Don't delete asm's just because their inputs are undefined;
xor R, R is a common and valid idiom for zeroing a register, for example.
llvm-svn: 75571
diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index f6cffdd..155d5d8 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -109,6 +109,8 @@
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 @@
}
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()))
diff --git a/llvm/test/Transforms/SimplifyCFG/2009-07-13-no-delete-asm.ll b/llvm/test/Transforms/SimplifyCFG/2009-07-13-no-delete-asm.ll
new file mode 100644
index 0000000..4664ee0
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/2009-07-13-no-delete-asm.ll
@@ -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
+}