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Don't delete asm's just because their inputs are undefined;

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xor R, R is a common and valid idiom for zeroing a register, for example.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75571 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dale Johannesen 2009-07-14 00:45:38 +00:00
parent d9ef1a860e
commit 4458ab0d83
2 changed files with 28 additions and 8 deletions
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25
lib/Transforms/Scalar/SimplifyCFGPass.cpp
View File

@ -109,6 +109,8 @@ static bool MarkAliveBlocks(BasicBlock *BB,
if (!Reachable.insert(BB))
continue;
bool AsmFound = false;
StoreInst *UndefStore = 0;
// Do a quick scan of the basic block, turning any obviously unreachable
// instructions into LLVM unreachable insts. The instruction combining pass
// canonicalizes unreachable insts into stores to null or undef.
@ -125,20 +127,27 @@ static bool MarkAliveBlocks(BasicBlock *BB,
}
break;
}
if (isa<InlineAsm>(CI->getOperand(0)))
AsmFound = true;
}
if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
Value *Ptr = SI->getOperand(1);
if (isa<UndefValue>(Ptr) ||
(isa<ConstantPointerNull>(Ptr) &&
cast<PointerType>(Ptr->getType())->getAddressSpace() == 0)) {
ChangeToUnreachable(SI, Context);
Changed = true;
break;
}
if ((isa<UndefValue>(Ptr) ||
(isa<ConstantPointerNull>(Ptr) &&
cast<PointerType>(Ptr->getType())->getAddressSpace() == 0)) &&
!UndefStore)
UndefStore = SI;
}
}
// We can't delete asm's just because their inputs are undefined;
// xor R, R is a common idiom for zeroing a register, for example.
// Assume user knows what he is doing.
if (UndefStore && !AsmFound) {
ChangeToUnreachable(UndefStore, Context);
Changed = true;
}
// Turn invokes that call 'nounwind' functions into ordinary calls.
if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))

11
test/Transforms/SimplifyCFG/2009-07-13-no-delete-asm.ll Normal file
View File

@ -0,0 +1,11 @@
; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | grep xor
; ModuleID = '<stdin>'
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i386-apple-darwin9.6"
define void @bar() nounwind {
entry:
store i16 undef, i16* null
%asmtmp = call i32 asm sideeffect "xor $0, $0", "=={bx},rm,~{dirflag},~{fpsr},~{flags},~{memory}"(i16 undef) nounwind ; <i32> [#uses=0]
ret void
}