[llvm] [GISel][RISCV]Implement indirect parameter passing (PR #95429)

[Michael Maitland via llvm-commits]

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@@ -765,23 +772,32 @@ bool CallLowering::handleAssignments(ValueHandler &Handler,
       // intermediate values.
       Args[i].Regs.resize(NumParts);
 
-      // For each split register, create and assign a vreg that will store
-      // the incoming component of the larger value. These will later be
-      // merged to form the final vreg.
-      for (unsigned Part = 0; Part < NumParts; ++Part)
-        Args[i].Regs[Part] = MRI.createGenericVirtualRegister(NewLLT);
+      // When we have indirect parameter passing we are receiving a pointer,
+      // that points to the actual value, so we need one "temporary" pointer.
+      if (VA.getLocInfo() == CCValAssign::Indirect) {
+        if (Handler.isIncomingArgumentHandler())
+          Args[i].Regs[0] = MRI.createGenericVirtualRegister(PointerTy);
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michaelmaitland wrote:

nit: can you assert that `i == 0` when `VA.getLocInfo() == CCValAssign::Indirect`? We should only have indirect for the first index. it would be a mistake if any other index was indirect.

https://github.com/llvm/llvm-project/pull/95429