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[InstCombine][NFC] Refactor llvm.stackrestore handling 

Hoist the instruction classification logic outside the loop
in preparation for reuse in a future commit.

Signed-off-by: Itay Bookstein <itay.bookstein@nextsilicon.com>

Reviewed By: lebedev.ri

Differential Revision: https://reviews.llvm.org/D113464
This commit is contained in:
Itay Bookstein 2021-11-09 09:06:30 +02:00
parent 82ce912743
commit fe7491d32f
1 changed files with 42 additions and 20 deletions
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52
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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@ -1776,6 +1776,32 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
break;
}
case Intrinsic::stackrestore: {
enum class ClassifyResult {
None,
Alloca,
StackRestore,
CallWithSideEffects,
};
auto Classify = [](const Instruction *I) {
if (isa<AllocaInst>(I))
return ClassifyResult::Alloca;
if (auto *CI = dyn_cast<CallInst>(I)) {
if (auto *II = dyn_cast<IntrinsicInst>(CI)) {
if (II->getIntrinsicID() == Intrinsic::stackrestore)
return ClassifyResult::StackRestore;
if (II->mayHaveSideEffects())
return ClassifyResult::CallWithSideEffects;
} else {
// Consider all non-intrinsic calls to be side effects
return ClassifyResult::CallWithSideEffects;
}
}
return ClassifyResult::None;
};
// If the save is right next to the restore, remove the restore. This can
// happen when variable allocas are DCE'd.
if (IntrinsicInst *SS = dyn_cast<IntrinsicInst>(II->getArgOperand(0))) {
@ -1793,30 +1819,26 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
Instruction *TI = II->getParent()->getTerminator();
bool CannotRemove = false;
for (++BI; &*BI != TI; ++BI) {
if (isa<AllocaInst>(BI)) {
CannotRemove = true;
switch (Classify(&*BI)) {
case ClassifyResult::None:
// So far so good, look at next instructions.
break;
}
if (CallInst *BCI = dyn_cast<CallInst>(BI)) {
if (auto *II2 = dyn_cast<IntrinsicInst>(BCI)) {
case ClassifyResult::StackRestore:
// If there is a stackrestore below this one, remove this one.
if (II2->getIntrinsicID() == Intrinsic::stackrestore)
return eraseInstFromFunction(CI);
// Bail if we cross over an intrinsic with side effects, such as
// llvm.stacksave, or llvm.read_register.
if (II2->mayHaveSideEffects()) {
case ClassifyResult::Alloca:
case ClassifyResult::CallWithSideEffects:
// If we found an alloca, a non-intrinsic call, or an intrinsic call
// with side effects (such as llvm.stacksave and llvm.read_register),
// we can't remove the stack restore.
CannotRemove = true;
break;
}
} else {
// If we found a non-intrinsic call, we can't remove the stack
// restore.
CannotRemove = true;
if (CannotRemove)
break;
}
}
}
// If the stack restore is in a return, resume, or unwind block and if there
// are no allocas or calls between the restore and the return, nuke the