[llvm] [RISCV] Move performCombineVMergeAndVOps into RISCVFoldMasks (PR #71764)

[Philip Reames via llvm-commits]

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@@ -133,6 +438,48 @@ bool RISCVFoldMasks::convertVMergeToVMv(MachineInstr &MI, MachineInstr *V0Def) {
   return true;
 }
 
+bool RISCVFoldMasks::convertToUnmasked(MachineInstr &MI,
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preames wrote:

I didn't understand this, so I took my own shot at it (stealing your code as a starting point).  https://github.com/llvm/llvm-project/pull/72441 shows the result, and has a fixme which explains the coupling.  We could either land the half split state (my change), or leave it rolled in here.  

https://github.com/llvm/llvm-project/pull/71764