[all-commits] [llvm/llvm-project] 31b7d4: [DAG] Extend extract_element(bitcast(scalar_to_vec...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 31b7d4333a6c10aa8b7e1a7ca5aa0e281f124ec2
      https://github.com/llvm/llvm-project/commit/31b7d4333a6c10aa8b7e1a7ca5aa0e281f124ec2
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2024-11-29 (Fri, 29 Nov 2024)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/test/CodeGen/AArch64/extract-insert.ll
    M llvm/test/CodeGen/AArch64/vec3-loads-ext-trunc-stores.ll
    M llvm/test/CodeGen/PowerPC/scalar_vector_test_5.ll
    M llvm/test/CodeGen/X86/load-partial.ll

  Log Message:
  -----------
  [DAG] Extend extract_element(bitcast(scalar_to_vector(X))) -> trunc(srl(X,C)) (#117900)

When extracting a smaller integer from a scalar_to_vector source, we were limited to only folding/truncating the lowest bits of the scalar source.

This patch extends the fold to handle extraction of any other element, by right shifting the source before truncation.

Fixes a regression from #117884



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