[Bug rtl-optimization/58662] [4.9 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu (in 64-bit mode)

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58662

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #5)
> It looks like changing the testcase line
> 
>   d = foo (a == 0, (0, 35536)); 
> 
> to
> 
>   d = foo (a == 0, -30000);  
> 
> fixes it.  _No_ IL difference in 065t.mergephi2, but then 066t.vrp1 has
> 
>  main ()
>  {
>    char e;
> @@ -39,6 +35,7 @@
>    _Bool _4;
>    int _5;
>    int _7;
> +  int c.4_9;
>    int b.5_11;
>    int _12;
>  
> @@ -46,22 +43,37 @@
>    a.0_3 = a;
>    _4 = a.0_3 == 0;
>    _5 = (int) _4;
> -  _12 = 0;
> -  d = 0;
> -  _7 = 0;
> -  e_8 = 0;
> -  iftmp.3_1 = 0;
> -  b ={v} 0;
> -  b.5_11 ={v} b;
> -  if (b.5_11 != 0)
> +  _12 = _5 / -30000;
> +  d = _12;
> +  _7 = _12 % 14;
> +  e_8 = (char) _7;
> +  if (_7 != 0)
>      goto <bb 3>;
>    else
>      goto <bb 4>;
>  
>    <bb 3>:
> -  abort ();
> +  c.4_9 = c;
> +  if (c.4_9 != 0)
> +    goto <bb 5>;
> +  else
> +    goto <bb 4>;
>  
>    <bb 4>:
> +
> +  <bb 5>:
> +  # iftmp.3_1 = PHI <1(3), 0(4)>
> +  b ={v} iftmp.3_1;
> +  b.5_11 ={v} b;
> +  if (b.5_11 != 0)
> +    goto <bb 6>;
> +  else
> +    goto <bb 7>;
> +
> +  <bb 6>:
> +  abort ();
> +
> +  <bb 7>:
>    return 0;
>  
>  }
> 
> what?!

That's because there _is_ a IL difference.  With (0, 35536) the
-30000 tree constant has TREE_OVERFLOW set while with literal
-30000 in the source it does not.

Due to VRP relying on some fold-const.c overflow detection with
TREE_OVERFLOW this effect is to be expected.

[but in reality GIMPLE should not have any TREE_OVERFLOW constants
in the IL, though that's hard to avoid]