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//===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
// 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 PHITransAddr class.
#include "llvm/Analysis/PHITransAddr.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
static bool CanPHITrans(Instruction *Inst) {
if (isa<PHINode>(Inst) ||
return true;
if (isa<CastInst>(Inst) &&
return true;
if (Inst->getOpcode() == Instruction::Add &&
return true;
// cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
// if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
// cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
return false;
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void PHITransAddr::dump() const {
if (!Addr) {
dbgs() << "PHITransAddr: null\n";
dbgs() << "PHITransAddr: " << *Addr << "\n";
for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
dbgs() << " Input #" << i << " is " << *InstInputs[i] << "\n";
static bool VerifySubExpr(Value *Expr,
SmallVectorImpl<Instruction*> &InstInputs) {
// If this is a non-instruction value, there is nothing to do.
Instruction *I = dyn_cast<Instruction>(Expr);
if (!I) return true;
// If it's an instruction, it is either in Tmp or its operands recursively
// are.
SmallVectorImpl<Instruction *>::iterator Entry = find(InstInputs, I);
if (Entry != InstInputs.end()) {
return true;
// If it isn't in the InstInputs list it is a subexpr incorporated into the
// address. Sanity check that it is phi translatable.
if (!CanPHITrans(I)) {
errs() << "Instruction in PHITransAddr is not phi-translatable:\n";
errs() << *I << '\n';
llvm_unreachable("Either something is missing from InstInputs or "
"CanPHITrans is wrong.");
// Validate the operands of the instruction.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (!VerifySubExpr(I->getOperand(i), InstInputs))
return false;
return true;
/// Verify - Check internal consistency of this data structure. If the
/// structure is valid, it returns true. If invalid, it prints errors and
/// returns false.
bool PHITransAddr::Verify() const {
if (!Addr) return true;
SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());
if (!VerifySubExpr(Addr, Tmp))
return false;
if (!Tmp.empty()) {
errs() << "PHITransAddr contains extra instructions:\n";
for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
errs() << " InstInput #" << i << " is " << *InstInputs[i] << "\n";
llvm_unreachable("This is unexpected.");
// a-ok.
return true;
/// IsPotentiallyPHITranslatable - If this needs PHI translation, return true
/// if we have some hope of doing it. This should be used as a filter to
/// avoid calling PHITranslateValue in hopeless situations.
bool PHITransAddr::IsPotentiallyPHITranslatable() const {
// If the input value is not an instruction, or if it is not defined in CurBB,
// then we don't need to phi translate it.
Instruction *Inst = dyn_cast<Instruction>(Addr);
return !Inst || CanPHITrans(Inst);
static void RemoveInstInputs(Value *V,
SmallVectorImpl<Instruction*> &InstInputs) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return;
// If the instruction is in the InstInputs list, remove it.
SmallVectorImpl<Instruction *>::iterator Entry = find(InstInputs, I);
if (Entry != InstInputs.end()) {
assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");
// Otherwise, it must have instruction inputs itself. Zap them recursively.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
RemoveInstInputs(Op, InstInputs);
Value *PHITransAddr::PHITranslateSubExpr(Value *V, BasicBlock *CurBB,
BasicBlock *PredBB,
const DominatorTree *DT) {
// If this is a non-instruction value, it can't require PHI translation.
Instruction *Inst = dyn_cast<Instruction>(V);
if (!Inst) return V;
// Determine whether 'Inst' is an input to our PHI translatable expression.
bool isInput = is_contained(InstInputs, Inst);
// Handle inputs instructions if needed.
if (isInput) {
if (Inst->getParent() != CurBB) {
// If it is an input defined in a different block, then it remains an
// input.
return Inst;
// If 'Inst' is defined in this block and is an input that needs to be phi
// translated, we need to incorporate the value into the expression or fail.
// In either case, the instruction itself isn't an input any longer.
InstInputs.erase(find(InstInputs, Inst));
// If this is a PHI, go ahead and translate it.
if (PHINode *PN = dyn_cast<PHINode>(Inst))
return AddAsInput(PN->getIncomingValueForBlock(PredBB));
// If this is a non-phi value, and it is analyzable, we can incorporate it
// into the expression by making all instruction operands be inputs.
if (!CanPHITrans(Inst))
return nullptr;
// All instruction operands are now inputs (and of course, they may also be
// defined in this block, so they may need to be phi translated themselves.
for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
if (Instruction *Op = dyn_cast<Instruction>(Inst->getOperand(i)))
// Ok, it must be an intermediate result (either because it started that way
// or because we just incorporated it into the expression). See if its
// operands need to be phi translated, and if so, reconstruct it.
if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
if (!isSafeToSpeculativelyExecute(Cast)) return nullptr;
Value *PHIIn = PHITranslateSubExpr(Cast->getOperand(0), CurBB, PredBB, DT);
if (!PHIIn) return nullptr;
if (PHIIn == Cast->getOperand(0))
return Cast;
// Find an available version of this cast.
// Constants are trivial to find.
if (Constant *C = dyn_cast<Constant>(PHIIn))
return AddAsInput(ConstantExpr::getCast(Cast->getOpcode(),
C, Cast->getType()));
// Otherwise we have to see if a casted version of the incoming pointer
// is available. If so, we can use it, otherwise we have to fail.
for (User *U : PHIIn->users()) {
if (CastInst *CastI = dyn_cast<CastInst>(U))
if (CastI->getOpcode() == Cast->getOpcode() &&
CastI->getType() == Cast->getType() &&
(!DT || DT->dominates(CastI->getParent(), PredBB)))
return CastI;
return nullptr;
// Handle getelementptr with at least one PHI translatable operand.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
SmallVector<Value*, 8> GEPOps;
bool AnyChanged = false;
for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
Value *GEPOp = PHITranslateSubExpr(GEP->getOperand(i), CurBB, PredBB, DT);
if (!GEPOp) return nullptr;
AnyChanged |= GEPOp != GEP->getOperand(i);
if (!AnyChanged)
return GEP;
// Simplify the GEP to handle 'gep x, 0' -> x etc.
if (Value *V = SimplifyGEPInst(GEP->getSourceElementType(),
GEPOps, {DL, TLI, DT, AC})) {
for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
RemoveInstInputs(GEPOps[i], InstInputs);
return AddAsInput(V);
// Scan to see if we have this GEP available.
Value *APHIOp = GEPOps[0];
for (User *U : APHIOp->users()) {
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U))
if (GEPI->getType() == GEP->getType() &&
GEPI->getNumOperands() == GEPOps.size() &&
GEPI->getParent()->getParent() == CurBB->getParent() &&
(!DT || DT->dominates(GEPI->getParent(), PredBB))) {
if (std::equal(GEPOps.begin(), GEPOps.end(), GEPI->op_begin()))
return GEPI;
return nullptr;
// Handle add with a constant RHS.
if (Inst->getOpcode() == Instruction::Add &&
isa<ConstantInt>(Inst->getOperand(1))) {
// PHI translate the LHS.
Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();
Value *LHS = PHITranslateSubExpr(Inst->getOperand(0), CurBB, PredBB, DT);
if (!LHS) return nullptr;
// If the PHI translated LHS is an add of a constant, fold the immediates.
if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
if (BOp->getOpcode() == Instruction::Add)
if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
LHS = BOp->getOperand(0);
RHS = ConstantExpr::getAdd(RHS, CI);
isNSW = isNUW = false;
// If the old 'LHS' was an input, add the new 'LHS' as an input.
if (is_contained(InstInputs, BOp)) {
RemoveInstInputs(BOp, InstInputs);
// See if the add simplifies away.
if (Value *Res = SimplifyAddInst(LHS, RHS, isNSW, isNUW, {DL, TLI, DT, AC})) {
// If we simplified the operands, the LHS is no longer an input, but Res
// is.
RemoveInstInputs(LHS, InstInputs);
return AddAsInput(Res);
// If we didn't modify the add, just return it.
if (LHS == Inst->getOperand(0) && RHS == Inst->getOperand(1))
return Inst;
// Otherwise, see if we have this add available somewhere.
for (User *U : LHS->users()) {
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U))
if (BO->getOpcode() == Instruction::Add &&
BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
BO->getParent()->getParent() == CurBB->getParent() &&
(!DT || DT->dominates(BO->getParent(), PredBB)))
return BO;
return nullptr;
// Otherwise, we failed.
return nullptr;
/// PHITranslateValue - PHI translate the current address up the CFG from
/// CurBB to Pred, updating our state to reflect any needed changes. If
/// 'MustDominate' is true, the translated value must dominate
/// PredBB. This returns true on failure and sets Addr to null.
bool PHITransAddr::PHITranslateValue(BasicBlock *CurBB, BasicBlock *PredBB,
const DominatorTree *DT,
bool MustDominate) {
assert(DT || !MustDominate);
assert(Verify() && "Invalid PHITransAddr!");
if (DT && DT->isReachableFromEntry(PredBB))
Addr =
PHITranslateSubExpr(Addr, CurBB, PredBB, MustDominate ? DT : nullptr);
Addr = nullptr;
assert(Verify() && "Invalid PHITransAddr!");
if (MustDominate)
// Make sure the value is live in the predecessor.
if (Instruction *Inst = dyn_cast_or_null<Instruction>(Addr))
if (!DT->dominates(Inst->getParent(), PredBB))
Addr = nullptr;
return Addr == nullptr;
/// PHITranslateWithInsertion - PHI translate this value into the specified
/// predecessor block, inserting a computation of the value if it is
/// unavailable.
/// All newly created instructions are added to the NewInsts list. This
/// returns null on failure.
Value *PHITransAddr::
PHITranslateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
const DominatorTree &DT,
SmallVectorImpl<Instruction*> &NewInsts) {
unsigned NISize = NewInsts.size();
// Attempt to PHI translate with insertion.
Addr = InsertPHITranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);
// If successful, return the new value.
if (Addr) return Addr;
// If not, destroy any intermediate instructions inserted.
while (NewInsts.size() != NISize)
return nullptr;
/// InsertPHITranslatedPointer - Insert a computation of the PHI translated
/// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
/// block. All newly created instructions are added to the NewInsts list.
/// This returns null on failure.
Value *PHITransAddr::
InsertPHITranslatedSubExpr(Value *InVal, BasicBlock *CurBB,
BasicBlock *PredBB, const DominatorTree &DT,
SmallVectorImpl<Instruction*> &NewInsts) {
// See if we have a version of this value already available and dominating
// PredBB. If so, there is no need to insert a new instance of it.
PHITransAddr Tmp(InVal, DL, AC);
if (!Tmp.PHITranslateValue(CurBB, PredBB, &DT, /*MustDominate=*/true))
return Tmp.getAddr();
// We don't need to PHI translate values which aren't instructions.
auto *Inst = dyn_cast<Instruction>(InVal);
if (!Inst)
return nullptr;
// Handle cast of PHI translatable value.
if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
if (!isSafeToSpeculativelyExecute(Cast)) return nullptr;
Value *OpVal = InsertPHITranslatedSubExpr(Cast->getOperand(0),
CurBB, PredBB, DT, NewInsts);
if (!OpVal) return nullptr;
// Otherwise insert a cast at the end of PredBB.
CastInst *New = CastInst::Create(Cast->getOpcode(), OpVal, InVal->getType(),
InVal->getName() + ".phi.trans.insert",
return New;
// Handle getelementptr with at least one PHI operand.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
SmallVector<Value*, 8> GEPOps;
BasicBlock *CurBB = GEP->getParent();
for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
Value *OpVal = InsertPHITranslatedSubExpr(GEP->getOperand(i),
CurBB, PredBB, DT, NewInsts);
if (!OpVal) return nullptr;
GetElementPtrInst *Result = GetElementPtrInst::Create(
GEP->getSourceElementType(), GEPOps[0], makeArrayRef(GEPOps).slice(1),
InVal->getName() + ".phi.trans.insert", PredBB->getTerminator());
return Result;
#if 0
// FIXME: This code works, but it is unclear that we actually want to insert
// a big chain of computation in order to make a value available in a block.
// This needs to be evaluated carefully to consider its cost trade offs.
// Handle add with a constant RHS.
if (Inst->getOpcode() == Instruction::Add &&
isa<ConstantInt>(Inst->getOperand(1))) {
// PHI translate the LHS.
Value *OpVal = InsertPHITranslatedSubExpr(Inst->getOperand(0),
CurBB, PredBB, DT, NewInsts);
if (OpVal == 0) return 0;
BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
return Res;
return nullptr;