[all-commits] [llvm/llvm-project] 5c5a1a: [RISCV] Introduce RISCVISD::CZERO_{EQZ, NEZ} nodes ...

[Alex Bradbury via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5c5a1a2927118eb9cc51c7b98c959a30524cc491
      https://github.com/llvm/llvm-project/commit/5c5a1a2927118eb9cc51c7b98c959a30524cc491
  Author: Alex Bradbury <asb at igalia.com>
  Date:   2023-07-14 (Fri, 14 Jul 2023)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    M llvm/lib/Target/RISCV/RISCVISelLowering.h
    M llvm/lib/Target/RISCV/RISCVInstrInfoZicond.td
    M llvm/test/CodeGen/RISCV/condops.ll
    M llvm/test/CodeGen/RISCV/select.ll

  Log Message:
  -----------
  [RISCV] Introduce RISCVISD::CZERO_{EQZ,NEZ} nodes produce them when zicond is present in lowerSELECT

This patch is a step towards altering how we handle the emission of
condops. Marking ISD::SELECT as legal is a major change in the codegen
path, and gives few options for maintaining the old codegen path when
it is believed to be better (e.g. a better branchless sequence is
possible using non-zicond instructions, or the branch-based sequence is
preferable).

This removes the existing SelectionDAG patterns and moves the logic into
lowerSELECT. Along some small codegen changes you'll note a few minor
regressions in the generated code quality - this are due to the fact
that by lowering the SELECT node early we miss out on combines that
would kick in later when setcc condcodes that aren't natively supported
have been expanded (thus exposing opportunities for optimisation by
performing logical negation and swapping truev/falsev). I've opted to
split out work that addresses these into follow-on patches (especially
as zicond is still 'experimental').

matchSetCC is a straight-forward translation from the version in
RISCVISelDAGToDAG. Ideally, in the future it can be converted to a
helper shared between both files.

Differential Revision: https://reviews.llvm.org/D155083