[Bug tree-optimization/20725] New: [tcb] FRE does not remove a fully redundant load.
kazu at cs dot umass dot edu
gcc-bugzilla@gcc.gnu.org
Sat Apr 2 04:37:00 GMT 2005
Consider:
struct s {
int *n;
};
int
foo (unsigned int i, struct s *array)
{
int *p = array[i].n;
if (p)
{
int *q = array[i].n;
if (p != q)
return 1;
}
return 0;
}
Note that the second load is unnecessary, but FRE does not remove it.
Here is the dump before FRE.
foo (i, array)
{
int * q;
int * p;
int D.1142;
struct s * D.1141;
struct s * D.1140;
unsigned int D.1139;
<bb 0>:
D.1139_3 = i_2 * 4;
D.1140_4 = (struct s *) D.1139_3;
D.1141_6 = D.1140_4 + array_5;
# VUSE <TMT.0_15>;
p_7 = D.1141_6->n;
if (p_7 != 0B) goto <L0>; else goto <L2>;
<L0>:;
D.1139_10 = i_2 * 4;
D.1140_11 = (struct s *) D.1139_10;
D.1141_12 = array_5 + D.1140_11;
# VUSE <TMT.0_15>;
q_13 = D.1141_12->n;
if (p_7 != q_13) goto <L1>; else goto <L2>;
<L1>:;
D.1142_14 = 1;
goto <bb 4> (<L4>);
<L2>:;
D.1142_9 = 0;
# D.1142_1 = PHI <1(2), 0(3)>;
<L4>:;
return D.1142_1;
}
After FRE:
foo (i, array)
{
int * q;
int * p;
int D.1142;
struct s * D.1141;
struct s * D.1140;
unsigned int D.1139;
<bb 0>:
D.1139_3 = i_2 * 4;
D.1140_4 = (struct s *) D.1139_3;
D.1141_6 = D.1140_4 + array_5;
# VUSE <TMT.0_15>;
p_7 = D.1141_6->n;
if (p_7 != 0B) goto <L0>; else goto <L2>;
<L0>:;
D.1139_10 = D.1139_3;
D.1140_11 = D.1140_4;
D.1141_12 = D.1141_6;
# VUSE <TMT.0_15>;
q_13 = D.1141_12->n;
if (p_7 != q_13) goto <L1>; else goto <L2>;
<L1>:;
D.1142_14 = 1;
goto <bb 4> (<L4>);
<L2>:;
D.1142_9 = 0;
# D.1142_1 = PHI <1(2), 0(3)>;
<L4>:;
return D.1142_1;
}
--
Summary: [tcb] FRE does not remove a fully redundant load.
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P2
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: kazu at cs dot umass dot edu
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20725
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