tejohnson marked an inline comment as done.
tejohnson added inline comments.


================
Comment at: llvm/test/tools/gold/X86/opt-level.ll:53
+  ; CHECK-O1-OLDPM: select
+  ; The new PM does not do as many optimizations at O1
+  ; CHECK-O1-NEWPM: phi
----------------
tejohnson wrote:
> mehdi_amini wrote:
> > This is intended? I'm surprised the two PMs don't have the same list of 
> > passes for a given opt level?
> I'm really not sure. I did compare the post-link LTO pipelines of both PMs at 
> O0/O1/O2 and confirmed that the old PM is doing many more passes than the new 
> PM at O1. Probably a question for @chandlerc ? In any case, I didn't want to 
> address it here since it is orthogonal.
Some more info:

This is the regular LTO post-link pipeline, ThinLTO post-link pipeline uses 
essentially the same as a normal opt pipeline so would be consistent at -O1.

The optimization missing from the new PM regular LTO post link pipeline that 
affects this test is SimplifyCFG. This and a few other optimizations are added 
in the old PM at O1 via PassManagerBuilder::addLateLTOOptimizationPasses. Note 
that PassManagerBuilder::addLTOOptimizationPasses does exit early at -O1 
(similar to where we exit early in the new PM for the regular LTO post link 
compilation). But the "late" LTO optimization passes are added unconditionally 
above -O0. Is this correct/desired? There isn't an equivalent in the new PM.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D61022/new/

https://reviews.llvm.org/D61022



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