[all-commits] [llvm/llvm-project] cb6f02: [RISCV][VLOPT] Remove unnecessary passthru restric...

[Luke Lau via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cb6f021af2354761357684ffa26ebbe718615244
      https://github.com/llvm/llvm-project/commit/cb6f021af2354761357684ffa26ebbe718615244
  Author: Luke Lau <luke at igalia.com>
  Date:   2025-01-27 (Mon, 27 Jan 2025)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
    M llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp.ll
    M llvm/test/CodeGen/RISCV/rvv/vl-opt.ll

  Log Message:
  -----------
  [RISCV][VLOPT] Remove unnecessary passthru restriction (#124549)

We currently check for passthrus in two places, on the instruction to
reduce in isCandidate, and on the users in checkUsers.

We cannot reduce the VL if an instruction has a user that's a passthru,
because the user will read elements past VL in the tail.

However it's fine to reduce an instruction if it itself contains a
non-undef passthru. Since the VL can only be reduced, not increased, the
previous tail will always remain the same.



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