[PATCH] D86156: [BFI] Preserve BFI information through loop passes via VH callbacks inside LoopStandardAnalysisResults

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modimo created this revision.
modimo added reviewers: wenlei, asbirlea, vsk.
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Herald added subscribers: llvm-commits, cfe-commits, dexonsmith, steven_wu, hiraditya.
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modimo requested review of this revision.

D65060 <https://reviews.llvm.org/D65060> uncovered that trying to use BFI in loop passes can lead to non-deterministic behavior when blocks are re-used while retaining old BFI data.

To make sure BFI is preserved through loop passes a Value Handle (VH) callback is registered on blocks themselves. When a block is freed it now also wipes out the accompanying BFI entry such that stale BFI data can no longer persist resolving the determinism issue.

An optimistic approach would be to incrementally update BFI information throughout the loop passes rather than only invalidating them on removed blocks. The issues with that are:

1. It is not clear how BFI information should be incrementally updated: If a block is duplicated does its BFI information come with? How about if it's split/modified/moved around?
2. Assuming we can address these problems the implementation here will be a massive undertaking.

There's a known need of BFI in LICM analysis which requires correct but not incrementally updated BFI data. Other loop passes can now also use this level of information and richer updates can be made as needed.

This diff also moves BFI to be a part of LoopStandardAnalysisResults since the previous method using getCachedResults now (correctly!) statically asserts (D72893 <https://reviews.llvm.org/D72893>) that this data isn't static through the loop passes.

Testing
Ninja check


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86156

Files:
  clang/test/CodeGen/thinlto-distributed-newpm.ll
  llvm/include/llvm/Analysis/BlockFrequencyInfo.h
  llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
  llvm/include/llvm/Analysis/LoopAnalysisManager.h
  llvm/include/llvm/Transforms/Scalar/LoopPassManager.h
  llvm/lib/Analysis/BlockFrequencyInfo.cpp
  llvm/lib/Transforms/Scalar/LoopDistribute.cpp
  llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
  llvm/lib/Transforms/Utils/LoopVersioning.cpp
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/test/Other/loop-pm-invalidation.ll
  llvm/test/Other/new-pass-manager.ll
  llvm/test/Other/new-pm-defaults.ll
  llvm/test/Other/new-pm-thinlto-defaults.ll
  llvm/test/Other/pass-pipelines.ll
  llvm/test/Transforms/LoopRotate/pr35210.ll
  llvm/unittests/Transforms/Scalar/LoopPassManagerTest.cpp

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