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

[Gábor Spaits via llvm-commits]

================
@@ -845,30 +898,58 @@ bool CallLowering::handleAssignments(ValueHandler &Handler,
                                      DstMPO, DstAlign, SrcMPO, SrcAlign,
                                      MemSize, VA);
         }
-        continue;
-      }
-
-      assert(!VA.needsCustom() && "custom loc should have been handled already");
-
-      if (i == 0 && !ThisReturnRegs.empty() &&
-          Handler.isIncomingArgumentHandler() &&
-          isTypeIsValidForThisReturn(ValVT)) {
+      } else if (i == 0 && !ThisReturnRegs.empty() &&
+                 Handler.isIncomingArgumentHandler() &&
+                 isTypeIsValidForThisReturn(ValVT)) {
         Handler.assignValueToReg(ArgReg, ThisReturnRegs[Part], VA);
-        continue;
-      }
-
-      if (Handler.isIncomingArgumentHandler())
+      } else if (Handler.isIncomingArgumentHandler()) {
         Handler.assignValueToReg(ArgReg, VA.getLocReg(), VA);
-      else {
+      } else {
         DelayedOutgoingRegAssignments.emplace_back([=, &Handler]() {
           Handler.assignValueToReg(ArgReg, VA.getLocReg(), VA);
         });
       }
+
+      // Finish the handling of indirect parameter passing when receiving
+      // the value (we are in the called function or the caller when receiving
+      // the return value).
+      if (VA.getLocInfo() == CCValAssign::Indirect &&
+          Handler.isIncomingArgumentHandler()) {
+        Align Alignment = DL.getABITypeAlign(Args[i].Ty);
+        MachinePointerInfo MPO;
+
+        if (VA.isMemLoc()) {
+          if (!Flags.isByRef()) {
+            LLT MemTy = Handler.getStackValueStoreType(DL, VA, Flags);
+            Handler.getStackAddress(
+              MemTy.getSizeInBytes(), VA.getLocMemOffset(), MPO, Flags);
+          } else {
+            uint64_t MemSize = Flags.getByValSize();
+            int64_t Offset = VA.getLocMemOffset();
+  
+            Handler.getStackAddress(MemSize, Offset, MPO, Flags);
----------------
spaits wrote:

For example `assignValueToAddress` has this non virtual wrapper wrapper:
```cpp
virtual void assignValueToAddress(const ArgInfo &Arg, unsigned ValRegIndex,
                                      Register Addr, LLT MemTy,
                                      const MachinePointerInfo &MPO,
                                      const CCValAssign &VA) {
      assignValueToAddress(Arg.Regs[ValRegIndex], Addr, MemTy, MPO, VA);
    }
```
To get the concrete register out with and index.

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