[llvm] [RISCV] Enable (non trivial) remat for most scalar instructions (PR #162311)

[Philip Reames via llvm-commits]

preames wrote:

Haven't gotten to looking at the regalloc bit yet, but this example is illustrating a wildly unprofitable loop-term-fold case.  We've got a multiply being inserted into a loop, and redundant instructions in the pre-header block just to remove one scalar increment in the loop.  I'm going to switch to looking at the regalloc bit, but we should remember to come back to this aspect as it's likely a generic problem.  

https://github.com/llvm/llvm-project/pull/162311