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

[Michael Maitland via llvm-commits]

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@@ -303,6 +307,9 @@ static bool isSupportedArgumentType(Type *T, const RISCVSubtarget &Subtarget) {
     return true;
   if (T->isPointerTy())
     return true;
+  // TODO: Support fixed vector types.
+  if (T->isVectorTy() && T->isScalableTy() && Subtarget.hasVInstructions())
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michaelmaitland wrote:

Implementing vector store could do the same thing. I was planning on doing lowerReturn right after this patch. Do you want me to add it to this one?  I still think this patch unblocks work on GISel for vectors at O0 without returns and stores.

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