[RISCV] Introduce new AND combine to expose additional load narrowing opportunities (#170483) The standard codegen pipeline sometimes ends up with a shift followed by a mask. If doing the mask first would have enabled load narrowing, then it is preferable to do so. The motivating example was seen in povray from SPEC where we had something like: ``` lh a0, 0(a0) slli a0, a0, 56 srli a0, a0, 52 ``` Which can be better implemented as: ``` lbu a0, 0(a0) slli a0, a0, 4 ``` Although this is the only SPEC benchmark where the pattern shows up in a way that reduces dynamic instruction count, adding this optimisation does succeed in reducing the povray dynamic instruction count by 0.17% on an RVA22 O3 build.
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