[llvm] [RISCV][GlobalISel] Vector Extension vadd Legalizer (PR #71400)

[Jiahan Xie via llvm-commits]

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@@ -1966,6 +1969,11 @@ void MachineVerifier::visitMachineInstrBefore(const MachineInstr *MI) {
     if (SrcReg.isVirtual() && DstReg.isPhysical() && SrcSize.isScalable() &&
         !DstSize.isScalable())
       break;
+    // If the Src is scalable and the Dst is fixed, then Dest can only hold
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jiahanxie353 wrote:

I accidentally "squashed" my cherry-picked commits from #70882 and [this commit](https://github.com/llvm/llvm-project/commit/4832c88e4956b3c7dc0a5064d946477448d5239d) together. 
I was trying to use rebase interactive to extract them apart but couldn't figure out a neat way. Any suggestion?

https://github.com/llvm/llvm-project/pull/71400