bug#36370: 27.0.50; XFIXNAT called on negative numbers

[Bruno Haible <bruno@clisp.org>]

Oops, the test case that I meant to show is this one:

================================ foo.c =================================
#include <stdio.h>

#define assume(R) ((R) ? (void) 0 : __builtin_unreachable ())
//#define assume(R) (!__builtin_constant_p (!(R) == !(R)) || (R) ? (void) 0 : __builtin_unreachable ())

extern int complicated (int i);
extern int nonnegative (int i);

int f_generic (int i)
{
  printf("%d\n", i & 0x80000000);
  return 0;
}

int f_condition (int i)
{
  if (complicated (i) && nonnegative (i))
    printf("%d\n", i & 0x80000000);
  return 0;
}

int f_assume (int i)
{
  assume (complicated (i) && nonnegative (i));
  printf("%d\n", i & 0x80000000);
  return 0;
}
================================ bar.c =================================
int complicated (int i) { return (i & 7) == 3; }
int nonnegative (int i) { return i >= 0; }
========================================================================
The results are as shown: the optimization in f_assume is performed
with the old 'assume' definition, but not with the new one.