[Bug tree-optimization/52081] New: Missed tail merging with pure calls
vries at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Wed Feb 1 10:24:00 GMT 2012
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52081
Bug #: 52081
Summary: Missed tail merging with pure calls
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: vries@gcc.gnu.org
pr51879-12.c:
...
__attribute__((pure)) int bar (int);
__attribute__((pure)) int bar2 (int);
void baz (int);
int x, z;
void
foo (int y)
{
int a = 0;
if (y == 6)
{
a += bar (7);
a += bar2 (6);
}
else
{
a += bar2 (6);
a += bar (7);
}
baz (a);
}
...
When compiling at -O2, pr51879-12.c.094t.pre looks like this:
...
# BLOCK 3 freq:1991
# PRED: 2 [19.9%] (true,exec)
# VUSE <.MEMD.1722_12(D)>
# USE = nonlocal escaped
D.1717_4 = barD.1703 (7);
# VUSE <.MEMD.1722_12(D)>
# USE = nonlocal escaped
D.1718_6 = bar2D.1705 (6);
aD.1713_7 = D.1717_4 + D.1718_6;
goto <bb 5>;
# SUCC: 5 [100.0%] (fallthru,exec)
# BLOCK 4 freq:8009
# PRED: 2 [80.1%] (false,exec)
# VUSE <.MEMD.1722_12(D)>
# USE = nonlocal escaped
D.1720_8 = bar2D.1705 (6);
# VUSE <.MEMD.1722_12(D)>
# USE = nonlocal escaped
D.1721_10 = barD.1703 (7);
aD.1713_11 = D.1720_8 + D.1721_10;
# SUCC: 5 [100.0%] (fallthru,exec)
# BLOCK 5 freq:10000
# PRED: 3 [100.0%] (fallthru,exec) 4 [100.0%] (fallthru,exec)
# aD.1713_1 = PHI <aD.1713_7(3), aD.1713_11(4)>
# .MEMD.1722_13 = VDEF <.MEMD.1722_12(D)>
# USE = nonlocal
# CLB = nonlocal
bazD.1707 (aD.1713_1);
# VUSE <.MEMD.1722_13>
return;
...
Value numbering numbers the two phi arguments a_7 and a_11 the same so the
problem is not in value numbering:
...
Setting value number of a_11 to a_7 (changed)
...
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