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

[Richard Biener <rguenther@suse.de>]

On November 14, 2015 9:49:28 AM GMT+01:00, Senthil Kumar Selvaraj <senthil_kumar.selvaraj@atmel.com> wrote:
>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. 

I didn't mean to suggest narrowing is not OK.  In fact narrowing is always OK.

Richard.

>Richard?
>
>Regards
>Senthil
>> 
>> -- 
>> Marc Glisse