory access targets propagated");
59 STATISTIC(NumCmps, "Number of comparisons propagated");
60 STATISTIC(NumReturns, "Number of return values propagated");
61 STATISTIC(NumDeadCases, "Number of switch cases removed");
62 STATISTIC(NumSDivs, "Number of sdiv converted to udiv");
63 STATISTIC(NumUDivs, "Number of udivs whose width was decreased");
64 STATISTIC(NumAShrs, "Number of ashr converted to lshr");
65 STATISTIC(NumSRems, "Number of srem converted to urem");
66 STATISTIC(NumSExt, "Number of sext converted to zext");
67 STATISTIC(NumAnd, "Number of ands removed");
68 STATISTIC(NumNW, "Number of no-wrap deductions");
69 STATISTIC(NumNSW, "Number of no-signed-wrap deductions");
70 STATISTIC(NumNUW, "Number of no-unsigned-wrap deductions");
71 STATISTIC(NumAddNW, "Number of no-wrap deductions for add");
72 STATISTIC(NumAddNSW, "Number of no-signed-wrap deductions for add");
73 STATISTIC(NumAddNUW, "Number of no-unsigned-wrap deductions for add");
74 STATISTIC(NumSubNW, "Number of no-wrap deductions for sub");
75 STATISTIC(NumSubNSW, "Number of no-signed-wrap deductions for sub");
76 STATISTIC(NumSubNUW, "Number of no-unsigned-wrap deductions for sub");
77 STATISTIC(NumMulNW, "Number of no-wrap deductions for mul");
78 STATISTIC(NumMulNSW, "Number of no-signed-wrap deductions for mul");
79 STATISTIC(NumMulNUW, "Number of no-unsigned-wrap deductions for mul");
80 STATISTIC(NumShlNW, "Number of no-wrap deductions for shl");
81 STATISTIC(NumShlNSW, "Number of no-signed-wrap deductions for shl");
82 STATISTIC(NumShlNUW, "Number of no-unsigned-wrap deductions for shl");
83 STATISTIC(NumOverflows, "Number of overflow checks removed");
84 STATISTIC(NumSaturating,
85 "Number of saturating arithmetics converted to normal arithmetics");
87 static cl::opt<bool> DontAddNoWrapFlags("cvp-dont-add-nowrap-flags", cl::init(false));
91 class CorrelatedValuePropagation : public FunctionPass {
95 CorrelatedValuePropagation(): FunctionPass(ID) {
96 initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
99 bool runOnFunction(Function &F) override;
101 void getAnalysisUsage(AnalysisUsage &AU) const override {
102 AU.addRequired<DominatorTreeWrapperPass>();
103 AU.addRequired<LazyValueInfoWrapperPass>();
104 AU.addPreserved<GlobalsAAWrapperPass>();
105 AU.addPreserved<DominatorTreeWrapperPass>();
106 AU.addPreserved<LazyValueInfoWrapperPass>();
110 } // end anonymous namespace
112 char CorrelatedValuePropagation::ID = 0;
114 INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
115 "Value Propagation", false, false)
116 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
117 INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)
118 INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
119 "Value Propagation", false, false)
121 // Public interface to the Value Propagation pass
122 Pass *llvm::createCorrelatedValuePropagationPass() {
123 return new CorrelatedValuePropagation();
126 static bool processSelect(SelectInst *S, LazyValueInfo *LVI) {
127 if (S->getType()->isVectorTy()) return false;
128 if (isa<Constant>(S->getOperand(0))) return false;
130 Constant *C = LVI->getConstant(S->getCondition(), S->getParent(), S);
131 if (!C) return false;
133 ConstantInt *CI = dyn_cast<ConstantInt>(C);
134 if (!CI) return false;
136 Value *ReplaceWith = S->getTrueValue();
137 Value *Other = S->getFalseValue();
138 if (!CI->isOne()) std::swap(ReplaceWith, Other);
139 if (ReplaceWith == S) ReplaceWith = UndefValue::get(S->getType());
141 S->replaceAllUsesWith(ReplaceWith);
142 S->eraseFromParent();
149 /// Try to simplify a phi with constant incoming values that match the edge
150 /// values of a non-constant value on all other edges:
152 /// %isnull = icmp eq i8* %x, null
153 /// br i1 %isnull, label %bb2, label %bb1
157 /// %r = phi i8* [ %x, %bb1 ], [ null, %bb0 ]
160 static bool simplifyCommonValuePhi(PHINode *P, LazyValueInfo *LVI,
162 // Collect incoming constants and initialize possible common value.
163 SmallVector<std::pair<Constant *, unsigned>, 4> IncomingConstants;
164 Value *CommonValue = nullptr;
165 for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
166 Value *Incoming = P->getIncomingValue(i);
167 if (auto *IncomingConstant = dyn_cast<Constant>(Incoming)) {
168 IncomingConstants.push_back(std::make_pair(IncomingConstant, i));
169 } else if (!CommonValue) {
170 // The potential common value is initialized to the first non-constant.
171 CommonValue = Incoming;
172 } else if (Incoming != CommonValue) {
173 // There can be only one non-constant common value.
178 if (!CommonValue || IncomingConstants.empty())
181 // The common value must be valid in all incoming blocks.
182 BasicBlock *ToBB = P->getParent();
183 if (auto *CommonInst = dyn_cast<Instruction>(CommonValue))
184 if (!DT->dominates(CommonInst, ToBB))
187 // We have a phi with exactly 1 variable incoming value and 1 or more constant
188 // incoming values. See if all constant incoming values can be mapped back to
189 // the same incoming variable value.
190 for (auto &IncomingConstant : IncomingConstants) {
191 Constant *C = IncomingConstant.first;
192 BasicBlock *IncomingBB = P->getIncomingBlock(IncomingConstant.second);
193 if (C != LVI->getConstantOnEdge(CommonValue, IncomingBB, ToBB, P))
197 // All constant incoming values map to the same variable along the incoming
198 // edges of the phi. The phi is unnecessary. However, we must drop all
199 // poison-generating flags to ensure that no poison is propagated to the phi
200 // location by performing this substitution.
201 // Warning: If the underlying analysis changes, this may not be enough to
202 // guarantee that poison is not propagated.
203 // TODO: We may be able to re-infer flags by re-analyzing the instruction.
204 if (auto *CommonInst = dyn_cast<Instruction>(CommonValue))
205 CommonInst->dropPoisonGeneratingFlags();
206 P->replaceAllUsesWith(CommonValue);
207 P->eraseFromParent();
212 static bool processPHI(PHINode *P, LazyValueInfo *LVI, DominatorTree *DT,
213 const SimplifyQuery &SQ) {
214 bool Changed = false;
216 BasicBlock *BB = P->getParent();
217 for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
218 Value *Incoming = P->getIncomingValue(i);
219 if (isa<Constant>(Incoming)) continue;
221 Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB, P);
223 // Look if the incoming value is a select with a scalar condition for which
224 // LVI can tells us the value. In that case replace the incoming value with
225 // the appropriate value of the select. This often allows us to remove the
228 SelectInst *SI = dyn_cast<SelectInst>(Incoming);
231 Value *Condition = SI->getCondition();
232 if (!Condition->getType()->isVectorTy()) {
233 if (Constant *C = LVI->getConstantOnEdge(
234 Condition, P->getIncomingBlock(i), BB, P)) {
235 if (C->isOneValue()) {
236 V = SI->getTrueValue();
237 } else if (C->isZeroValue()) {
238 V = SI->getFalseValue();
240 // Once LVI learns to handle vector types, we could also add support
241 // for vector type constants that are not all zeroes or all ones.
245 // Look if the select has a constant but LVI tells us that the incoming
246 // value can never be that constant. In that case replace the incoming
247 // value with the other value of the select. This often allows us to
248 // remove the select later.
250 Constant *C = dyn_cast<Constant>(SI->getFalseValue());
253 if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
254 P->getIncomingBlock(i), BB, P) !=
255 LazyValueInfo::False)
257 V = SI->getTrueValue();
260 LLVM_DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
263 P->setIncomingValue(i, V);
267 if (Value *V = SimplifyInstruction(P, SQ)) {
268 P->replaceAllUsesWith(V);
269 P->eraseFromParent();
274 Changed = simplifyCommonValuePhi(P, LVI, DT);
282 static bool processMemAccess(Instruction *I, LazyValueInfo *LVI) {
283 Value *Pointer = nullptr;
284 if (LoadInst *L = dyn_cast<LoadInst>(I))
285 Pointer = L->getPointerOperand();
287 Pointer = cast<StoreInst>(I)->getPointerOperand();
289 if (isa<Constant>(Pointer)) return false;
291 Constant *C = LVI->getConstant(Pointer, I->getParent(), I);
292 if (!C) return false;
295 I->replaceUsesOfWith(Pointer, C);
299 /// See if LazyValueInfo's ability to exploit edge conditions or range
300 /// information is sufficient to prove this comparison. Even for local
301 /// conditions, this can sometimes prove conditions instcombine can't by
302 /// exploiting range information.
303 static bool processCmp(CmpInst *Cmp, LazyValueInfo *LVI) {
304 Value *Op0 = Cmp->getOperand(0);
305 auto *C = dyn_cast<Constant>(Cmp->getOperand(1));
309 // As a policy choice, we choose not to waste compile time on anything where
310 // the comparison is testing local values. While LVI can sometimes reason
311 // about such cases, it's not its primary purpose. We do make sure to do
312 // the block local query for uses from terminator instructions, but that's
313 // handled in the code for each terminator.
314 auto *I = dyn_cast<Instruction>(Op0);
315 if (I && I->getParent() == Cmp->getParent())
318 LazyValueInfo::Tristate Result =
319 LVI->getPredicateAt(Cmp->getPredicate(), Op0, C, Cmp);
320 if (Result == LazyValueInfo::Unknown)
324 Constant *TorF = ConstantInt::get(Type::getInt1Ty(Cmp->getContext()), Result);
325 Cmp->replaceAllUsesWith(TorF);
326 Cmp->eraseFromParent();
330 /// Simplify a switch instruction by removing cases which can never fire. If the
331 /// uselessness of a case could be determined locally then constant propagation
332 /// would already have figured it out. Instead, walk the predecessors and
333 /// statically evaluate cases based on information available on that edge. Cases
334 /// that cannot fire no matter what the incoming edge can safely be removed. If
335 /// a case fires on every incoming edge then the entire switch can be removed
336 /// and replaced with a branch to the case destination.
337 static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
339 DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Lazy);
340 Value *Cond = I->getCondition();
341 BasicBlock *BB = I->getParent();
343 // If the condition was defined in same block as the switch then LazyValueInfo
344 // currently won't say anything useful about it, though in theory it could.
345 if (isa<Instruction>(Cond) && cast<Instruction>(Cond)->getParent() == BB)
348 // If the switch is unreachable then trying to improve it is a waste of time.
349 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
350 if (PB == PE) return false;
352 // Analyse each switch case in turn.
353 bool Changed = false;
354 DenseMap<BasicBlock*, int> SuccessorsCount;
355 for (auto *Succ : successors(BB))
356 SuccessorsCount[Succ]++;
358 { // Scope for SwitchInstProfUpdateWrapper. It must not live during
359 // ConstantFoldTerminator() as the underlying SwitchInst can be changed.
360 SwitchInstProfUpdateWrapper SI(*I);
362 for (auto CI = SI->case_begin(), CE = SI->case_end(); CI != CE;) {
363 ConstantInt *Case = CI->getCaseValue();
365 // Check to see if the switch condition is equal to/not equal to the case
366 // value on every incoming edge, equal/not equal being the same each time.
367 LazyValueInfo::Tristate State = LazyValueInfo::Unknown;
368 for (pred_iterator PI = PB; PI != PE; ++PI) {
369 // Is the switch condition equal to the case value?
370 LazyValueInfo::Tristate Value = LVI->getPredicateOnEdge(CmpInst::ICMP_EQ,
373 // Give up on this case if nothing is known.
374 if (Value == LazyValueInfo::Unknown) {
375 State = LazyValueInfo::Unknown;
379 // If this was the first edge to be visited, record that all other edges
380 // need to give the same result.
386 // If this case is known to fire for some edges and known not to fire for
387 // others then there is nothing we can do - give up.
388 if (Value != State) {
389 State = LazyValueInfo::Unknown;
394 if (State == LazyValueInfo::False) {
395 // This case never fires - remove it.
396 BasicBlock *Succ = CI->getCaseSuccessor();
397 Succ->removePredecessor(BB);
398 CI = SI.removeCase(CI);
401 // The condition can be modified by removePredecessor's PHI simplification
403 Cond = SI->getCondition();
407 if (--SuccessorsCount[Succ] == 0)
408 DTU.applyUpdatesPermissive({{DominatorTree::Delete, BB, Succ}});
411 if (State == LazyValueInfo::True) {
412 // This case always fires. Arrange for the switch to be turned into an
413 // unconditional branch by replacing the switch condition with the case
415 SI->setCondition(Case);
416 NumDeadCases += SI->getNumCases();
421 // Increment the case iterator since we didn't delete it.
427 // If the switch has been simplified to the point where it can be replaced
428 // by a branch then do so now.
429 ConstantFoldTerminator(BB, /*DeleteDeadConditions = */ false,
430 /*TLI = */ nullptr, &DTU);
434 // See if we can prove that the given binary op intrinsic will not overflow.
435 static bool willNotOverflow(BinaryOpIntrinsic *BO, LazyValueInfo *LVI) {
436 ConstantRange LRange = LVI->getConstantRange(
437 BO->getLHS(), BO->getParent(), BO);
438 ConstantRange RRange = LVI->getConstantRange(
439 BO->getRHS(), BO->getParent(), BO);
440 ConstantRange NWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
441 BO->getBinaryOp(), RRange, BO->getNoWrapKind());
442 return NWRegion.contains(LRange);
445 static void setDeducedOverflowingFlags(Value *V, Instruction::BinaryOps Opcode,
446 bool NewNSW, bool NewNUW) {
447 Statistic *OpcNW, *OpcNSW, *OpcNUW;
449 case Instruction::Add:
454 case Instruction::Sub:
459 case Instruction::Mul:
464 case Instruction::Shl:
470 llvm_unreachable("Will not be called with other binops");
473 auto *Inst = dyn_cast<Instruction>(V);
480 Inst->setHasNoSignedWrap();
488 Inst->setHasNoUnsignedWrap();
492 static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI);
494 // Rewrite this with.overflow intrinsic as non-overflowing.
495 static void processOverflowIntrinsic(WithOverflowInst *WO, LazyValueInfo *LVI) {
497 Instruction::BinaryOps Opcode = WO->getBinaryOp();
498 bool NSW = WO->isSigned();
499 bool NUW = !WO->isSigned();
502 B.CreateBinOp(Opcode, WO->getLHS(), WO->getRHS(), WO->getName());
503 setDeducedOverflowingFlags(NewOp, Opcode, NSW, NUW);
505 StructType *ST = cast<StructType>(WO->getType());
506 Constant *Struct = ConstantStruct::get(ST,
507 { UndefValue::get(ST->getElementType(0)),
508 ConstantInt::getFalse(ST->getElementType(1)) });
509 Value *NewI = B.CreateInsertValue(Struct, NewOp, 0);
510 WO->replaceAllUsesWith(NewI);
511 WO->eraseFromParent();
514 // See if we can infer the other no-wrap too.
515 if (auto *BO = dyn_cast<BinaryOperator>(NewOp))
516 processBinOp(BO, LVI);
519 static void processSaturatingInst(SaturatingInst *SI, LazyValueInfo *LVI) {
520 Instruction::BinaryOps Opcode = SI->getBinaryOp();
521 bool NSW = SI->isSigned();
522 bool NUW = !SI->isSigned();
523 BinaryOperator *BinOp = BinaryOperator::Create(
524 Opcode, SI->getLHS(), SI->getRHS(), SI->getName(), SI);
525 BinOp->setDebugLoc(SI->getDebugLoc());
526 setDeducedOverflowingFlags(BinOp, Opcode, NSW, NUW);
528 SI->replaceAllUsesWith(BinOp);
529 SI->eraseFromParent();
532 // See if we can infer the other no-wrap too.
533 if (auto *BO = dyn_cast<BinaryOperator>(BinOp))
534 processBinOp(BO, LVI);
537 /// Infer nonnull attributes for the arguments at the specified callsite.
538 static bool processCallSite(CallSite CS, LazyValueInfo *LVI) {
539 SmallVector<unsigned, 4> ArgNos;
542 if (auto *WO = dyn_cast<WithOverflowInst>(CS.getInstruction())) {
543 if (WO->getLHS()->getType()->isIntegerTy() && willNotOverflow(WO, LVI)) {
544 processOverflowIntrinsic(WO, LVI);
549 if (auto *SI = dyn_cast<SaturatingInst>(CS.getInstruction())) {
550 if (SI->getType()->isIntegerTy() && willNotOverflow(SI, LVI)) {
551 processSaturatingInst(SI, LVI);
556 // Deopt bundle operands are intended to capture state with minimal
557 // perturbance of the code otherwise. If we can find a constant value for
558 // any such operand and remove a use of the original value, that's
559 // desireable since it may allow further optimization of that value (e.g. via
560 // single use rules in instcombine). Since deopt uses tend to,
561 // idiomatically, appear along rare conditional paths, it's reasonable likely
562 // we may have a conditional fact with which LVI can fold.
563 if (auto DeoptBundle = CS.getOperandBundle(LLVMContext::OB_deopt)) {
564 bool Progress = false;
565 for (const Use &ConstU : DeoptBundle->Inputs) {
566 Use &U = const_cast<Use&>(ConstU);
568 if (V->getType()->isVectorTy()) continue;
569 if (isa<Constant>(V)) continue;
571 Constant *C = LVI->getConstant(V, CS.getParent(), CS.getInstruction());
580 for (Value *V : CS.args()) {
581 PointerType *Type = dyn_cast<PointerType>(V->getType());
582 // Try to mark pointer typed parameters as non-null. We skip the
583 // relatively expensive analysis for constants which are obviously either
584 // null or non-null to start with.
585 if (Type && !CS.paramHasAttr(ArgNo, Attribute::NonNull) &&
587 LVI->getPredicateAt(ICmpInst::ICMP_EQ, V,
588 ConstantPointerNull::get(Type),
589 CS.getInstruction()) == LazyValueInfo::False)
590 ArgNos.push_back(ArgNo);
594 assert(ArgNo == CS.arg_size() && "sanity check");
599 AttributeList AS = CS.getAttributes();
600 LLVMContext &Ctx = CS.getInstruction()->getContext();
601 AS = AS.addParamAttribute(Ctx, ArgNos,
602 Attribute::get(Ctx, Attribute::NonNull));
603 CS.setAttributes(AS);
608 static bool hasPositiveOperands(BinaryOperator *SDI, LazyValueInfo *LVI) {
609 Constant *Zero = ConstantInt::get(SDI->getType(), 0);
610 for (Value *O : SDI->operands()) {
611 auto Result = LVI->getPredicateAt(ICmpInst::ICMP_SGE, O, Zero, SDI);
612 if (Result != LazyValueInfo::True)
618 /// Try to shrink a udiv/urem's width down to the smallest power of two that's
619 /// sufficient to contain its operands.
620 static bool processUDivOrURem(BinaryOperator *Instr, LazyValueInfo *LVI) {
621 assert(Instr->getOpcode() == Instruction::UDiv ||
622 Instr->getOpcode() == Instruction::URem);
623 if (Instr->getType()->isVectorTy())
626 // Find the smallest power of two bitwidth that's sufficient to hold Instr's
628 auto OrigWidth = Instr->getType()->getIntegerBitWidth();
629 ConstantRange OperandRange(OrigWidth, /*isFullSet=*/false);
630 for (Value *Operand : Instr->operands()) {
631 OperandRange = OperandRange.unionWith(
632 LVI->getConstantRange(Operand, Instr->getParent()));
634 // Don't shrink below 8 bits wide.
635 unsigned NewWidth = std::max<unsigned>(
636 PowerOf2Ceil(OperandRange.getUnsignedMax().getActiveBits()), 8);
637 // NewWidth might be greater than OrigWidth if OrigWidth is not a power of
639 if (NewWidth >= OrigWidth)
643 IRBuilder<> B{Instr};
644 auto *TruncTy = Type::getIntNTy(Instr->getContext(), NewWidth);
645 auto *LHS = B.CreateTruncOrBitCast(Instr->getOperand(0), TruncTy,
646 Instr->getName() + ".lhs.trunc");
647 auto *RHS = B.CreateTruncOrBitCast(Instr->getOperand(1), TruncTy,
648 Instr->getName() + ".rhs.trunc");
649 auto *BO = B.CreateBinOp(Instr->getOpcode(), LHS, RHS, Instr->getName());
650 auto *Zext = B.CreateZExt(BO, Instr->getType(), Instr->getName() + ".zext");
651 if (auto *BinOp = dyn_cast<BinaryOperator>(BO))
652 if (BinOp->getOpcode() == Instruction::UDiv)
653 BinOp->setIsExact(Instr->isExact());
655 Instr->replaceAllUsesWith(Zext);
656 Instr->eraseFromParent();
660 static bool processSRem(BinaryOperator *SDI, LazyValueInfo *LVI) {
661 if (SDI->getType()->isVectorTy() || !hasPositiveOperands(SDI, LVI))
665 auto *BO = BinaryOperator::CreateURem(SDI->getOperand(0), SDI->getOperand(1),
666 SDI->getName(), SDI);
667 BO->setDebugLoc(SDI->getDebugLoc());
668 SDI->replaceAllUsesWith(BO);
669 SDI->eraseFromParent();
671 // Try to process our new urem.
672 processUDivOrURem(BO, LVI);
677 /// See if LazyValueInfo's ability to exploit edge conditions or range
678 /// information is sufficient to prove the both operands of this SDiv are
679 /// positive. If this is the case, replace the SDiv with a UDiv. Even for local
680 /// conditions, this can sometimes prove conditions instcombine can't by
681 /// exploiting range information.
682 static bool processSDiv(BinaryOperator *SDI, LazyValueInfo *LVI) {
683 if (SDI->getType()->isVectorTy() || !hasPositiveOperands(SDI, LVI))
687 auto *BO = BinaryOperator::CreateUDiv(SDI->getOperand(0), SDI->getOperand(1),
688 SDI->getName(), SDI);
689 BO->setDebugLoc(SDI->getDebugLoc());
690 BO->setIsExact(SDI->isExact());
691 SDI->replaceAllUsesWith(BO);
692 SDI->eraseFromParent();
694 // Try to simplify our new udiv.
695 processUDivOrURem(BO, LVI);
700 static bool processAShr(BinaryOperator *SDI, LazyValueInfo *LVI) {
701 if (SDI->getType()->isVectorTy())
704 Constant *Zero = ConstantInt::get(SDI->getType(), 0);
705 if (LVI->getPredicateAt(ICmpInst::ICMP_SGE, SDI->getOperand(0), Zero, SDI) !=
710 auto *BO = BinaryOperator::CreateLShr(SDI->getOperand(0), SDI->getOperand(1),
711 SDI->getName(), SDI);
712 BO->setDebugLoc(SDI->getDebugLoc());
713 BO->setIsExact(SDI->isExact());
714 SDI->replaceAllUsesWith(BO);
715 SDI->eraseFromParent();
720 static bool processSExt(SExtInst *SDI, LazyValueInfo *LVI) {
721 if (SDI->getType()->isVectorTy())
724 Value *Base = SDI->getOperand(0);
726 Constant *Zero = ConstantInt::get(Base->getType(), 0);
727 if (LVI->getPredicateAt(ICmpInst::ICMP_SGE, Base, Zero, SDI) !=
733 CastInst::CreateZExtOrBitCast(Base, SDI->getType(), SDI->getName(), SDI);
734 ZExt->setDebugLoc(SDI->getDebugLoc());
735 SDI->replaceAllUsesWith(ZExt);
736 SDI->eraseFromParent();
741 static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI) {
742 using OBO = OverflowingBinaryOperator;
744 if (DontAddNoWrapFlags)
747 if (BinOp->getType()->isVectorTy())
750 bool NSW = BinOp->hasNoSignedWrap();
751 bool NUW = BinOp->hasNoUnsignedWrap();
755 BasicBlock *BB = BinOp->getParent();
757 Instruction::BinaryOps Opcode = BinOp->getOpcode();
758 Value *LHS = BinOp->getOperand(0);
759 Value *RHS = BinOp->getOperand(1);
761 ConstantRange LRange = LVI->getConstantRange(LHS, BB, BinOp);
762 ConstantRange RRange = LVI->getConstantRange(RHS, BB, BinOp);
764 bool Changed = false;
765 bool NewNUW = false, NewNSW = false;
767 ConstantRange NUWRange = ConstantRange::makeGuaranteedNoWrapRegion(
768 Opcode, RRange, OBO::NoUnsignedWrap);
769 NewNUW = NUWRange.contains(LRange);
773 ConstantRange NSWRange = ConstantRange::makeGuaranteedNoWrapRegion(
774 Opcode, RRange, OBO::NoSignedWrap);
775 NewNSW = NSWRange.contains(LRange);
779 setDeducedOverflowingFlags(BinOp, Opcode, NewNSW, NewNUW);
784 static bool processAnd(BinaryOperator *BinOp, LazyValueInfo *LVI) {
785 if (BinOp->getType()->isVectorTy())
788 // Pattern match (and lhs, C) where C includes a superset of bits which might
789 // be set in lhs. This is a common truncation idiom created by instcombine.
790 BasicBlock *BB = BinOp->getParent();
791 Value *LHS = BinOp->getOperand(0);
792 ConstantInt *RHS = dyn_cast<ConstantInt>(BinOp->getOperand(1));
793 if (!RHS || !RHS->getValue().isMask())
796 ConstantRange LRange = LVI->getConstantRange(LHS, BB, BinOp);
797 if (!LRange.getUnsignedMax().ule(RHS->getValue()))
800 BinOp->replaceAllUsesWith(LHS);
801 BinOp->eraseFromParent();
807 static Constant *getConstantAt(Value *V, Instruction *At, LazyValueInfo *LVI) {
808 if (Constant *C = LVI->getConstant(V, At->getParent(), At))
811 // TODO: The following really should be sunk inside LVI's core algorithm, or
812 // at least the outer shims around such.
813 auto *C = dyn_cast<CmpInst>(V);
814 if (!C) return nullptr;
816 Value *Op0 = C->getOperand(0);
817 Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
818 if (!Op1) return nullptr;
820 LazyValueInfo::Tristate Result =
821 LVI->getPredicateAt(C->getPredicate(), Op0, Op1, At);
822 if (Result == LazyValueInfo::Unknown)
825 return (Result == LazyValueInfo::True) ?
826 ConstantInt::getTrue(C->getContext()) :
827 ConstantInt::getFalse(C->getContext());
830 static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT,
831 const SimplifyQuery &SQ) {
832 bool FnChanged = false;
833 // Visiting in a pre-order depth-first traversal causes us to simplify early
834 // blocks before querying later blocks (which require us to analyze early
835 // blocks). Eagerly simplifying shallow blocks means there is strictly less
836 // work to do for deep blocks. This also means we don't visit unreachable
838 for (BasicBlock *BB : depth_first(&F.getEntryBlock())) {
839 bool BBChanged = false;
840 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
841 Instruction *II = &*BI++;
842 switch (II->getOpcode()) {
843 case Instruction::Select:
844 BBChanged |= processSelect(cast<SelectInst>(II), LVI);
846 case Instruction::PHI:
847 BBChanged |= processPHI(cast<PHINode>(II), LVI, DT, SQ);
849 case Instruction::ICmp:
850 case Instruction::FCmp:
851 BBChanged |= processCmp(cast<CmpInst>(II), LVI);
853 case Instruction::Load:
854 case Instruction::Store:
855 BBChanged |= processMemAccess(II, LVI);
857 case Instruction::Call:
858 case Instruction::Invoke:
859 BBChanged |= processCallSite(CallSite(II), LVI);
861 case Instruction::SRem:
862 BBChanged |= processSRem(cast<BinaryOperator>(II), LVI);
864 case Instruction::SDiv:
865 BBChanged |= processSDiv(cast<BinaryOperator>(II), LVI);
867 case Instruction::UDiv:
868 case Instruction::URem:
869 BBChanged |= processUDivOrURem(cast<BinaryOperator>(II), LVI);
871 case Instruction::AShr:
872 BBChanged |= processAShr(cast<BinaryOperator>(II), LVI);
874 case Instruction::SExt:
875 BBChanged |= processSExt(cast<SExtInst>(II), LVI);
877 case Instruction::Add:
878 case Instruction::Sub:
879 case Instruction::Mul:
880 case Instruction::Shl:
881 BBChanged |= processBinOp(cast<BinaryOperator>(II), LVI);
883 case Instruction::And:
884 BBChanged |= processAnd(cast<BinaryOperator>(II), LVI);
889 Instruction *Term = BB->getTerminator();
890 switch (Term->getOpcode()) {
891 case Instruction::Switch:
892 BBChanged |= processSwitch(cast<SwitchInst>(Term), LVI, DT);
894 case Instruction::Ret: {
895 auto *RI = cast<ReturnInst>(Term);
896 // Try to determine the return value if we can. This is mainly here to
897 // simplify the writing of unit tests, but also helps to enable IPO by
898 // constant folding the return values of callees.
899 auto *RetVal = RI->getReturnValue();
900 if (!RetVal) break; // handle "ret void"
901 if (isa<Constant>(RetVal)) break; // nothing to do
902 if (auto *C = getConstantAt(RetVal, RI, LVI)) {
904 RI->replaceUsesOfWith(RetVal, C);
910 FnChanged |= BBChanged;
916 bool CorrelatedValuePropagation::runOnFunction(Function &F) {
920 LazyValueInfo *LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
921 DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
923 return runImpl(F, LVI, DT, getBestSimplifyQuery(*this, F));
927 CorrelatedValuePropagationPass::run(Function &F, FunctionAnalysisManager &AM) {
928 LazyValueInfo *LVI = &AM.getResult<LazyValueAnalysis>(F);
929 DominatorTree *DT = &AM.getResult<DominatorTreeAnalysis>(F);
931 bool Changed = runImpl(F, LVI, DT, getBestSimplifyQuery(AM, F));
934 return PreservedAnalyses::all();
935 PreservedAnalyses PA;
936 PA.preserve<GlobalsAA>();
937 PA.preserve<DominatorTreeAnalysis>();
938 PA.preserve<LazyValueAnalysis>();