[all-commits] [llvm/llvm-project] 6c6c96: [AggressiveInstCombine] Bail out on graph nodes in...

[Timur Baidusenov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6c6c968398f25c2a56705004f2eb68d21d5de900
      https://github.com/llvm/llvm-project/commit/6c6c968398f25c2a56705004f2eb68d21d5de900
  Author: Timur Baidusenov <timurbaidusenov at gmail.com>
  Date:   2026-09-25 (Fri, 25 Sep 2026)

  Changed paths:
    M llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp
    M llvm/test/Transforms/AggressiveInstCombine/trunc_unreachable_bb.ll

  Log Message:
  -----------
  [AggressiveInstCombine] Bail out on graph nodes in unreachable blocks (#226383)

TruncInstCombine::run() already skips truncs in unreachable blocks, but
the expression graph of reachable trunc can still be extended into an
unreachable block through a phi incoming value. Dead code may contain an
instruction that is its own operand, and buildTruncExpressionGraph only
breaks cycles at phi nodes, so such a cycle leaves the graph unorderable
and ReduceExpressionGraph asks for the reduced value of a node it has
not built yet.

Solution: Bail out as soon as a graph node is found in an unreachable
block, which extends the existing rule from the trunc itself to the
whole graph.

Fixes #58008.



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