Let's try this again; this has been reverted/recommited a few times. Last time
this got reverted because for this loop:
void a() {
#pragma clang loop vectorize(disable)
for (;;)
;
}
vectorisation was incorrectly enabled and the vectorize.enable metadata was set
due to a logic error. But with this fixed, we now imply vectorisation when:
1) vectorisation is enabled, which means: VectorizeWidth > 1,
2) and don't want to add it when it is disabled or enabled, otherwise we would
be incorrectly setting it or duplicating the metadata, respectively.
This should fix PR27643.
Differential Revision: https://reviews.llvm.org/D69628
Sjoerd Meijer