[Bug optimization/13521] New: Endless loop in calculate_global_regs_live
jakub at gcc dot gnu dot org
gcc-bugzilla@gcc.gnu.org
Tue Dec 30 15:36:00 GMT 2003
Following testcase at -O2 and higher loops forever in calculate_global_regs_live.
extern int f1 (int, void *);
extern int *f2 (void) __attribute__ ((__const__));
extern int f3 (int, void *);
int
test (int x, char *y, int z)
{
int b = 0;
if (x < 1024)
{
y[0] = '\0';
do
{
switch (f1 (x, y + b))
{
case -1:
if (b == 0)
return -1;
else
return b;
default:
b++;
}
}
while (y[b - 1] != '\0' && y[b - 1] != '\n' && b < z);
}
else
{
do
{
switch (f3 (x, y + b))
{
case -1:
if ((*f2 ()) == 4)
continue;
if (b == 0)
return -1;
else
return b;
default:
b++;
}
}
while (y[b - 1] != '\0' && y[b - 1] != '\n' && b < z);
}
return b;
}
The problem seems to be that 1) cse finds out that the -1 constant in both return -1;
statements is already in the pseudo holding return value of f1() resp. f3()
and changes (set (reg:SI X) (const_int -1)) to (set (reg:SI X) (reg:SI Y)) REG_EQUAL (const_int -1).
2) during reload, this pseudo (Y above) is %eax after f1() and %r14d after f3()
(as in the latter case there is another function call in between)
3) during flow2 GCC replaces the pseudo with REG_EQUAL, so it is again:
(set (reg:SI %edx) (const_int -1)) REG_DEAD %r14d REG_EQUAL (const_int -1)
(in the f3() case and then merges both return -1's together).
The problem is REG_DEAD %r14d now, because it is set only in one of the predecessors
of the merged basic block, which causes the endless loop in calculate_global_regs_live
(as it keeps alternating between having %r14 live and not having it live).
Should cfg* not attempt to merge if there are different REG_DEAD notes
or do you have other ideas?
--
Summary: Endless loop in calculate_global_regs_live
Product: gcc
Version: 3.3.3
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jakub at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org,jh at suse dot cz,rth at
redhat dot com
GCC build triplet: *-*-*
GCC host triplet: *-*-*
GCC target triplet: x86_64-redhat-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13521
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