Re: [PATCH v3 1/5] LoongArch: Fix usage of LSX and LASX frint/ftint instructions [PR112578]

[chenglulu <chenglulu@loongson.cn>]

在 2023/11/20 上午8:47, Xi Ruoyao 写道:
> The usage LSX and LASX frint/ftint instructions had some problems:
>
> 1. These instructions raises FE_INEXACT, which is not allowed with
>     -fno-fp-int-builtin-inexact for most C2x section F.10.6 functions
>     (the only exceptions are rint, lrint, and llrint).
> 2. The "frint" instruction without explicit rounding mode is used for
>     roundM2, this is incorrect because roundM2 is defined "rounding
>     operand 1 to the *nearest* integer, rounding away from zero in the
>     event of a tie".  We actually don't have such an instruction.  Our
>     frintrne instruction is roundevenM2 (unfortunately, this is not
>     documented).
> 3. These define_insn's are written in a way not so easy to hack.
>
> So I removed these instructions and created a "simd.md" file, then added
> them and the corresponding expanders there.  The advantage of the
> simd.md file is we don't need to duplicate the RTL template twice (in
> lsx.md and lasx.md).
/* snip */
> +;; fix_trunc is allowed to raise inexact exception even if
> +;; -fno-fp-int-builtin-inexact.  Because the middle end trys to match
> +;; (FIX x) and it does not know (FIX (UNSPEC_SIMD_FRINTRZ x)), we need
> +;; to use define_insn_and_split instead of define_expand (expanders are
> +;; not considered during matching).

Hi,

  I don’t quite understand this part. Is it because define_insn would be 
duplicated with the above implementation,

so define_insn_and_split is used?


Thanks.

> +(define_insn_and_split "fix_trunc<mode><vimode>2"
> +  [(set (match_operand:<VIMODE> 0 "register_operand" "=f")
> +	(fix:<VIMODE> (match_operand:FVEC 1 "register_operand" "f")))]
> +  ""
> +  "#"
> +  ""
> +  [(const_int 0)]
> +  {
> +    emit_insn (gen_<simd_isa>_<x>vftintrz_<simdifmt_for_f>_<simdfmt> (
> +      operands[0], operands[1]));
> +    DONE;
> +  }
> +  [(set_attr "type" "simd_fcvt")
> +   (set_attr "mode" "<MODE>")])