[all-commits] [llvm/llvm-project] 34dff4: [SLP]Flatten fsub/fneg chains into fadd reductions...

[Alexey Bataev via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 34dff487dd711a6a6d6a22f474ce475bce757b47
      https://github.com/llvm/llvm-project/commit/34dff487dd711a6a6d6a22f474ce475bce757b47
  Author: Alexey Bataev <a.bataev at outlook.com>
  Date:   2026-09-07 (Mon, 07 Sep 2026)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
    M llvm/lib/Transforms/Vectorize/SLPVectorizer/SLPCompatibilityAnalysis.cpp
    M llvm/lib/Transforms/Vectorize/SLPVectorizer/SLPCompatibilityAnalysis.h
    M llvm/test/Transforms/SLPVectorizer/AArch64/loop-accumulator-reduction.ll
    M llvm/test/Transforms/SLPVectorizer/AArch64/many-uses-fma-candidate.ll
    M llvm/test/Transforms/SLPVectorizer/AMDGPU/reduction.ll
    M llvm/test/Transforms/SLPVectorizer/X86/fma-operand-index.ll
    M llvm/test/Transforms/SLPVectorizer/X86/horizontal-fadd-with-sub.ll
    M llvm/test/Transforms/SLPVectorizer/X86/horizontal-list.ll
    M llvm/test/Transforms/SLPVectorizer/X86/loop-accumulator-reduction.ll
    M llvm/test/Transforms/SLPVectorizer/X86/ordered-reduction-replaced.ll
    M llvm/test/Transforms/SLPVectorizer/X86/reduction-fadd-reassoc.ll

  Log Message:
  -----------
  [SLP]Flatten fsub/fneg chains into fadd reductions with per-operand signs

For unordered fadd reductions, reassociable (reassoc+nsz) fsub/fneg
chain links are recursed into and their leaves tracked with a flipped
sign, which is part of the grouping key, so reduced-values groups are
sign-uniform by construction. If per-value signs cannot model the
chain, the analysis restarts once without the flattening. Negated
parts are combined with vector fsub (may form per-lane fma) and
subtracted once in the final combine; no extra negations are emitted.

Fixes #211521

Reviewers: hiraditya, RKSimon

Pull Request: https://github.com/llvm/llvm-project/pull/215840



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