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[SimplifyCFG] `markAliveBlocks()`: recognize that normal dest of `invoke`d `noreturn` function is `unreachable` 

As per LangRef's definition of `noreturn` attribute:
```
noreturn
  This function attribute indicates that the function never returns
  normally, hence through a return instruction.
  This produces undefined behavior at runtime if the function
  ever does dynamically return. nnotated functions may still
  raise an exception, i.a., nounwind is not implied.
```
This commit is contained in:
Roman Lebedev 2022-02-05 01:28:24 +03:00
parent 75c1d1dab4
commit 598833c987
No known key found for this signature in database
GPG Key ID: 083C3EBB4A1689E0
3 changed files with 28 additions and 16 deletions
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39
llvm/lib/Transforms/Utils/Local.cpp
View File

@ -2349,19 +2349,32 @@ static bool markAliveBlocks(Function &F,
isa<UndefValue>(Callee)) {
changeToUnreachable(II, false, DTU);
Changed = true;
} else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
if (II->use_empty() && II->onlyReadsMemory()) {
// jump to the normal destination branch.
BasicBlock *NormalDestBB = II->getNormalDest();
BasicBlock *UnwindDestBB = II->getUnwindDest();
BranchInst::Create(NormalDestBB, II);
UnwindDestBB->removePredecessor(II->getParent());
II->eraseFromParent();
if (DTU)
DTU->applyUpdates({{DominatorTree::Delete, BB, UnwindDestBB}});
} else
changeToCall(II, DTU);
Changed = true;
} else {
if (II->doesNotReturn()) {
// If we found an invoke of a no-return function,
// insert an unreachable instruction after it (on the normal dest).
// Make sure there isn't *already* one there though.
Instruction *FirstNormalInst = &II->getNormalDest()->front();
if (!isa<UnreachableInst>(FirstNormalInst)) {
// Don't insert a call to llvm.trap right before the unreachable.
changeToUnreachable(FirstNormalInst, false, DTU);
Changed = true;
}
}
if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
if (II->use_empty() && II->onlyReadsMemory()) {
// jump to the normal destination branch.
BasicBlock *NormalDestBB = II->getNormalDest();
BasicBlock *UnwindDestBB = II->getUnwindDest();
BranchInst::Create(NormalDestBB, II);
UnwindDestBB->removePredecessor(II->getParent());
II->eraseFromParent();
if (DTU)
DTU->applyUpdates({{DominatorTree::Delete, BB, UnwindDestBB}});
} else
changeToCall(II, DTU);
Changed = true;
}
}
} else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(Terminator)) {
// Remove catchpads which cannot be reached.

2
llvm/test/CodeGen/X86/catchret-regmask.ll
View File

@ -4,7 +4,7 @@ target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-windows-msvc"
declare i32 @__CxxFrameHandler3(...)
declare void @throw() noreturn uwtable
declare void @throw() uwtable
declare i8* @getval()
declare void @llvm.trap()

3
llvm/test/Transforms/SimplifyCFG/invoke.ll
View File

@ -198,8 +198,7 @@ define void @invoke_of_noreturn() personality i8* bitcast (i32 (...)* @__gxx_per
; CHECK-NEXT: invoke void @simple_throw()
; CHECK-NEXT: to label [[INVOKE_CONT:%.*]] unwind label [[LPAD:%.*]]
; CHECK: invoke.cont:
; CHECK-NEXT: call void @sideeffect(i32 0)
; CHECK-NEXT: ret void
; CHECK-NEXT: unreachable
; CHECK: lpad:
; CHECK-NEXT: [[EH:%.*]] = landingpad { i8*, i32 }
; CHECK-NEXT: cleanup