[Bug tree-optimization/51988] New: value_replacement in PHIOPT should handle even the cases where there are other PHIs even with non equal value
pinskia at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Wed Jan 25 00:25:00 GMT 2012
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51988
Bug #: 51988
Summary: value_replacement in PHIOPT should handle even the
cases where there are other PHIs even with non equal
value
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: pinskia@gcc.gnu.org
Take:
int g(int,int);
int f(int t, int c)
{
int d = 0;
int e = 0;
if (t)
{
d = t;
if (c) e = 1;
}
else d = 0, e = 0;
return g(d,e);
}
--- CUT ---
Currently we get:
<bb 2>:
if (t_5(D) != 0)
goto <bb 3>;
else
goto <bb 5>;
<bb 3>:
if (c_7(D) != 0)
goto <bb 4>;
else
goto <bb 5>;
<bb 4>:
<bb 5>:
# d_1 = PHI <t_5(D)(4), 0(2), t_5(D)(3)>
# e_2 = PHI <3(4), 0(2), 0(3)>
But we could reduce it down to:
<bb 2>:
if (t_5(D) != 0)
goto <bb 3>;
else
goto <bb 5>;
<bb 3>:
if (c_7(D) != 0)
goto <bb 4>;
else
goto <bb 5>;
<bb 4>:
<bb 5>:
# d_1 = PHI <t_5(D)(4), t_5(D)(2), t_5(D)(3)>
# e_2 = PHI <3(4), 0(2), 0(3)>
As t_5 on the edge from bb 2 to bb 5, t_5 is 0.
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