Fold obj.GetType to a constant (#87101)

dotnet · Jun 5, 2023 · 404aede · 404aede
1 parent 18c6495
commit 404aede
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diff --git a/src/coreclr/jit/gentree.cpp b/src/coreclr/jit/gentree.cpp
@@ -17888,6 +17888,7 @@ CORINFO_CLASS_HANDLE Compiler::gtGetClassHandle(GenTree* tree, bool* pIsExact, b
                 {
                     // if we managed to get a class handle it's definitely not null
                     *pIsNonNull = true;
+                    *pIsExact   = true;
                 }
             }
             break;

diff --git a/src/coreclr/jit/valuenum.cpp b/src/coreclr/jit/valuenum.cpp
@@ -11393,6 +11393,23 @@ void Compiler::fgValueNumberIntrinsic(GenTree* tree)
     else
     {
         assert(intrinsic->gtIntrinsicName == NI_System_Object_GetType);
+
+        // Try to fold obj.GetType() if we know the exact type of obj.
+        bool                 isExact   = false;
+        bool                 isNonNull = false;
+        CORINFO_CLASS_HANDLE cls       = gtGetClassHandle(tree->gtGetOp1(), &isExact, &isNonNull);
+        if ((cls != NO_CLASS_HANDLE) && isExact && isNonNull)
+        {
+            CORINFO_OBJECT_HANDLE typeObj = info.compCompHnd->getRuntimeTypePointer(cls);
+            if (typeObj != nullptr)
+            {
+                setMethodHasFrozenObjects();
+                ValueNum handleVN   = vnStore->VNForHandle((ssize_t)typeObj, GTF_ICON_OBJ_HDL);
+                intrinsic->gtVNPair = vnStore->VNPWithExc(ValueNumPair(handleVN, handleVN), arg0VNPx);
+                return;
+            }
+        }
+
         intrinsic->gtVNPair =
             vnStore->VNPWithExc(vnStore->VNPairForFunc(intrinsic->TypeGet(), VNF_ObjGetType, arg0VNP), arg0VNPx);
     }