https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79245
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note the trivial fix will FAIL gcc.dg/tree-ssa/ldist-23.c which looks like
int i;
for (i = 0; i < 128; ++i)
{
a[i] = a[i] + 1;
b[i] = d[i];
c[i] = a[i] / d[i];
}
where the testcase expects b[i] = d[i] to be split out as memcpy but
the other two partitions to be fused.
Generally the cost model lacks computing the number of input/output streams
of a partition and a target interface to query it about limits. Usually
store bandwidth is not equal to load bandwidth and not re-used store streams
can benefit from non-temporal stores being used by libc.
In your testcase I wonder whether distributing to
for (int j = 0; j < x; j++)
{
for (int i = 0; i < y; i++)
{
c[j][i] = b[j][i] - a[j][i];
}
}
memcpy (a, b, ...);
would be faster in the end (or even doing the memcpy first in this case).
Well, for now let's be more conservative given the cost model really is
lacking.
