https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89908
Bug ID: 89908
Summary: Unnecessary rejection of dependence for outer loop
vectorisation
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rsandifo at gcc dot gnu.org
Target Milestone: ---
This loop:
void __attribute__ ((noipa))
f (int a[][N], int b[restrict])
{
for (int i = N - 1; i-- > 0; )
for (int j = 0; j < N - 1; ++j)
a[j + 1][i] = a[j][i + 1] + b[i];
}
should be vectorisable using outer loop vectorisation, since the
dependence between the lhs and rhs is in the same nonzero direction
for both loops.
See https://gcc.gnu.org/ml/gcc-patches/2019-03/msg01224.html for
some discussion about how the dependence checks could be handled.
