[patch] (-fstrict-overflow) optimize counted loops on signed iv

[Zdenek Dvorak]

Hello,

> But of course the following is the problem:
> 
> Index: fold-const.c
> ===================================================================
> *** fold-const.c        (revision 121992)
> --- fold-const.c        (working copy)
> *************** tree_swap_operands_p (tree arg0, tree ar
> *** 6668,6676 ****
>        && (TREE_SIDE_EFFECTS (arg0) || TREE_SIDE_EFFECTS (arg1)))
>      return 0;
> 
> !   if (DECL_P (arg1))
>      return 0;
> !   if (DECL_P (arg0))
>      return 1;
> 
>    /* It is preferable to swap two SSA_NAME to ensure a canonical form
> --- 6668,6676 ----
>        && (TREE_SIDE_EFFECTS (arg0) || TREE_SIDE_EFFECTS (arg1)))
>      return 0;
> 
> !   if (DECL_P (arg1) || TREE_CODE (arg1) == SSA_NAME)
>      return 0;
> !   if (DECL_P (arg0) || TREE_CODE (arg0) == SSA_NAME)
>      return 1;
> 
>    /* It is preferable to swap two SSA_NAME to ensure a canonical form
> 
> I'll bootstrap and test it.

makes sense, although it won't fix the problem in general (e.g.,
2 * a < 2 * a + 4 still would not be folded).

Zdenek