[llvm] [RISCV][GISel] Instruction select for vector G_ADD, G_SUB (PR #74114)

[Michael Maitland via llvm-commits]

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@@ -57,6 +60,22 @@ const RegisterBankInfo::ValueMapping ValueMappings[] = {
     {&PartMappings[PMI_FPRB64], 1},
     {&PartMappings[PMI_FPRB64], 1},
     {&PartMappings[PMI_FPRB64], 1},
+    // Maximum 3 VR LMUL=1 operands.
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michaelmaitland wrote:

```suggestion
    // Maximum 3 VR LMUL={1, MF2, MF4, MF8} operands.
```

https://github.com/llvm/llvm-project/pull/74114