[all-commits] [llvm/llvm-project] 874202: [RISCV] Canonicalize foldable branch conditions in...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 8742022ec74c54f1415707261ccc2054a3decd5f
      https://github.com/llvm/llvm-project/commit/8742022ec74c54f1415707261ccc2054a3decd5f
  Author: Philip Reames <preames at rivosinc.com>
  Date:   2025-03-27 (Thu, 27 Mar 2025)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
    M llvm/test/CodeGen/RISCV/bfloat-br-fcmp.ll
    M llvm/test/CodeGen/RISCV/double-br-fcmp.ll
    M llvm/test/CodeGen/RISCV/float-br-fcmp.ll
    M llvm/test/CodeGen/RISCV/half-br-fcmp.ll
    M llvm/test/CodeGen/RISCV/machine-sink-load-immediate.ll

  Log Message:
  -----------
  [RISCV] Canonicalize foldable branch conditions in optimizeCondBranch (#132988)

optimizeCondBranch isn't allowed to modify the CFG, but it can rewrite
the branch condition freely. However, If we could fold a conditional
branch to an unconditional one (aside from that restriction), we can
also rewrite it into some canonical conditional branch instead.

Looking at the diffs, the only cases this catches in tree tests are
cases where we could have constant folded during lowering from IR, but
didn't. This is inspired by trying to salvage code from
https://github.com/llvm/llvm-project/pull/131684 which might be useful.
Given the test impact, it's of questionable merits. The main advantage
over only the late cleanup pass is that it kills off the LIs for the
constants early - which can help e.g. register allocation.



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