[PATCH] D26037: Add LoopSink pass for PGO.

[Xinliang David Li via llvm-commits]

On Fri, Oct 28, 2016 at 9:40 AM, Dehao Chen <danielcdh at gmail.com> wrote:

> danielcdh added a comment.
>
> We need this pass to remove LCSSA nodes because this will be the last loop
> pass.
>
> Another question is: shall we pin this pass to PGO only? If not, we can
> simply add it to lib/Transforms/IPO/PassManagerBuilder.cpp
>

Static branch prediction is conservative in predicting loop iterations
(loop scale). This means it is likely some blocks (if wrapped under
__builtin_expect) inside the loop will be wrongly marked as colder than
preheader  which can trigger loop sinking wrongly.   Making this pass
depending on PGO is a safer thing to do.

David


>
> https://reviews.llvm.org/D26037
>
>
>
>
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