[PATCH] D15449: [PassManagerBuilder] Add a few more scalar optimization passes

[James Molloy via llvm-commits]

Hi,

> - I'd rather see this as two patches: one for the GlobalOpt and the other
for the scalar optimizations

Sure, that's easily done. Would you prefer me to open another phab review
or are happy with it being committed split apart?

> - Do you have benchmark results before/after?

Yes and no. The mem2reg changes do affect benchmarks I care about, but
they're not in test-suite and I'm not allowed to quote numbers from them.

I don't have an LTO setup of the test-suite to get numbers for the LTO
portions either (although I do have LTO set up for third party test suites
that I can't quote numbers from!). I haven't seen any regressions in any
test, and some improve drastically. Sorry for the weasel words.

As a general principle, I think the LTO driver isn't currently doing enough
scalar optimization. I've seen several cases where really poor code gets
through to late passes like CGP purely because SimplifyCFG/InstCombine
weren't run enough.

> - See also: http://reviews.llvm.org/D13443 ; I paused my work on this
till January because of the ThinLTO bringup, but I still plan to move
forward with it.

This looks good. It looks like a real reegineering of the pipeline, which
is a bit more work than I was hoping to chew off - I hope that my work
might go some way towards improving the LTO codegen without requiring
thousands of benchmarking hours to check it's OK!

(Aside, in D13443 you don't run GlobalOpt/Mem2Reg early. I think
functionattrs+globalopt+mem2reg needs to run as early as possible so that
demoted globals become first class SSA values for the whole of the pass
pipeline).

James

On Fri, 11 Dec 2015 at 16:08 Mehdi AMINI via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> joker.eph added a comment.
>
> Hi James,
>
> A few points:
>
> - I'd rather see this as two patches: one for the GlobalOpt and the other
> for the scalar optimizations
> - Do you have benchmark results before/after?
> - See also: http://reviews.llvm.org/D13443 ; I paused my work on this
> till January because of the ThinLTO bringup, but I still plan to move
> forward with it.
>
> Thanks!
>
>
> Repository:
>   rL LLVM
>
> http://reviews.llvm.org/D15449
>
>
>
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