[PATCH] Keep lattice abstract in the SSA propagator, substitue lattice values at defs

[Eric Botcazou]

> I looked at the VRP dump and it derives perfectly valid assumptions.
> From
>
>   <various bounds checking concludes ident_int_2_12 is [1, 4]
>    and ident_int_1_10 is [1, 4]>
>
> <bb 15>:
>   D.2465_155 = ident_int_2_12 + 1;
>   L27b_156 = D.2465_155 - ident_int_1_10;
>   L29b_159 = L27b_156 + 1;
>
> <bb 16>:
>   # L29b_363 = PHI <L29b_159(15), 1(14)>
> ...
>
>   and we arrive with [-3, 9] for prephitmp.53_302 and [-1, 5] for L29b_363
>
>   if (prephitmp.53_302 > L29b_363)
>     goto <bb 27>;
>
> <bb 27>:
>
>   thus we can conclude that prephitmp.53_302 is [0, 9] here.
>   The following statement then produces a range of [2147483647, overflow].
>   So we happily substitute a constant value of 2147483647 for D.2544_253.
>
>   D.2544_253 = prephitmp.53_302 + 2147483647;
>   D.2553_254 = (size_type) D.2544_253;
> ...
>   D.2554_257 = D.2553_254 + 1;

I'll look into it.

-- 
Eric Botcazou