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//===- InstCombinePHI.cpp -------------------------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the visitPHINode function.
#include "InstCombineInternal.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/InstCombine/InstCombiner.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "instcombine"
static cl::opt<unsigned>
MaxNumPhis("instcombine-max-num-phis", cl::init(512),
cl::desc("Maximum number phis to handle in intptr/ptrint folding"));
"Number of phi-of-insertvalue turned into insertvalue-of-phis");
"Number of phi-of-extractvalue turned into extractvalue-of-phi");
STATISTIC(NumPHICSEs, "Number of PHI's that got CSE'd");
/// The PHI arguments will be folded into a single operation with a PHI node
/// as input. The debug location of the single operation will be the merged
/// locations of the original PHI node arguments.
void InstCombinerImpl::PHIArgMergedDebugLoc(Instruction *Inst, PHINode &PN) {
auto *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
// We do not expect a CallInst here, otherwise, N-way merging of DebugLoc
// will be inefficient.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
auto *I = cast<Instruction>(PN.getIncomingValue(i));
Inst->applyMergedLocation(Inst->getDebugLoc(), I->getDebugLoc());
// Replace Integer typed PHI PN if the PHI's value is used as a pointer value.
// If there is an existing pointer typed PHI that produces the same value as PN,
// replace PN and the IntToPtr operation with it. Otherwise, synthesize a new
// PHI node:
// Case-1:
// bb1:
// int_init = PtrToInt(ptr_init)
// br label %bb2
// bb2:
// int_val = PHI([int_init, %bb1], [int_val_inc, %bb2]
// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2]
// ptr_val2 = IntToPtr(int_val)
// ...
// use(ptr_val2)
// ptr_val_inc = ...
// inc_val_inc = PtrToInt(ptr_val_inc)
// ==>
// bb1:
// br label %bb2
// bb2:
// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2]
// ...
// use(ptr_val)
// ptr_val_inc = ...
// Case-2:
// bb1:
// int_ptr = BitCast(ptr_ptr)
// int_init = Load(int_ptr)
// br label %bb2
// bb2:
// int_val = PHI([int_init, %bb1], [int_val_inc, %bb2]
// ptr_val2 = IntToPtr(int_val)
// ...
// use(ptr_val2)
// ptr_val_inc = ...
// inc_val_inc = PtrToInt(ptr_val_inc)
// ==>
// bb1:
// ptr_init = Load(ptr_ptr)
// br label %bb2
// bb2:
// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2]
// ...
// use(ptr_val)
// ptr_val_inc = ...
// ...
Instruction *InstCombinerImpl::foldIntegerTypedPHI(PHINode &PN) {
if (!PN.getType()->isIntegerTy())
return nullptr;
if (!PN.hasOneUse())
return nullptr;
auto *IntToPtr = dyn_cast<IntToPtrInst>(PN.user_back());
if (!IntToPtr)
return nullptr;
// Check if the pointer is actually used as pointer:
auto HasPointerUse = [](Instruction *IIP) {
for (User *U : IIP->users()) {
Value *Ptr = nullptr;
if (LoadInst *LoadI = dyn_cast<LoadInst>(U)) {
Ptr = LoadI->getPointerOperand();
} else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
Ptr = SI->getPointerOperand();
} else if (GetElementPtrInst *GI = dyn_cast<GetElementPtrInst>(U)) {
Ptr = GI->getPointerOperand();
if (Ptr && Ptr == IIP)
return true;
return false;
if (!HasPointerUse(IntToPtr))
return nullptr;
if (DL.getPointerSizeInBits(IntToPtr->getAddressSpace()) !=
return nullptr;
SmallVector<Value *, 4> AvailablePtrVals;
for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) {
Value *Arg = PN.getIncomingValue(i);
// First look backward:
if (auto *PI = dyn_cast<PtrToIntInst>(Arg)) {
// Next look forward:
Value *ArgIntToPtr = nullptr;
for (User *U : Arg->users()) {
if (isa<IntToPtrInst>(U) && U->getType() == IntToPtr->getType() &&
(DT.dominates(cast<Instruction>(U), PN.getIncomingBlock(i)) ||
cast<Instruction>(U)->getParent() == PN.getIncomingBlock(i))) {
ArgIntToPtr = U;
if (ArgIntToPtr) {
// If Arg is defined by a PHI, allow it. This will also create
// more opportunities iteratively.
if (isa<PHINode>(Arg)) {
// For a single use integer load:
auto *LoadI = dyn_cast<LoadInst>(Arg);
if (!LoadI)
return nullptr;
if (!LoadI->hasOneUse())
return nullptr;
// Push the integer typed Load instruction into the available
// value set, and fix it up later when the pointer typed PHI
// is synthesized.
// Now search for a matching PHI
auto *BB = PN.getParent();
assert(AvailablePtrVals.size() == PN.getNumIncomingValues() &&
"Not enough available ptr typed incoming values");
PHINode *MatchingPtrPHI = nullptr;
unsigned NumPhis = 0;
for (auto II = BB->begin(); II != BB->end(); II++, NumPhis++) {
// FIXME: consider handling this in AggressiveInstCombine
PHINode *PtrPHI = dyn_cast<PHINode>(II);
if (!PtrPHI)
if (NumPhis > MaxNumPhis)
return nullptr;
if (PtrPHI == &PN || PtrPHI->getType() != IntToPtr->getType())
MatchingPtrPHI = PtrPHI;
for (unsigned i = 0; i != PtrPHI->getNumIncomingValues(); ++i) {
if (AvailablePtrVals[i] !=
PtrPHI->getIncomingValueForBlock(PN.getIncomingBlock(i))) {
MatchingPtrPHI = nullptr;
if (MatchingPtrPHI)
if (MatchingPtrPHI) {
assert(MatchingPtrPHI->getType() == IntToPtr->getType() &&
"Phi's Type does not match with IntToPtr");
// The PtrToCast + IntToPtr will be simplified later
return CastInst::CreateBitOrPointerCast(MatchingPtrPHI,
// If it requires a conversion for every PHI operand, do not do it.
if (all_of(AvailablePtrVals, [&](Value *V) {
return (V->getType() != IntToPtr->getType()) || isa<IntToPtrInst>(V);
return nullptr;
// If any of the operand that requires casting is a terminator
// instruction, do not do it. Similarly, do not do the transform if the value
// is PHI in a block with no insertion point, for example, a catchswitch
// block, since we will not be able to insert a cast after the PHI.
if (any_of(AvailablePtrVals, [&](Value *V) {
if (V->getType() == IntToPtr->getType())
return false;
auto *Inst = dyn_cast<Instruction>(V);
if (!Inst)
return false;
if (Inst->isTerminator())
return true;
auto *BB = Inst->getParent();
if (isa<PHINode>(Inst) && BB->getFirstInsertionPt() == BB->end())
return true;
return false;
return nullptr;
PHINode *NewPtrPHI = PHINode::Create(
IntToPtr->getType(), PN.getNumIncomingValues(), PN.getName() + ".ptr");
InsertNewInstBefore(NewPtrPHI, PN);
SmallDenseMap<Value *, Instruction *> Casts;
for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) {
auto *IncomingBB = PN.getIncomingBlock(i);
auto *IncomingVal = AvailablePtrVals[i];
if (IncomingVal->getType() == IntToPtr->getType()) {
NewPtrPHI->addIncoming(IncomingVal, IncomingBB);
#ifndef NDEBUG
LoadInst *LoadI = dyn_cast<LoadInst>(IncomingVal);
assert((isa<PHINode>(IncomingVal) ||
IncomingVal->getType()->isPointerTy() ||
(LoadI && LoadI->hasOneUse())) &&
"Can not replace LoadInst with multiple uses");
// Need to insert a BitCast.
// For an integer Load instruction with a single use, the load + IntToPtr
// cast will be simplified into a pointer load:
// %v = load i64, i64* %a.ip, align 8
// %v.cast = inttoptr i64 %v to float **
// ==>
// %v.ptrp = bitcast i64 * %a.ip to float **
// %v.cast = load float *, float ** %v.ptrp, align 8
Instruction *&CI = Casts[IncomingVal];
if (!CI) {
CI = CastInst::CreateBitOrPointerCast(IncomingVal, IntToPtr->getType(),
IncomingVal->getName() + ".ptr");
if (auto *IncomingI = dyn_cast<Instruction>(IncomingVal)) {
BasicBlock::iterator InsertPos(IncomingI);
BasicBlock *BB = IncomingI->getParent();
if (isa<PHINode>(IncomingI))
InsertPos = BB->getFirstInsertionPt();
assert(InsertPos != BB->end() && "should have checked above");
InsertNewInstBefore(CI, *InsertPos);
} else {
auto *InsertBB = &IncomingBB->getParent()->getEntryBlock();
InsertNewInstBefore(CI, *InsertBB->getFirstInsertionPt());
NewPtrPHI->addIncoming(CI, IncomingBB);
// The PtrToCast + IntToPtr will be simplified later
return CastInst::CreateBitOrPointerCast(NewPtrPHI,
/// If we have something like phi [insertvalue(a,b,0), insertvalue(c,d,0)],
/// turn this into a phi[a,c] and phi[b,d] and a single insertvalue.
Instruction *
InstCombinerImpl::foldPHIArgInsertValueInstructionIntoPHI(PHINode &PN) {
auto *FirstIVI = cast<InsertValueInst>(PN.getIncomingValue(0));
// Scan to see if all operands are `insertvalue`'s with the same indicies,
// and all have a single use.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
auto *I = dyn_cast<InsertValueInst>(PN.getIncomingValue(i));
if (!I || !I->hasOneUser() || I->getIndices() != FirstIVI->getIndices())
return nullptr;
// For each operand of an `insertvalue`
std::array<PHINode *, 2> NewOperands;
for (int OpIdx : {0, 1}) {
auto *&NewOperand = NewOperands[OpIdx];
// Create a new PHI node to receive the values the operand has in each
// incoming basic block.
NewOperand = PHINode::Create(
FirstIVI->getOperand(OpIdx)->getType(), PN.getNumIncomingValues(),
FirstIVI->getOperand(OpIdx)->getName() + ".pn");
// And populate each operand's PHI with said values.
for (auto Incoming : zip(PN.blocks(), PN.incoming_values()))
InsertNewInstBefore(NewOperand, PN);
// And finally, create `insertvalue` over the newly-formed PHI nodes.
auto *NewIVI = InsertValueInst::Create(NewOperands[0], NewOperands[1],
FirstIVI->getIndices(), PN.getName());
PHIArgMergedDebugLoc(NewIVI, PN);
return NewIVI;
/// If we have something like phi [extractvalue(a,0), extractvalue(b,0)],
/// turn this into a phi[a,b] and a single extractvalue.
Instruction *
InstCombinerImpl::foldPHIArgExtractValueInstructionIntoPHI(PHINode &PN) {
auto *FirstEVI = cast<ExtractValueInst>(PN.getIncomingValue(0));
// Scan to see if all operands are `extractvalue`'s with the same indicies,
// and all have a single use.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
auto *I = dyn_cast<ExtractValueInst>(PN.getIncomingValue(i));
if (!I || !I->hasOneUser() || I->getIndices() != FirstEVI->getIndices() ||
I->getAggregateOperand()->getType() !=
return nullptr;
// Create a new PHI node to receive the values the aggregate operand has
// in each incoming basic block.
auto *NewAggregateOperand = PHINode::Create(
FirstEVI->getAggregateOperand()->getType(), PN.getNumIncomingValues(),
FirstEVI->getAggregateOperand()->getName() + ".pn");
// And populate the PHI with said values.
for (auto Incoming : zip(PN.blocks(), PN.incoming_values()))
InsertNewInstBefore(NewAggregateOperand, PN);
// And finally, create `extractvalue` over the newly-formed PHI nodes.
auto *NewEVI = ExtractValueInst::Create(NewAggregateOperand,
FirstEVI->getIndices(), PN.getName());
PHIArgMergedDebugLoc(NewEVI, PN);
return NewEVI;
/// If we have something like phi [add (a,b), add(a,c)] and if a/b/c and the
/// adds all have a single user, turn this into a phi and a single binop.
Instruction *InstCombinerImpl::foldPHIArgBinOpIntoPHI(PHINode &PN) {
Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
assert(isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst));
unsigned Opc = FirstInst->getOpcode();
Value *LHSVal = FirstInst->getOperand(0);
Value *RHSVal = FirstInst->getOperand(1);
Type *LHSType = LHSVal->getType();
Type *RHSType = RHSVal->getType();
// Scan to see if all operands are the same opcode, and all have one user.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
if (!I || I->getOpcode() != Opc || !I->hasOneUser() ||
// Verify type of the LHS matches so we don't fold cmp's of different
// types.
I->getOperand(0)->getType() != LHSType ||
I->getOperand(1)->getType() != RHSType)
return nullptr;
// If they are CmpInst instructions, check their predicates
if (CmpInst *CI = dyn_cast<CmpInst>(I))
if (CI->getPredicate() != cast<CmpInst>(FirstInst)->getPredicate())
return nullptr;
// Keep track of which operand needs a phi node.
if (I->getOperand(0) != LHSVal) LHSVal = nullptr;
if (I->getOperand(1) != RHSVal) RHSVal = nullptr;
// If both LHS and RHS would need a PHI, don't do this transformation,
// because it would increase the number of PHIs entering the block,
// which leads to higher register pressure. This is especially
// bad when the PHIs are in the header of a loop.
if (!LHSVal && !RHSVal)
return nullptr;
// Otherwise, this is safe to transform!
Value *InLHS = FirstInst->getOperand(0);
Value *InRHS = FirstInst->getOperand(1);
PHINode *NewLHS = nullptr, *NewRHS = nullptr;
if (!LHSVal) {
NewLHS = PHINode::Create(LHSType, PN.getNumIncomingValues(),
FirstInst->getOperand(0)->getName() + ".pn");
NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0));
InsertNewInstBefore(NewLHS, PN);
LHSVal = NewLHS;
if (!RHSVal) {
NewRHS = PHINode::Create(RHSType, PN.getNumIncomingValues(),
FirstInst->getOperand(1)->getName() + ".pn");
NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0));
InsertNewInstBefore(NewRHS, PN);
RHSVal = NewRHS;
// Add all operands to the new PHIs.
if (NewLHS || NewRHS) {
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i));
if (NewLHS) {
Value *NewInLHS = InInst->getOperand(0);
NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i));
if (NewRHS) {
Value *NewInRHS = InInst->getOperand(1);
NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i));
if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst)) {
CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
LHSVal, RHSVal);
PHIArgMergedDebugLoc(NewCI, PN);
return NewCI;
BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst);
BinaryOperator *NewBinOp =
BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal);
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i)
PHIArgMergedDebugLoc(NewBinOp, PN);
return NewBinOp;
Instruction *InstCombinerImpl::foldPHIArgGEPIntoPHI(PHINode &PN) {
GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0));
SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(),
// This is true if all GEP bases are allocas and if all indices into them are
// constants.
bool AllBasePointersAreAllocas = true;
// We don't want to replace this phi if the replacement would require
// more than one phi, which leads to higher register pressure. This is
// especially bad when the PHIs are in the header of a loop.
bool NeededPhi = false;
bool AllInBounds = true;
// Scan to see if all operands are the same opcode, and all have one user.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
GetElementPtrInst *GEP =
if (!GEP || !GEP->hasOneUser() || GEP->getType() != FirstInst->getType() ||
GEP->getNumOperands() != FirstInst->getNumOperands())
return nullptr;
AllInBounds &= GEP->isInBounds();
// Keep track of whether or not all GEPs are of alloca pointers.
if (AllBasePointersAreAllocas &&
(!isa<AllocaInst>(GEP->getOperand(0)) ||
AllBasePointersAreAllocas = false;
// Compare the operand lists.
for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) {
if (FirstInst->getOperand(op) == GEP->getOperand(op))
// Don't merge two GEPs when two operands differ (introducing phi nodes)
// if one of the PHIs has a constant for the index. The index may be
// substantially cheaper to compute for the constants, so making it a
// variable index could pessimize the path. This also handles the case
// for struct indices, which must always be constant.
if (isa<ConstantInt>(FirstInst->getOperand(op)) ||
return nullptr;
if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType())
return nullptr;
// If we already needed a PHI for an earlier operand, and another operand
// also requires a PHI, we'd be introducing more PHIs than we're
// eliminating, which increases register pressure on entry to the PHI's
// block.
if (NeededPhi)
return nullptr;
FixedOperands[op] = nullptr; // Needs a PHI.
NeededPhi = true;
// If all of the base pointers of the PHI'd GEPs are from allocas, don't
// bother doing this transformation. At best, this will just save a bit of
// offset calculation, but all the predecessors will have to materialize the
// stack address into a register anyway. We'd actually rather *clone* the
// load up into the predecessors so that we have a load of a gep of an alloca,
// which can usually all be folded into the load.
if (AllBasePointersAreAllocas)
return nullptr;
// Otherwise, this is safe to transform. Insert PHI nodes for each operand
// that is variable.
SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size());
bool HasAnyPHIs = false;
for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) {
if (FixedOperands[i]) continue; // operand doesn't need a phi.
Value *FirstOp = FirstInst->getOperand(i);
PHINode *NewPN = PHINode::Create(FirstOp->getType(), e,
InsertNewInstBefore(NewPN, PN);
NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0));
OperandPhis[i] = NewPN;
FixedOperands[i] = NewPN;
HasAnyPHIs = true;
// Add all operands to the new PHIs.
if (HasAnyPHIs) {
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i));
BasicBlock *InBB = PN.getIncomingBlock(i);
for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op)
if (PHINode *OpPhi = OperandPhis[op])
OpPhi->addIncoming(InGEP->getOperand(op), InBB);
Value *Base = FixedOperands[0];
GetElementPtrInst *NewGEP =
GetElementPtrInst::Create(FirstInst->getSourceElementType(), Base,
if (AllInBounds) NewGEP->setIsInBounds();
PHIArgMergedDebugLoc(NewGEP, PN);
return NewGEP;
/// Return true if we know that it is safe to sink the load out of the block
/// that defines it. This means that it must be obvious the value of the load is
/// not changed from the point of the load to the end of the block it is in.
/// Finally, it is safe, but not profitable, to sink a load targeting a
/// non-address-taken alloca. Doing so will cause us to not promote the alloca
/// to a register.
static bool isSafeAndProfitableToSinkLoad(LoadInst *L) {
BasicBlock::iterator BBI = L->getIterator(), E = L->getParent()->end();
for (++BBI; BBI != E; ++BBI)
if (BBI->mayWriteToMemory()) {
// Calls that only access inaccessible memory do not block sinking the
// load.
if (auto *CB = dyn_cast<CallBase>(BBI))
if (CB->onlyAccessesInaccessibleMemory())
return false;
// Check for non-address taken alloca. If not address-taken already, it isn't
// profitable to do this xform.
if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) {
bool isAddressTaken = false;
for (User *U : AI->users()) {
if (isa<LoadInst>(U)) continue;
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
// If storing TO the alloca, then the address isn't taken.
if (SI->getOperand(1) == AI) continue;
isAddressTaken = true;
if (!isAddressTaken && AI->isStaticAlloca())
return false;
// If this load is a load from a GEP with a constant offset from an alloca,
// then we don't want to sink it. In its present form, it will be
// load [constant stack offset]. Sinking it will cause us to have to
// materialize the stack addresses in each predecessor in a register only to
// do a shared load from register in the successor.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(L->getOperand(0)))
if (AllocaInst *AI = dyn_cast<AllocaInst>(GEP->getOperand(0)))
if (AI->isStaticAlloca() && GEP->hasAllConstantIndices())
return false;
return true;
Instruction *InstCombinerImpl::foldPHIArgLoadIntoPHI(PHINode &PN) {
LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0));
// FIXME: This is overconservative; this transform is allowed in some cases
// for atomic operations.
if (FirstLI->isAtomic())
return nullptr;
// When processing loads, we need to propagate two bits of information to the
// sunk load: whether it is volatile, and what its alignment is. We currently
// don't sink loads when some have their alignment specified and some don't.
// visitLoadInst will propagate an alignment onto the load when TD is around,
// and if TD isn't around, we can't handle the mixed case.
bool isVolatile = FirstLI->isVolatile();
Align LoadAlignment = FirstLI->getAlign();
unsigned LoadAddrSpace = FirstLI->getPointerAddressSpace();
// We can't sink the load if the loaded value could be modified between the
// load and the PHI.
if (FirstLI->getParent() != PN.getIncomingBlock(0) ||
return nullptr;
// If the PHI is of volatile loads and the load block has multiple
// successors, sinking it would remove a load of the volatile value from
// the path through the other successor.
if (isVolatile &&
FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1)
return nullptr;
// Check to see if all arguments are the same operation.
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
LoadInst *LI = dyn_cast<LoadInst>(PN.getIncomingValue(i));
if (!LI || !LI->hasOneUser())
return nullptr;
// We can't sink the load if the loaded value could be modified between
// the load and the PHI.
if (LI->isVolatile() != isVolatile ||
LI->getParent() != PN.getIncomingBlock(i) ||
LI->getPointerAddressSpace() != LoadAddrSpace ||
return nullptr;
LoadAlignment = std::min(LoadAlignment, Align(LI->getAlign()));
// If the PHI is of volatile loads and the load block has multiple
// successors, sinking it would remove a load of the volatile value from
// the path through the other successor.
if (isVolatile &&
LI->getParent()->getTerminator()->getNumSuccessors() != 1)
return nullptr;
// Okay, they are all the same operation. Create a new PHI node of the
// correct type, and PHI together all of the LHS's of the instructions.
PHINode *NewPN = PHINode::Create(FirstLI->getOperand(0)->getType(),
Value *InVal = FirstLI->getOperand(0);
NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
LoadInst *NewLI =
new LoadInst(FirstLI->getType(), NewPN, "", isVolatile, LoadAlignment);
unsigned KnownIDs[] = {
for (unsigned ID : KnownIDs)
NewLI->setMetadata(ID, FirstLI->getMetadata(ID));
// Add all operands to the new PHI and combine TBAA metadata.
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
LoadInst *LI = cast<LoadInst>(PN.getIncomingValue(i));
combineMetadata(NewLI, LI, KnownIDs, true);
Value *NewInVal = LI->getOperand(0);
if (NewInVal != InVal)
InVal = nullptr;
NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
if (InVal) {
// The new PHI unions all of the same values together. This is really
// common, so we handle it intelligently here for compile-time speed.
NewLI->setOperand(0, InVal);
delete NewPN;
} else {
InsertNewInstBefore(NewPN, PN);
// If this was a volatile load that we are merging, make sure to loop through
// and mark all the input loads as non-volatile. If we don't do this, we will
// insert a new volatile load and the old ones will not be deletable.
if (isVolatile)
for (Value *IncValue : PN.incoming_values())
PHIArgMergedDebugLoc(NewLI, PN);
return NewLI;
/// TODO: This function could handle other cast types, but then it might
/// require special-casing a cast from the 'i1' type. See the comment in
/// FoldPHIArgOpIntoPHI() about pessimizing illegal integer types.
Instruction *InstCombinerImpl::foldPHIArgZextsIntoPHI(PHINode &Phi) {
// We cannot create a new instruction after the PHI if the terminator is an
// EHPad because there is no valid insertion point.
if (Instruction *TI = Phi.getParent()->getTerminator())
if (TI->isEHPad())
return nullptr;
// Early exit for the common case of a phi with two operands. These are
// handled elsewhere. See the comment below where we check the count of zexts
// and constants for more details.
unsigned NumIncomingValues = Phi.getNumIncomingValues();
if (NumIncomingValues < 3)
return nullptr;
// Find the narrower type specified by the first zext.
Type *NarrowType = nullptr;
for (Value *V : Phi.incoming_values()) {
if (auto *Zext = dyn_cast<ZExtInst>(V)) {
NarrowType = Zext->getSrcTy();
if (!NarrowType)
return nullptr;
// Walk the phi operands checking that we only have zexts or constants that
// we can shrink for free. Store the new operands for the new phi.
SmallVector<Value *, 4> NewIncoming;
unsigned NumZexts = 0;
unsigned NumConsts = 0;
for (Value *V : Phi.incoming_values()) {
if (auto *Zext = dyn_cast<ZExtInst>(V)) {
// All zexts must be identical and have one user.
if (Zext->getSrcTy() != NarrowType || !Zext->hasOneUser())
return nullptr;
} else if (auto *C = dyn_cast<Constant>(V)) {
// Make sure that constants can fit in the new type.
Constant *Trunc = ConstantExpr::getTrunc(C, NarrowType);
if (ConstantExpr::getZExt(Trunc, C->getType()) != C)
return nullptr;
} else {
// If it's not a cast or a constant, bail out.
return nullptr;
// The more common cases of a phi with no constant operands or just one
// variable operand are handled by FoldPHIArgOpIntoPHI() and foldOpIntoPhi()
// respectively. foldOpIntoPhi() wants to do the opposite transform that is
// performed here. It tries to replicate a cast in the phi operand's basic
// block to expose other folding opportunities. Thus, InstCombine will
// infinite loop without this check.
if (NumConsts == 0 || NumZexts < 2)
return nullptr;
// All incoming values are zexts or constants that are safe to truncate.
// Create a new phi node of the narrow type, phi together all of the new
// operands, and zext the result back to the original type.
PHINode *NewPhi = PHINode::Create(NarrowType, NumIncomingValues,
Phi.getName() + ".shrunk");
for (unsigned i = 0; i != NumIncomingValues; ++i)
NewPhi->addIncoming(NewIncoming[i], Phi.getIncomingBlock(i));
InsertNewInstBefore(NewPhi, Phi);
return CastInst::CreateZExtOrBitCast(NewPhi, Phi.getType());
/// If all operands to a PHI node are the same "unary" operator and they all are
/// only used by the PHI, PHI together their inputs, and do the operation once,
/// to the result of the PHI.
Instruction *InstCombinerImpl::foldPHIArgOpIntoPHI(PHINode &PN) {
// We cannot create a new instruction after the PHI if the terminator is an
// EHPad because there is no valid insertion point.
if (Instruction *TI = PN.getParent()->getTerminator())
if (TI->isEHPad())
return nullptr;
Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
if (isa<GetElementPtrInst>(FirstInst))
return foldPHIArgGEPIntoPHI(PN);
if (isa<LoadInst>(FirstInst))
return foldPHIArgLoadIntoPHI(PN);
if (isa<InsertValueInst>(FirstInst))
return foldPHIArgInsertValueInstructionIntoPHI(PN);
if (isa<ExtractValueInst>(FirstInst))
return foldPHIArgExtractValueInstructionIntoPHI(PN);
// Scan the instruction, looking for input operations that can be folded away.
// If all input operands to the phi are the same instruction (e.g. a cast from
// the same type or "+42") we can pull the operation through the PHI, reducing
// code size and simplifying code.
Constant *ConstantOp = nullptr;
Type *CastSrcTy = nullptr;
if (isa<CastInst>(FirstInst)) {
CastSrcTy = FirstInst->getOperand(0)->getType();
// Be careful about transforming integer PHIs. We don't want to pessimize
// the code by turning an i32 into an i1293.
if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) {
if (!shouldChangeType(PN.getType(), CastSrcTy))
return nullptr;
} else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) {
// Can fold binop, compare or shift here if the RHS is a constant,
// otherwise call FoldPHIArgBinOpIntoPHI.
ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1));
if (!ConstantOp)
return foldPHIArgBinOpIntoPHI(PN);
} else {
return nullptr; // Cannot fold this operation.
// Check to see if all arguments are the same operation.
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
if (!I || !I->hasOneUser() || !I->isSameOperationAs(FirstInst))
return nullptr;
if (CastSrcTy) {
if (I->getOperand(0)->getType() != CastSrcTy)
return nullptr; // Cast operation must match.
} else if (I->getOperand(1) != ConstantOp) {
return nullptr;
// Okay, they are all the same operation. Create a new PHI node of the
// correct type, and PHI together all of the LHS's of the instructions.
PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(),
Value *InVal = FirstInst->getOperand(0);
NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
// Add all operands to the new PHI.
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0);
if (NewInVal != InVal)
InVal = nullptr;
NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
Value *PhiVal;
if (InVal) {
// The new PHI unions all of the same values together. This is really
// common, so we handle it intelligently here for compile-time speed.
PhiVal = InVal;
delete NewPN;
} else {
InsertNewInstBefore(NewPN, PN);
PhiVal = NewPN;
// Insert and return the new operation.
if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst)) {
CastInst *NewCI = CastInst::Create(FirstCI->getOpcode(), PhiVal,
PHIArgMergedDebugLoc(NewCI, PN);
return NewCI;
if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) {
BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp);
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i)
PHIArgMergedDebugLoc(BinOp, PN);
return BinOp;
CmpInst *CIOp = cast<CmpInst>(FirstInst);
CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
PhiVal, ConstantOp);
PHIArgMergedDebugLoc(NewCI, PN);
return NewCI;
/// Return true if this PHI node is only used by a PHI node cycle that is dead.
static bool DeadPHICycle(PHINode *PN,
SmallPtrSetImpl<PHINode*> &PotentiallyDeadPHIs) {
if (PN->use_empty()) return true;
if (!PN->hasOneUse()) return false;
// Remember this node, and if we find the cycle, return.
if (!PotentiallyDeadPHIs.insert(PN).second)
return true;
// Don't scan crazily complex things.
if (PotentiallyDeadPHIs.size() == 16)
return false;
if (PHINode *PU = dyn_cast<PHINode>(PN->user_back()))
return DeadPHICycle(PU, PotentiallyDeadPHIs);
return false;
/// Return true if this phi node is always equal to NonPhiInVal.
/// This happens with mutually cyclic phi nodes like:
/// z = some value; x = phi (y, z); y = phi (x, z)
static bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal,
SmallPtrSetImpl<PHINode*> &ValueEqualPHIs) {
// See if we already saw this PHI node.
if (!ValueEqualPHIs.insert(PN).second)
return true;
// Don't scan crazily complex things.
if (ValueEqualPHIs.size() == 16)
return false;
// Scan the operands to see if they are either phi nodes or are equal to
// the value.
for (Value *Op : PN->incoming_values()) {
if (PHINode *OpPN = dyn_cast<PHINode>(Op)) {
if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs))
return false;
} else if (Op != NonPhiInVal)
return false;
return true;
/// Return an existing non-zero constant if this phi node has one, otherwise
/// return constant 1.
static ConstantInt *GetAnyNonZeroConstInt(PHINode &PN) {
assert(isa<IntegerType>(PN.getType()) && "Expect only integer type phi");
for (Value *V : PN.operands())
if (auto *ConstVA = dyn_cast<ConstantInt>(V))
if (!ConstVA->isZero())
return ConstVA;
return ConstantInt::get(cast<IntegerType>(PN.getType()), 1);
namespace {
struct PHIUsageRecord {
unsigned PHIId; // The ID # of the PHI (something determinstic to sort on)
unsigned Shift; // The amount shifted.
Instruction *Inst; // The trunc instruction.
PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User)
: PHIId(pn), Shift(Sh), Inst(User) {}
bool operator<(const PHIUsageRecord &RHS) const {
if (PHIId < RHS.PHIId) return true;
if (PHIId > RHS.PHIId) return false;
if (Shift < RHS.Shift) return true;
if (Shift > RHS.Shift) return false;
return Inst->getType()->getPrimitiveSizeInBits() <
struct LoweredPHIRecord {
PHINode *PN; // The PHI that was lowered.
unsigned Shift; // The amount shifted.
unsigned Width; // The width extracted.
LoweredPHIRecord(PHINode *pn, unsigned Sh, Type *Ty)
: PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {}
// Ctor form used by DenseMap.
LoweredPHIRecord(PHINode *pn, unsigned Sh)
: PN(pn), Shift(Sh), Width(0) {}
} // namespace
namespace llvm {
struct DenseMapInfo<LoweredPHIRecord> {
static inline LoweredPHIRecord getEmptyKey() {
return LoweredPHIRecord(nullptr, 0);
static inline LoweredPHIRecord getTombstoneKey() {
return LoweredPHIRecord(nullptr, 1);
static unsigned getHashValue(const LoweredPHIRecord &Val) {
return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^
static bool isEqual(const LoweredPHIRecord &LHS,
const LoweredPHIRecord &RHS) {
return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift &&
LHS.Width == RHS.Width;
} // namespace llvm
/// This is an integer PHI and we know that it has an illegal type: see if it is
/// only used by trunc or trunc(lshr) operations. If so, we split the PHI into
/// the various pieces being extracted. This sort of thing is introduced when
/// SROA promotes an aggregate to large integer values.
/// TODO: The user of the trunc may be an bitcast to float/double/vector or an
/// inttoptr. We should produce new PHIs in the right type.
Instruction *InstCombinerImpl::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) {
// PHIUsers - Keep track of all of the truncated values extracted from a set
// of PHIs, along with their offset. These are the things we want to rewrite.
SmallVector<PHIUsageRecord, 16> PHIUsers;
// PHIs are often mutually cyclic, so we keep track of a whole set of PHI
// nodes which are extracted from. PHIsToSlice is a set we use to avoid
// revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to
// check the uses of (to ensure they are all extracts).
SmallVector<PHINode*, 8> PHIsToSlice;
SmallPtrSet<PHINode*, 8> PHIsInspected;
for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) {
PHINode *PN = PHIsToSlice[PHIId];
// Scan the input list of the PHI. If any input is an invoke, and if the
// input is defined in the predecessor, then we won't be split the critical
// edge which is required to insert a truncate. Because of this, we have to
// bail out.
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i));
if (!II) continue;
if (II->getParent() != PN->getIncomingBlock(i))
// If we have a phi, and if it's directly in the predecessor, then we have
// a critical edge where we need to put the truncate. Since we can't
// split the edge in instcombine, we have to bail out.
return nullptr;
for (User *U : PN->users()) {
Instruction *UserI = cast<Instruction>(U);
// If the user is a PHI, inspect its uses recursively.
if (PHINode *UserPN = dyn_cast<PHINode>(UserI)) {
if (PHIsInspected.insert(UserPN).second)
// Truncates are always ok.
if (isa<TruncInst>(UserI)) {
PHIUsers.push_back(PHIUsageRecord(PHIId, 0, UserI));
// Otherwise it must be a lshr which can only be used by one trunc.
if (UserI->getOpcode() != Instruction::LShr ||
!UserI->hasOneUse() || !isa<TruncInst>(UserI->user_back()) ||
return nullptr;
// Bail on out of range shifts.
unsigned SizeInBits = UserI->getType()->getScalarSizeInBits();
if (cast<ConstantInt>(UserI->getOperand(1))->getValue().uge(SizeInBits))
return nullptr;
unsigned Shift = cast<ConstantInt>(UserI->getOperand(1))->getZExtValue();
PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, UserI->user_back()));
// If we have no users, they must be all self uses, just nuke the PHI.
if (PHIUsers.empty())
return replaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType()));
// If this phi node is transformable, create new PHIs for all the pieces
// extracted out of it. First, sort the users by their offset and size.
array_pod_sort(PHIUsers.begin(), PHIUsers.end());
LLVM_DEBUG(dbgs() << "SLICING UP PHI: " << FirstPhi << '\n';
for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) dbgs()
<< "AND USER PHI #" << i << ": " << *PHIsToSlice[i] << '\n';);
// PredValues - This is a temporary used when rewriting PHI nodes. It is
// hoisted out here to avoid construction/destruction thrashing.
DenseMap<BasicBlock*, Value*> PredValues;
// ExtractedVals - Each new PHI we introduce is saved here so we don't
// introduce redundant PHIs.
DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals;
for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) {
unsigned PHIId = PHIUsers[UserI].PHIId;
PHINode *PN = PHIsToSlice[PHIId];
unsigned Offset = PHIUsers[UserI].Shift;
Type *Ty = PHIUsers[UserI].Inst->getType();
PHINode *EltPHI;
// If we've already lowered a user like this, reuse the previously lowered
// value.
if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == nullptr) {
// Otherwise, Create the new PHI node for this user.
EltPHI = PHINode::Create(Ty, PN->getNumIncomingValues(),
PN->getName()+".off"+Twine(Offset), PN);
assert(EltPHI->getType() != PN->getType() &&
"Truncate didn't shrink phi?");
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *Pred = PN->getIncomingBlock(i);
Value *&PredVal = PredValues[Pred];
// If we already have a value for this predecessor, reuse it.
if (PredVal) {
EltPHI->addIncoming(PredVal, Pred);
// Handle the PHI self-reuse case.
Value *InVal = PN->getIncomingValue(i);
if (InVal == PN) {
PredVal = EltPHI;
EltPHI->addIncoming(PredVal, Pred);
if (PHINode *InPHI = dyn_cast<PHINode>(PN)) {
// If the incoming value was a PHI, and if it was one of the PHIs we
// already rewrote it, just use the lowered value.
if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) {
PredVal = Res;
EltPHI->addIncoming(PredVal, Pred);
// Otherwise, do an extract in the predecessor.
Value *Res = InVal;
if (Offset)
Res = Builder.CreateLShr(Res, ConstantInt::get(InVal->getType(),
Offset), "extract");
Res = Builder.CreateTrunc(Res, Ty, "extract.t");
PredVal = Res;
EltPHI->addIncoming(Res, Pred);
// If the incoming value was a PHI, and if it was one of the PHIs we are
// rewriting, we will ultimately delete the code we inserted. This
// means we need to revisit that PHI to make sure we extract out the
// needed piece.
if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i)))
if (PHIsInspected.count(OldInVal)) {
unsigned RefPHIId =
find(PHIsToSlice, OldInVal) - PHIsToSlice.begin();
PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset,
LLVM_DEBUG(dbgs() << " Made element PHI for offset " << Offset << ": "
<< *EltPHI << '\n');
ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI;
// Replace the use of this piece with the PHI node.
replaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI);
// Replace all the remaining uses of the PHI nodes (self uses and the lshrs)
// with undefs.
Value *Undef = UndefValue::get(FirstPhi.getType());
for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i)
replaceInstUsesWith(*PHIsToSlice[i], Undef);
return replaceInstUsesWith(FirstPhi, Undef);
static Value *SimplifyUsingControlFlow(InstCombiner &Self, PHINode &PN,
const DominatorTree &DT) {
// Simplify the following patterns:
// if (cond)
// / \
// ... ...
// \ /
// phi [true] [false]
if (!PN.getType()->isIntegerTy(1))
return nullptr;
if (PN.getNumOperands() != 2)
return nullptr;
// Make sure all inputs are constants.
if (!all_of(PN.operands(), [](Value *V) { return isa<ConstantInt>(V); }))
return nullptr;
BasicBlock *BB = PN.getParent();
// Do not bother with unreachable instructions.
if (!DT.isReachableFromEntry(BB))
return nullptr;
// Same inputs.
if (PN.getOperand(0) == PN.getOperand(1))
return PN.getOperand(0);
BasicBlock *TruePred = nullptr, *FalsePred = nullptr;
for (auto *Pred : predecessors(BB)) {
auto *Input = cast<ConstantInt>(PN.getIncomingValueForBlock(Pred));
if (Input->isAllOnesValue())
TruePred = Pred;
FalsePred = Pred;
assert(TruePred && FalsePred && "Must be!");
// Check which edge of the dominator dominates the true input. If it is the
// false edge, we should invert the condition.
auto *IDom = DT.getNode(BB)->getIDom()->getBlock();
auto *BI = dyn_cast<BranchInst>(IDom->getTerminator());
if (!BI || BI->isUnconditional())
return nullptr;
// Check that edges outgoing from the idom's terminators dominate respective
// inputs of the Phi.
BasicBlockEdge TrueOutEdge(IDom, BI->getSuccessor(0));
BasicBlockEdge FalseOutEdge(IDom, BI->getSuccessor(1));
BasicBlockEdge TrueIncEdge(TruePred, BB);
BasicBlockEdge FalseIncEdge(FalsePred, BB);
auto *Cond = BI->getCondition();
if (DT.dominates(TrueOutEdge, TrueIncEdge) &&
DT.dominates(FalseOutEdge, FalseIncEdge))
// This Phi is actually equivalent to branching condition of IDom.
return Cond;
else if (DT.dominates(TrueOutEdge, FalseIncEdge) &&
DT.dominates(FalseOutEdge, TrueIncEdge)) {
// This Phi is actually opposite to branching condition of IDom. We invert
// the condition that will potentially open up some opportunities for
// sinking.
auto InsertPt = BB->getFirstInsertionPt();
if (InsertPt != BB->end()) {
return Self.Builder.CreateNot(Cond);
return nullptr;
// PHINode simplification
Instruction *InstCombinerImpl::visitPHINode(PHINode &PN) {
if (Value *V = SimplifyInstruction(&PN, SQ.getWithInstruction(&PN)))
return replaceInstUsesWith(PN, V);
if (Instruction *Result = foldPHIArgZextsIntoPHI(PN))
return Result;
// If all PHI operands are the same operation, pull them through the PHI,
// reducing code size.
if (isa<Instruction>(PN.getIncomingValue(0)) &&
isa<Instruction>(PN.getIncomingValue(1)) &&
cast<Instruction>(PN.getIncomingValue(0))->getOpcode() ==
cast<Instruction>(PN.getIncomingValue(1))->getOpcode() &&
if (Instruction *Result = foldPHIArgOpIntoPHI(PN))
return Result;
// If the incoming values are pointer casts of the same original value,
// replace the phi with a single cast.
if (PN.getType()->isPointerTy()) {
Value *IV0 = PN.getIncomingValue(0);
Value *IV0Stripped = IV0->stripPointerCasts();
// Set to keep track of values known to be equal to IV0Stripped after
// stripping pointer casts.
SmallPtrSet<Value *, 4> CheckedIVs;
if (IV0 != IV0Stripped &&
all_of(PN.incoming_values(), [&CheckedIVs, IV0Stripped](Value *IV) {
return !CheckedIVs.insert(IV).second ||
IV0Stripped == IV->stripPointerCasts();
})) {
return CastInst::CreatePointerCast(IV0Stripped, PN.getType());
// If this is a trivial cycle in the PHI node graph, remove it. Basically, if
// this PHI only has a single use (a PHI), and if that PHI only has one use (a
// PHI)... break the cycle.
if (PN.hasOneUse()) {
if (Instruction *Result = foldIntegerTypedPHI(PN))
return Result;
Instruction *PHIUser = cast<Instruction>(PN.user_back());
if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs;
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
return replaceInstUsesWith(PN, UndefValue::get(PN.getType()));
// If this phi has a single use, and if that use just computes a value for
// the next iteration of a loop, delete the phi. This occurs with unused
// induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this
// common case here is good because the only other things that catch this
// are induction variable analysis (sometimes) and ADCE, which is only run
// late.
if (PHIUser->hasOneUse() &&
(isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) &&
PHIUser->user_back() == &PN) {
return replaceInstUsesWith(PN, UndefValue::get(PN.getType()));
// When a PHI is used only to be compared with zero, it is safe to replace
// an incoming value proved as known nonzero with any non-zero constant.
// For example, in the code below, the incoming value %v can be replaced
// with any non-zero constant based on the fact that the PHI is only used to
// be compared with zero and %v is a known non-zero value:
// %v = select %cond, 1, 2
// %p = phi [%v, BB] ...
// icmp eq, %p, 0
auto *CmpInst = dyn_cast<ICmpInst>(PHIUser);
// FIXME: To be simple, handle only integer type for now.
if (CmpInst && isa<IntegerType>(PN.getType()) && CmpInst->isEquality() &&
match(CmpInst->getOperand(1), m_Zero())) {
ConstantInt *NonZeroConst = nullptr;
bool MadeChange = false;
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
Instruction *CtxI = PN.getIncomingBlock(i)->getTerminator();
Value *VA = PN.getIncomingValue(i);
if (isKnownNonZero(VA, DL, 0, &AC, CtxI, &DT)) {
if (!NonZeroConst)
NonZeroConst = GetAnyNonZeroConstInt(PN);
if (NonZeroConst != VA) {
replaceOperand(PN, i, NonZeroConst);
MadeChange = true;
if (MadeChange)
return &PN;
// We sometimes end up with phi cycles that non-obviously end up being the
// same value, for example:
// z = some value; x = phi (y, z); y = phi (x, z)
// where the phi nodes don't necessarily need to be in the same block. Do a
// quick check to see if the PHI node only contains a single non-phi value, if
// so, scan to see if the phi cycle is actually equal to that value.
unsigned InValNo = 0, NumIncomingVals = PN.getNumIncomingValues();
// Scan for the first non-phi operand.
while (InValNo != NumIncomingVals &&
if (InValNo != NumIncomingVals) {
Value *NonPhiInVal = PN.getIncomingValue(InValNo);
// Scan the rest of the operands to see if there are any conflicts, if so
// there is no need to recursively scan other phis.
for (++InValNo; InValNo != NumIncomingVals; ++InValNo) {
Value *OpVal = PN.getIncomingValue(InValNo);
if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal))
// If we scanned over all operands, then we have one unique value plus
// phi values. Scan PHI nodes to see if they all merge in each other or
// the value.
if (InValNo == NumIncomingVals) {
SmallPtrSet<PHINode*, 16> ValueEqualPHIs;
if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs))
return replaceInstUsesWith(PN, NonPhiInVal);
// If there are multiple PHIs, sort their operands so that they all list
// the blocks in the same order. This will help identical PHIs be eliminated
// by other passes. Other passes shouldn't depend on this for correctness
// however.
PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin());
if (&PN != FirstPN)
for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *BBA = PN.getIncomingBlock(i);
BasicBlock *BBB = FirstPN->getIncomingBlock(i);
if (BBA != BBB) {
Value *VA = PN.getIncomingValue(i);
unsigned j = PN.getBasicBlockIndex(BBB);
Value *VB = PN.getIncomingValue(j);
PN.setIncomingBlock(i, BBB);
PN.setIncomingValue(i, VB);
PN.setIncomingBlock(j, BBA);
PN.setIncomingValue(j, VA);
// NOTE: Instcombine normally would want us to "return &PN" if we
// modified any of the operands of an instruction. However, since we
// aren't adding or removing uses (just rearranging them) we don't do
// this in this case.
// Is there an identical PHI node in this basic block?
for (PHINode &IdenticalPN : PN.getParent()->phis()) {
// Ignore the PHI node itself.
if (&IdenticalPN == &PN)
// Note that even though we've just canonicalized this PHI, due to the
// worklist visitation order, there are no guarantess that *every* PHI
// has been canonicalized, so we can't just compare operands ranges.
if (!PN.isIdenticalToWhenDefined(&IdenticalPN))
// Just use that PHI instead then.
return replaceInstUsesWith(PN, &IdenticalPN);
// If this is an integer PHI and we know that it has an illegal type, see if
// it is only used by trunc or trunc(lshr) operations. If so, we split the
// PHI into the various pieces being extracted. This sort of thing is
// introduced when SROA promotes an aggregate to a single large integer type.
if (PN.getType()->isIntegerTy() &&
if (Instruction *Res = SliceUpIllegalIntegerPHI(PN))
return Res;
// Ultimately, try to replace this Phi with a dominating condition.
if (auto *V = SimplifyUsingControlFlow(*this, PN, DT))
return replaceInstUsesWith(PN, V);
return nullptr;