[llvm] [RISCV][TII] Add and use new hook to optimize/canonicalize instructions after MachineCopyPropagation (PR #137973)

[Craig Topper via llvm-commits]

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@@ -2344,6 +2344,21 @@ static unsigned getSHXADDShiftAmount(unsigned Opc) {
   }
 }
 
+// Returns the shift amount from a SHXADD.UW instruction. Returns 0 if the
+// instruction is not a SHXADD.UW.
+static unsigned getSHXADDUWShiftAmount(unsigned Opc) {
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topperc wrote:

I almost made the same comment, but the original caller of the other function uses the return value to know if the instruction is a SHXADD. That caller would be incorrect for SHXADD_UW.

https://github.com/llvm/llvm-project/pull/137973