https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99918
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-04-06
Blocks| |85316
Ever confirmed|0 |1
Target Milestone|--- |9.4
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
The main issue is optimize_bit_field_compare in fold-const.c which produces
during GENERIC folding in .005t.original:
if ((BIT_FIELD_REF <b, 8, 0> & 1) != 0)
{
b.j = 0;
}
else
{
b.j = b.i;
}
return b.j;
that's premature in this place. For f() it also takes until DOM3 to do
the folding unless you disable SRA which then makes EVRP recognize the
second store as a.j = 0. With SRA we fail to derive ranges for a_10 in
a_10 = MEM <unsigned char> [(struct A *)&a];
a$1_11 = MEM <unsigned char> [(struct A *)&a + 1B];
_1 = VIEW_CONVERT_EXPR<_Bool>(a_10);
if (_1 != 0)
goto <bb 4>; [INV]
else
goto <bb 3>; [INV]
<bb 3> :
<bb 4> :
# a$1_9 = PHI <0(2), a_10(3)>
_7 = VIEW_CONVERT_EXPR<_Bool>(a$1_9);
thus we're missing looking through VIEW_CONVERT_EXPR in register_assert_for.
Amending that would eventually also allow optimizing the prematurely folded
vairant.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85316
[Bug 85316] [meta-bug] VRP range propagation missed cases
