Re: [PATCH] Fix i?86/x86_64 pre-SSE4.1 rint expansion (PR target/81906)

[Uros Bizjak <ubizjak at gmail dot com>]

On Thu, Dec 7, 2017 at 5:48 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> As mentioned in the PR, the code emitted by ix86_expand_rint
> doesn't work with rounding to +/- infinity.
> This patch adjusts it if flag_rounding_math to do something that works
> well even for that case (should be just one insn longer).
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2017-12-07  Joseph Myers  <joseph@codesourcery.com>
>             Alexander Monakov  <amonakov@ispras.ru>
>             Jakub Jelinek  <jakub@redhat.com>
>
>         PR target/81906
>         * config/i386/i386.c (ix86_expand_rint): Handle flag_rounding_math.
>
>         * gcc.target/i386/pr81906.c: New test.

OK for trunk and release branches.

Thanks,
Uros.

> --- gcc/config/i386/i386.c.jj   2017-12-05 10:15:31.000000000 +0100
> +++ gcc/config/i386/i386.c      2017-12-07 11:58:15.159881741 +0100
> @@ -44255,8 +44255,7 @@ ix86_expand_lfloorceil (rtx op0, rtx op1
>    emit_move_insn (op0, ireg);
>  }
>
> -/* Expand rint (IEEE round to nearest) rounding OPERAND1 and storing the
> -   result in OPERAND0.  */
> +/* Expand rint rounding OPERAND1 and storing the result in OPERAND0.  */
>  void
>  ix86_expand_rint (rtx operand0, rtx operand1)
>  {
> @@ -44264,11 +44263,17 @@ ix86_expand_rint (rtx operand0, rtx oper
>         xa = fabs (operand1);
>          if (!isless (xa, 2**52))
>           return operand1;
> -        xa = xa + 2**52 - 2**52;
> +        two52 = 2**52;
> +        if (flag_rounding_math)
> +         {
> +           two52 = copysign (two52, operand1);
> +           xa = operand1;
> +         }
> +        xa = xa + two52 - two52;
>          return copysign (xa, operand1);
>     */
>    machine_mode mode = GET_MODE (operand0);
> -  rtx res, xa, TWO52, mask;
> +  rtx res, xa, TWO52, two52, mask;
>    rtx_code_label *label;
>
>    res = gen_reg_rtx (mode);
> @@ -44281,8 +44286,16 @@ ix86_expand_rint (rtx operand0, rtx oper
>    TWO52 = ix86_gen_TWO52 (mode);
>    label = ix86_expand_sse_compare_and_jump (UNLE, TWO52, xa, false);
>
> -  xa = expand_simple_binop (mode, PLUS, xa, TWO52, NULL_RTX, 0, OPTAB_DIRECT);
> -  xa = expand_simple_binop (mode, MINUS, xa, TWO52, xa, 0, OPTAB_DIRECT);
> +  two52 = TWO52;
> +  if (flag_rounding_math)
> +    {
> +      two52 = gen_reg_rtx (mode);
> +      ix86_sse_copysign_to_positive (two52, TWO52, res, mask);
> +      xa = res;
> +    }
> +
> +  xa = expand_simple_binop (mode, PLUS, xa, two52, NULL_RTX, 0, OPTAB_DIRECT);
> +  xa = expand_simple_binop (mode, MINUS, xa, two52, xa, 0, OPTAB_DIRECT);
>
>    ix86_sse_copysign_to_positive (res, xa, res, mask);
>
> --- gcc/testsuite/gcc.target/i386/pr81906.c.jj  2017-12-07 11:38:06.730812658 +0100
> +++ gcc/testsuite/gcc.target/i386/pr81906.c     2017-12-07 11:38:14.488716544 +0100
> @@ -0,0 +1,37 @@
> +/* PR target/81906 */
> +/* { dg-do run { target *-*-linux* *-*-gnu* } }
> +/* { dg-options "-O2 -frounding-math" } */
> +
> +#include <fenv.h>
> +
> +int
> +main ()
> +{
> +  #define N 12
> +  double a[N] = { 2.0, 2.25, 2.5, 2.75, 3.5, -2.0, -2.25, -2.5, -2.75, -3.5, 0x2.0p53, -0x2.0p53 };
> +  double b[N], c[N], d[N], e[N];
> +  double be[N] = { 2.0, 2.0, 2.0, 3.0, 4.0, -2.0, -2.0, -2.0, -3.0, -4.0, 0x2.0p53, -0x2.0p53 };
> +  double ce[N] = { 2.0, 2.0, 2.0, 2.0, 3.0, -2.0, -3.0, -3.0, -3.0, -4.0, 0x2.0p53, -0x2.0p53 };
> +  double de[N] = { 2.0, 3.0, 3.0, 3.0, 4.0, -2.0, -2.0, -2.0, -2.0, -3.0, 0x2.0p53, -0x2.0p53 };
> +  double ee[N] = { 2.0, 2.0, 2.0, 2.0, 3.0, -2.0, -2.0, -2.0, -2.0, -3.0, 0x2.0p53, -0x2.0p53 };
> +  asm volatile ("" : : "g" (a), "g" (be), "g" (ce), "g" (de), "g" (ee) : "memory");
> +
> +  int i;
> +  fesetround (FE_TONEAREST);
> +  for (i = 0; i < N; ++i)
> +    b[i] = __builtin_rint (a[i]);
> +  fesetround (FE_DOWNWARD);
> +  for (i = 0; i < N; ++i)
> +    c[i] = __builtin_rint (a[i]);
> +  fesetround (FE_UPWARD);
> +  for (i = 0; i < N; ++i)
> +    d[i] = __builtin_rint (a[i]);
> +  fesetround (FE_TOWARDZERO);
> +  for (i = 0; i < N; ++i)
> +    e[i] = __builtin_rint (a[i]);
> +  fesetround (FE_TONEAREST);
> +  for (i = 0; i < N; ++i)
> +    if (b[i] != be[i] || c[i] != ce[i] || d[i] != de[i] || e[i] != ee[i])
> +      __builtin_abort ();
> +  return 0;
> +}
>
>         Jakub