[PATCH] D43256: [MBP] Move a latch block with conditional exit and multi predecessors to top of loop

Mon Jul 29 23:02:53 PDT 2019

ebrevnov added a comment.

In D43256#1604069 <https://reviews.llvm.org/D43256#1604069>, @Carrot wrote:

> In D43256#1602841 <https://reviews.llvm.org/D43256#1602841>, @hans wrote:
>
> > In D43256#1550842 <https://reviews.llvm.org/D43256#1550842>, @Carrot wrote:
> >
> > > In D43256#1545519 <https://reviews.llvm.org/D43256#1545519>, @samparker wrote:
> > >
> > > > Do you have any benchmark numbers to show that this is generally profitable? From our downstream testing, it is not clear that this change is beneficial.
> > >
> > >
> > > We got performance improvement in our internal search benchmark.
> >
> >
> > How does this transformation impact the benchmark when not using profile data?
>
>
> In plain mode we also got performance improvement, the speedup is a little smaller than FDO Mode.

I have a general question/comment.  By now it's more or less evident that benefit of optimization heavily depends  on correctness of profile information. That means in general case there is no way to reason about its effectiveness. Thus I believe it should be turned off if there is no profile.

Repository:
  rL LLVM

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  https://reviews.llvm.org/D43256/new/

https://reviews.llvm.org/D43256