[llvm] [RISCV] Add 2^N + 2^M expanding pattern for mul (PR #137954)

[Philip Reames via llvm-commits]

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@@ -15694,6 +15703,9 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
     }
   }
 
+  if (SDValue V = expandMulToAddOrSubOfShl(N, DAG, MulAmt))
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preames wrote:

I vaguely remember there being a reason I broke the conditions in this order, but it looks like there's no test diffs resulting from this, so it's probably(?) fine.  

https://github.com/llvm/llvm-project/pull/137954