[all-commits] [llvm/llvm-project] e4af48: [LoopFusion] Cleanup control flow before Fusion (#...

[Ehsan Amiri via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e4af48bd3b330282f36f075d6fa7a4a0742376c1
      https://github.com/llvm/llvm-project/commit/e4af48bd3b330282f36f075d6fa7a4a0742376c1
  Author: Ehsan Amiri <ehsan.amiri at huawei.com>
  Date:   2026-09-25 (Fri, 25 Sep 2026)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopFuse.cpp
    A llvm/test/Transforms/LoopFusion/guard_skip_empty_block.ll

  Log Message:
  -----------
  [LoopFusion] Cleanup control flow before Fusion (#226289)

Non-loop successor of loop guard is sometimes modified by JumpThreading
(and potentially some other passes) to jump to a new block, that doesn't
post dominate the exit block of the loop:

   Guard:    br %c, %Preheader, %Skip
   Skip:     br %Merge
   ...
   Exit:     br %Merge
   Merge:    ...

Later on, this block becomes empty, so it can be removed. Its presence
prevents Loop::getLoopGuardBranch() from detecting the loop guard which
results in missed fusion opportunities. SimplifyCFG will run when "Skip"
is still not optimzied, so it cannot resolve this issue.

Assisted by Claude Code



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