src/share/classes/sun/invoke/util/VerifyType.java

rev 9491 : 8037209: Improvements and cleanups to bytecode assembly for lambda forms
Reviewed-by: ?
Contributed-by: john.r.rose@oracle.com

*** 38,59 ****
      private VerifyType() { }  // cannot instantiate
  
      /**
       * True if a value can be stacked as the source type and unstacked as the
       * destination type, without violating the JVM's type consistency.
       *
       * @param src the type of a stacked value
       * @param dst the type by which we'd like to treat it
       * @return whether the retyping can be done without motion or reformatting
       */
!     public static boolean isNullConversion(Class<?> src, Class<?> dst) {
          if (src == dst)            return true;
          // Verifier allows any interface to be treated as Object:
          if (dst.isInterface())     dst = Object.class;
          if (src.isInterface())     src = Object.class;
          if (src == dst)            return true;  // check again
!         if (dst == void.class)     return true;  // drop any return value
          if (isNullType(src))       return !dst.isPrimitive();
          if (!src.isPrimitive())    return dst.isAssignableFrom(src);
          if (!dst.isPrimitive())    return false;
          // Verifier allows an int to carry byte, short, char, or even boolean:
          Wrapper sw = Wrapper.forPrimitiveType(src);
--- 38,79 ----
      private VerifyType() { }  // cannot instantiate
  
      /**
       * True if a value can be stacked as the source type and unstacked as the
       * destination type, without violating the JVM's type consistency.
+      * <p>
+      * If both types are references, we apply the verifier's subclass check
+      * (or subtyping, if keepInterfaces).
+      * If the src type is a type guaranteed to be null (Void) it can be converted
+      * to any other reference type.
+      * <p>
+      * If both types are primitives, we apply the verifier's primitive conversions.
+      * These do not include Java conversions such as long to double, since those
+      * require computation and (in general) stack depth changes.
+      * But very simple 32-bit viewing changes, such as byte to int,
+      * are null conversions, because they do not require any computation.
+      * These conversions are from any type to a wider type up to 32 bits,
+      * as long as the conversion is not signed to unsigned (byte to char).
+      * <p>
+      * The primitive type 'void' does not interconvert with any other type,
+      * even though it is legal to drop any type from the stack and "return void".
+      * The stack effects, though are difference between void and any other type,
+      * so it is safer to report a non-trivial conversion.
       *
       * @param src the type of a stacked value
       * @param dst the type by which we'd like to treat it
+      * @param keepInterfaces if false, we treat any interface as if it were Object
       * @return whether the retyping can be done without motion or reformatting
       */
!     public static boolean isNullConversion(Class<?> src, Class<?> dst, boolean keepInterfaces) {
          if (src == dst)            return true;
          // Verifier allows any interface to be treated as Object:
+         if (!keepInterfaces) {
              if (dst.isInterface())  dst = Object.class;
              if (src.isInterface())  src = Object.class;
              if (src == dst)         return true;  // check again
!         }
          if (isNullType(src))       return !dst.isPrimitive();
          if (!src.isPrimitive())    return dst.isAssignableFrom(src);
          if (!dst.isPrimitive())    return false;
          // Verifier allows an int to carry byte, short, char, or even boolean:
          Wrapper sw = Wrapper.forPrimitiveType(src);
*** 80,126 ****
  
      /**
       * Is the given type java.lang.Null or an equivalent null-only type?
       */
      public static boolean isNullType(Class<?> type) {
!         if (type == null)  return false;
!         return type == NULL_CLASS
!             // This one may also be used as a null type.
!             // TO DO: Decide if we really want to legitimize it here.
!             // Probably we do, unless java.lang.Null really makes it into Java 7
!             //|| type == Void.class
              // Locally known null-only class:
!             || type == Empty.class
!             ;
!     }
!     private static final Class<?> NULL_CLASS;
!     static {
!         Class<?> nullClass = null;
!         try {
!             nullClass = Class.forName("java.lang.Null");
!         } catch (ClassNotFoundException ex) {
!             // OK, we'll cope
!         }
!         NULL_CLASS = nullClass;
      }
  
      /**
       * True if a method handle can receive a call under a slightly different
       * method type, without moving or reformatting any stack elements.
       *
       * @param call the type of call being made
       * @param recv the type of the method handle receiving the call
       * @return whether the retyping can be done without motion or reformatting
       */
!     public static boolean isNullConversion(MethodType call, MethodType recv) {
          if (call == recv)  return true;
          int len = call.parameterCount();
          if (len != recv.parameterCount())  return false;
          for (int i = 0; i < len; i++)
!             if (!isNullConversion(call.parameterType(i), recv.parameterType(i)))
                  return false;
!         return isNullConversion(recv.returnType(), call.returnType());
      }
  
      /**
       * Determine if the JVM verifier allows a value of type call to be
       * passed to a formal parameter (or return variable) of type recv.
--- 100,134 ----
  
      /**
       * Is the given type java.lang.Null or an equivalent null-only type?
       */
      public static boolean isNullType(Class<?> type) {
!         // Any reference statically typed as Void is guaranteed to be null.
!         // Therefore, it can be safely treated as a value of any
!         // other type that admits null, i.e., a reference type.
!         if (type == Void.class)  return true;
          // Locally known null-only class:
!         if (type == Empty.class)  return true;
!         return false;
      }
  
      /**
       * True if a method handle can receive a call under a slightly different
       * method type, without moving or reformatting any stack elements.
       *
       * @param call the type of call being made
       * @param recv the type of the method handle receiving the call
       * @return whether the retyping can be done without motion or reformatting
       */
!     public static boolean isNullConversion(MethodType call, MethodType recv, boolean keepInterfaces) {
          if (call == recv)  return true;
          int len = call.parameterCount();
          if (len != recv.parameterCount())  return false;
          for (int i = 0; i < len; i++)
!             if (!isNullConversion(call.parameterType(i), recv.parameterType(i), keepInterfaces))
                  return false;
!         return isNullConversion(recv.returnType(), call.returnType(), keepInterfaces);
      }
  
      /**
       * Determine if the JVM verifier allows a value of type call to be
       * passed to a formal parameter (or return variable) of type recv.