[all-commits] [llvm/llvm-project] e94713: [SDAG] Disable illegal extract_subvector splitting...

[Benjamin Maxwell via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e947139f082f16c654e6536a90221e15bc0fc96c
      https://github.com/llvm/llvm-project/commit/e947139f082f16c654e6536a90221e15bc0fc96c
  Author: Benjamin Maxwell <benjamin.maxwell at arm.com>
  Date:   2025-12-03 (Wed, 03 Dec 2025)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
    A llvm/test/CodeGen/AArch64/sve-fixed-vector-extract-256-bits.ll

  Log Message:
  -----------
  [SDAG] Disable illegal extract_subvector splitting for scalable vectors (#170315)

The "half spanning" legalization of extract_subvector is only valid for
fixed-length vectors. This patch disables it for scalable vectors and
makes more careful use of ElementCount in the lowering.

Fixes regression from https://github.com/llvm/llvm-project/pull/154101,
which was encountered here:
https://github.com/llvm/llvm-project/pull/166748#issuecomment-3600498185

Note: We could optimize this case given the known vscale, but this patch
only attempts to fix the miscompile.



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