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PATCH RFC: Ensure TREE_TYPE (TYPE_MIN_VALUE (t)) == t
- From: Ian Lance Taylor <iant at google dot com>
- To: dnovillo at redhat dot com, rguenther at suse dot de
- Cc: gcc-patches at gcc dot gnu dot org
- Date: 27 Apr 2007 10:56:30 -0700
- Subject: PATCH RFC: Ensure TREE_TYPE (TYPE_MIN_VALUE (t)) == t
VRP currently assumes that TREE_TYPE (TYPE_MIN_VALUE (t)) == t. This
shows up in == and != comparisons of values with TYPE_MIN_VALUE of the
value's type. Those comparisons are normally valid because
build_int_cst_wide uniqifies all integer constants based on the value
and the type. However, when TREE_TYPE (TYPE_MIN_VALUE (t)) != t, then
any comparison against TYPE_MIN_VALUE will return unequal even if the
values are the same.
PR 31710 provides a test case in which VRP does the wrong thing. The
problem is noticed by a warning check I recently added.
At the moment TREE_TYPE (TYPE_MIN_VALUE (t)) != t for a typedef,
because build_distinct_type_copy, called from build_variant_type_copy,
simply copies the fields without giving them new types. I've
bootstrapped and tested the appended patch to fix this.
My question is: do you think this is the right fix, or should we
instead change VRP to use operand_equal_p or simply
tree_int_cst_equal? My patch seems a little more right, since having
TREE_TYPE (TYPE_MIN_VALUE (t)) == t seems more consistent. On the
other hand it will increase memory usage for no very obvious gain.
Any thoughts?
(If I commit this patch I will also add the test case from PR 31710).
Ian
2007-04-27 Ian Lance Taylor <iant@google.com>
PR middle-end/31710
* tree.c (build_distinct_type_copy): If TYPE_MIN_VALUE or
TYPE_MAX_VALUE exist, convert them to the new type.
Index: gcc/tree.c
===================================================================
--- gcc/tree.c (revision 124119)
+++ gcc/tree.c (working copy)
@@ -4165,6 +4165,15 @@ build_distinct_type_copy (tree type)
TYPE_MAIN_VARIANT (t) = t;
TYPE_NEXT_VARIANT (t) = 0;
+ /* VRP assumes that TREE_TYPE (TYPE_MIN_VALUE (type)) == type. */
+ if (INTEGRAL_TYPE_P (t) || SCALAR_FLOAT_TYPE_P (t))
+ {
+ if (TYPE_MIN_VALUE (t) != NULL_TREE)
+ TYPE_MIN_VALUE (t) = fold_convert (t, TYPE_MIN_VALUE (t));
+ if (TYPE_MAX_VALUE (t) != NULL_TREE)
+ TYPE_MAX_VALUE (t) = fold_convert (t, TYPE_MAX_VALUE (t));
+ }
+
return t;
}