[SVE][LoopVectorize] Verify support for vectorizing loops with invariant loads
D95598 added a cost model for broadcast shuffle, which should enable loops
such as the following to vectorize, where the load of b is invariant
and can be done using a scalar load + splat:
for (int i=0; i<n; ++i) a[i] = b[i] + b;
This patch adds tests to verify that we can vectorize such loops.
Reviewed By: joechrisellis
Differential Revision: https://reviews.llvm.org/D98506