http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56962
Bug #: 56962
Summary: [4.8/4.9 Regression] SLSR caused miscompilation of
fftw
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: ja...@gcc.gnu.org
Reduced testcase:
extern void abort (void);
long double v[144];
__attribute__((noinline, noclone)) void
bar (long double *x)
{
if (x != &v[29])
abort ();
}
__attribute__((noinline, noclone)) void
foo (long double *x, long y, long z)
{
long double a, b, c;
a = x[z * 4 + y * 3];
b = x[z * 5 + y * 3];
c = x[z * 5 + y * 4];
x[y * 4] = a;
bar (&x[z * 5 + y]);
x[z * 5 + y * 5] = b + c;
}
int
main ()
{
foo (v, 24, 1);
return 0;
}
This fails at -O2, works with -O2 -fno-tree-slsr. Started with
http://gcc.gnu.org/r190220
The *.reassoc2 to *.slsr diff with unimportant stuff removed:
...
_2 = z_1(D) * 4;
_4 = y_3(D) * 3;
_5 = _2 + _4;
...
_12 = z_1(D) * 5;
- _13 = _4 + _12;
+ _13 = _5 + z_1(D);
...
_18 = y_3(D) * 4;
- _19 = _12 + _18;
+ _19 = _13 + y_3(D);
...
- _28 = y_3(D) + _12;
+ _28 = _19 - _5;
...
Here before slsr we have:
_5 = y*3+z*4
_13 = y*3+z*5
_19 = y*4+z*5
_28 = y+z*5
and the _13 and _19 changes look just fine, but the _28 change is changing the
value from y+z*5 to y+z.
