[PATCH] D124159: [SimplifyCFG] Thread branches on same condition in more cases (PR54980)

[Nikita Popov via Phabricator via llvm-commits]

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SimplifyCFG implements basic jump threading, if a branch is performed on a phi node with constant operands. However, InstCombine canonicalizes such phis to the condition value of a previous branch, if possible. SimplifyCFG does support this as well, but only in the very limited case where the same condition is used in a direct predecessor -- notably, this does not include the common diamond pattern (i.e. two consecutive if/elses on the same condition).

This patch extends the code to look back a limited number of blocks to find a branch on the same value, rather than only looking at the direct predecessor.

Fixes https://github.com/llvm/llvm-project/issues/54980.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124159

Files:
  llvm/lib/Transforms/Utils/SimplifyCFG.cpp
  llvm/test/CodeGen/AArch64/arm64-andCmpBrToTBZ.ll
  llvm/test/Transforms/GVNSink/sink-common-code.ll
  llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
  llvm/test/Transforms/SimplifyCFG/jump-threading.ll
  llvm/test/Transforms/SimplifyCFG/wc-widen-block.ll

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