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[NFC][SimplifyCFG] Refactor passingValueIsAlwaysUndefined to work on Use #125519

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merged 1 commit into from
Feb 3, 2025
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[NFC][SimplifyCFG] Refactor passingValueIsAlwaysUndefined to work on Use #125519

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59 changes: 25 additions & 34 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8175,8 +8175,8 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
if (C->isNullValue() || isa<UndefValue>(C)) {
// Only look at the first use we can handle, avoid hurting compile time with
// long uselists
auto FindUse = llvm::find_if(I->users(), [](auto *U) {
auto *Use = cast<Instruction>(U);
auto FindUse = llvm::find_if(I->uses(), [](auto &U) {
auto *Use = cast<Instruction>(U.getUser());
// Change this list when we want to add new instructions.
switch (Use->getOpcode()) {
default:
Expand All @@ -8199,26 +8199,28 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
return true;
}
});
if (FindUse == I->user_end())
if (FindUse == I->use_end())
return false;
auto *Use = cast<Instruction>(*FindUse);
// Bail out if Use is not in the same BB as I or Use == I or Use comes
// before I in the block. The latter two can be the case if Use is a
auto &Use = *FindUse;
auto *User = cast<Instruction>(Use.getUser());
// Bail out if User is not in the same BB as I or User == I or User comes
// before I in the block. The latter two can be the case if User is a
// PHI node.
if (Use->getParent() != I->getParent() || Use == I || Use->comesBefore(I))
if (User->getParent() != I->getParent() || User == I ||
User->comesBefore(I))
return false;

// Now make sure that there are no instructions in between that can alter
// control flow (eg. calls)
auto InstrRange =
make_range(std::next(I->getIterator()), Use->getIterator());
make_range(std::next(I->getIterator()), User->getIterator());
if (any_of(InstrRange, [](Instruction &I) {
return !isGuaranteedToTransferExecutionToSuccessor(&I);
}))
return false;

// Look through GEPs. A load from a GEP derived from NULL is still undefined
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User))
if (GEP->getPointerOperand() == I) {
// The current base address is null, there are four cases to consider:
// getelementptr (TY, null, 0) -> null
Expand All @@ -8235,7 +8237,7 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
}

// Look through return.
if (ReturnInst *Ret = dyn_cast<ReturnInst>(Use)) {
if (ReturnInst *Ret = dyn_cast<ReturnInst>(User)) {
bool HasNoUndefAttr =
Ret->getFunction()->hasRetAttribute(Attribute::NoUndef);
// Return undefined to a noundef return value is undefined.
Expand All @@ -8249,56 +8251,45 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
}

// Load from null is undefined.
if (LoadInst *LI = dyn_cast<LoadInst>(Use))
if (LoadInst *LI = dyn_cast<LoadInst>(User))
if (!LI->isVolatile())
return !NullPointerIsDefined(LI->getFunction(),
LI->getPointerAddressSpace());

// Store to null is undefined.
if (StoreInst *SI = dyn_cast<StoreInst>(Use))
if (StoreInst *SI = dyn_cast<StoreInst>(User))
if (!SI->isVolatile())
return (!NullPointerIsDefined(SI->getFunction(),
SI->getPointerAddressSpace())) &&
SI->getPointerOperand() == I;

// llvm.assume(false/undef) always triggers immediate UB.
if (auto *Assume = dyn_cast<AssumeInst>(Use)) {
if (auto *Assume = dyn_cast<AssumeInst>(User)) {
// Ignore assume operand bundles.
if (I == Assume->getArgOperand(0))
return true;
}

if (auto *CB = dyn_cast<CallBase>(Use)) {
if (auto *CB = dyn_cast<CallBase>(User)) {
if (C->isNullValue() && NullPointerIsDefined(CB->getFunction()))
return false;
// A call to null is undefined.
if (CB->getCalledOperand() == I)
return true;

if (C->isNullValue()) {
for (const llvm::Use &Arg : CB->args())
if (Arg == I) {
unsigned ArgIdx = CB->getArgOperandNo(&Arg);
if (CB->isPassingUndefUB(ArgIdx) &&
CB->paramHasAttr(ArgIdx, Attribute::NonNull)) {
// Passing null to a nonnnull+noundef argument is undefined.
return !PtrValueMayBeModified;
}
}
} else if (isa<UndefValue>(C)) {
if (CB->isArgOperand(&Use)) {
unsigned ArgIdx = CB->getArgOperandNo(&Use);
// Passing null to a nonnnull+noundef argument is undefined.
if (C->isNullValue() && CB->isPassingUndefUB(ArgIdx) &&
CB->paramHasAttr(ArgIdx, Attribute::NonNull))
return !PtrValueMayBeModified;
// Passing undef to a noundef argument is undefined.
for (const llvm::Use &Arg : CB->args())
if (Arg == I) {
unsigned ArgIdx = CB->getArgOperandNo(&Arg);
if (CB->isPassingUndefUB(ArgIdx)) {
// Passing undef to a noundef argument is undefined.
return true;
}
}
if (isa<UndefValue>(C) && CB->isPassingUndefUB(ArgIdx))
return true;
}
}
// Div/Rem by zero is immediate UB
if (match(Use, m_BinOp(m_Value(), m_Specific(I))) && Use->isIntDivRem())
if (match(User, m_BinOp(m_Value(), m_Specific(I))) && User->isIntDivRem())
return true;
}
return false;
Expand Down