8337418: Fix -Wzero-as-null-pointer-constant warnings in prims code

Reviewed-by: dholmes, shade, jwaters, sspitsyn

Author: Kim Barrett

src/hotspot/share/prims/jni.cpp

@@ -1148,7 +1148,7 @@ JNI_ENTRY(ResultType, \
           jni_Call##Result##Method(JNIEnv *env, jobject obj, jmethodID methodID, ...)) \
 \
   EntryProbe; \
-  ResultType ret = 0;\
+  ResultType ret{}; \
   DT_RETURN_MARK_FOR(Result, Call##Result##Method, ResultType, \
                      (const ResultType&)ret);\
 \
@@ -1203,7 +1203,7 @@ JNI_ENTRY(ResultType, \
           jni_Call##Result##MethodV(JNIEnv *env, jobject obj, jmethodID methodID, va_list args)) \
 \
   EntryProbe;\
-  ResultType ret = 0;\
+  ResultType ret{}; \
   DT_RETURN_MARK_FOR(Result, Call##Result##MethodV, ResultType, \
                      (const ResultType&)ret);\
 \
@@ -1254,7 +1254,7 @@ DEFINE_CALLMETHODV(jdouble,  Double,  T_DOUBLE
 JNI_ENTRY(ResultType, \
           jni_Call##Result##MethodA(JNIEnv *env, jobject obj, jmethodID methodID, const jvalue *args)) \
   EntryProbe; \
-  ResultType ret = 0;\
+  ResultType ret{}; \
   DT_RETURN_MARK_FOR(Result, Call##Result##MethodA, ResultType, \
                      (const ResultType&)ret);\
 \
@@ -1546,7 +1546,7 @@ JNI_ENTRY(ResultType, \
           jni_CallStatic##Result##Method(JNIEnv *env, jclass cls, jmethodID methodID, ...)) \
 \
   EntryProbe; \
-  ResultType ret = 0;\
+  ResultType ret{}; \
   DT_RETURN_MARK_FOR(Result, CallStatic##Result##Method, ResultType, \
                      (const ResultType&)ret);\
 \
@@ -1601,7 +1601,7 @@ JNI_ENTRY(ResultType, \
           jni_CallStatic##Result##MethodV(JNIEnv *env, jclass cls, jmethodID methodID, va_list args)) \
 \
   EntryProbe; \
-  ResultType ret = 0;\
+  ResultType ret{}; \
   DT_RETURN_MARK_FOR(Result, CallStatic##Result##MethodV, ResultType, \
                      (const ResultType&)ret);\
 \
@@ -1657,7 +1657,7 @@ JNI_ENTRY(ResultType, \
           jni_CallStatic##Result##MethodA(JNIEnv *env, jclass cls, jmethodID methodID, const jvalue *args)) \
 \
   EntryProbe; \
-  ResultType ret = 0;\
+  ResultType ret{}; \
   DT_RETURN_MARK_FOR(Result, CallStatic##Result##MethodA, ResultType, \
                      (const ResultType&)ret);\
 \
@@ -1750,7 +1750,7 @@ DT_RETURN_MARK_DECL(GetFieldID, jfieldID
 JNI_ENTRY(jfieldID, jni_GetFieldID(JNIEnv *env, jclass clazz,
           const char *name, const char *sig))
   HOTSPOT_JNI_GETFIELDID_ENTRY(env, clazz, (char *) name, (char *) sig);
-  jfieldID ret = 0;
+  jfieldID ret = nullptr;
   DT_RETURN_MARK(GetFieldID, jfieldID, (const jfieldID&)ret);
 
   Klass* k = java_lang_Class::as_Klass(JNIHandles::resolve_non_null(clazz));
@@ -3035,12 +3035,12 @@ extern "C" void* JNICALL jni_GetDirectBufferAddress(JNIEnv *env, jobject buf)
 
   if (!directBufferSupportInitializeEnded) {
     if (!initializeDirectBufferSupport(env, thread)) {
-      return 0;
+      return nullptr;
     }
   }
 
   if ((buf != nullptr) && (!env->IsInstanceOf(buf, directBufferClass))) {
-    return 0;
+    return nullptr;
   }
 
   ret = (void*)(intptr_t)env->GetLongField(buf, directBufferAddressField);
@@ -3647,8 +3647,8 @@ static jint JNI_CreateJavaVM_inner(JavaVM **vm, void **penv, void *args) {
     }
 
     // Creation failed. We must reset vm_created
-    *vm = 0;
-    *(JNIEnv**)penv = 0;
+    *vm = nullptr;
+    *(JNIEnv**)penv = nullptr;
     // reset vm_created last to avoid race condition. Use OrderAccess to
     // control both compiler and architectural-based reordering.
     assert(vm_created == IN_PROGRESS, "must be");

src/hotspot/share/prims/jvm.cpp

@@ -3747,21 +3747,21 @@ JVM_ENTRY(jobjectArray, JVM_DumpThreads(JNIEnv *env, jclass threadClass, jobject
 
   // Check if threads is null
   if (threads == nullptr) {
-    THROW_(vmSymbols::java_lang_NullPointerException(), 0);
+    THROW_NULL(vmSymbols::java_lang_NullPointerException());
   }
 
   objArrayOop a = objArrayOop(JNIHandles::resolve_non_null(threads));
   objArrayHandle ah(THREAD, a);
   int num_threads = ah->length();
   // check if threads is non-empty array
   if (num_threads == 0) {
-    THROW_(vmSymbols::java_lang_IllegalArgumentException(), 0);
+    THROW_NULL(vmSymbols::java_lang_IllegalArgumentException());
   }
 
   // check if threads is not an array of objects of Thread class
   Klass* k = ObjArrayKlass::cast(ah->klass())->element_klass();
   if (k != vmClasses::Thread_klass()) {
-    THROW_(vmSymbols::java_lang_IllegalArgumentException(), 0);
+    THROW_NULL(vmSymbols::java_lang_IllegalArgumentException());
   }
 
   ResourceMark rm(THREAD);

src/hotspot/share/prims/jvmtiExport.cpp

@@ -2068,7 +2068,7 @@ void JvmtiExport::post_exception_throw(JavaThread *thread, Method* method, addre
 
         jmethodID catch_jmethodID;
         if (current_bci < 0) {
-          catch_jmethodID = 0;
+          catch_jmethodID = nullptr;
           current_bci = 0;
         } else {
           catch_jmethodID = jem.to_jmethodID(current_mh);
@@ -2105,8 +2105,8 @@ void JvmtiExport::notice_unwind_due_to_exception(JavaThread *thread, Method* met
                      JvmtiTrace::safe_get_thread_name(thread),
                      (mh() == nullptr) ? "null" : mh()->klass_name()->as_C_string(),
                      (mh() == nullptr) ? "null" : mh()->name()->as_C_string(),
-                     location==0? "no location:" : "",
-                     location==0? 0 : location - mh()->code_base(),
+                     location == nullptr ? "no location:" : "",
+                     location == nullptr ? 0 : location - mh()->code_base(),
                      in_handler_frame? "in handler frame" : "not handler frame" ));
 
   if (state->is_exception_detected()) {

src/hotspot/share/prims/jvmtiTrace.cpp

@@ -261,7 +261,7 @@ void JvmtiTrace::shutdown() {
 
 
 const char* JvmtiTrace::enum_name(const char** names, const jint* values, jint value) {
-  for (int index = 0; names[index] != 0; ++index) {
+  for (int index = 0; names[index] != nullptr; ++index) {
     if (values[index] == value) {
       return names[index];
     }

src/hotspot/share/prims/methodHandles.cpp

@@ -436,7 +436,6 @@ Symbol* MethodHandles::signature_polymorphic_intrinsic_name(vmIntrinsics::ID iid
   case vmIntrinsics::_linkToNative:     return vmSymbols::linkToNative_name();
   default:
     fatal("unexpected intrinsic id: %d %s", vmIntrinsics::as_int(iid), vmIntrinsics::name_at(iid));
-    return 0;
   }
 }
 
@@ -449,7 +448,6 @@ Bytecodes::Code MethodHandles::signature_polymorphic_intrinsic_bytecode(vmIntrin
     case vmIntrinsics::_invokeBasic:     return Bytecodes::_invokehandle;
     default:
       fatal("unexpected id: (%d) %s", (uint)id, vmIntrinsics::name_at(id));
-      return Bytecodes::_illegal;
   }
 }
 
@@ -463,7 +461,6 @@ int MethodHandles::signature_polymorphic_intrinsic_ref_kind(vmIntrinsics::ID iid
   case vmIntrinsics::_linkToInterface:  return JVM_REF_invokeInterface;
   default:
     fatal("unexpected intrinsic id: %d %s", vmIntrinsics::as_int(iid), vmIntrinsics::name_at(iid));
-    return 0;
   }
 }
 

src/hotspot/share/prims/perf.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -68,7 +68,7 @@ PERF_ENTRY(jobject, Perf_Attach(JNIEnv *env, jobject unused, int vmid))
 
   PerfWrapper("Perf_Attach");
 
-  char* address = 0;
+  char* address = nullptr;
   size_t capacity = 0;
 
   // attach to the PerfData memory region for the specified VM
@@ -90,7 +90,7 @@ PERF_ENTRY(void, Perf_Detach(JNIEnv *env, jobject unused, jobject buffer))
     return;
   }
 
-  void* address = 0;
+  void* address = nullptr;
   jlong capacity = 0;
 
   // get buffer address and capacity

src/hotspot/share/prims/unsafe.cpp

@@ -652,7 +652,7 @@ static jclass Unsafe_DefineClass_impl(JNIEnv *env, jstring name, jbyteArray data
 
   jbyte *body;
   char *utfName = nullptr;
-  jclass result = 0;
+  jclass result = nullptr;
   char buf[128];
 
   assert(data != nullptr, "Class bytes must not be null");
@@ -665,7 +665,7 @@ static jclass Unsafe_DefineClass_impl(JNIEnv *env, jstring name, jbyteArray data
   body = NEW_C_HEAP_ARRAY_RETURN_NULL(jbyte, length, mtInternal);
   if (body == nullptr) {
     throw_new(env, "java/lang/OutOfMemoryError");
-    return 0;
+    return nullptr;
   }
 
   env->GetByteArrayRegion(data, offset, length, body);