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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109008] [13 Regression] Wrong code in scipy
 package since r13-3926-gd4c2f1d376da6f
Date: Wed, 08 Mar 2023 15:07:27 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109008

--- Comment #34 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Testing I've performed so far (though on 10000 iterations rather than 30000=
0,
that is ongoing), once with the
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109008#c33 patch alone, once=
 with
that patch and https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109008#c32.

First step, generate a random testcase:
pr109008-gen.c:
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

static long rand_n;
static int rand_c;

static uint32_t
get_rand32 (void)
{
  uint32_t ret =3D 0;
  if (rand_c =3D=3D 0)
    {
      ret =3D random () & 0x7fffffff;
      rand_c =3D 31;
    }
  else
    ret =3D rand_n & (((uint32_t) 1 << rand_c) - 1);
  ret <<=3D (32 - rand_c);
  rand_n =3D random ();
  ret |=3D rand_n & (((uint32_t) 1 << (32 - rand_c)) - 1);
  rand_n >>=3D (32 - rand_c);
  rand_c =3D 31 - (32 - rand_c);
  return ret;
}

static uint64_t
get_rand64 (void)
{
  return (((uint64_t) get_rand32 ()) << 32) | get_rand32 ();
}

static float
get_randf (void)
{
  uint32_t i =3D get_rand32 ();
  float f;
  memcpy (&f, &i, sizeof (f));
  return f;
}

int
main ()
{
  printf ("#define nanf __builtin_nanf (\"\")\n");
  printf ("#define inf __builtin_inff ()\n");
  for (int n =3D 0; n < 300000; ++n)
    {
      float n1 =3D get_randf ();
      float n2 =3D get_randf ();
      uint32_t x =3D get_rand32 ();
      if ((x & 7) =3D=3D 0)
        n2 =3D n1;
      x >>=3D 3;
      printf ("float f%d (float eps) { float f =3D ", n);
      switch (x % 3)
        {
        case 0: printf ("%af + eps", n1); break;
        case 1: printf ("%af - eps", n1); break;
        case 2: printf ("eps - %af", n1); break;
        }
      printf ("; if (f =3D=3D %af) return eps; return __builtin_nanf (\"42\=
");
}\n", n2);
    }
  return 0;
}
pr109008-main.c:
#include <math.h>

#include "pr109008.c"

struct S { float (*fn) (float); float lb, ub; };
struct S arr[] =3D {
#include "pr109008.h"
};

int
main ()
{
  float plus_inf =3D __builtin_inf ();
  float minus_inf =3D -plus_inf;
  for (int i =3D 0; i < sizeof (arr) / sizeof (arr[0]); ++i)
    {
      float lb =3D nextafterf (arr[i].lb, minus_inf);
      float ub =3D nextafterf (arr[i].ub, plus_inf);
      if (!__builtin_isnan (arr[i].fn (lb)) || !__builtin_isnan (arr[i].fn
(ub)))
        __builtin_printf ("%p err\n", arr[i].fn);
    }
}
gcc -g -O2 -o pr109008-gen{,.c}; ./pr109008-gen > pr109008.c
Next, with cc1 built with just #c33 patch:
rm -f /tmp/ranges; ./cc1 -quiet -O2 pr109008.c; sort -u /tmp/ranges >
pr109008.h
gcc -g -o pr109008-main{,.c}; ./pr109008-main
For 10000 iterations this showed 872 errors.
Next, with cc1 built with both #c32 and #c33 patches:
rm -f /tmp/ranges; ./cc1 -quiet -O2 pr109008.c; sort -u /tmp/ranges >
pr109008.h
gcc -g -o pr109008-main{,.c}; ./pr109008-main
This didn't print any errors, so at least for foperator_plus and
foperator_minus seems
to be from this limited testing conservatively correct.
Want to finish now this testing also for 300000 iterations and then perhaps=
 try
the #c30 patch with variant of #c33 to check also that implementation.
And finally compare the #c32+#c33 vs. #c30+#c33variant ranges.

Another thing which would be nice to think about is whether
float_widen_lhs_range
needs to extend even real_{min,max}_representable () bounds towards -+inf, =
or
whether
that case can't happen (and check that separately for + or - and * or /),
because e.g. for mult/div whether lhs is finite is quite important.=