RFR: 8318827: RISC-V: Improve readability of fclass result testing

[Ludovic Henry]

On Wed, 25 Oct 2023 14:42:07 GMT, Feilong Jiang <fjiang at openjdk.org> wrote:

> Hi, please consider.
> 
> Currently, we test results of `fclass` instruction with hard-coded bits which has bad readability. This patch adds an enumeration of the flcass mask bits for ease of use.
> 
> Testing:
> 
> - [ ] tier1 with release build

src/hotspot/cpu/riscv/assembler_riscv.hpp line 1094:

> 1092:   FCLASS_NAN        = FCLASS_SNAN     | FCLASS_QNAN,
> 1093:   FCLASS_FINITE     = FCLASS_ZERO     | FCLASS_SUBNORM   | FCLASS_NORM,
> 1094: };

We use lower-case and no prefix for similar enums (ex: https://github.com/openjdk/jdk/blob/069bb87693ec7944f08062e3a7e460653324e6cb/src/hotspot/cpu/riscv/assembler_riscv.hpp#L1119-L1145)

Suggestion:

enum fclass_mask {
  minf       = 1 << 0,   // negative infinite
  mnorm      = 1 << 1,   // negative normal number
  msubnorm   = 1 << 2,   // negative subnormal number
  mzero      = 1 << 3,   // negative zero
  pzero      = 1 << 4,   // positive zero
  psubnorm   = 1 << 5,   // positive subnormal number
  pnorm      = 1 << 6,   // positive normal number
  pinf       = 1 << 7,   // positive infinite
  snan       = 1 << 8,   // signaling NaN
  qnan       = 1 << 9,   // quiet NaN
  zero       = mzero    | pzero,
  subnorm    = msubnorm | psubnorm,
  norm       = mnorm    | pnorm,
  inf        = minf     | pinf,
  nan        = snan     | qnan,
  finite     = zero     | subnorm   | norm,
};

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PR Review Comment: https://git.openjdk.org/jdk/pull/16362#discussion_r1371949559