single-def ret-expr spills

Author: AndyAyersMS

src/jit/flowgraph.cpp

@@ -5910,6 +5910,12 @@ void Compiler::fgFindBasicBlocks()
                         lvaTable[lvaInlineeReturnSpillTemp].lvSingleDef = 1;
                         JITDUMP("Marked return spill temp V%02u as a single def temp\n", lvaInlineeReturnSpillTemp);
                     }
+                    else
+                    {
+                        // We may have co-opted an existing temp for the return spill.
+                        // Make sure it is not marked single-def.
+                        assert(lvaTable[lvaInlineeReturnSpillTemp].lvSingleDef == 0);
+                    }
 
                     CORINFO_CLASS_HANDLE retClassHnd = impInlineInfo->inlineCandidateInfo->methInfo.args.retTypeClass;
                     if (retClassHnd != nullptr)

src/jit/importer.cpp

@@ -20619,10 +20619,25 @@ class SpillRetExprHelper
     {
         GenTree* retExpr = *pRetExpr;
         assert(retExpr->OperGet() == GT_RET_EXPR);
-        JITDUMP("Store return expression %u  as a local var.\n", retExpr->gtTreeID);
-        unsigned tmp = comp->lvaGrabTemp(true DEBUGARG("spilling ret_expr"));
+        const unsigned tmp = comp->lvaGrabTemp(true DEBUGARG("spilling ret_expr"));
+        JITDUMP("Storing return expression [%06u] to a local var V%02u.\n", comp->dspTreeID(retExpr), tmp);
         comp->impAssignTempGen(tmp, retExpr, (unsigned)Compiler::CHECK_SPILL_NONE);
         *pRetExpr = comp->gtNewLclvNode(tmp, retExpr->TypeGet());
+
+        if (retExpr->TypeGet() == TYP_REF)
+        {
+            assert(comp->lvaTable[tmp].lvSingleDef == 0);
+            comp->lvaTable[tmp].lvSingleDef = 1;
+            JITDUMP("Marked V%02u as a single def temp\n", tmp);
+
+            bool                 isExact   = false;
+            bool                 isNonNull = false;
+            CORINFO_CLASS_HANDLE retClsHnd = comp->gtGetClassHandle(retExpr, &isExact, &isNonNull);
+            if (retClsHnd != nullptr)
+            {
+                comp->lvaSetClass(tmp, retClsHnd, isExact);
+            }
+        }
     }
 
 private: