[PATCH] D102537: [SampleFDO] Overwrite branch weight annotated in previous pass.

[Hongtao Yu via Phabricator via llvm-commits]

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Sample profile loader can be run in both LTO prelink and postlink. Currently the counts annoation in postilnk doesn't fully overwrite what's done in prelink. I'm adding a switch (`-overwrite-existing-weights=1`) to enable a full overwrite, which includes:

1. Clear old metadata for calls when their parent block has a zero count. This could be caused by prelink code duplication.

2. Clear indirect call metadata if somehow all the rest targets have a sum of zero count.

3. Overwrite branch weight for basic blocks.

When counts are accurate, I was seeing #1 and #2 help reduce code size by preventing post-sample ICP and CGSCC inliner working on obselete metedata.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D102537

Files:
  llvm/lib/Transforms/IPO/SampleProfile.cpp
  llvm/test/Transforms/SampleProfile/branch.ll
  llvm/test/Transforms/SampleProfile/pseudo-probe-profile-metadata-2.ll

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