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Update SimplifyCFG for atomic operations. 

This commit includes a mention of the landingpad instruction, but it's not
changing the behavior around it.  I think the current behavior is correct,
though.  Bill, can you double-check that?

llvm-svn: 137691
This commit is contained in:
Eli Friedman 2011-08-15 23:59:28 +00:00
parent 01a67111d1
commit 0ffdf2ea0b
2 changed files with 69 additions and 10 deletions
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36
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2244,18 +2244,34 @@ bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
while (UI != BB->begin()) {
BasicBlock::iterator BBI = UI;
--BBI;
// Do not delete instructions that can have side effects, like calls
// (which may never return) and volatile loads and stores.
// Do not delete instructions that can have side effects which might cause
// the unreachable to not be reachable; specifically, calls and volatile
// operations may have this effect.
if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
if (SI->isVolatile())
if (BBI->mayHaveSideEffects()) {
if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
if (SI->isVolatile())
break;
} else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
if (LI->isVolatile())
break;
} else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
if (RMWI->isVolatile())
break;
} else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
if (CXI->isVolatile())
break;
} else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
!isa<LandingPadInst>(BBI)) {
break;
if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
if (LI->isVolatile())
break;
}
// Note that deleting LandingPad's here is in fact okay, although it
// involves a bit of subtle reasoning. If this inst is a LandingPad,
// all the predecessors of this block will be the unwind edges of Invokes,
// and we can therefore guaranteed this block will be erased.
}
// Delete this instruction (any uses are guaranteed to be dead)
if (!BBI->use_empty())
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));

43
llvm/test/Transforms/SimplifyCFG/trapping-load-unreachable.ll
View File

@ -42,3 +42,46 @@ entry:
; CHECK: store volatile i32 4, i32* null
; CHECK: ret
}
; Check store before unreachable.
define void @test4(i1 %C, i32* %P) {
; CHECK: @test4
; CHECK: entry:
; CHECK-NEXT: br i1 %C
entry:
br i1 %C, label %T, label %F
T:
store volatile i32 0, i32* %P
unreachable
F:
ret void
}
; Check cmpxchg before unreachable.
define void @test5(i1 %C, i32* %P) {
; CHECK: @test5
; CHECK: entry:
; CHECK-NEXT: br i1 %C
entry:
br i1 %C, label %T, label %F
T:
cmpxchg volatile i32* %P, i32 0, i32 1 seq_cst
unreachable
F:
ret void
}
; Check atomicrmw before unreachable.
define void @test6(i1 %C, i32* %P) {
; CHECK: @test6
; CHECK: entry:
; CHECK-NEXT: br i1 %C
entry:
br i1 %C, label %T, label %F
T:
atomicrmw volatile xchg i32* %P, i32 0 seq_cst
unreachable
F:
ret void
}