src/java.base/share/classes/java/lang/invoke/MethodHandles.java

rev 14211 : 8154751: MethodHandles.countedLoop does not accept empty bodies

*** 4474,4489 ****
       * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
       *
       * @since 9
       */
      public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
!         MethodHandle returnVar = dropArguments(init == null || init.type().returnType() == void.class ?
!                 zero(void.class) : identity(init.type().returnType()), 0, int.class, int.class);
          MethodHandle[] indexVar = {start, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep)};
          MethodHandle[] loopLimit = {end, null, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred), returnVar};
          MethodHandle[] bodyClause = {init,
!                 filterArgument(dropArguments(body, 1, int.class), 0,
                          MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_decrementCounter))};
          return loop(indexVar, loopLimit, bodyClause);
      }
  
      /**
--- 4474,4493 ----
       * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
       *
       * @since 9
       */
      public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
!         boolean voidReturn = init == null || init.type().returnType() == void.class;
!         MethodHandle adaptedBody = body == null ?
!                 dropArguments(voidReturn ? zero(void.class) : identity(init.type().returnType()), 0, int.class) :
!                 body;
!         MethodHandle returnVar = dropArguments(voidReturn ? zero(void.class) : identity(init.type().returnType()),
!                 0, int.class, int.class);
          MethodHandle[] indexVar = {start, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep)};
          MethodHandle[] loopLimit = {end, null, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred), returnVar};
          MethodHandle[] bodyClause = {init,
!                 filterArgument(dropArguments(adaptedBody, 1, int.class), 0,
                          MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_decrementCounter))};
          return loop(indexVar, loopLimit, bodyClause);
      }
  
      /**