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

[Senthil Kumar Selvaraj <senthil_kumar.selvaraj@atmel.com>]

On Sat, Nov 14, 2015 at 09:13:41AM +0100, Marc Glisse wrote:
> 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.

Hmm, I came to the opposite conclusion - I thought Richard only okayed
"widening upto word-mode", not the narrowing. 

Richard?

Regards
Senthil
> 
> -- 
> Marc Glisse