[llvm] [RISCV] Expand `X * (2^N - 2^M)` where `N < M` (PR #168843)

[Sergei Barannikov via llvm-commits]

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@@ -16854,35 +16854,41 @@ static SDValue expandMulToNAFSequence(SDNode *N, SelectionDAG &DAG,
 // X * (2^N +/- 2^M) -> (add/sub (shl X, C1), (shl X, C2))
 static SDValue expandMulToAddOrSubOfShl(SDNode *N, SelectionDAG &DAG,
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s-barannikov wrote:

It looks like decomposeMulByConstant could handle all/some of these cases?

https://github.com/llvm/llvm-project/pull/168843