[llvm] r327761 - [GlobalsAA] Fix a pretty terrible bug that has been in GlobalsAA for

[Chandler Carruth via llvm-commits]

Absolutely. Thanks for spotting that.

On Fri, Mar 16, 2018 at 8:03 PM Tom Stellard via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> On 03/16/2018 04:51 PM, Chandler Carruth via llvm-commits wrote:
> > Author: chandlerc
> > Date: Fri Mar 16 16:51:33 2018
> > New Revision: 327761
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=327761&view=rev
>
> Hi Chandler,
>
> Is this a candidate for 6.0.1?
>
> -Tom
>
> > Log:
> > [GlobalsAA] Fix a pretty terrible bug that has been in GlobalsAA for
> > a long time.
> >
> > The key thing is that we need to create value handles for every function
> > that we create a `FunctionInfo` object around. Without this, when that
> > function is deleted we can end up creating a new function that collides
> > with its address and look up a stale AA result. With that AA result we
> > can in turn miscompile code in ways that break.
> >
> > This is seriously one of the most absurd miscompiles I've seen. It only
> > reproduced for us recently and only when building a very large server
> > with both ThinLTO and PGO.
> >
> > A *HUGE* shout out to Wei Mi who tracked all of this down and came up
> > with this patch. I'm just landing it because I happened to still by at
> > a computer.
> >
> > He or I can work on crafting a test case to hit this (now that we know
> > what to target) but it'll take a while, and we've been chasing this for
> > a long time and need it fix Right Now.
> >
> > Modified:
> >     llvm/trunk/lib/Analysis/GlobalsModRef.cpp
> >
> > Modified: llvm/trunk/lib/Analysis/GlobalsModRef.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/GlobalsModRef.cpp?rev=327761&r1=327760&r2=327761&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/lib/Analysis/GlobalsModRef.cpp (original)
> > +++ llvm/trunk/lib/Analysis/GlobalsModRef.cpp Fri Mar 16 16:51:33 2018
> > @@ -502,6 +502,8 @@ void GlobalsAAResult::AnalyzeCallGraph(C
> >      }
> >
> >      FunctionInfo &FI = FunctionInfos[F];
> > +    Handles.emplace_front(*this, F);
> > +    Handles.front().I = Handles.begin();
> >      bool KnowNothing = false;
> >
> >      // Collect the mod/ref properties due to called functions.  We only
> compute
> >
> >
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> >
>
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