As shown in #70473, the following loop was not considered safe to
vectorize. When determining the memory access dependencies in
a loop which has negative iteration step, we invert the source and
sink of the dependence. Perhaps we should just invert the operands
to getMinusSCEV(). This way the dependency is not regarded to be
true, since the users of the `IsWrite` variables, which correspond to
each of the memory accesses, rely on program order and therefore
should not be swapped.
void vectorizable_Read_Write(int *A) {
for (unsigned i = 1022; i >= 0; i--)
A[i+1] = A[i] + 1;
}
Add an additional test case where we currently incorrectly identify a
dependence as Foward instead of ForwardButPreventsForwarding.
Also cleans up the names in the tests a bit to improve readability.
Currently the loop access analysis classifies this loop as unsafe to
vectorize because the memory dependencies are
'ForwardButPreventsForwarding'. However, the access pattern is
'write-after-read' with no subsequent read accessing the written memory
locations. I can't see how store-to-load forwarding is applicable here.
void vectorizable_Read_Write(int *A) {
for (unsigned i = 1022; i >= 0; i--)
A[i+1] = A[i] + 1;
}
