[Bug ipa/65765] [5/6 Regression] Compiling Firefox with GCC 5 leads to broken javascript engine on x86-64

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65765

--- Comment #3 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
markus@x4 tc % cat main.ii
int a, b, c, d, e;
unsigned char h[] = { 1, 1 };

__attribute__ ((cold)) int ModRM_Mode () { return a; }

int
ModRM_RM (int p1)
{
  return p1;
}

__attribute__ ((cold)) static bool ModRM_hasSIB (unsigned char p1)
{
  return ModRM_Mode () != 1 && ModRM_RM (p1);
}

__attribute__ ((cold)) static bool ModRM_hasRIP (unsigned char p1)
{
  return ModRM_Mode () && ModRM_RM (p1);
}

unsigned char *
DisassembleHeapAccess (unsigned char *p1)
{
  b = *p1++;
  if (ModRM_hasSIB (b))
    c = *p1++;
  int f = c, g = 0;
  d = ModRM_hasRIP (g);
  e = f == 0;
  if (e)
    p1 += sizeof 0;
  return p1;
}

int
main ()
{
  DisassembleHeapAccess (h) == h + 2 ? static_cast<void> (0)
                                     : __builtin_abort ();
}

markus@x4 tc % g++ -O2 main.ii && ./a.out
[1]    19854 abort      ./a.out
markus@x4 tc % g++ -O2 -fno-ipa-icf main.ii && ./a.out
markus@x4 tc %