Build error: "statement has no effect" with J9CLASS_DEPTH() in java_lang_invoke_MethodHandleNatives.cpp

[knn-k]

Building OpenJ9 Java 17 with GCC 13.2.0 on Ubuntu 24.04.1 generates the following error:

/home/openj9/openj9-openjdk-jdk17/openj9/runtime/jcl/common/java_lang_invoke_MethodHandleNatives.cpp: In function 'j
int Java_java_lang_invoke_MethodHandleNatives_getMembers(JNIEnv*, jclass, jclass, jstring, jstring, jint, jclass, jint,
jobjectArray)':
/home/openj9/openj9-openjdk-jdk17/openj9/runtime/oti/j9class.h:35:68: error: statement has no effect [-Werror=unused-value]
   35 | #define J9CLASS_DEPTH(clazz) (((UDATA)(clazz)->classDepthAndFlags) & J9AccClassDepthMask)
      |                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/home/openj9/openj9-openjdk-jdk17/openj9/runtime/jcl/common/java_lang_invoke_MethodHandleNatives.cpp:1466:49: note: in expansion of macro 'J9CLASS_DEPTH'
 1466 |                                                 J9CLASS_DEPTH(defClass);
      |                                                 ^~~~~~~~~~~~~
/home/openj9/openj9-openjdk-jdk17/openj9/runtime/oti/j9class.h:35:68: error: statement has no effect [-Werror=unused-value]
   35 | #define J9CLASS_DEPTH(clazz) (((UDATA)(clazz)->classDepthAndFlags) & J9AccClassDepthMask)
      |                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/home/openj9/openj9-openjdk-jdk17/openj9/runtime/jcl/common/java_lang_invoke_MethodHandleNatives.cpp:1571:49: note: in expansion of macro 'J9CLASS_DEPTH'
 1571 |                                                 J9CLASS_DEPTH(defClass);
      |                                                 ^~~~~~~~~~~~~

$ gcc --version
gcc (Ubuntu 13.2.0-23ubuntu4) 13.2.0

openj9/runtime/jcl/common/java_lang_invoke_MethodHandleNatives.cpp

Lines 1463 to 1467 in 0985ff3

	UDATA classDepth = 0;
	if (J9_ARE_ANY_BITS_SET(matchFlags, MN_SEARCH_SUPERCLASSES)) {
	/* walk superclasses */
	J9CLASS_DEPTH(defClass);
	}

openj9/runtime/jcl/common/java_lang_invoke_MethodHandleNatives.cpp

Lines 1568 to 1572 in 0985ff3

	UDATA classDepth = 0;
	if (J9_ARE_ANY_BITS_SET(matchFlags, MN_SEARCH_SUPERCLASSES)) {
	/* walk superclasses */
	J9CLASS_DEPTH(defClass);
	}

[knn-k]

The results of J9CLASS_DEPTH(defClass) are not used at all in these places.
I guess these lines should be changed to classDepth = J9CLASS_DEPTH(defClass), but I am not sure.

[knn-k]

Another build error with GCC 13.2.0: #20171

[knn-k]

The following part is never executed because classDepth is unchanged after initialized by 0 at L.1463.

openj9/runtime/jcl/common/java_lang_invoke_MethodHandleNatives.cpp

Lines 1514 to 1515 in 0985ff3

	classDepth -= 1;
	currentClass = defClass->superclasses[classDepth];

It is the same for L.1626-1627.

[knn-k]

I opened a draft PR: #20173

[keithc-ca]

The following part is never executed because classDepth is unchanged after initialized by 0 at L.1463.

openj9/runtime/jcl/common/java_lang_invoke_MethodHandleNatives.cpp

Lines 1514 to 1515 in 0985ff3

	classDepth -= 1;
	currentClass = defClass->superclasses[classDepth];

It is the same for L.1626-1627.

I think that is just a bug. However, it will only affect Java 17. Earlier versions do not use OpenJDK method handles (J9VM_OPT_OPENJDK_METHODHANDLE) by default, and later versions don't have that native method.