[all-commits] [llvm/llvm-project] 04e5e6: [VectorCombine] Generalize foldBitOpOfBitcasts to ...

[Rahul Yadav via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 04e5e643f526090ec872c0e505c487918992e21d
      https://github.com/llvm/llvm-project/commit/04e5e643f526090ec872c0e505c487918992e21d
  Author: Rahul Yadav <rahul4talk at gmail.com>
  Date:   2025-07-21 (Mon, 21 Jul 2025)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/VectorCombine.cpp
    A llvm/test/Transforms/VectorCombine/X86/bitop-of-castops.ll

  Log Message:
  -----------
  [VectorCombine] Generalize foldBitOpOfBitcasts to support more cast operations (#148350)

This patch generalizes the existing foldBitOpOfBitcasts optimization in the VectorCombine pass to handle additional cast operations beyond just bitcast.

  Fixes: [#146037](https://github.com/llvm/llvm-project/issues/146037)

  Summary

The optimization now supports folding bitwise operations (AND/OR/XOR)
with the following cast operations:
  - bitcast (original functionality)
  - trunc (truncate)
  - sext (sign extend)
  - zext (zero extend)

  The transformation pattern is:
  bitop(castop(x), castop(y)) -> castop(bitop(x, y))

This reduces the number of cast instructions from 2 to 1, improving
performance on targets where cast operations
are expensive or where performing bitwise operations on narrower types
is beneficial.
  
  Implementation Details

- Renamed foldBitOpOfBitcasts to foldBitOpOfCastops to reflect broader
functionality
  - Extended pattern matching to handle any CastInst operation
- Added validation for each cast type's constraints (e.g., trunc
requires source > dest)
  - Updated cost model to use the actual cast opcode
  - Preserves IR flags from original instructions
  - Handles multi-use scenarios appropriately

  Testing

- Added comprehensive tests in
test/Transforms/VectorCombine/bitop-of-castops.ll
  - Tests cover all supported cast types with all bitwise operations
  - Includes negative tests for unsupported patterns
  - All existing VectorCombine tests pass



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