[all-commits] [llvm/llvm-project] 23f09f: [VectorCombine] Fold permute of intrinsics into in...

[Jerry Dang via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 23f09fd3e9efd43c58dcc42f001aeda139f429f8
      https://github.com/llvm/llvm-project/commit/23f09fd3e9efd43c58dcc42f001aeda139f429f8
  Author: Jerry Dang <kuroyukiasuna at gmail.com>
  Date:   2025-12-05 (Fri, 05 Dec 2025)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/VectorCombine.cpp
    A llvm/test/Transforms/VectorCombine/AArch64/shuffle-of-intrinsic-permute.ll
    M llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll
    M llvm/test/Transforms/VectorCombine/X86/shuffle-of-fma-const.ll

  Log Message:
  -----------
  [VectorCombine] Fold permute of intrinsics into intrinsic of permutes: shuffle(intrinsic, poison/undef) -> intrinsic(shuffle) (#170052)

[VectorCombine] Fold permute of intrinsics into intrinsic of permutes

Add foldPermuteOfIntrinsic to transform:
  shuffle(intrinsic(args), poison) -> intrinsic(shuffle(args))
when the shuffle is a permute (operates on single vector) and the cost
model determines the transformation is profitable.

This optimization is particularly beneficial for subvector extractions
where we can avoid computing unused elements.

For example:
  %fma = call <8 x float> @llvm.fma.v8f32(<8 x float> %a, %b, %c)
  %result = shufflevector <8 x float> %fma, poison, <4 x i32> <0,1,2,3>
transforms to:
  %a_low = shufflevector <8 x float> %a, poison, <4 x i32> <0,1,2,3>
  %b_low = shufflevector <8 x float> %b, poison, <4 x i32> <0,1,2,3>
  %c_low = shufflevector <8 x float> %c, poison, <4 x i32> <0,1,2,3>
  %result = call <4 x float> @llvm.fma.v4f32(%a_low, %b_low, %c_low)

The transformation creates one shuffle per vector argument and calls the
intrinsic with smaller vector types, reducing computation when only a
subset of elements is needed.

The existing foldShuffleOfIntrinsics handled the blend case (two
intrinsic inputs), this adds support for the permute case (single
intrinsic input).

Fixes #170002



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