[Bug middle-end/63184] New: [4.8/4.9/5 Regression] Fails to simplify comparison

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63184

            Bug ID: 63184
           Summary: [4.8/4.9/5 Regression] Fails to simplify comparison
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org

c-c++-common/pr19807-2.c

/* { dg-do link } */

extern void link_error(void);
int i;
int main()
{
  int a[4];
  if ((char*)&a[1] + 4*i + 4 != (char*)&a[i+2])
    link_error();
  return 0;
}

Fails with all optimization levels for all compilers.

c-c++-common/pr19807-3.c

/* { dg-do link } */

extern void link_error(void);
int i;
int main()
{
  int a[4];
  if (&a[1] + i + 1 != &a[i+2])
    link_error();
  return 0;
}

gcc 4.7 passes with -O[01] but fails with -O2+
gcc 4.8 and 4.9 fail with -O0 but passes with -O1+ (thanks to SLSR)
gcc 5.0 since the fix for PR63148 fails

which is a regression.

We don't seem to systematically use sth like the tree-affine.c framework
to simplify address comparisons and the fact that tree-reassoc.c doesn't
in any way associate pointer arithmetic doesn't help either.