[all-commits] [llvm/llvm-project] 5a1202: [RISCV] Optimize lowering of floating-point -0.0

[Fraser Cormack via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5a12024b95e4bdac8719f18a0e58c692aa471534
      https://github.com/llvm/llvm-project/commit/5a12024b95e4bdac8719f18a0e58c692aa471534
  Author: Fraser Cormack <fraser at codeplay.com>
  Date:   2022-01-20 (Thu, 20 Jan 2022)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    M llvm/lib/Target/RISCV/RISCVInstrInfoD.td
    M llvm/lib/Target/RISCV/RISCVInstrInfoF.td
    M llvm/lib/Target/RISCV/RISCVInstrInfoZfh.td
    M llvm/test/CodeGen/RISCV/fp-imm.ll
    M llvm/test/CodeGen/RISCV/rvv/fixed-vectors-reduction-fp.ll
    M llvm/test/CodeGen/RISCV/rvv/vreductions-fp-sdnode.ll
    M llvm/test/CodeGen/RISCV/zfh-imm.ll

  Log Message:
  -----------
  [RISCV] Optimize lowering of floating-point -0.0

This idea has come up in several reviews -- D115978 and D105902 -- so I
can't take any credit for the idea. Instead of using a constant pool to
lower -0.0, we can emit a sequence of two instructions:

    fmv.[hwd].x freg, zero
    fsgnjn.[hsd] freg, freg, freg

This is only done when the floating-point type is legal.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D117687