[llvm] r214336 - SimplifyCFG: Avoid miscompilations due to removed lifetime intrinsics.

[Björn Steinbrink]

Hi Tom,
Hi Rafael,

Can we get this into 3.5.2? The rust compiler emits lifetime intrinsics
and without this patch the optimized code is broken.

Cheers,
Björn

On 2014.07.30 21:04:00 -0000, Rafael Espindola wrote:
> Author: rafael
> Date: Wed Jul 30 16:04:00 2014
> New Revision: 214336
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=214336&view=rev
> Log:
> SimplifyCFG: Avoid miscompilations due to removed lifetime intrinsics.
> 
> The lifetime intrinsics need some work in order to make it clear which
> optimizations are or are not valid.
> 
> For now dropping this optimization avoids a miscompilation.
> 
> Patch by Bj?rn Steinbrink.
> 
> Modified:
>     llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
>     llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll
> 
> Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=214336&r1=214335&r2=214336&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Wed Jul 30 16:04:00 2014
> @@ -4008,7 +4008,7 @@ bool SimplifyCFGOpt::SimplifyUncondBranc
>      return true;
>  
>    // If the Terminator is the only non-phi instruction, simplify the block.
> -  BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
> +  BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
>    if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
>        TryToSimplifyUncondBranchFromEmptyBlock(BB))
>      return true;
> 
> Modified: llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll?rev=214336&r1=214335&r2=214336&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll (original)
> +++ llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll Wed Jul 30 16:04:00 2014
> @@ -1,11 +1,11 @@
>  ; RUN: opt < %s -simplifycfg -S | FileCheck %s
>  
> -; Test that a lifetime intrinsic doesn't prevent us from simplifying this.
> +; Test that a lifetime intrinsic isn't removed because that would change semantics
>  
>  ; CHECK: foo
>  ; CHECK: entry:
> -; CHECK-NOT: bb0:
> -; CHECK-NOT: bb1:
> +; CHECK: bb0:
> +; CHECK: bb1:
>  ; CHECK: ret
>  define void @foo(i1 %x) {
>  entry:
> 
>