Enreg structs x86 windows. (#55535)

* Mark more cases as DoNotEnreg before CSE.

There are CSE metrics that take into account how many potential enreg locals
do we have.

* enable for x86.

src/coreclr/jit/gentree.h

@@ -6801,6 +6801,7 @@ struct GenTreeCopyOrReload : public GenTreeUnOp
 
     GenTreeCopyOrReload(genTreeOps oper, var_types type, GenTree* op1) : GenTreeUnOp(oper, type, op1)
     {
+        assert(type != TYP_STRUCT || op1->IsMultiRegNode());
         SetRegNum(REG_NA);
         ClearOtherRegs();
     }

src/coreclr/jit/jitconfigvalues.h

@@ -555,7 +555,7 @@ CONFIG_INTEGER(JitSaveFpLrWithCalleeSavedRegisters, W("JitSaveFpLrWithCalleeSave
 #endif // defined(TARGET_ARM64)
 #endif // DEBUG
 
-#if defined(TARGET_AMD64) && defined(TARGET_WINDOWS)
+#if defined(TARGET_WINDOWS) && defined(TARGET_XARCH)
 CONFIG_INTEGER(JitEnregStructLocals, W("JitEnregStructLocals"), 1) // Allow to enregister locals with struct type.
 #else
 CONFIG_INTEGER(JitEnregStructLocals, W("JitEnregStructLocals"), 0) // Don't allow to enregister locals with struct type

src/coreclr/jit/lclvars.cpp

@@ -3497,6 +3497,10 @@ void Compiler::lvaSortByRefCount()
             {
                 lvaSetVarDoNotEnregister(lclNum DEBUGARG(DNER_IsStruct));
             }
+            else if (!varDsc->IsEnregisterableType())
+            {
+                lvaSetVarDoNotEnregister(lclNum DEBUGARG(DNER_IsStruct));
+            }
         }
         if (varDsc->lvIsStructField && (lvaGetParentPromotionType(lclNum) != PROMOTION_TYPE_INDEPENDENT))
         {

src/coreclr/jit/lsra.cpp

@@ -6180,10 +6180,21 @@ void LinearScan::insertCopyOrReload(BasicBlock* block, GenTree* tree, unsigned m
     }
     else
     {
-        // Create the new node, with "tree" as its only child.
-        var_types treeType = tree->TypeGet();
+        var_types regType = tree->TypeGet();
+        if ((regType == TYP_STRUCT) && !tree->IsMultiRegNode())
+        {
+            assert(compiler->compEnregStructLocals());
+            assert(tree->IsLocal());
+            const GenTreeLclVarCommon* lcl    = tree->AsLclVarCommon();
+            const LclVarDsc*           varDsc = compiler->lvaGetDesc(lcl);
+            // We create struct copies with a primitive type so we don't bother copy node with parsing structHndl.
+            // Note that for multiReg node we keep each regType in the tree and don't need this.
+            regType = varDsc->GetRegisterType(lcl);
+            assert(regType != TYP_UNDEF);
+        }
 
-        GenTreeCopyOrReload* newNode = new (compiler, oper) GenTreeCopyOrReload(oper, treeType, tree);
+        // Create the new node, with "tree" as its only child.
+        GenTreeCopyOrReload* newNode = new (compiler, oper) GenTreeCopyOrReload(oper, regType, tree);
         assert(refPosition->registerAssignment != RBM_NONE);
         SetLsraAdded(newNode);
         newNode->SetRegNumByIdx(refPosition->assignedReg(), multiRegIdx);