8380025: C2: Missed Value() optimization opportunity in CCP with LoadUB

Reviewed-by: vlivanov, dlong, jrose

Author: Vladimir Kozlov

src/hotspot/share/ci/ciEnv.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2026, 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
@@ -236,6 +236,9 @@ class ciEnv : StackObj {
     ciInstanceKlass* declared_holder = get_instance_klass_for_declared_method_holder(holder);
     return _factory->get_unloaded_method(declared_holder, name, signature, accessor);
   }
+  InstanceKlass::ClassState get_cached_init_state(uint id) {
+    return (InstanceKlass::ClassState)_factory->cached_init_state(id);
+  }
 
   // Get a ciKlass representing an unloaded klass.
   // Ensures uniqueness of the result.

src/hotspot/share/ci/ciInstanceKlass.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2026, 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
@@ -136,12 +136,14 @@ ciInstanceKlass::ciInstanceKlass(ciSymbol* name,
 
 
 // ------------------------------------------------------------------
-// ciInstanceKlass::compute_shared_is_initialized
-void ciInstanceKlass::compute_shared_init_state() {
-  GUARDED_VM_ENTRY(
-    InstanceKlass* ik = get_instanceKlass();
-    _init_state = ik->init_state();
-  )
+InstanceKlass::ClassState ciInstanceKlass::compute_init_state() {
+  if (_is_shared && is_loaded()) {
+    // Return cached init state of shared klass
+    ciEnv* env = CURRENT_ENV;
+    assert(env->task() != nullptr, "only calls from compilation are expected here");
+    return env->get_cached_init_state(ident());
+  }
+  return _init_state;
 }
 
 // ------------------------------------------------------------------
@@ -319,11 +321,11 @@ void ciInstanceKlass::print_impl(outputStream* st) {
               bool_to_str(has_subklass()),
               layout_helper());
 
-    _flags.print_klass_flags();
+    _flags.print_klass_flags(st);
 
     if (_super) {
       st->print(" super=");
-      _super->print_name();
+      _super->print_name_on(st);
     }
     if (_java_mirror) {
       st->print(" mirror=PRESENT");

src/hotspot/share/ci/ciInstanceKlass.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2026, 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
@@ -106,43 +106,36 @@ class ciInstanceKlass : public ciKlass {
 
   bool is_shared() { return _is_shared; }
 
-  void compute_shared_init_state();
+  InstanceKlass::ClassState compute_init_state();
   bool compute_shared_has_subklass();
   int  compute_nonstatic_fields();
   GrowableArray<ciField*>* compute_nonstatic_fields_impl(GrowableArray<ciField*>* super_fields);
   bool compute_has_trusted_loader();
 
-  // Update the init_state for shared klasses
-  void update_if_shared(InstanceKlass::ClassState expected) {
-    if (_is_shared && _init_state != expected) {
-      if (is_loaded()) compute_shared_init_state();
-    }
-  }
-
 public:
   // Has this klass been initialized?
   bool                   is_initialized() {
-    update_if_shared(InstanceKlass::fully_initialized);
-    return _init_state == InstanceKlass::fully_initialized;
+    InstanceKlass::ClassState state = compute_init_state();
+    return state == InstanceKlass::fully_initialized;
   }
   bool                   is_not_initialized() {
-    update_if_shared(InstanceKlass::fully_initialized);
-    return _init_state < InstanceKlass::being_initialized;
+    InstanceKlass::ClassState state = compute_init_state();
+    return state < InstanceKlass::being_initialized;
   }
   // Is this klass being initialized?
   bool                   is_being_initialized() {
-    update_if_shared(InstanceKlass::being_initialized);
-    return _init_state == InstanceKlass::being_initialized;
+    InstanceKlass::ClassState state = compute_init_state();
+    return state == InstanceKlass::being_initialized;
   }
   // Has this klass been linked?
   bool                   is_linked() {
-    update_if_shared(InstanceKlass::linked);
-    return _init_state >= InstanceKlass::linked;
+    InstanceKlass::ClassState state = compute_init_state();
+    return state >= InstanceKlass::linked;
   }
   // Is this klass in error state?
   bool                   is_in_error_state() {
-    update_if_shared(InstanceKlass::initialization_error);
-    return _init_state == InstanceKlass::initialization_error;
+    InstanceKlass::ClassState state = compute_init_state();
+    return state == InstanceKlass::initialization_error;
   }
 
   // General klass information.

src/hotspot/share/ci/ciObjectFactory.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2026, 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
@@ -48,6 +48,7 @@
 #include "gc/shared/collectedHeap.inline.hpp"
 #include "memory/allocation.inline.hpp"
 #include "memory/universe.hpp"
+#include "oops/instanceKlass.hpp"
 #include "oops/oop.inline.hpp"
 #include "oops/trainingData.hpp"
 #include "runtime/handles.inline.hpp"
@@ -83,6 +84,7 @@ ciObjectFactory::ciObjectFactory(Arena* arena,
                                  int expected_size)
                                  : _arena(arena),
                                    _ci_metadata(arena, expected_size, 0, nullptr),
+                                   _cached_init_state(arena, _shared_ident_limit, 0, (u1)0),
                                    _unloaded_methods(arena, 4, 0, nullptr),
                                    _unloaded_klasses(arena, 8, 0, nullptr),
                                    _unloaded_instances(arena, 4, 0, nullptr),
@@ -97,6 +99,28 @@ ciObjectFactory::ciObjectFactory(Arena* arena,
   // If the shared ci objects exist append them to this factory's objects
   if (_shared_ci_metadata != nullptr) {
     _ci_metadata.appendAll(_shared_ci_metadata);
+    // ciInstanceKlass for well-known class is shared by all
+    // compiler threads and can be updated concurrently by
+    // other compiler threads during compilation.
+    // Make local copy of class state to avoid state change
+    // during compilation.
+    int len = _ci_metadata.length();
+    for (int i = 0; i < len; i++) {
+      ciMetadata* obj = _ci_metadata.at(i);
+      if (obj->is_loaded() && obj->is_instance_klass()) {
+        ciInstanceKlass* cik = obj->as_instance_klass();
+        precond(cik->is_shared());
+        InstanceKlass::ClassState current_state = cik->_init_state;
+        InstanceKlass::ClassState state = InstanceKlass::fully_initialized;
+        if (current_state != state) {
+          GUARDED_VM_ENTRY( state = cik->get_instanceKlass()->init_state(); )
+          // Update state of shared ciInstanceKlass
+          cik->_init_state = state;
+        }
+        // Cache state for current compilation
+        _cached_init_state.at_put_grow(cik->ident(), (u1)state, 0);
+      }
+    }
   }
 }
 

src/hotspot/share/ci/ciObjectFactory.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2026, 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
@@ -47,6 +47,8 @@ class ciObjectFactory : public ArenaObj {
 
   Arena*                           _arena;
   GrowableArray<ciMetadata*>       _ci_metadata;
+  // Local copy of shared ciInstanceKlass init state for current compilation
+  GrowableArray<u1>                _cached_init_state;
   GrowableArray<ciMethod*>         _unloaded_methods;
   GrowableArray<ciKlass*>          _unloaded_klasses;
   GrowableArray<ciInstance*>       _unloaded_instances;
@@ -103,6 +105,11 @@ class ciObjectFactory : public ArenaObj {
   ciMetadata* cached_metadata(Metadata* key);
   ciSymbol* get_symbol(Symbol* key);
 
+  // Get cached init state of shared ciInstanceKlass
+  u1 cached_init_state(uint id) {
+    return _cached_init_state.at(id);
+  }
+
   // Get the ciSymbol corresponding to one of the vmSymbols.
   static ciSymbol* vm_symbol_at(vmSymbolID index);