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

[Sergei Barannikov via llvm-commits]

================
@@ -845,32 +908,49 @@ 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)) {
+        // QUESTION: How to keep this assert with the new if then else
+        // structured code?
+        // assert(!VA.needsCustom() && "custom loc should have been handled
+        // already");
+
+      } else if (i == 0 && !ThisReturnRegs.empty() &&
+                 Handler.isIncomingArgumentHandler() &&
+                 isTypeIsValidForThisReturn(ValVT) && VA.isRegLoc()) {
         Handler.assignValueToReg(ArgReg, ThisReturnRegs[Part], VA);
-        continue;
-      }
-
-      if (Handler.isIncomingArgumentHandler())
+      } else if (Handler.isIncomingArgumentHandler() && VA.isRegLoc()) {
         Handler.assignValueToReg(ArgReg, VA.getLocReg(), VA);
-      else {
+      } else if (VA.isRegLoc()) {
         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 && Flags.isSplit() &&
+          Handler.isIncomingArgumentHandler()) {
+        Align Alignment = DL.getABITypeAlign(Args[i].Ty);
+        MachinePointerInfo DstMPO;
+
+        // Since we are doing indirect parameter passing, we know that the value
+        // in the temporary register is not the value passed to the function,
+        // but rather a pointer to that value. Let's load that value into the
+        // virtual register where the parameter should go.
+        MIRBuilder.buildLoad(Args[i].OrigRegs[0], Args[i].Regs[0], DstMPO,
+                             Alignment);
+
+        IndirectParameterPassingHandled = true;
+      }
+
+      if (IndirectParameterPassingHandled)
+        break;
     }
 
-    // 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.
+    if (Handler.isIncomingArgumentHandler() && OrigVT != LocVT &&
+        !IndirectParameterPassingHandled) {
+      // Now that all pieces have been assigned, re-pack the register typed
+      // values into the original value typed registers.
----------------
s-barannikov wrote:

Please restore the comments from the left (extending them if necessary).


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