https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81505
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2017-07-21
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot
gnu.org
Target Milestone|--- |5.5
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
90 if (TREE_CODE (step) == INTEGER_CST)
91 {
92 if (TYPE_UNSIGNED (TREE_TYPE (step)))
93 {
94 step1 = fold_build1 (NEGATE_EXPR, TREE_TYPE (step), step);
95 if (tree_int_cst_lt (step1, step))
96 {
(gdb) p debug_generic_expr (step)
-4B(OVF)
note this is a POINTER_TYPE constant. fold_negate_const produces a
non-overflown 4B from that which is what confuses things.
Of course pointers should never get TREE_OVERFLOW set IMHO. It gets that
from
#1 0x0000000000b079aa in fold_convert_const_int_from_int (
type=<pointer_type 0x7ffff69d6690>, arg1=0x7ffff6a0bb70)
at /tmp/trunk/gcc/fold-const.c:1869
1869 TREE_OVERFLOW (arg1));
(gdb) l
1864 /* Given an integer constant, make new constant with new type,
1865 appropriately sign-extended or truncated. Use widest_int
1866 so that any extension is done according ARG1's type. */
1867 return force_fit_type (type, wi::to_widest (arg1),
1868 !POINTER_TYPE_P (TREE_TYPE (arg1)),
1869 TREE_OVERFLOW (arg1));
1870 }
1871
1872 /* A subroutine of fold_convert_const handling conversions a REAL_CST
1873 to an integer type. */
(gdb) p arg1
$18 = (const_tree) 0x7ffff6a0bb70
(gdb) p debug_generic_expr (arg1)
-4(OVF)
so somewhat reasonable. So the bug is in fold_negate_const loosing the
overflow
flag. Fix:
Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c (revision 250386)
+++ gcc/fold-const.c (working copy)
@@ -13693,8 +13693,8 @@ fold_negate_const (tree arg0, tree type)
bool overflow;
wide_int val = wi::neg (arg0, &overflow);
t = force_fit_type (type, val, 1,
- (overflow | TREE_OVERFLOW (arg0))
- && !TYPE_UNSIGNED (type));
+ (overflow && ! TYPE_UNSIGNED (type))
+ || TREE_OVERFLOW (arg0));
break;
}
