[PATCH] D63626: [clang][NewPM] Remove exception handling before loading pgo sample profile data

[Chandler Carruth via Phabricator via cfe-commits]

chandlerc added a comment.

FWIW, I think we can wait for a bug to be filed or report come in with some functional test case before we change any behavior here.

I'm just suggesting how to make the test better below.



================
Comment at: llvm/lib/Passes/PassBuilder.cpp:665-668
+    // We must also remove exception handling before attaching sample profile
+    // data.
+    MPM.addPass(
+        createModuleToPostOrderCGSCCPassAdaptor(PostOrderFunctionAttrsPass()));
----------------
leonardchan wrote:
> tejohnson wrote:
> > chandlerc wrote:
> > > Does the this need to go before the EarlyFPM as well as before the sample profile loader?
> > > 
> > > Also, this is ... a pretty expensive thing to do... Do we really need this? We've been using ThinLTO and sample PGO with the new PM for a long time and haven't seen any real issue. I think we can probably just leave this difference between the two pass managers and remove the test for this pass running rather than adding it.
> > > 
> > > CC-ing some others just to double check, but I'm not aware of any issues we've seen with PGO that were because of this discrepancy.
> > We don't tend to use exception handling so might not be hitting the issue described in the headline.
> > 
> > If this is fixing an issue with SamplePGO and EH cleanup interactions, can you add a test that tests for that (i.e. is there a code optimization issue currently?).
> I'm not entirely familiar with the expected codegen for SamplePGO or PruneEH and don't really know if not adding these 2 passes breaks anything.
> 
> Under the legacy PM, exception handling was removed via `PruneEH` before creating the sample profile loader, so this change was meant to match the behavior since `function-attrs` and `function(simplify-cfg)` (the new PM equivalent for `-prune-eh`) did not initially run before `SampleProfileLoaderPass` was added to the pipeline.
> 
> The original patch that added `CodeGen/pgo-sample.c` (D21197) doesn't seem to have any codegen tests either and only checks that PruneEH runs before sample profile loader creation, so I'm also unsure of what code optimizations are meant to happen.
Going back to this original issue, I think I understand more what is going on...

Specifically, I can imagine that having `invoke` still in place caused some issues.

So I would just keep the testing that (in the new PM) SimplifyCFG is run before the profile loading pass, and ignore function attrs.



Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D63626/new/

https://reviews.llvm.org/D63626