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

[Marc Glisse]

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.selva...@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