[all-commits] [llvm/llvm-project] e964ac: [DAG] Fold mismatched widened avg idioms to narrow...

[Lauren via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e964acf85f6d964fe5a1996289f34759cceeca3f
      https://github.com/llvm/llvm-project/commit/e964acf85f6d964fe5a1996289f34759cceeca3f
  Author: Lauren <38364197+laurenmchin at users.noreply.github.com>
  Date:   2025-10-27 (Mon, 27 Oct 2025)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/test/CodeGen/AArch64/arm64-vhadd.ll

  Log Message:
  -----------
  [DAG] Fold mismatched widened avg idioms to narrow form (#147946) (#163366)

[DAG] Fold mismatched widened avg idioms to narrow form (fixes half of
[llvm#147946](https://github.com/llvm/llvm-project/issues/147946))

1. `trunc(avgceilu(sext(x), sext(y))) -> avgceils(x, y)` 
2. `trunc(avgceils(zext(x), zext(y))) -> avgceilu(x, y)`

When inputs are sign-extended, unsigned and signed averaging operations
produce identical results after truncation, allowing us to use the
semantically correct narrow operation.

alive2: https://alive2.llvm.org/ce/z/ZRbfHT



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