http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40979
--- Comment #15 from Sebastian Pop <spop at gcc dot gnu.org> 2011-02-01
16:46:54 UTC ---
The vectorizer does not apply because it does not match the canonical
form of a reduction: here is the reduction after graphite-identity:
# l12__lsm.18_179 = PHI <l12__lsm.18_183(5), l12__lsm.18_154(7)>
S1: l12_lower_188 = l12__lsm.18_179;
l12_lower_184 = D.1589_34 + l12_lower_188;
S2: l12__lsm.18_154 = l12_lower_184;
Without S1 and S2, this would be recognized as a reduction by the
vectorizer.
Why we end up with the two extra copies?
Here is the original code:
# l12_lower_5 = PHI <l12_lower_4(4), l12_lower_36(6)>
l12_lower_36 = D.1589_321 + l12_lower_5;
Graphite does the following:
l12_lower_5 = *l12_43(D);
l12_lower_36 = D.1589_321 + l12_lower_5;
*l12_43(D) = l12_lower_36;
Note that at this point we cannot construct this code because we use
data references and we are in Gimple form:
*l12_43(D) = D.1589_321 + *l12_43(D);
So I think that the code produced by Graphite is fine, and the problem
is in the cleanups that we're doing after: for instance loop invariant
motion could be improved to avoid the extra two statements S1 and S2:
# l12__lsm.18_179 = PHI <l12__lsm.18_183(5), l12__lsm.18_154(7)>
S1: l12_lower_188 = l12__lsm.18_179;
l12_lower_184 = D.1589_34 + l12_lower_188;
S2: l12__lsm.18_154 = l12_lower_184;
I also have tried to run pass_rename_ssa_copies but that would just
rename the base variable l12__lsm.18 into l12_lower and wait for the
out-of-SSA to remove the extra copies. Constant propagation does not
help either... any other suggestions?
