8301123: Enable Symbol refcounting underflow checks in PRODUCT

Reviewed-by: fparain, iklam

src/hotspot/share/oops/symbol.cpp

@@ -340,10 +340,8 @@ bool Symbol::try_increment_refcount() {
 // this caller.
 void Symbol::increment_refcount() {
   if (!try_increment_refcount()) {
-#ifdef ASSERT
     print();
     fatal("refcount has gone to zero");
-#endif
   }
 #ifndef PRODUCT
   if (refcount() != PERM_REFCOUNT) { // not a permanent symbol
@@ -363,10 +361,8 @@ void Symbol::decrement_refcount() {
     if (refc == PERM_REFCOUNT) {
       return;  // refcount is permanent, permanent is sticky
     } else if (refc == 0) {
-#ifdef ASSERT
       print();
       fatal("refcount underflow");
-#endif
       return;
     } else {
       found = Atomic::cmpxchg(&_hash_and_refcount, old_value, old_value - 1);
@@ -386,10 +382,8 @@ void Symbol::make_permanent() {
     if (refc == PERM_REFCOUNT) {
       return;  // refcount is permanent, permanent is sticky
     } else if (refc == 0) {
-#ifdef ASSERT
       print();
       fatal("refcount underflow");
-#endif
       return;
     } else {
       int hash = extract_hash(old_value);

test/hotspot/gtest/classfile/test_symbolTable.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2023, 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
@@ -118,3 +118,10 @@ TEST_VM(SymbolTable, test_symbol_refcount_parallel) {
   ttg.doit();
   ttg.join();
 }
+
+TEST_VM_FATAL_ERROR_MSG(SymbolTable, test_symbol_underflow, ".*refcount has gone to zero.*") {
+  Symbol* my_symbol = SymbolTable::new_symbol("my_symbol2023");
+  EXPECT_TRUE(my_symbol->refcount() == 1) << "Symbol refcount just created is 1";
+  my_symbol->decrement_refcount();
+  my_symbol->increment_refcount();  // Should crash even in PRODUCT mode
+}