[llvm-dev] AtomicExpandPass and branch weighting

[Hal Finkel via llvm-dev]

----- Original Message -----

> From: "Kyle Butt via llvm-dev" <llvm-dev at lists.llvm.org>
> To: "Tim Northover" <t.p.northover at gmail.com>
> Cc: "LLVM Developers" <llvm-dev at lists.llvm.org>
> Sent: Monday, December 12, 2016 11:30:32 AM
> Subject: [llvm-dev] AtomicExpandPass and branch weighting

> I'm working on a change to the layout algorithm, and I noted that
> test/CodeGen/ARM/cmpxchg-weak.ll was affected.

> Normally, that would be fine, but I noted that the layout changed the
> fallthrough from the success case to the failure case. I was
> surprised to see that the success case isn't annotated with a branch
> weight by AtomicExpandPass.cpp

> Would it make sense to annotate the success case as more likely when
> we expand the intrinsic to help guarantee that the success case
> remains the fallthrough?
Certainly makes sense to me. 

-Hal 

> Even a 2:1 or 3:2 weighting would correct the layout issue I noted.

> Thanks,
> Kyle.
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-- 

Hal Finkel 
Lead, Compiler Technology and Programming Languages 
Leadership Computing Facility 
Argonne National Laboratory 
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