http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56474
--- Comment #16 from Richard Biener <rguenth at gcc dot gnu.org> 2013-04-22
13:34:40 UTC ---
The testcase in the patch posted to the mailing list is
-- { dg-do compile }
with Ada.Streams;
package Array3 is
use type Ada.Streams.Stream_Element_Offset;
type Vector (Size : Ada.Streams.Stream_Element_Offset) is record
Value : Ada.Streams.Stream_Element_Array (0 .. Size);
end record;
Empty_Vector : Vector (-1);
end Array3;
is the testcase when changed to 'Empty_Vector : Vector (-2);' valid?
In any case, in 0 .. Size, Size seems to be signed.
Also, there is the special-case
/* Similarly, if one of the values overflows in sizetype and the
range is null, use 1..0 for the sizetype bounds. */
else if (TREE_CODE (gnu_min) == INTEGER_CST
&& TREE_CODE (gnu_max) == INTEGER_CST
&& (TREE_OVERFLOW (gnu_min) || TREE_OVERFLOW (gnu_max))
&& tree_int_cst_lt (gnu_orig_max, gnu_orig_min))
{
gnu_min = size_one_node;
gnu_max = size_zero_node;
gnu_high = gnu_max;
}
that simply chooses [1, 0] as "empty" domain, regardless of the original
min or max. So both cases (of which you fix only one),
/* Otherwise, if the high bound is constant but the low bound is
not, we use the expression (hb >= lb) ? lb : hb + 1 for the
lower bound. Note that the comparison must be done in the
original type to avoid any overflow during the conversion. */
else if (TREE_CODE (gnu_max) == INTEGER_CST
&& TREE_CODE (gnu_min) != INTEGER_CST)
{
gnu_high = gnu_max;
gnu_min
= build_cond_expr (sizetype,
build_binary_op (GE_EXPR,
boolean_type_node,
gnu_orig_max,
gnu_orig_min),
gnu_min,
size_binop (PLUS_EXPR, gnu_max,
size_one_node));
}
/* Finally we use (hb >= lb) ? hb : lb - 1 for the upper bound
in all the other cases. Note that, here as well as above,
the condition used in the comparison must be equivalent to
the condition (length != 0). This is relied upon in order
to optimize array comparisons in compare_arrays. */
else
gnu_high
= build_cond_expr (sizetype,
build_binary_op (GE_EXPR,
boolean_type_node,
gnu_orig_max,
gnu_orig_min),
gnu_max,
size_binop (MINUS_EXPR, gnu_min,
size_one_node));
could be combined to
else
{
gnu_min
= build_cond_expr (sizetype,
build_binary_op (GE_EXPR,
boolean_type_node,
gnu_orig_max,
gnu_orig_min),
gnu_min,
size_one_node));
gnu_high
= build_cond_expr (sizetype,
build_binary_op (GE_EXPR,
boolean_type_node,
gnu_orig_max,
gnu_orig_min),
gnu_max,
size_zero_node);
}
which fixes the issue for me.
I can also easily guard the existing size_binop (MINUS_EXPR, gnu_min,
size_one_node) for gnu_min being zero, or I can simply use
int_const_binop here instead, as you expect that operation to _never_
set TREE_OVERFLOW if not gnu_min had TREE_OVERFLOW set.
Note that if gnu_max - 1 is not computable as compile-time constant here,
but is retained as tree expression and folded later overflow will not
be considered either (it doesn't go the size_* API way, which is supposed
to be the interface giving overflow hints to the FEs via means of
TREE_OVERFLOW which better should not appear later during optimization).
