Re: [Patch, vrp] Allow VRP type conversion folding only for widenings upto word mode

[Marc Glisse <marc.glisse@inria.fr>]

On Sat, 14 Nov 2015, Senthil Kumar Selvaraj wrote:

> This patch came out of a discussion held in the gcc mailing list
> (https://gcc.gnu.org/ml/gcc/2015-11/msg00067.html).
>
> The patch restricts folding of conditional exprs with lhs previously
> set by a type conversion to occur only if the source of the type
> conversion's mode is word mode or smaller.
>
> Bootstrapped and reg tested on x86_64 (with --enable-languages=c,c++).
>
> If ok, could you commit please? I don't have commit access.
>
> Regards
> Senthil
>
> gcc/ChangeLog
>
> 2015-11-11  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>
>
> 	* tree-vrp.c (simplify_cond_using_ranges): Fold only
> 	if innerop's mode is word_mode or smaller.
>
>
> diff --git gcc/tree-vrp.c gcc/tree-vrp.c
> index e2393e4..c139bc6 100644
> --- gcc/tree-vrp.c
> +++ gcc/tree-vrp.c
> @@ -9467,6 +9467,8 @@ simplify_cond_using_ranges (gcond *stmt)
>       innerop = gimple_assign_rhs1 (def_stmt);
>
>       if (TREE_CODE (innerop) == SSA_NAME
> +         && (GET_MODE_SIZE(TYPE_MODE(TREE_TYPE(innerop)))
> +           <= GET_MODE_SIZE(word_mode))
> 	  && !POINTER_TYPE_P (TREE_TYPE (innerop)))
> 	{
> 	  value_range *vr = get_value_range (innerop);

I thought the result of the discussion was that the transformation is ok 
if either it is narrowing or it widens but to something no bigger than 
word_mode. So you should have 2 comparisons, or 1 with a max.

-- 
Marc Glisse