[PATCH] D71263: AMDGPU: Don't run redundant GlobalDCE

Tue Dec 10 08:53:20 PST 2019

rampitec added a comment.

In D71263#1777573 <https://reviews.llvm.org/D71263#1777573>, @arsenm wrote:

> In D71263#1777570 <https://reviews.llvm.org/D71263#1777570>, @rampitec wrote:
>
> > The idea to run it was to speedup compilation. After internalize we have an opportunity to remove some functions and do not spend time optimizing them. As far as I understand GlobalDCE is really cheap, unlike passes running before its next invocation.
> >
> > Did you make any compile time measurements to support it?
>
>
> I found this patch lying around from 2017, and don't remember why I was looking at this. There aren't many passes run between the internalize here and GlobalOpt:
>
>   Internalize Global Symbols
>   Dead Global Elimination
>   Interprocedural Sparse Conditional Constant Propagation
>     FunctionPass Manager
>       Dominator Tree Construction
>   Called Value Propagation
>   Deduce and propagate attributes
>   Global Variable Optimizer

AFAIR initially GlobalDCE was added to skip unused library functions after link. Anyway, do you think GlobalDCE adds any visible slowdown, which is more than DT construction?

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