8353175: Eliminate double iteration of stream in FieldDescriptor reinitialization

src/hotspot/share/oops/fieldStreams.hpp

@@ -120,7 +120,7 @@ class FieldStreamBase : public StackObj {
 
   // Convenient methods
 
-  FieldInfo to_FieldInfo() {
+  const FieldInfo& to_FieldInfo() const {
     return _fi_buf;
   }
 
@@ -131,7 +131,7 @@ class FieldStreamBase : public StackObj {
   // bridge to a heavier API:
   fieldDescriptor& field_descriptor() const {
     fieldDescriptor& field = const_cast<fieldDescriptor&>(_fd_buf);
-    field.reinitialize(field_holder(), _index);
+    field.reinitialize(field_holder(), to_FieldInfo());
     return field;
   }
 };

src/hotspot/share/oops/instanceKlass.cpp

@@ -1649,7 +1649,7 @@ bool InstanceKlass::find_local_field(Symbol* name, Symbol* sig, fieldDescriptor*
     Symbol* f_name = fs.name();
     Symbol* f_sig  = fs.signature();
     if (f_name == name && f_sig == sig) {
-      fd->reinitialize(const_cast<InstanceKlass*>(this), fs.index());
+      fd->reinitialize(const_cast<InstanceKlass*>(this), fs.to_FieldInfo());
       return true;
     }
   }
@@ -1718,7 +1718,7 @@ Klass* InstanceKlass::find_field(Symbol* name, Symbol* sig, bool is_static, fiel
 bool InstanceKlass::find_local_field_from_offset(int offset, bool is_static, fieldDescriptor* fd) const {
   for (JavaFieldStream fs(this); !fs.done(); fs.next()) {
     if (fs.offset() == offset) {
-      fd->reinitialize(const_cast<InstanceKlass*>(this), fs.index());
+      fd->reinitialize(const_cast<InstanceKlass*>(this), fs.to_FieldInfo());
       if (fd->is_static() == is_static) return true;
     }
   }
@@ -1779,19 +1779,16 @@ void InstanceKlass::do_nonstatic_fields(FieldClosure* cl) {
   if (super != nullptr) {
     super->do_nonstatic_fields(cl);
   }
-  fieldDescriptor fd;
-  int length = java_fields_count();
-  for (int i = 0; i < length; i += 1) {
-    fd.reinitialize(this, i);
+  for (JavaFieldStream fs(this); !fs.done(); fs.next()) {
+    fieldDescriptor& fd = fs.field_descriptor();
     if (!fd.is_static()) {
       cl->do_field(&fd);
     }
   }
 }
 
-// first in Pair is offset, second is index.
-static int compare_fields_by_offset(Pair<int,int>* a, Pair<int,int>* b) {
-  return a->first - b->first;
+static int compare_fields_by_offset(FieldInfo* a, FieldInfo* b) {
+  return a->offset() - b->offset();
 }
 
 void InstanceKlass::print_nonstatic_fields(FieldClosure* cl) {
@@ -1800,26 +1797,20 @@ void InstanceKlass::print_nonstatic_fields(FieldClosure* cl) {
     super->print_nonstatic_fields(cl);
   }
   ResourceMark rm;
-  fieldDescriptor fd;
   // In DebugInfo nonstatic fields are sorted by offset.
-  GrowableArray<Pair<int,int> > fields_sorted;
-  int i = 0;
+  GrowableArray<FieldInfo> fields_sorted;
   for (AllFieldStream fs(this); !fs.done(); fs.next()) {
     if (!fs.access_flags().is_static()) {
-      fd = fs.field_descriptor();
-      Pair<int,int> f(fs.offset(), fs.index());
-      fields_sorted.push(f);
-      i++;
+      fields_sorted.push(fs.to_FieldInfo());
     }
   }
-  if (i > 0) {
-    int length = i;
-    assert(length == fields_sorted.length(), "duh");
-    // _sort_Fn is defined in growableArray.hpp.
+  int length = fields_sorted.length();
+  if (length > 0) {
     fields_sorted.sort(compare_fields_by_offset);
+    fieldDescriptor fd;
     for (int i = 0; i < length; i++) {
-      fd.reinitialize(this, fields_sorted.at(i).second);
-      assert(!fd.is_static() && fd.offset() == fields_sorted.at(i).first, "only nonstatic fields");
+      fd.reinitialize(this, fields_sorted.at(i));
+      assert(!fd.is_static() && fd.offset() == checked_cast<int>(fields_sorted.at(i).offset()), "only nonstatic fields");
       cl->do_field(&fd);
     }
   }

src/hotspot/share/oops/instanceKlass.hpp

@@ -134,6 +134,7 @@ class InstanceKlass: public Klass {
   friend class JVMCIVMStructs;
   friend class ClassFileParser;
   friend class CompileReplay;
+  friend class FieldStream;
 
  public:
   static const KlassKind Kind = InstanceKlassKind;

src/hotspot/share/prims/jvm.cpp

@@ -1787,7 +1787,7 @@ JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredFields(JNIEnv *env, jclass ofClass,
   fieldDescriptor fd;
   for (JavaFieldStream fs(k); !fs.done(); fs.next()) {
     if (!publicOnly || fs.access_flags().is_public()) {
-      fd.reinitialize(k, fs.index());
+      fd.reinitialize(k, fs.to_FieldInfo());
       oop field = Reflection::new_field(&fd, CHECK_NULL);
       result->obj_at_put(out_idx, field);
       ++out_idx;

src/hotspot/share/runtime/fieldDescriptor.cpp

@@ -87,16 +87,15 @@ oop fieldDescriptor::string_initial_value(TRAPS) const {
   return constants()->uncached_string_at(initial_value_index(), THREAD);
 }
 
-void fieldDescriptor::reinitialize(InstanceKlass* ik, int index) {
+void fieldDescriptor::reinitialize(InstanceKlass* ik, const FieldInfo& fieldinfo) {
   if (_cp.is_null() || field_holder() != ik) {
     _cp = constantPoolHandle(Thread::current(), ik->constants());
     // _cp should now reference ik's constant pool; i.e., ik is now field_holder.
     // If the class is a scratch class, the constant pool points to the original class,
     // but that's ok because of constant pool merging.
     assert(field_holder() == ik || ik->is_scratch_class(), "must be already initialized to this class");
   }
-  _fieldinfo= ik->field(index);
-  assert((int)_fieldinfo.index() == index, "just checking");
+  _fieldinfo = fieldinfo;
   guarantee(_fieldinfo.name_index() != 0 && _fieldinfo.signature_index() != 0, "bad constant pool index for fieldDescriptor");
 }
 

src/hotspot/share/runtime/fieldDescriptor.hpp

@@ -46,7 +46,7 @@ class fieldDescriptor {
  public:
   fieldDescriptor() {}
   fieldDescriptor(InstanceKlass* ik, int index) {
-    reinitialize(ik, index);
+    reinitialize(ik, ik->field(index));
   }
   inline Symbol* name() const;
   inline Symbol* signature() const;
@@ -102,7 +102,7 @@ class fieldDescriptor {
   inline void set_has_initialized_final_update(const bool value);
 
   // Initialization
-  void reinitialize(InstanceKlass* ik, int index);
+  void reinitialize(InstanceKlass* ik, const FieldInfo& fieldinfo);
 
   // Print
   void print() const;

src/hotspot/share/runtime/reflectionUtils.hpp

@@ -152,7 +152,7 @@ class FieldStream : public KlassStream {
   // bridge to a heavier API:
   fieldDescriptor& field_descriptor() const {
     fieldDescriptor& field = const_cast<fieldDescriptor&>(_fd_buf);
-    field.reinitialize(_klass, _index);
+    field.reinitialize(_klass, _klass->field(_index));
     return field;
   }
 };