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[AArch64] Update getCmpSelInstrCost #145568

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[AArch64] Update getCmpSelInstrCost #145568

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This currently

  • The AArch64TTIImpl::getCmpSelInstrCost functoin now tried to handle all cost kinds, not just TCK_RecipThroughput.
  • Updates fcmp costs to correctly model the cost of fcmp's predicates that require expansion into multiple instructions.
  • Adds a target feature for when SVE fcmxx instructions have a lower throughput than the Neon versions.
  • Some of the old select code that assumed they would not be well lowered were removed.

@davemgreen
[AArch64] Update getCmpSelInstrCost
3daea67 
This currently
  - The AArch64TTIImpl::getCmpSelInstrCost functoin now tried to handle all
    cost kinds, not just TCK_RecipThroughput.
  - Updates fcmp costs to correctly model the cost of fcmp's predicates that
    require expansion into multiple instructions.
  - Adds a target feature for when SVE fcmxx instructions have a lower
    throughput than the Neon versions.
  - Some of the old select code that assumed they would not be well lowered
    were removed.
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davemgreen added a commit to davemgreen/llvm-project that referenced this pull request Jun 27, 2025
@davemgreen
[AArch64] Enable other cost kinds for getCmpSelInstrCost.
5695f9b 
This removes the CostKind == TCK_RecipThroughput limitation from
getCmpSelInstrCost, allowing it to return more accurate costs for CodeSize and
Lat / SizeLat. Especially for larger vectors under CodeSize, the returned costs
are currently 1, not the legalization cost.

There are further ideas for improvement in llvm#145568, this is the first step.
@davemgreen davemgreen mentioned this pull request Jun 29, 2025
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@davemgreen