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

[Tom Stellard]

On Fri, Mar 13, 2015 at 01:42:09AM +0100, Björn Steinbrink wrote:
> 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.
> 

This looks OK to me, we don't really have a code owner for this, so I'm
cc'ing Chris.

> 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:
> > 
> >