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

[Sergei Barannikov via llvm-commits]

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@@ -790,6 +805,62 @@ bool CallLowering::handleAssignments(ValueHandler &Handler,
       CCValAssign &VA = ArgLocs[j + Idx];
       const ISD::ArgFlagsTy Flags = Args[i].Flags[Part];
 
+      // We found an indirect parameter passing and we are at the first part of
+      // the value being passed. In this case copy the incoming pointer into a
+      // virtual register so later we can load it.
+      if (VA.getLocInfo() == CCValAssign::Indirect && Flags.isSplit()) {
+        IndirectParameterPassingHandled = true;
+        bool IsInStack = false;
+        Register PhysReg;
+        if (VA.isRegLoc()) {
+          PhysReg = VA.getLocReg();
+        } else if (VA.isMemLoc()) {
+          IsInStack = true;
+          LLT MemTy = Handler.getStackValueStoreType(DL, VA, Flags);
+          MachinePointerInfo MPO;
+          PhysReg = Handler.getStackAddress(
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s-barannikov wrote:

I'd also suggest to look into how `sret` arguments are handled, as they are also passed indirectly.

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