[all-commits] [llvm/llvm-project] 552c0d: [RISCV] Use XORI/SLLI/ADDI to when materializing s...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 552c0d14d13df8d05fc970425b806bc7e2ca9c8c
      https://github.com/llvm/llvm-project/commit/552c0d14d13df8d05fc970425b806bc7e2ca9c8c
  Author: Philip Reames <preames at rivosinc.com>
  Date:   2025-08-28 (Thu, 28 Aug 2025)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    M llvm/test/CodeGen/RISCV/select-const.ll
    M llvm/test/CodeGen/RISCV/select.ll

  Log Message:
  -----------
  [RISCV] Use XORI/SLLI/ADDI to when materializing select of constants (#155845)

This case is the inverse of the one introduced in #155644. The
complexity with the inversion is that we need to also invert the
condition before shifting it. I had originally planned to only do so
when the condition was "cheaply" invertible (i.e. didn't require the
xori), but when looking more closely at the diffs I noticed that while
the XORI prevents this from being an icount improvement, and actually
lengthens slightly the critical path, it does still reduce the number of
registers needed.



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