Currently, when vectorizing stores to uniform addresses, the only
instance we prevent vectorization is if there are multiple stores to the
same uniform address.
This patch teaches LAA to avoid vectorizing loops that have an unsafe
cross-iteration dependency between a load and a store to the same uniform address.
We cannot vectorize loops that load from a uniform address where in the
previous iteration we stored to the same uniform address.
Two test cases are added to show safe and unsafe dependencies for
vectorization. Fixes PR39653.
Note: Initially tried setting CanVecMem to false and returning from the
LAA analysis, when we came across unsafe dependencies. However, this
broke some tests in LoopVersioningLICM. So, the patch changes the
HasNonVectorizableStoresToInvariantAddress. This allows ORE to
state the reason we could not vectorize the loop.