[llvm] [RISCV][GISEL] Add support for lowerFormalArguments that contain scalable vector types (PR #70882)

[Michael Maitland via llvm-commits]

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@@ -1956,10 +1957,21 @@ void MachineVerifier::visitMachineInstrBefore(const MachineInstr *MI) {
         DstSize = TRI->getRegSizeInBits(*DstRC);
     }
 
-    if (DstSize == 0)
+    if (DstSize.isZero())
       DstSize = TRI->getRegSizeInBits(DstReg, *MRI);
 
-    if (SrcSize != 0 && DstSize != 0 && SrcSize != DstSize) {
+    // If the Dst is scalable and the Src is fixed, then the Dst can only hold
+    // the Src if the minimum size Dst can hold is at least as big as Src.
+    if (DstSize.isScalable() && !SrcSize.isScalable() &&
+        DstSize.getKnownMinValue() <= SrcSize.getFixedValue())
+      break;
+    // If the Src is scalable and the Dst is fixed, then Dest can only hold
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michaelmaitland wrote:

This case is removed in https://github.com/llvm/llvm-project/pull/70881 (this PR is stacked on that one). I would greatly appreciate your input on the conversation going on that PR, because I'm not quite sure that we've got the correct approach. 

https://github.com/llvm/llvm-project/pull/70882