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

[Craig Topper via llvm-commits]

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@@ -765,31 +770,72 @@ 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);
+      } else {
+        // 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);
+      }
     }
 
     assert((j + (NumParts - 1)) < ArgLocs.size() &&
            "Too many regs for number of args");
 
     // Coerce into outgoing value types before register assignment.
-    if (!Handler.isIncomingArgumentHandler() && OrigTy != ValTy) {
+    if (!Handler.isIncomingArgumentHandler() && OrigTy != ValTy &&
+        VA.getLocInfo() != CCValAssign::Indirect) {
       assert(Args[i].OrigRegs.size() == 1);
       buildCopyToRegs(MIRBuilder, Args[i].Regs, Args[i].OrigRegs[0], OrigTy,
                       ValTy, extendOpFromFlags(Args[i].Flags[0]));
     }
 
+    bool IndirectParameterPassingHandled = false;
     bool BigEndianPartOrdering = TLI->hasBigEndianPartOrdering(OrigVT, DL);
     for (unsigned Part = 0; Part < NumParts; ++Part) {
+      assert((VA.getLocInfo() != CCValAssign::Indirect || Part == 0) &&
+             "Only the first parameter should be processed when "
+             "handling indirect passing!");
       Register ArgReg = Args[i].Regs[Part];
       // There should be Regs.size() ArgLocs per argument.
       unsigned Idx = BigEndianPartOrdering ? NumParts - 1 - Part : Part;
       CCValAssign &VA = ArgLocs[j + Idx];
       const ISD::ArgFlagsTy Flags = Args[i].Flags[Part];
 
+      // We found an indirect parameter passing, and we have an
+      // OutgoingValueHandler as our handler (so we are at the call site or the
+      // return value). In this case, start the construction of the following
+      // GMIR, that is responsible for the preparation of indirect parameter
+      // passing:
+      //
+      // %1(indirectly passed type) = The value to pass
+      // %3(pointer) = G_FRAME_INDEX %stack.0
+      // G_STORE %1, %3 :: (store (s128), align 8)
+      //
+      // After this GMIR, the remaining part of the loop body will decide how
+      // to get the value to the caller and we break out of the loop.
+      if (VA.getLocInfo() == CCValAssign::Indirect &&
+          !Handler.isIncomingArgumentHandler()) {
+        Align StackAlign = DL.getPrefTypeAlign(Args[i].Ty);
+        MachineFrameInfo &MFI = MF.getFrameInfo();
+        int FrameIdx = MFI.CreateStackObject(OrigTy.getScalarSizeInBits(),
+                                             StackAlign, false);
+        Register PointerToStackReg =
+            MIRBuilder.buildFrameIndex(PointerTy, FrameIdx).getReg(0);
+        MachinePointerInfo DstMPO =
+            MachinePointerInfo::getFixedStack(MF, FrameIdx);
+        MIRBuilder.buildStore(Args[i].OrigRegs[Part], PointerToStackReg, DstMPO,
+                              inferAlignFromPtrInfo(MF, DstMPO));
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topperc wrote:

Why do we need to infer align? Isn't it just `StackAlign`?

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