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llvm-project/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp

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//===- InstCombinePHI.cpp -------------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the visitPHINode function.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/InstructionSimplify.h"
using namespace llvm;
#define DEBUG_TYPE "instcombine"
/// If we have something like phi [add (a,b), add(a,c)] and if a/b/c and the
/// adds all have a single use, turn this into a phi and a single binop.
Instruction *InstCombiner::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();
bool isNUW = false, isNSW = false, isExact = false;
if (OverflowingBinaryOperator *BO =
dyn_cast<OverflowingBinaryOperator>(FirstInst)) {
isNUW = BO->hasNoUnsignedWrap();
isNSW = BO->hasNoSignedWrap();
} else if (PossiblyExactOperator *PEO =
dyn_cast<PossiblyExactOperator>(FirstInst))
isExact = PEO->isExact();
// Scan to see if all operands are the same opcode, and all have one use.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
if (!I || I->getOpcode() != Opc || !I->hasOneUse() ||
// 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;
if (isNUW)
isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap();
if (isNSW)
isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
if (isExact)
isExact = cast<PossiblyExactOperator>(I)->isExact();
// 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);
NewCI->setDebugLoc(FirstInst->getDebugLoc());
return NewCI;
}
BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst);
BinaryOperator *NewBinOp =
BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal);
if (isNUW) NewBinOp->setHasNoUnsignedWrap();
if (isNSW) NewBinOp->setHasNoSignedWrap();
if (isExact) NewBinOp->setIsExact();
NewBinOp->setDebugLoc(FirstInst->getDebugLoc());
return NewBinOp;
}
Instruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) {
GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0));
SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(),
FirstInst->op_end());
// 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 use.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i));
if (!GEP || !GEP->hasOneUse() || 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)) ||
!GEP->hasAllConstantIndices()))
AllBasePointersAreAllocas = false;
// Compare the operand lists.
for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) {
if (FirstInst->getOperand(op) == GEP->getOperand(op))
continue;
// 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)) ||
isa<ConstantInt>(GEP->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,
FirstOp->getName()+".pn");
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,
makeArrayRef(FixedOperands).slice(1));
if (AllInBounds) NewGEP->setIsInBounds();
NewGEP->setDebugLoc(FirstInst->getDebugLoc());
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, E = L->getParent()->end();
for (++BBI; BBI != E; ++BBI)
if (BBI->mayWriteToMemory())
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;
break;
}
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 *InstCombiner::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();
unsigned LoadAlignment = FirstLI->getAlignment();
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) ||
!isSafeAndProfitableToSinkLoad(FirstLI))
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->hasOneUse())
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 ||
!isSafeAndProfitableToSinkLoad(LI))
return nullptr;
// If some of the loads have an alignment specified but not all of them,
// we can't do the transformation.
if ((LoadAlignment != 0) != (LI->getAlignment() != 0))
return nullptr;
LoadAlignment = std::min(LoadAlignment, LI->getAlignment());
// 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(),
PN.getNumIncomingValues(),
PN.getName()+".in");
Value *InVal = FirstLI->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<LoadInst>(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;
}
// 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())
cast<LoadInst>(IncValue)->setVolatile(false);
LoadInst *NewLI = new LoadInst(PhiVal, "", isVolatile, LoadAlignment);
NewLI->setDebugLoc(FirstLI->getDebugLoc());
return NewLI;
}
/// 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 *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
if (isa<GetElementPtrInst>(FirstInst))
return FoldPHIArgGEPIntoPHI(PN);
if (isa<LoadInst>(FirstInst))
return FoldPHIArgLoadIntoPHI(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;
bool isNUW = false, isNSW = false, isExact = false;
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);
if (OverflowingBinaryOperator *BO =
dyn_cast<OverflowingBinaryOperator>(FirstInst)) {
isNUW = BO->hasNoUnsignedWrap();
isNSW = BO->hasNoSignedWrap();
} else if (PossiblyExactOperator *PEO =
dyn_cast<PossiblyExactOperator>(FirstInst))
isExact = PEO->isExact();
} 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->hasOneUse() || !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;
}
if (isNUW)
isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap();
if (isNSW)
isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
if (isExact)
isExact = cast<PossiblyExactOperator>(I)->isExact();
}
// 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(),
PN.getNumIncomingValues(),
PN.getName()+".in");
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,
PN.getType());
NewCI->setDebugLoc(FirstInst->getDebugLoc());
return NewCI;
}
if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) {
BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp);
if (isNUW) BinOp->setHasNoUnsignedWrap();
if (isNSW) BinOp->setHasNoSignedWrap();
if (isExact) BinOp->setIsExact();
BinOp->setDebugLoc(FirstInst->getDebugLoc());
return BinOp;
}
CmpInst *CIOp = cast<CmpInst>(FirstInst);
CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
PhiVal, ConstantOp);
NewCI->setDebugLoc(FirstInst->getDebugLoc());
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;
}
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() <
RHS.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 llvm {
template<>
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) ^
(Val.Width>>3);
}
static bool isEqual(const LoweredPHIRecord &LHS,
const LoweredPHIRecord &RHS) {
return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift &&
LHS.Width == RHS.Width;
}
};
}
/// 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 *InstCombiner::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;
PHIsToSlice.push_back(&FirstPhi);
PHIsInspected.insert(&FirstPhi);
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))
continue;
// 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)
PHIsToSlice.push_back(UserPN);
continue;
}
// Truncates are always ok.
if (isa<TruncInst>(UserI)) {
PHIUsers.push_back(PHIUsageRecord(PHIId, 0, UserI));
continue;
}
// 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()) ||
!isa<ConstantInt>(UserI->getOperand(1)))
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());
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);
continue;
}
// Handle the PHI self-reuse case.
Value *InVal = PN->getIncomingValue(i);
if (InVal == PN) {
PredVal = EltPHI;
EltPHI->addIncoming(PredVal, Pred);
continue;
}
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);
continue;
}
}
// Otherwise, do an extract in the predecessor.
Builder->SetInsertPoint(Pred, Pred->getTerminator());
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 = std::find(PHIsToSlice.begin(),PHIsToSlice.end(),
OldInVal)-PHIsToSlice.begin();
PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset,
cast<Instruction>(Res)));
++UserE;
}
}
PredValues.clear();
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);
}
// PHINode simplification
//
Instruction *InstCombiner::visitPHINode(PHINode &PN) {
if (Value *V = SimplifyInstruction(&PN, DL, TLI, DT, AC))
return ReplaceInstUsesWith(PN, V);
// 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() &&
// FIXME: The hasOneUse check will fail for PHIs that use the value more
// than themselves more than once.
PN.getIncomingValue(0)->hasOneUse())
if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
return Result;
// 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()) {
Instruction *PHIUser = cast<Instruction>(PN.user_back());
if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs;
PotentiallyDeadPHIs.insert(&PN);
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()));
}
}
// 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 &&
isa<PHINode>(PN.getIncomingValue(InValNo)))
++InValNo;
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))
break;
}
// 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.
}
}
// 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() &&
!DL.isLegalInteger(PN.getType()->getPrimitiveSizeInBits()))
if (Instruction *Res = SliceUpIllegalIntegerPHI(PN))
return Res;
return nullptr;
}
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