Minor style/comments improvements

Author: steve-s

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/function/BuiltinMethodDescriptor.java

@@ -148,7 +148,7 @@ private static Builtin findBuiltinAnnotation(String name, NodeFactory<? extends
     // The builtin annotation allows us to differentiate between builtins shared for reversible
     // operations, such as int.__mul__ and int.__rmul__, which have the same node factory
     private final Builtin builtinAnnotation;
-    // Name and isReverseOperation are shortcuts for builtinAnnotation.name()/reverseOperation()
+    // Shortcuts for fields of builtinAnnotation that are accessed on a fast-path
     private final String name;
     private final boolean isReverseOperation;
     private final int minNumOfPositionalArgs;

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/function/PBuiltinFunction.java

@@ -50,6 +50,7 @@
 import com.oracle.truffle.api.interop.InteropLibrary;
 import com.oracle.truffle.api.library.ExportLibrary;
 import com.oracle.truffle.api.library.ExportMessage;
+import com.oracle.truffle.api.memory.MemoryFence;
 import com.oracle.truffle.api.nodes.RootNode;
 import com.oracle.truffle.api.object.Shape;
 
@@ -230,10 +231,21 @@ String getExecutableName() {
         return getName();
     }
 
-    public void setDescriptor(BuiltinMethodDescriptor descriptor) {
-        this.descriptor = descriptor;
+    public void setDescriptor(BuiltinMethodDescriptor value) {
+        assert value.getName().equals(getName()) && getBuiltinNodeFactory() == value.getFactory() : getName() + " vs " + value;
+        // Only make sure that info is fully initialized, otherwise it is fine if it is set multiple
+        // times from different threads, all of them should set the same value
+        MemoryFence.storeStore();
+        BuiltinMethodDescriptor local = descriptor;
+        assert local == null || local == value : value;
+        this.descriptor = value;
     }
 
+    /**
+     * The descriptor is set lazily once this builtin function is stored in any special method slot.
+     * I.e., one can assume that any builtin function looked up via special method slots has its
+     * descriptor set.
+     */
     public BuiltinMethodDescriptor getDescriptor() {
         return descriptor;
     }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/type/SpecialMethodSlot.java

@@ -140,7 +140,6 @@
 import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.dsl.NodeFactory;
-import com.oracle.truffle.api.memory.MemoryFence;
 import com.oracle.truffle.api.object.DynamicObject;
 import com.oracle.truffle.api.object.DynamicObjectLibrary;
 
@@ -658,10 +657,6 @@ private static Object asSlotValue(SpecialMethodSlot slot, Object value, PythonLa
                     // Note: number of all builtins >> number of builtins used in slots, so it is
                     // better to do this lazily
                     language.registerBuiltinDescriptorCallTarget(info, builtinFun.getCallTarget());
-                    // Only make sure that info is fully initialized, otherwise it is fine if it is
-                    // set multiple times from different threads, all of them should set the same
-                    // value
-                    MemoryFence.storeStore();
                     builtinFun.setDescriptor(info);
                 }
                 return info;