[PATCH] D37460: [GVN] Prevent LoadPRE from hoisting through guards

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev updated this revision to Diff 114311.
mkazantsev added a comment.

Actually we don't even need OrderedInstructions to do that. It's enough to maintain a set of blocks where we have ever seen the guards. We iterate through blocks in reverse postorder which guarantees us that if a block has one predecessor it will be visited before the block. We also traverse block instructions in direct order. Using this, we just mark a block as having a guard when we meet one and know for sure that:

1. if the current block is marked, there is a guard above the current instruction, and we cannot hoist;
2. if the only predecessor (recursively) is marked, it also blocks us from hoisting.

I've updated the patch using this solution. Please let me know if it makes sense to you.


https://reviews.llvm.org/D37460

Files:
  include/llvm/Transforms/Scalar/GVN.h
  lib/Transforms/Scalar/GVN.cpp
  test/Transforms/GVN/PRE/pre-load-guards.ll

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