Enable TYP_STRUCT LCL_VAR/LCL_FLD call args on LA (#71327)

* Support "PUTARG_STK/SPLIT(STRUCT LCL_VAR/LCL_FLD)" on LA

* LA: [local] morph

* Delete now-not-needed "OBJ(ADDR(LCL_VAR))" wrapping

Author: SingleAccretion

src/coreclr/jit/lclmorph.cpp

@@ -1068,7 +1068,7 @@ class LocalAddressVisitor final : public GenTreeVisitor<LocalAddressVisitor>
         // | Partial    | LCL_FLD | LCL_FLD | LCL_FLD |
         // |------------|---------|---------|---------|
         //
-        // * - On XArch/Arm64 only.
+        // * - On XArch/Arm64/LA only.
         //
         // |------------|------|------|--------|----------|
         // | SIMD       | CALL | ASG  | RETURN | HWI/SIMD |
@@ -1086,9 +1086,9 @@ class LocalAddressVisitor final : public GenTreeVisitor<LocalAddressVisitor>
 
         if (user->IsCall())
         {
-#if !defined(TARGET_XARCH) && !defined(TARGET_ARM64)
+#ifdef TARGET_ARM
             return IndirTransform::None;
-#endif // !defined(TARGET_XARCH) && !defined(TARGET_ARM64)
+#endif // TARGET_ARM
         }
 
         if (match == StructMatch::Compatible)

src/coreclr/jit/lowerloongarch64.cpp

@@ -431,7 +431,37 @@ void Lowering::LowerPutArgStkOrSplit(GenTreePutArgStk* putArgNode)
         // STRUCT args (FIELD_LIST / OBJ) will always be contained.
         MakeSrcContained(putArgNode, src);
 
-        // Additionally, codegen supports containment of local addresses under OBJs.
+        // Currently, codegen does not support LCL_VAR/LCL_FLD sources, so we morph them to OBJs.
+        // TODO-ADDR: support the local nodes in codegen and remove this code.
+        if (src->OperIsLocalRead())
+        {
+            unsigned     lclNum  = src->AsLclVarCommon()->GetLclNum();
+            ClassLayout* layout  = nullptr;
+            GenTree*     lclAddr = nullptr;
+
+            if (src->OperIs(GT_LCL_VAR))
+            {
+                layout  = comp->lvaGetDesc(lclNum)->GetLayout();
+                lclAddr = comp->gtNewLclVarAddrNode(lclNum);
+
+                comp->lvaSetVarDoNotEnregister(lclNum DEBUGARG(DoNotEnregisterReason::IsStructArg));
+            }
+            else
+            {
+                layout  = src->AsLclFld()->GetLayout();
+                lclAddr = comp->gtNewLclFldAddrNode(lclNum, src->AsLclFld()->GetLclOffs());
+            }
+
+            src->ChangeOper(GT_OBJ);
+            src->AsObj()->SetAddr(lclAddr);
+            src->AsObj()->SetLayout(layout);
+            src->AsObj()->gtBlkOpKind     = GenTreeBlk::BlkOpKindInvalid;
+            src->AsObj()->gtBlkOpGcUnsafe = false;
+
+            BlockRange().InsertBefore(src, lclAddr);
+        }
+
+        // Codegen supports containment of local addresses under OBJs.
         if (src->OperIs(GT_OBJ) && src->AsObj()->Addr()->OperIs(GT_LCL_VAR_ADDR))
         {
             // TODO-LOONGARCH64-CQ: support containment of LCL_FLD_ADDR too.

src/coreclr/jit/morph.cpp

@@ -1500,14 +1500,6 @@ GenTree* CallArgs::MakeTmpArgNode(Compiler* comp, CallArg* arg)
         {
             // We are passing this struct by value in multiple registers and/or on stack.
             argNode = comp->gtNewLclvNode(lclNum, argType);
-
-#ifndef TARGET_XARCH
-            // ARM/ARM64/LoongArch64 backends do not support LCL_VARs as sources of some stack args.
-            // Wrap it in an "OBJ(ADDR(...))". TODO-ADDR: delete this code once all backends support
-            // LCL_VAR stack args.
-            argNode = comp->gtNewOperNode(GT_ADDR, TYP_BYREF, argNode);
-            argNode = comp->gtNewObjNode(varDsc->GetLayout(), argNode);
-#endif // !TARGET_XARCH
         }
     }
     else
@@ -3694,35 +3686,18 @@ GenTree* Compiler::fgMorphMultiregStructArg(CallArg* arg)
         {
             lcl = actualArg->AsLclVar();
         }
-        if (lcl != nullptr)
+        if ((lcl != nullptr) && (lvaGetPromotionType(lcl->GetLclNum()) == PROMOTION_TYPE_INDEPENDENT))
         {
-            if (lvaGetPromotionType(lcl->GetLclNum()) == PROMOTION_TYPE_INDEPENDENT)
+            if (argNode->OperIs(GT_LCL_VAR) ||
+                ClassLayout::AreCompatible(argNode->AsObj()->GetLayout(), lvaGetDesc(lcl)->GetLayout()))
             {
-                if (argNode->OperIs(GT_LCL_VAR) ||
-                    ClassLayout::AreCompatible(argNode->AsObj()->GetLayout(), lvaGetDesc(lcl)->GetLayout()))
-                {
-                    argNode = fgMorphLclArgToFieldlist(lcl);
-                }
-                else
-                {
-                    // Set DNER to block independent promotion.
-                    lvaSetVarDoNotEnregister(lcl->GetLclNum() DEBUGARG(DoNotEnregisterReason::IsStructArg));
-                }
+                argNode = fgMorphLclArgToFieldlist(lcl);
             }
-#ifdef TARGET_LOONGARCH64
-            else if (argNode->TypeGet() == TYP_STRUCT)
+            else
             {
-                // LoongArch64 backend does not support local nodes as sources of some stack args.
-                if (!actualArg->OperIs(GT_OBJ))
-                {
-                    // Create an Obj of the temp to use it as a call argument.
-                    argNode = gtNewOperNode(GT_ADDR, TYP_I_IMPL, argNode);
-                    argNode = gtNewObjNode(lvaGetStruct(lcl->GetLclNum()), argNode);
-                }
-                // Its fields will need to be accessed by address.
+                // Set DNER to block independent promotion.
                 lvaSetVarDoNotEnregister(lcl->GetLclNum() DEBUGARG(DoNotEnregisterReason::IsStructArg));
             }
-#endif // TARGET_LOONGARCH64
         }
 
         return argNode;