[RISCV] Implement isLoadFromStackSlot and isStoreToStackSlot

This causes some slight shuffling but no meaningful codegen differences on the 
corpus I used for testing, but it has a larger impact when combined with e.g. 
rematerialisation. Regardless, it makes sense to report as accurate 
target-specific information as possible.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330949 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed