[all-commits] [llvm/llvm-project] 2d0087: [DAG] Remove extract_vector_elt(freeze(x)), idx ->...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2d0087424f120c97c8fdecf50e6e5f6a1f3969f2
      https://github.com/llvm/llvm-project/commit/2d0087424f120c97c8fdecf50e6e5f6a1f3969f2
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2024-04-04 (Thu, 04 Apr 2024)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    M llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/freeze-vector.ll
    M llvm/test/CodeGen/X86/widen-load-of-small-alloca-with-zero-upper-half.ll

  Log Message:
  -----------
  [DAG] Remove extract_vector_elt(freeze(x)), idx -> freeze(extract_vector_elt(x), idx) fold (#87480)

Reverse the fold with handling inside canCreateUndefOrPoison for cases where we know that the extract index is in bounds.

This exposed a number or regressions, and required some initial freeze handling of SCALAR_TO_VECTOR, which will require us to properly improve demandedelts support to handle its undef upper elements.

There is still one outstanding regression to be addressed in the future - how do we want to handle folds involving frozen loads?

Fixes #86968



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