https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102879
Aldy Hernandez <aldyh at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |amacleod at redhat dot com
--- Comment #1 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
We should've elided the call to foo() in the 8->3 edge. This is the IL in
vrp-thread1 dump:
int main ()
{
int h;
int g;
int _3;
_Bool _5;
int _6;
char iftmp.4_11;
int _12;
int _19;
int _21;
char iftmp.4_22;
int d.0_25;
_Bool _26;
int _27;
int c.2_28;
char _29;
int _30;
int _42;
char iftmp.4_43;
int _48;
int _50;
_Bool _53;
int _56;
int _59;
char iftmp.4_60;
int _62;
<bb 2> [local count: 134197598]:
c = 2;
goto <bb 5>; [100.00%]
<bb 3> [local count: 88583700]:
foo ();
<bb 4> [local count: 268435457]:
g_18 = g_10 + 1;
<bb 5> [local count: 402633054]:
# g_10 = PHI <0(2), g_18(4)>
if (g_10 != 2)
goto <bb 6>; [66.67%]
else
goto <bb 9>; [33.33%]
<bb 6> [local count: 268435456]:
d.0_25 = d;
_26 = d.0_25 == 0;
_27 = (int) _26;
c.2_28 = c;
_29 = (char) c.2_28;
_30 = (int) _29;
if (_29 >= 0)
goto <bb 8>; [59.00%]
else
goto <bb 7>; [41.00%]
<bb 7> [local count: 110058536]:
# iftmp.4_11 = PHI <_29(6)>
_12 = (int) iftmp.4_11;
d = _12;
_48 = (int) _29;
d = _48;
_19 = (int) _29;
d = _19;
goto <bb 4>; [100.00%]
<bb 8> [local count: 158376920]:
_42 = _30 >> _27;
iftmp.4_43 = (char) _42;
_50 = _42;
d = _50;
_53 = _50 == 0;
_56 = (int) _53;
_21 = _30 >> _56;
iftmp.4_22 = (char) _21;
_3 = _21;
d = _3;
_5 = _3 == 0;
_6 = (int) _5;
_59 = _30 >> _6;
iftmp.4_60 = (char) _59;
_62 = _59;
d = _62;
if (_62 == 0)
goto <bb 3>; [66.33%]
else
goto <bb 4>; [33.67%]
<bb 9> [local count: 134197598]:
return 0;
}
So, presumably _62 == 0 cannot be true. If _62 == 0, then
0 = _30 >> _6;
But that cannot happen because _30 is 2 if you follow the series of copies from
the "c" global.
There is no way 0 = 2 >> x can ever be true.
There's probably a couple things missing here. Maybe
operator_rshift::op1_range needs to be taught that ~[0,0] = x >> y implies x is
non-zero. But also, we can't see through the load from the c=2 global.
Shouldn't that c=2 have been propagated by someone at this point? (VRP1?)
