[PATCH] D147114: [LV] Use BFI to adjust cost of predicated instructions

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:10586
     BlockFrequencyInfo *BFI = nullptr;
-    if (PSI && PSI->hasProfileSummary())
+    //if (PSI && PSI->hasProfileSummary())
       BFI = &AM.getResult<BlockFrequencyAnalysis>(F);
----------------
ebrevnov wrote:
> nikic wrote:
> > ebrevnov wrote:
> > > nikic wrote:
> > > > ebrevnov wrote:
> > > > > dmgreen wrote:
> > > > > > Is BFI intended to be required now? Some of the other code makes it look like it is still optional.
> > > > > > Is BFI intended to be required now? 
> > > > > Yes. In fact, it should look like:
> > > > > BlockFrequencyInfo *BFI = &AM.getResult<BlockFrequencyAnalysis>(F);
> > > > > Will fix.
> > > > > 
> > > > > > Some of the other code makes it look like it is still optional.
> > > > > Right. Before this change there was exactly one use of BFI guarded by PSI. I would suggest not to touch this place (at least now) because if compile time regression shows up we may want to conditionally request BFI for predicated loops only.
> > > > This will definitely regress compile-time. You are only allowed to query BFI in PGO builds, which implies presence of PSI.
> > > But that depends on BPI availability from previous passes and needs of  BPI by following passes, right? 
> > Not sure what you mean here. BPI is a dependency of BFI, so it will be calculated if not already available?
> > 
> > 
> I meant BFI (not BPI). Sorry for confusion.
I still don't really get what you mean here. If you use getResult (rather than getCachedResult) BFI will be fetched regardless of whether it is available from previous passes.

The important part is that you shouldn't fetch BFI if PSI is not available. In test cases, you need to request PSI explicitly, in the pass pipeline it will be automatically available for PGO builds.


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  https://reviews.llvm.org/D147114/new/

https://reviews.llvm.org/D147114