Test case is taken from bug 18046:
-----------------------------------------------------
extern void foo (void);
extern int i;
void
bar (void)
{
switch (i)
{
case 0:
foo ();
break;
case 1:
break;
}
switch (i)
{
case 0:
foo ();
break;
case 1:
break;
}
}
-----------------------------------------------------
the .012t.cfg dump with trunk (r156492) today looks like this:
bar ()
{
int i.0;
<bb 2>:
i.0 = i;
switch (i.0) <default: <L2>, case 0: <L0>, case 1: <L2>>
<L0>:
foo ();
<L2>:
i.0 = i;
switch (i.0) <default: <L6>, case 0: <L4>, case 1: <L6>>
<L4>:
foo ();
<L6>:
return;
}
The dump with "gcc (Debian 4.3.4-5) 4.3.4" looks better:
bar ()
{
int i.0;
# BLOCK 2
# PRED: ENTRY (fallthru)
i.0 = i;
switch (i.0)
{
case 0: goto <L0>;
default : goto <L1>;
}
# SUCC: 3 4
# BLOCK 3
# PRED: 2
<L0>:;
foo ();
# SUCC: 4 (fallthru)
# BLOCK 4
# PRED: 2 3 (fallthru)
<L1>:;
i.0 = i;
switch (i.0)
{
case 0: goto <L4>;
default : goto <L5>;
}
# SUCC: 5 6
# BLOCK 5
# PRED: 4
<L4>:;
foo ();
# SUCC: 6 (fallthru)
# BLOCK 6
# PRED: 4 5 (fallthru)
<L5>:;
return;
# SUCC: EXIT
}
Note how GCC 4.5 fails to clean up the "case 1" label. The label is retained
all the way through the .137t.nrv dump (at -O2) and only disappears in the
.139t.optimized dump.
This confuses things in a couple of places and costs memory for no reason.
--
Summary: [4,5 Regression] Redundant switch labels not cleaned up
anymore
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: steven at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42963
