[PATCH] D159084: InstCombine: Fold is.fpclass(x, fcInf) to fabs+fcmp

[Lu Weining via Phabricator via llvm-commits]

SixWeining added subscribers: wangleiat, SixWeining.
SixWeining added a comment.

If ISD::IS_FPCLASS is legal or custom on some targets, do we still need the transform?

For example on riscv64,

  // test.c
  _Bool check_isfpclass_inf(float x) {
    return __builtin_isfpclass(x, 516);
  }

`clang -S -O2 test.c --target=riscv64 -march=rv64g -o -`

Before this change, `fclass.s` is generated:

  fclass.s        a0, fa0
  andi    a0, a0, 129
  snez    a0, a0
  ret

After this change, one more insn is generated:

  fabs.s  fa5, fa0
  lui     a0, 522240
  fmv.w.x fa4, a0
  feq.s   a0, fa5, fa4
  ret


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D159084/new/

https://reviews.llvm.org/D159084