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llvm-mirror/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
Nikita Popov 021d70e8fc [CVP] Simplify and generalize switch handling 
CVP currently handles switches by checking an equality predicate
on all edges from predecessor blocks. Of course, this can only
work if the value being switched over is defined in a different block.

Replace this implementation with a call to getPredicateAt(), which
also does the predecessor edge predicate check (if not defined in
the same block), but can also do quite a bit more: It can reason
about phi-nodes by checking edge predicates for incoming values,
it can reason about assumes, and it can reason about block values.

As such, this makes the implementation both simpler and more
powerful. The compile-time impact on CTMark is in the noise.
2020-12-12 21:12:27 +01:00

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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/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(NumOverflows, "Number of overflow checks removed");
STATISTIC(NumSaturating,
"Number of saturating arithmetics converted to normal arithmetics");
static cl::opt<bool> DontAddNoWrapFlags("cvp-dont-add-nowrap-flags", cl::init(false));
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;
}
// All constant incoming values map to the same variable along the incoming
// edges of the phi. The phi is unnecessary. However, we must drop all
// poison-generating flags to ensure that no poison is propagated to the phi
// location by performing this substitution.
// Warning: If the underlying analysis changes, this may not be enough to
// guarantee that poison is not propagated.
// TODO: We may be able to re-infer flags by re-analyzing the instruction.
if (auto *CommonInst = dyn_cast<Instruction>(CommonValue))
CommonInst->dropPoisonGeneratingFlags();
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);
// Rewrite this with.overflow intrinsic as non-overflowing.
static void 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);
}
static void 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);
}
/// Infer nonnull attributes for the arguments at the specified callsite.
static bool processCallSite(CallBase &CB, LazyValueInfo *LVI) {
if (auto *WO = dyn_cast<WithOverflowInst>(&CB)) {
if (WO->getLHS()->getType()->isIntegerTy() && willNotOverflow(WO, LVI)) {
processOverflowIntrinsic(WO, LVI);
return true;
}
}
if (auto *SI = dyn_cast<SaturatingInst>(&CB)) {
if (SI->getType()->isIntegerTy() && willNotOverflow(SI, LVI)) {
processSaturatingInst(SI, LVI);
return true;
}
}
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) == LazyValueInfo::False)
ArgNos.push_back(ArgNo);
ArgNo++;
}
assert(ArgNo == CB.arg_size() && "sanity check");
if (ArgNos.empty())
return Changed;
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);
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);
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 (DontAddNoWrapFlags)
return false;
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);
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<GlobalsAA>();
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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