https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78312
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2016-11-11
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot
gnu.org
Target Milestone|--- |7.0
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmm.
So [0, 1] * ~[1, 65534] gets
MEET ([0, 1] * [0, 0] == [0, 0],
[0, 1] * [65535, 65535] == ~[1, 65534]) == ~[1, 65534]
that looks ok to me.
And then ~[1, 65534] * ~[1, 65534] is [0, 1], also ok.
But then somewhen the IL changes to
<bb 2>:
# RANGE [0, 1]
_1 = p1_8(D) > 0;
# RANGE [0, 1] NONZERO 1
_2 = (short unsigned int) _1;
# RANGE ~[1, 65534]
_3 = -_2;
# RANGE [0, 1]
_4 = _3 != 0;
# RANGE [0, 1] NONZERO 1
_5 = (short unsigned int) _4;
# RANGE ~[1, 65534]
_6 = _2 * _5;
and [0,1] * [0, 1] is not ~[1, 65534].
It is backprop messing up the IL, invalidating the range-info on SSA names.
Index: gcc/gimple-ssa-backprop.c
===================================================================
--- gcc/gimple-ssa-backprop.c (revision 242066)
+++ gcc/gimple-ssa-backprop.c (working copy)
@@ -728,6 +728,7 @@ backprop::prepare_change (tree var)
{
if (MAY_HAVE_DEBUG_STMTS)
insert_debug_temp_for_var_def (NULL, var);
+ reset_flow_sensitive_info (var);
}
/* STMT has been changed. Give the fold machinery a chance to simplify
