[llvm-mca] LSUnit: use a SmallSet to model load/store queues. NFCI

Also, try to minimize the number of queries to the memory queues to speedup the
analysis.

On average, this change gives a small 2% speedup. For memcpy-like kernels, the
speedup is up to 5.5%.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347469 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed