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llvm-project/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp

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//===- CorrelatedValuePropagation.cpp - Propagate CFG-derived info --------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements the Correlated Value Propagation pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/CorrelatedValuePropagation.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include <cassert>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "correlated-value-propagation"
STATISTIC(NumPhis, "Number of phis propagated");
STATISTIC(NumPhiCommon, "Number of phis deleted via common incoming value");
STATISTIC(NumSelects, "Number of selects propagated");
STATISTIC(NumMemAccess, "Number of memory access targets propagated");
STATISTIC(NumCmps, "Number of comparisons propagated");
STATISTIC(NumReturns, "Number of return values propagated");
STATISTIC(NumDeadCases, "Number of switch cases removed");
STATISTIC(NumSDivSRemsNarrowed,
"Number of sdivs/srems whose width was decreased");
STATISTIC(NumSDivs, "Number of sdiv converted to udiv");
STATISTIC(NumUDivURemsNarrowed,
"Number of udivs/urems whose width was decreased");
STATISTIC(NumAShrs, "Number of ashr converted to lshr");
STATISTIC(NumSRems, "Number of srem converted to urem");
STATISTIC(NumSExt, "Number of sext converted to zext");
STATISTIC(NumAnd, "Number of ands removed");
STATISTIC(NumNW, "Number of no-wrap deductions");
STATISTIC(NumNSW, "Number of no-signed-wrap deductions");
STATISTIC(NumNUW, "Number of no-unsigned-wrap deductions");
STATISTIC(NumAddNW, "Number of no-wrap deductions for add");
STATISTIC(NumAddNSW, "Number of no-signed-wrap deductions for add");
STATISTIC(NumAddNUW, "Number of no-unsigned-wrap deductions for add");
STATISTIC(NumSubNW, "Number of no-wrap deductions for sub");
STATISTIC(NumSubNSW, "Number of no-signed-wrap deductions for sub");
STATISTIC(NumSubNUW, "Number of no-unsigned-wrap deductions for sub");
STATISTIC(NumMulNW, "Number of no-wrap deductions for mul");
STATISTIC(NumMulNSW, "Number of no-signed-wrap deductions for mul");
STATISTIC(NumMulNUW, "Number of no-unsigned-wrap deductions for mul");
STATISTIC(NumShlNW, "Number of no-wrap deductions for shl");
STATISTIC(NumShlNSW, "Number of no-signed-wrap deductions for shl");
STATISTIC(NumShlNUW, "Number of no-unsigned-wrap deductions for shl");
STATISTIC(NumAbs, "Number of llvm.abs intrinsics removed");
STATISTIC(NumOverflows, "Number of overflow checks removed");
STATISTIC(NumSaturating,
"Number of saturating arithmetics converted to normal arithmetics");
STATISTIC(NumNonNull, "Number of function pointer arguments marked non-null");
STATISTIC(NumMinMax, "Number of llvm.[us]{min,max} intrinsics removed");
namespace {
class CorrelatedValuePropagation : public FunctionPass {
public:
static char ID;
CorrelatedValuePropagation(): FunctionPass(ID) {
initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<LazyValueInfoWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<LazyValueInfoWrapperPass>();
}
};
} // end anonymous namespace
char CorrelatedValuePropagation::ID = 0;
INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
"Value Propagation", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)
INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
"Value Propagation", false, false)
// Public interface to the Value Propagation pass
Pass *llvm::createCorrelatedValuePropagationPass() {
return new CorrelatedValuePropagation();
}
static bool processSelect(SelectInst *S, LazyValueInfo *LVI) {
if (S->getType()->isVectorTy()) return false;
if (isa<Constant>(S->getCondition())) return false;
Constant *C = LVI->getConstant(S->getCondition(), S);
if (!C) return false;
ConstantInt *CI = dyn_cast<ConstantInt>(C);
if (!CI) return false;
Value *ReplaceWith = CI->isOne() ? S->getTrueValue() : S->getFalseValue();
S->replaceAllUsesWith(ReplaceWith);
S->eraseFromParent();
++NumSelects;
return true;
}
/// Try to simplify a phi with constant incoming values that match the edge
/// values of a non-constant value on all other edges:
/// bb0:
/// %isnull = icmp eq i8* %x, null
/// br i1 %isnull, label %bb2, label %bb1
/// bb1:
/// br label %bb2
/// bb2:
/// %r = phi i8* [ %x, %bb1 ], [ null, %bb0 ]
/// -->
/// %r = %x
static bool simplifyCommonValuePhi(PHINode *P, LazyValueInfo *LVI,
DominatorTree *DT) {
// Collect incoming constants and initialize possible common value.
SmallVector<std::pair<Constant *, unsigned>, 4> IncomingConstants;
Value *CommonValue = nullptr;
for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = P->getIncomingValue(i);
if (auto *IncomingConstant = dyn_cast<Constant>(Incoming)) {
IncomingConstants.push_back(std::make_pair(IncomingConstant, i));
} else if (!CommonValue) {
// The potential common value is initialized to the first non-constant.
CommonValue = Incoming;
} else if (Incoming != CommonValue) {
// There can be only one non-constant common value.
return false;
}
}
if (!CommonValue || IncomingConstants.empty())
return false;
// The common value must be valid in all incoming blocks.
BasicBlock *ToBB = P->getParent();
if (auto *CommonInst = dyn_cast<Instruction>(CommonValue))
if (!DT->dominates(CommonInst, ToBB))
return false;
// We have a phi with exactly 1 variable incoming value and 1 or more constant
// incoming values. See if all constant incoming values can be mapped back to
// the same incoming variable value.
for (auto &IncomingConstant : IncomingConstants) {
Constant *C = IncomingConstant.first;
BasicBlock *IncomingBB = P->getIncomingBlock(IncomingConstant.second);
if (C != LVI->getConstantOnEdge(CommonValue, IncomingBB, ToBB, P))
return false;
}
// LVI only guarantees that the value matches a certain constant if the value
// is not poison. Make sure we don't replace a well-defined value with poison.
// This is usually satisfied due to a prior branch on the value.
if (!isGuaranteedNotToBePoison(CommonValue, nullptr, P, DT))
return false;
// All constant incoming values map to the same variable along the incoming
// edges of the phi. The phi is unnecessary.
P->replaceAllUsesWith(CommonValue);
P->eraseFromParent();
++NumPhiCommon;
return true;
}
static bool processPHI(PHINode *P, LazyValueInfo *LVI, DominatorTree *DT,
const SimplifyQuery &SQ) {
bool Changed = false;
BasicBlock *BB = P->getParent();
for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
Value *Incoming = P->getIncomingValue(i);
if (isa<Constant>(Incoming)) continue;
Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB, P);
// Look if the incoming value is a select with a scalar condition for which
// LVI can tells us the value. In that case replace the incoming value with
// the appropriate value of the select. This often allows us to remove the
// select later.
if (!V) {
SelectInst *SI = dyn_cast<SelectInst>(Incoming);
if (!SI) continue;
Value *Condition = SI->getCondition();
if (!Condition->getType()->isVectorTy()) {
if (Constant *C = LVI->getConstantOnEdge(
Condition, P->getIncomingBlock(i), BB, P)) {
if (C->isOneValue()) {
V = SI->getTrueValue();
} else if (C->isZeroValue()) {
V = SI->getFalseValue();
}
// Once LVI learns to handle vector types, we could also add support
// for vector type constants that are not all zeroes or all ones.
}
}
// Look if the select has a constant but LVI tells us that the incoming
// value can never be that constant. In that case replace the incoming
// value with the other value of the select. This often allows us to
// remove the select later.
if (!V) {
Constant *C = dyn_cast<Constant>(SI->getFalseValue());
if (!C) continue;
if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
P->getIncomingBlock(i), BB, P) !=
LazyValueInfo::False)
continue;
V = SI->getTrueValue();
}
LLVM_DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
}
P->setIncomingValue(i, V);
Changed = true;
}
if (Value *V = SimplifyInstruction(P, SQ)) {
P->replaceAllUsesWith(V);
P->eraseFromParent();
Changed = true;
}
if (!Changed)
Changed = simplifyCommonValuePhi(P, LVI, DT);
if (Changed)
++NumPhis;
return Changed;
}
static bool processMemAccess(Instruction *I, LazyValueInfo *LVI) {
Value *Pointer = nullptr;
if (LoadInst *L = dyn_cast<LoadInst>(I))
Pointer = L->getPointerOperand();
else
Pointer = cast<StoreInst>(I)->getPointerOperand();
if (isa<Constant>(Pointer)) return false;
Constant *C = LVI->getConstant(Pointer, I);
if (!C) return false;
++NumMemAccess;
I->replaceUsesOfWith(Pointer, C);
return true;
}
/// See if LazyValueInfo's ability to exploit edge conditions or range
/// information is sufficient to prove this comparison. Even for local
/// conditions, this can sometimes prove conditions instcombine can't by
/// exploiting range information.
static bool processCmp(CmpInst *Cmp, LazyValueInfo *LVI) {
Value *Op0 = Cmp->getOperand(0);
auto *C = dyn_cast<Constant>(Cmp->getOperand(1));
if (!C)
return false;
LazyValueInfo::Tristate Result =
LVI->getPredicateAt(Cmp->getPredicate(), Op0, C, Cmp,
/*UseBlockValue=*/true);
if (Result == LazyValueInfo::Unknown)
return false;
++NumCmps;
Constant *TorF = ConstantInt::get(Type::getInt1Ty(Cmp->getContext()), Result);
Cmp->replaceAllUsesWith(TorF);
Cmp->eraseFromParent();
return true;
}
/// Simplify a switch instruction by removing cases which can never fire. If the
/// uselessness of a case could be determined locally then constant propagation
/// would already have figured it out. Instead, walk the predecessors and
/// statically evaluate cases based on information available on that edge. Cases
/// that cannot fire no matter what the incoming edge can safely be removed. If
/// a case fires on every incoming edge then the entire switch can be removed
/// and replaced with a branch to the case destination.
static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
DominatorTree *DT) {
DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Lazy);
Value *Cond = I->getCondition();
BasicBlock *BB = I->getParent();
// Analyse each switch case in turn.
bool Changed = false;
DenseMap<BasicBlock*, int> SuccessorsCount;
for (auto *Succ : successors(BB))
SuccessorsCount[Succ]++;
{ // Scope for SwitchInstProfUpdateWrapper. It must not live during
// ConstantFoldTerminator() as the underlying SwitchInst can be changed.
SwitchInstProfUpdateWrapper SI(*I);
for (auto CI = SI->case_begin(), CE = SI->case_end(); CI != CE;) {
ConstantInt *Case = CI->getCaseValue();
LazyValueInfo::Tristate State =
LVI->getPredicateAt(CmpInst::ICMP_EQ, Cond, Case, I,
/* UseBlockValue */ true);
if (State == LazyValueInfo::False) {
// This case never fires - remove it.
BasicBlock *Succ = CI->getCaseSuccessor();
Succ->removePredecessor(BB);
CI = SI.removeCase(CI);
CE = SI->case_end();
// The condition can be modified by removePredecessor's PHI simplification
// logic.
Cond = SI->getCondition();
++NumDeadCases;
Changed = true;
if (--SuccessorsCount[Succ] == 0)
DTU.applyUpdatesPermissive({{DominatorTree::Delete, BB, Succ}});
continue;
}
if (State == LazyValueInfo::True) {
// This case always fires. Arrange for the switch to be turned into an
// unconditional branch by replacing the switch condition with the case
// value.
SI->setCondition(Case);
NumDeadCases += SI->getNumCases();
Changed = true;
break;
}
// Increment the case iterator since we didn't delete it.
++CI;
}
}
if (Changed)
// If the switch has been simplified to the point where it can be replaced
// by a branch then do so now.
ConstantFoldTerminator(BB, /*DeleteDeadConditions = */ false,
/*TLI = */ nullptr, &DTU);
return Changed;
}
// See if we can prove that the given binary op intrinsic will not overflow.
static bool willNotOverflow(BinaryOpIntrinsic *BO, LazyValueInfo *LVI) {
ConstantRange LRange = LVI->getConstantRange(BO->getLHS(), BO);
ConstantRange RRange = LVI->getConstantRange(BO->getRHS(), BO);
ConstantRange NWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
BO->getBinaryOp(), RRange, BO->getNoWrapKind());
return NWRegion.contains(LRange);
}
static void setDeducedOverflowingFlags(Value *V, Instruction::BinaryOps Opcode,
bool NewNSW, bool NewNUW) {
Statistic *OpcNW, *OpcNSW, *OpcNUW;
switch (Opcode) {
case Instruction::Add:
OpcNW = &NumAddNW;
OpcNSW = &NumAddNSW;
OpcNUW = &NumAddNUW;
break;
case Instruction::Sub:
OpcNW = &NumSubNW;
OpcNSW = &NumSubNSW;
OpcNUW = &NumSubNUW;
break;
case Instruction::Mul:
OpcNW = &NumMulNW;
OpcNSW = &NumMulNSW;
OpcNUW = &NumMulNUW;
break;
case Instruction::Shl:
OpcNW = &NumShlNW;
OpcNSW = &NumShlNSW;
OpcNUW = &NumShlNUW;
break;
default:
llvm_unreachable("Will not be called with other binops");
}
auto *Inst = dyn_cast<Instruction>(V);
if (NewNSW) {
++NumNW;
++*OpcNW;
++NumNSW;
++*OpcNSW;
if (Inst)
Inst->setHasNoSignedWrap();
}
if (NewNUW) {
++NumNW;
++*OpcNW;
++NumNUW;
++*OpcNUW;
if (Inst)
Inst->setHasNoUnsignedWrap();
}
}
static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI);
// See if @llvm.abs argument is alays positive/negative, and simplify.
// Notably, INT_MIN can belong to either range, regardless of the NSW,
// because it is negation-invariant.
static bool processAbsIntrinsic(IntrinsicInst *II, LazyValueInfo *LVI) {
Value *X = II->getArgOperand(0);
bool IsIntMinPoison = cast<ConstantInt>(II->getArgOperand(1))->isOne();
Type *Ty = X->getType();
Constant *IntMin =
ConstantInt::get(Ty, APInt::getSignedMinValue(Ty->getScalarSizeInBits()));
LazyValueInfo::Tristate Result;
// Is X in [0, IntMin]? NOTE: INT_MIN is fine!
Result = LVI->getPredicateAt(CmpInst::Predicate::ICMP_ULE, X, IntMin, II,
/*UseBlockValue=*/true);
if (Result == LazyValueInfo::True) {
++NumAbs;
II->replaceAllUsesWith(X);
II->eraseFromParent();
return true;
}
// Is X in [IntMin, 0]? NOTE: INT_MIN is fine!
Constant *Zero = ConstantInt::getNullValue(Ty);
Result = LVI->getPredicateAt(CmpInst::Predicate::ICMP_SLE, X, Zero, II,
/*UseBlockValue=*/true);
assert(Result != LazyValueInfo::False && "Should have been handled already.");
if (Result == LazyValueInfo::Unknown) {
// Argument's range crosses zero.
bool Changed = false;
if (!IsIntMinPoison) {
// Can we at least tell that the argument is never INT_MIN?
Result = LVI->getPredicateAt(CmpInst::Predicate::ICMP_NE, X, IntMin, II,
/*UseBlockValue=*/true);
if (Result == LazyValueInfo::True) {
++NumNSW;
++NumSubNSW;
II->setArgOperand(1, ConstantInt::getTrue(II->getContext()));
Changed = true;
}
}
return Changed;
}
IRBuilder<> B(II);
Value *NegX = B.CreateNeg(X, II->getName(), /*HasNUW=*/false,
/*HasNSW=*/IsIntMinPoison);
++NumAbs;
II->replaceAllUsesWith(NegX);
II->eraseFromParent();
// See if we can infer some no-wrap flags.
if (auto *BO = dyn_cast<BinaryOperator>(NegX))
processBinOp(BO, LVI);
return true;
}
// See if this min/max intrinsic always picks it's one specific operand.
static bool processMinMaxIntrinsic(MinMaxIntrinsic *MM, LazyValueInfo *LVI) {
CmpInst::Predicate Pred = CmpInst::getNonStrictPredicate(MM->getPredicate());
LazyValueInfo::Tristate Result = LVI->getPredicateAt(
Pred, MM->getLHS(), MM->getRHS(), MM, /*UseBlockValue=*/true);
if (Result == LazyValueInfo::Unknown)
return false;
++NumMinMax;
MM->replaceAllUsesWith(MM->getOperand(!Result));
MM->eraseFromParent();
return true;
}
// Rewrite this with.overflow intrinsic as non-overflowing.
static bool processOverflowIntrinsic(WithOverflowInst *WO, LazyValueInfo *LVI) {
IRBuilder<> B(WO);
Instruction::BinaryOps Opcode = WO->getBinaryOp();
bool NSW = WO->isSigned();
bool NUW = !WO->isSigned();
Value *NewOp =
B.CreateBinOp(Opcode, WO->getLHS(), WO->getRHS(), WO->getName());
setDeducedOverflowingFlags(NewOp, Opcode, NSW, NUW);
StructType *ST = cast<StructType>(WO->getType());
Constant *Struct = ConstantStruct::get(ST,
{ UndefValue::get(ST->getElementType(0)),
ConstantInt::getFalse(ST->getElementType(1)) });
Value *NewI = B.CreateInsertValue(Struct, NewOp, 0);
WO->replaceAllUsesWith(NewI);
WO->eraseFromParent();
++NumOverflows;
// See if we can infer the other no-wrap too.
if (auto *BO = dyn_cast<BinaryOperator>(NewOp))
processBinOp(BO, LVI);
return true;
}
static bool processSaturatingInst(SaturatingInst *SI, LazyValueInfo *LVI) {
Instruction::BinaryOps Opcode = SI->getBinaryOp();
bool NSW = SI->isSigned();
bool NUW = !SI->isSigned();
BinaryOperator *BinOp = BinaryOperator::Create(
Opcode, SI->getLHS(), SI->getRHS(), SI->getName(), SI);
BinOp->setDebugLoc(SI->getDebugLoc());
setDeducedOverflowingFlags(BinOp, Opcode, NSW, NUW);
SI->replaceAllUsesWith(BinOp);
SI->eraseFromParent();
++NumSaturating;
// See if we can infer the other no-wrap too.
if (auto *BO = dyn_cast<BinaryOperator>(BinOp))
processBinOp(BO, LVI);
return true;
}
/// Infer nonnull attributes for the arguments at the specified callsite.
static bool processCallSite(CallBase &CB, LazyValueInfo *LVI) {
if (CB.getIntrinsicID() == Intrinsic::abs) {
return processAbsIntrinsic(&cast<IntrinsicInst>(CB), LVI);
}
if (auto *MM = dyn_cast<MinMaxIntrinsic>(&CB)) {
return processMinMaxIntrinsic(MM, LVI);
}
if (auto *WO = dyn_cast<WithOverflowInst>(&CB)) {
if (WO->getLHS()->getType()->isIntegerTy() && willNotOverflow(WO, LVI)) {
return processOverflowIntrinsic(WO, LVI);
}
}
if (auto *SI = dyn_cast<SaturatingInst>(&CB)) {
if (SI->getType()->isIntegerTy() && willNotOverflow(SI, LVI)) {
return processSaturatingInst(SI, LVI);
}
}
bool Changed = false;
// Deopt bundle operands are intended to capture state with minimal
// perturbance of the code otherwise. If we can find a constant value for
// any such operand and remove a use of the original value, that's
// desireable since it may allow further optimization of that value (e.g. via
// single use rules in instcombine). Since deopt uses tend to,
// idiomatically, appear along rare conditional paths, it's reasonable likely
// we may have a conditional fact with which LVI can fold.
if (auto DeoptBundle = CB.getOperandBundle(LLVMContext::OB_deopt)) {
for (const Use &ConstU : DeoptBundle->Inputs) {
Use &U = const_cast<Use&>(ConstU);
Value *V = U.get();
if (V->getType()->isVectorTy()) continue;
if (isa<Constant>(V)) continue;
Constant *C = LVI->getConstant(V, &CB);
if (!C) continue;
U.set(C);
Changed = true;
}
}
SmallVector<unsigned, 4> ArgNos;
unsigned ArgNo = 0;
for (Value *V : CB.args()) {
PointerType *Type = dyn_cast<PointerType>(V->getType());
// Try to mark pointer typed parameters as non-null. We skip the
// relatively expensive analysis for constants which are obviously either
// null or non-null to start with.
if (Type && !CB.paramHasAttr(ArgNo, Attribute::NonNull) &&
!isa<Constant>(V) &&
LVI->getPredicateAt(ICmpInst::ICMP_EQ, V,
ConstantPointerNull::get(Type), &CB,
/*UseBlockValue=*/false) == LazyValueInfo::False)
ArgNos.push_back(ArgNo);
ArgNo++;
}
assert(ArgNo == CB.arg_size() && "sanity check");
if (ArgNos.empty())
return Changed;
NumNonNull += ArgNos.size();
AttributeList AS = CB.getAttributes();
LLVMContext &Ctx = CB.getContext();
AS = AS.addParamAttribute(Ctx, ArgNos,
Attribute::get(Ctx, Attribute::NonNull));
CB.setAttributes(AS);
return true;
}
static bool isNonNegative(Value *V, LazyValueInfo *LVI, Instruction *CxtI) {
Constant *Zero = ConstantInt::get(V->getType(), 0);
auto Result = LVI->getPredicateAt(ICmpInst::ICMP_SGE, V, Zero, CxtI,
/*UseBlockValue=*/true);
return Result == LazyValueInfo::True;
}
static bool isNonPositive(Value *V, LazyValueInfo *LVI, Instruction *CxtI) {
Constant *Zero = ConstantInt::get(V->getType(), 0);
auto Result = LVI->getPredicateAt(ICmpInst::ICMP_SLE, V, Zero, CxtI,
/*UseBlockValue=*/true);
return Result == LazyValueInfo::True;
}
enum class Domain { NonNegative, NonPositive, Unknown };
Domain getDomain(Value *V, LazyValueInfo *LVI, Instruction *CxtI) {
if (isNonNegative(V, LVI, CxtI))
return Domain::NonNegative;
if (isNonPositive(V, LVI, CxtI))
return Domain::NonPositive;
return Domain::Unknown;
}
/// Try to shrink a sdiv/srem's width down to the smallest power of two that's
/// sufficient to contain its operands.
static bool narrowSDivOrSRem(BinaryOperator *Instr, LazyValueInfo *LVI) {
assert(Instr->getOpcode() == Instruction::SDiv ||
Instr->getOpcode() == Instruction::SRem);
if (Instr->getType()->isVectorTy())
return false;
// Find the smallest power of two bitwidth that's sufficient to hold Instr's
// operands.
unsigned OrigWidth = Instr->getType()->getIntegerBitWidth();
// What is the smallest bit width that can accomodate the entire value ranges
// of both of the operands?
std::array<Optional<ConstantRange>, 2> CRs;
unsigned MinSignedBits = 0;
for (auto I : zip(Instr->operands(), CRs)) {
std::get<1>(I) = LVI->getConstantRange(std::get<0>(I), Instr);
MinSignedBits = std::max(std::get<1>(I)->getMinSignedBits(), MinSignedBits);
}
// sdiv/srem is UB if divisor is -1 and divident is INT_MIN, so unless we can
// prove that such a combination is impossible, we need to bump the bitwidth.
if (CRs[1]->contains(APInt::getAllOnesValue(OrigWidth)) &&
CRs[0]->contains(
APInt::getSignedMinValue(MinSignedBits).sextOrSelf(OrigWidth)))
++MinSignedBits;
// Don't shrink below 8 bits wide.
unsigned NewWidth = std::max<unsigned>(PowerOf2Ceil(MinSignedBits), 8);
// NewWidth might be greater than OrigWidth if OrigWidth is not a power of
// two.
if (NewWidth >= OrigWidth)
return false;
++NumSDivSRemsNarrowed;
IRBuilder<> B{Instr};
auto *TruncTy = Type::getIntNTy(Instr->getContext(), NewWidth);
auto *LHS = B.CreateTruncOrBitCast(Instr->getOperand(0), TruncTy,
Instr->getName() + ".lhs.trunc");
auto *RHS = B.CreateTruncOrBitCast(Instr->getOperand(1), TruncTy,
Instr->getName() + ".rhs.trunc");
auto *BO = B.CreateBinOp(Instr->getOpcode(), LHS, RHS, Instr->getName());
auto *Sext = B.CreateSExt(BO, Instr->getType(), Instr->getName() + ".sext");
if (auto *BinOp = dyn_cast<BinaryOperator>(BO))
if (BinOp->getOpcode() == Instruction::SDiv)
BinOp->setIsExact(Instr->isExact());
Instr->replaceAllUsesWith(Sext);
Instr->eraseFromParent();
return true;
}
/// Try to shrink a udiv/urem's width down to the smallest power of two that's
/// sufficient to contain its operands.
static bool processUDivOrURem(BinaryOperator *Instr, LazyValueInfo *LVI) {
assert(Instr->getOpcode() == Instruction::UDiv ||
Instr->getOpcode() == Instruction::URem);
if (Instr->getType()->isVectorTy())
return false;
// Find the smallest power of two bitwidth that's sufficient to hold Instr's
// operands.
// What is the smallest bit width that can accomodate the entire value ranges
// of both of the operands?
unsigned MaxActiveBits = 0;
for (Value *Operand : Instr->operands()) {
ConstantRange CR = LVI->getConstantRange(Operand, Instr);
MaxActiveBits = std::max(CR.getActiveBits(), MaxActiveBits);
}
// Don't shrink below 8 bits wide.
unsigned NewWidth = std::max<unsigned>(PowerOf2Ceil(MaxActiveBits), 8);
// NewWidth might be greater than OrigWidth if OrigWidth is not a power of
// two.
if (NewWidth >= Instr->getType()->getIntegerBitWidth())
return false;
++NumUDivURemsNarrowed;
IRBuilder<> B{Instr};
auto *TruncTy = Type::getIntNTy(Instr->getContext(), NewWidth);
auto *LHS = B.CreateTruncOrBitCast(Instr->getOperand(0), TruncTy,
Instr->getName() + ".lhs.trunc");
auto *RHS = B.CreateTruncOrBitCast(Instr->getOperand(1), TruncTy,
Instr->getName() + ".rhs.trunc");
auto *BO = B.CreateBinOp(Instr->getOpcode(), LHS, RHS, Instr->getName());
auto *Zext = B.CreateZExt(BO, Instr->getType(), Instr->getName() + ".zext");
if (auto *BinOp = dyn_cast<BinaryOperator>(BO))
if (BinOp->getOpcode() == Instruction::UDiv)
BinOp->setIsExact(Instr->isExact());
Instr->replaceAllUsesWith(Zext);
Instr->eraseFromParent();
return true;
}
static bool processSRem(BinaryOperator *SDI, LazyValueInfo *LVI) {
assert(SDI->getOpcode() == Instruction::SRem);
if (SDI->getType()->isVectorTy())
return false;
struct Operand {
Value *V;
Domain D;
};
std::array<Operand, 2> Ops;
for (const auto I : zip(Ops, SDI->operands())) {
Operand &Op = std::get<0>(I);
Op.V = std::get<1>(I);
Op.D = getDomain(Op.V, LVI, SDI);
if (Op.D == Domain::Unknown)
return false;
}
// We know domains of both of the operands!
++NumSRems;
// We need operands to be non-negative, so negate each one that isn't.
for (Operand &Op : Ops) {
if (Op.D == Domain::NonNegative)
continue;
auto *BO =
BinaryOperator::CreateNeg(Op.V, Op.V->getName() + ".nonneg", SDI);
BO->setDebugLoc(SDI->getDebugLoc());
Op.V = BO;
}
auto *URem =
BinaryOperator::CreateURem(Ops[0].V, Ops[1].V, SDI->getName(), SDI);
URem->setDebugLoc(SDI->getDebugLoc());
Value *Res = URem;
// If the divident was non-positive, we need to negate the result.
if (Ops[0].D == Domain::NonPositive)
Res = BinaryOperator::CreateNeg(Res, Res->getName() + ".neg", SDI);
SDI->replaceAllUsesWith(Res);
SDI->eraseFromParent();
// Try to simplify our new urem.
processUDivOrURem(URem, LVI);
return true;
}
/// See if LazyValueInfo's ability to exploit edge conditions or range
/// information is sufficient to prove the signs of both operands of this SDiv.
/// If this is the case, replace the SDiv with a UDiv. Even for local
/// conditions, this can sometimes prove conditions instcombine can't by
/// exploiting range information.
static bool processSDiv(BinaryOperator *SDI, LazyValueInfo *LVI) {
assert(SDI->getOpcode() == Instruction::SDiv);
if (SDI->getType()->isVectorTy())
return false;
struct Operand {
Value *V;
Domain D;
};
std::array<Operand, 2> Ops;
for (const auto I : zip(Ops, SDI->operands())) {
Operand &Op = std::get<0>(I);
Op.V = std::get<1>(I);
Op.D = getDomain(Op.V, LVI, SDI);
if (Op.D == Domain::Unknown)
return false;
}
// We know domains of both of the operands!
++NumSDivs;
// We need operands to be non-negative, so negate each one that isn't.
for (Operand &Op : Ops) {
if (Op.D == Domain::NonNegative)
continue;
auto *BO =
BinaryOperator::CreateNeg(Op.V, Op.V->getName() + ".nonneg", SDI);
BO->setDebugLoc(SDI->getDebugLoc());
Op.V = BO;
}
auto *UDiv =
BinaryOperator::CreateUDiv(Ops[0].V, Ops[1].V, SDI->getName(), SDI);
UDiv->setDebugLoc(SDI->getDebugLoc());
UDiv->setIsExact(SDI->isExact());
Value *Res = UDiv;
// If the operands had two different domains, we need to negate the result.
if (Ops[0].D != Ops[1].D)
Res = BinaryOperator::CreateNeg(Res, Res->getName() + ".neg", SDI);
SDI->replaceAllUsesWith(Res);
SDI->eraseFromParent();
// Try to simplify our new udiv.
processUDivOrURem(UDiv, LVI);
return true;
}
static bool processSDivOrSRem(BinaryOperator *Instr, LazyValueInfo *LVI) {
assert(Instr->getOpcode() == Instruction::SDiv ||
Instr->getOpcode() == Instruction::SRem);
if (Instr->getType()->isVectorTy())
return false;
if (Instr->getOpcode() == Instruction::SDiv)
if (processSDiv(Instr, LVI))
return true;
if (Instr->getOpcode() == Instruction::SRem)
if (processSRem(Instr, LVI))
return true;
return narrowSDivOrSRem(Instr, LVI);
}
static bool processAShr(BinaryOperator *SDI, LazyValueInfo *LVI) {
if (SDI->getType()->isVectorTy())
return false;
if (!isNonNegative(SDI->getOperand(0), LVI, SDI))
return false;
++NumAShrs;
auto *BO = BinaryOperator::CreateLShr(SDI->getOperand(0), SDI->getOperand(1),
SDI->getName(), SDI);
BO->setDebugLoc(SDI->getDebugLoc());
BO->setIsExact(SDI->isExact());
SDI->replaceAllUsesWith(BO);
SDI->eraseFromParent();
return true;
}
static bool processSExt(SExtInst *SDI, LazyValueInfo *LVI) {
if (SDI->getType()->isVectorTy())
return false;
Value *Base = SDI->getOperand(0);
if (!isNonNegative(Base, LVI, SDI))
return false;
++NumSExt;
auto *ZExt =
CastInst::CreateZExtOrBitCast(Base, SDI->getType(), SDI->getName(), SDI);
ZExt->setDebugLoc(SDI->getDebugLoc());
SDI->replaceAllUsesWith(ZExt);
SDI->eraseFromParent();
return true;
}
static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI) {
using OBO = OverflowingBinaryOperator;
if (BinOp->getType()->isVectorTy())
return false;
bool NSW = BinOp->hasNoSignedWrap();
bool NUW = BinOp->hasNoUnsignedWrap();
if (NSW && NUW)
return false;
Instruction::BinaryOps Opcode = BinOp->getOpcode();
Value *LHS = BinOp->getOperand(0);
Value *RHS = BinOp->getOperand(1);
ConstantRange LRange = LVI->getConstantRange(LHS, BinOp);
ConstantRange RRange = LVI->getConstantRange(RHS, BinOp);
bool Changed = false;
bool NewNUW = false, NewNSW = false;
if (!NUW) {
ConstantRange NUWRange = ConstantRange::makeGuaranteedNoWrapRegion(
Opcode, RRange, OBO::NoUnsignedWrap);
NewNUW = NUWRange.contains(LRange);
Changed |= NewNUW;
}
if (!NSW) {
ConstantRange NSWRange = ConstantRange::makeGuaranteedNoWrapRegion(
Opcode, RRange, OBO::NoSignedWrap);
NewNSW = NSWRange.contains(LRange);
Changed |= NewNSW;
}
setDeducedOverflowingFlags(BinOp, Opcode, NewNSW, NewNUW);
return Changed;
}
static bool processAnd(BinaryOperator *BinOp, LazyValueInfo *LVI) {
if (BinOp->getType()->isVectorTy())
return false;
// Pattern match (and lhs, C) where C includes a superset of bits which might
// be set in lhs. This is a common truncation idiom created by instcombine.
Value *LHS = BinOp->getOperand(0);
ConstantInt *RHS = dyn_cast<ConstantInt>(BinOp->getOperand(1));
if (!RHS || !RHS->getValue().isMask())
return false;
// We can only replace the AND with LHS based on range info if the range does
// not include undef.
ConstantRange LRange =
LVI->getConstantRange(LHS, BinOp, /*UndefAllowed=*/false);
if (!LRange.getUnsignedMax().ule(RHS->getValue()))
return false;
BinOp->replaceAllUsesWith(LHS);
BinOp->eraseFromParent();
NumAnd++;
return true;
}
static Constant *getConstantAt(Value *V, Instruction *At, LazyValueInfo *LVI) {
if (Constant *C = LVI->getConstant(V, At))
return C;
// TODO: The following really should be sunk inside LVI's core algorithm, or
// at least the outer shims around such.
auto *C = dyn_cast<CmpInst>(V);
if (!C) return nullptr;
Value *Op0 = C->getOperand(0);
Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
if (!Op1) return nullptr;
LazyValueInfo::Tristate Result = LVI->getPredicateAt(
C->getPredicate(), Op0, Op1, At, /*UseBlockValue=*/false);
if (Result == LazyValueInfo::Unknown)
return nullptr;
return (Result == LazyValueInfo::True) ?
ConstantInt::getTrue(C->getContext()) :
ConstantInt::getFalse(C->getContext());
}
static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT,
const SimplifyQuery &SQ) {
bool FnChanged = false;
// Visiting in a pre-order depth-first traversal causes us to simplify early
// blocks before querying later blocks (which require us to analyze early
// blocks). Eagerly simplifying shallow blocks means there is strictly less
// work to do for deep blocks. This also means we don't visit unreachable
// blocks.
for (BasicBlock *BB : depth_first(&F.getEntryBlock())) {
bool BBChanged = false;
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
Instruction *II = &*BI++;
switch (II->getOpcode()) {
case Instruction::Select:
BBChanged |= processSelect(cast<SelectInst>(II), LVI);
break;
case Instruction::PHI:
BBChanged |= processPHI(cast<PHINode>(II), LVI, DT, SQ);
break;
case Instruction::ICmp:
case Instruction::FCmp:
BBChanged |= processCmp(cast<CmpInst>(II), LVI);
break;
case Instruction::Load:
case Instruction::Store:
BBChanged |= processMemAccess(II, LVI);
break;
case Instruction::Call:
case Instruction::Invoke:
BBChanged |= processCallSite(cast<CallBase>(*II), LVI);
break;
case Instruction::SRem:
case Instruction::SDiv:
BBChanged |= processSDivOrSRem(cast<BinaryOperator>(II), LVI);
break;
case Instruction::UDiv:
case Instruction::URem:
BBChanged |= processUDivOrURem(cast<BinaryOperator>(II), LVI);
break;
case Instruction::AShr:
BBChanged |= processAShr(cast<BinaryOperator>(II), LVI);
break;
case Instruction::SExt:
BBChanged |= processSExt(cast<SExtInst>(II), LVI);
break;
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::Shl:
BBChanged |= processBinOp(cast<BinaryOperator>(II), LVI);
break;
case Instruction::And:
BBChanged |= processAnd(cast<BinaryOperator>(II), LVI);
break;
}
}
Instruction *Term = BB->getTerminator();
switch (Term->getOpcode()) {
case Instruction::Switch:
BBChanged |= processSwitch(cast<SwitchInst>(Term), LVI, DT);
break;
case Instruction::Ret: {
auto *RI = cast<ReturnInst>(Term);
// Try to determine the return value if we can. This is mainly here to
// simplify the writing of unit tests, but also helps to enable IPO by
// constant folding the return values of callees.
auto *RetVal = RI->getReturnValue();
if (!RetVal) break; // handle "ret void"
if (isa<Constant>(RetVal)) break; // nothing to do
if (auto *C = getConstantAt(RetVal, RI, LVI)) {
++NumReturns;
RI->replaceUsesOfWith(RetVal, C);
BBChanged = true;
}
}
}
FnChanged |= BBChanged;
}
return FnChanged;
}
bool CorrelatedValuePropagation::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
LazyValueInfo *LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
return runImpl(F, LVI, DT, getBestSimplifyQuery(*this, F));
}
PreservedAnalyses
CorrelatedValuePropagationPass::run(Function &F, FunctionAnalysisManager &AM) {
LazyValueInfo *LVI = &AM.getResult<LazyValueAnalysis>(F);
DominatorTree *DT = &AM.getResult<DominatorTreeAnalysis>(F);
bool Changed = runImpl(F, LVI, DT, getBestSimplifyQuery(AM, F));
PreservedAnalyses PA;
if (!Changed) {
PA = PreservedAnalyses::all();
} else {
PA.preserve<DominatorTreeAnalysis>();
PA.preserve<LazyValueAnalysis>();
}
// Keeping LVI alive is expensive, both because it uses a lot of memory, and
// because invalidating values in LVI is expensive. While CVP does preserve
// LVI, we know that passes after JumpThreading+CVP will not need the result
// of this analysis, so we forcefully discard it early.
PA.abandon<LazyValueAnalysis>();
return PA;
}
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