[Bug tree-optimization/51877] New: [4.7 Regression] XEmacs miscompilation due to tail merging
jakub at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Tue Jan 17 08:20:00 GMT 2012
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51877
Bug #: 51877
Summary: [4.7 Regression] XEmacs miscompilation due to tail
merging
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: jakub@gcc.gnu.org
ReportedBy: jakub@gcc.gnu.org
CC: vries@gcc.gnu.org
extern void abort (void);
struct A { int a; char b[32]; } a, b;
__attribute__((noinline, noclone))
struct A
bar (int x)
{
struct A r;
static int n;
r.a = ++n;
__builtin_memset (r.b, 0, sizeof (r.b));
r.b[0] = x;
return r;
}
__attribute__((noinline, noclone))
void
baz (void)
{
asm volatile ("" : : : "memory");
}
__attribute__((noinline, noclone))
void
foo (struct A *x, int y)
{
if (y == 6)
a = bar (7);
else
*x = bar (7);
baz ();
}
int
main ()
{
a = bar (3);
b = bar (4);
if (a.a != 1 || a.b[0] != 3 || b.a != 2 || b.b[0] != 4)
abort ();
foo (&b, 0);
if (a.a != 1 || a.b[0] != 3 || b.a != 3 || b.b[0] != 7)
abort ();
foo (&b, 6);
if (a.a != 4 || a.b[0] != 7 || b.a != 3 || b.b[0] != 7)
abort ();
return 0;
}
is miscompiled at -O2 (distilled from XEmacs). Tail merging surprisingly
decides to tail merge the two calls, eventhough they have different lhs.
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