[llvm] [RISCV] Reduce LMUL when index is known when lowering insert_vector_elt (PR #66087)

[Philip Reames via llvm-commits]

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@@ -7345,6 +7345,32 @@ RISCVTargetLowering::lowerVectorFPExtendOrRoundLike(SDValue Op,
   return Result;
 }
 
+// Given a scalable vector type and an index into it, returns the type for the
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preames wrote:

If this is just code motion, please go ahead and pre-commit the move.

https://github.com/llvm/llvm-project/pull/66087