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

[Michael Maitland via llvm-commits]

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@@ -866,11 +898,16 @@ bool CallLowering::handleAssignments(ValueHandler &Handler,
       }
     }
 
-    // Now that all pieces have been assigned, re-pack the register typed values
-    // into the original value typed registers.
-    if (Handler.isIncomingArgumentHandler() && OrigVT != LocVT) {
-      // Merge the split registers into the expected larger result vregs of
-      // the original call.
+    // In case of indirect parameter passing load the value referred to by
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michaelmaitland wrote:

nit: simplify `if` statements due to common conditions?
```
if (Handler.isIncomingArgumentHandler() && OrigVT != LocVT) {
  // In case of indirect parameter passing load the value referred to by the argument
  if (VA.getLocInfo() == CCValAssign::Indirect)
    Handler.assignValueToAddress(Args[i].OrigRegs[0], Args[i].Regs[0], OrigTy,
                                 MachinePointerInfo{}, VA);
  else
     // Now that all pieces have been assigned, re-pack the register typed values
     // into the original value typed registers.
     buildCopyFromRegs(MIRBuilder, Args[i].OrigRegs, Args[i].Regs, OrigTy,
                        LocTy, Args[i].Flags[0]);
}

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