Re: [PATCH] [i386] Prefer INT_SSE_REGS for SSE_FLOAT_MODE_P in preferred_reload_class.

[Hongtao Liu <crazylht@gmail.com>]

On Thu, Dec 2, 2021 at 4:27 PM liuhongt <hongtao.liu@intel.com> wrote:
>
>   The patch helps reload to choose GENENRAL_REGS alternatives for
> SSE_FLOAT_MODE and enabled optimization like
>
> -       vmovd   %xmm0, -4(%rsp)
> -       movl    $1, %eax
> -       addl    -4(%rsp), %eax
> +       movd    %xmm0, %eax
> +       addl    $1, %eax
>
> Bootstrapped anf regtested on x86_64-pc-linux-gnu{-m32,} and
> x86_64-pc-linux-gnu{-m32\ march=cascadelake,\ -march=cadcadelake}.
>
> No big performace impact is abserved for SPEC2017 on ICX/CLX with both
> Ofast -march=native -flto -funroll-loops and -O2 -mtune=generic options.
>
> Ok for trunk?
>
> gcc/ChangeLog:
>
>         PR target/95740
>         * config/i386/i386.c (ix86_preferred_reload_class): Prefer
>         INT_SSE_REGS for SSE_FLOAT_MODE_P.
>         * config/i386/i386.h (INT_SSE_CLASS_P): New.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/i386/pr95740.c: New test.
> ---
>  gcc/config/i386/i386.c                  |  5 +++--
>  gcc/config/i386/i386.h                  |  2 ++
>  gcc/testsuite/gcc.target/i386/pr95740.c | 26 +++++++++++++++++++++++++
>  3 files changed, 31 insertions(+), 2 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr95740.c
>
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index 80fee627358..977af1c31a7 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -19194,9 +19194,10 @@ ix86_preferred_reload_class (rtx x, reg_class_t regclass)
>        return NO_REGS;
>      }
>
> -  /* Prefer SSE regs only, if we can use them for math.  */
> +  /* Prefer INT_SSE_REGS, enable reload from SSE register to GENERAL_REGS,
> +     refer to PR95740.  */
>    if (SSE_FLOAT_MODE_P (mode) && TARGET_SSE_MATH)
> -    return SSE_CLASS_P (regclass) ? regclass : NO_REGS;
> +    return INT_SSE_CLASS_P (regclass) ? regclass : NO_REGS;
>
>    /* Generally when we see PLUS here, it's the function invariant
>       (plus soft-fp const_int).  Which can only be computed into general
> diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
> index 2fda1e0686e..ec90e47904b 100644
> --- a/gcc/config/i386/i386.h
> +++ b/gcc/config/i386/i386.h
> @@ -1283,6 +1283,8 @@ enum reg_class
>    reg_class_subset_p ((CLASS), FLOAT_REGS)
>  #define SSE_CLASS_P(CLASS) \
>    reg_class_subset_p ((CLASS), ALL_SSE_REGS)
> +#define INT_SSE_CLASS_P(CLASS) \
> +  reg_class_subset_p ((CLASS), INT_SSE_REGS)
>  #define MMX_CLASS_P(CLASS) \
>    ((CLASS) == MMX_REGS)
>  #define MASK_CLASS_P(CLASS) \
> diff --git a/gcc/testsuite/gcc.target/i386/pr95740.c b/gcc/testsuite/gcc.target/i386/pr95740.c
> new file mode 100644
> index 00000000000..9bc7b862787
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr95740.c
> @@ -0,0 +1,26 @@
> +/* { dg-do compile { target { ! ia32 } } } */
> +/* { dg-options "-msse2 -O2 -mtune-ctrl=use_incdec -masm=att -mfpmath=sse" } */
> +/* { dg-final { scan-assembler-times {(?n)movd[\t ]*%xmm0.*%eax} 1 } } */
> +/* { dg-final { scan-assembler-times {(?n)incl[\t ]*%eax} 1 } } */
> +/* { dg-final { scan-assembler-times {(?n)movq[\t ]*%xmm0.*%rax} 1 } } */
> +/* { dg-final { scan-assembler-times {(?n)incq[\t ]*%rax} 1 } } */
> +
> +int
> +foo (float a)
> +{
> +  union{
> +    int b;
> +    float a;}u;
> +  u.a = a;
> +  return u.b + 1;
> +}
> +
> +long long
> +foo1 (double a)
> +{
> +  union{
> +    long long b;
> +    double a;}u;
> +  u.a = a;
> +  return u.b + 1;
> +}
> --
> 2.18.1
>


-- 
BR,
Hongtao