1 /*
2 * Copyright (c) 1999, 2009, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
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23 */
24
25 #include "incls/_precompiled.incl"
26 #include "incls/_ciField.cpp.incl"
27
28 // ciField
29 //
30 // This class represents the result of a field lookup in the VM.
31 // The lookup may not succeed, in which case the information in
32 // the ciField will be incomplete.
33
34 // The ciObjectFactory cannot create circular data structures in one query.
35 // To avoid vicious circularities, we initialize ciField::_type to NULL
36 // for reference types and derive it lazily from the ciField::_signature.
37 // Primitive types are eagerly initialized, and basic layout queries
38 // can succeed without initialization, using only the BasicType of the field.
39
40 // Notes on bootstrapping and shared CI objects: A field is shared if and
41 // only if it is (a) non-static and (b) declared by a shared instance klass.
42 // This allows non-static field lists to be cached on shared types.
43 // Because the _type field is lazily initialized, however, there is a
44 // special restriction that a shared field cannot cache an unshared type.
45 // This puts a small performance penalty on shared fields with unshared
46 // types, such as StackTraceElement[] Throwable.stackTrace.
47 // (Throwable is shared because ClassCastException is shared, but
48 // StackTraceElement is not presently shared.)
49
50 // It is not a vicious circularity for a ciField to recursively create
51 // the ciSymbols necessary to represent its name and signature.
52 // Therefore, these items are created eagerly, and the name and signature
53 // of a shared field are themselves shared symbols. This somewhat
54 // pollutes the set of shared CI objects: It grows from 50 to 93 items,
55 // with all of the additional 43 being uninteresting shared ciSymbols.
56 // This adds at most one step to the binary search, an amount which
57 // decreases for complex compilation tasks.
58
59 // ------------------------------------------------------------------
60 // ciField::ciField
61 ciField::ciField(ciInstanceKlass* klass, int index): _known_to_link_with(NULL) {
62 ASSERT_IN_VM;
63 CompilerThread *thread = CompilerThread::current();
64
65 assert(ciObjectFactory::is_initialized(), "not a shared field");
66
67 assert(klass->get_instanceKlass()->is_linked(), "must be linked before using its constan-pool");
68
69 _cp_index = index;
70 constantPoolHandle cpool(thread, klass->get_instanceKlass()->constants());
71
72 // Get the field's name, signature, and type.
73 symbolHandle name (thread, cpool->name_ref_at(index));
74 _name = ciEnv::current(thread)->get_object(name())->as_symbol();
75
76 int nt_index = cpool->name_and_type_ref_index_at(index);
77 int sig_index = cpool->signature_ref_index_at(nt_index);
78 symbolHandle signature (thread, cpool->symbol_at(sig_index));
79 _signature = ciEnv::current(thread)->get_object(signature())->as_symbol();
80
81 BasicType field_type = FieldType::basic_type(signature());
82
83 // If the field is a pointer type, get the klass of the
84 // field.
85 if (field_type == T_OBJECT || field_type == T_ARRAY) {
86 bool ignore;
87 // This is not really a class reference; the index always refers to the
88 // field's type signature, as a symbol. Linkage checks do not apply.
89 _type = ciEnv::current(thread)->get_klass_by_index(cpool, sig_index, ignore, klass);
90 } else {
91 _type = ciType::make(field_type);
92 }
93
94 _name = (ciSymbol*)ciEnv::current(thread)->get_object(name());
95
96 // Get the field's declared holder.
97 //
98 // Note: we actually create a ciInstanceKlass for this klass,
99 // even though we may not need to.
100 int holder_index = cpool->klass_ref_index_at(index);
101 bool holder_is_accessible;
102 ciInstanceKlass* declared_holder =
103 ciEnv::current(thread)->get_klass_by_index(cpool, holder_index,
104 holder_is_accessible,
105 klass)->as_instance_klass();
106
107 // The declared holder of this field may not have been loaded.
108 // Bail out with partial field information.
109 if (!holder_is_accessible) {
110 // _cp_index and _type have already been set.
111 // The default values for _flags and _constant_value will suffice.
112 // We need values for _holder, _offset, and _is_constant,
113 _holder = declared_holder;
114 _offset = -1;
115 _is_constant = false;
116 return;
117 }
118
119 instanceKlass* loaded_decl_holder = declared_holder->get_instanceKlass();
120
121 // Perform the field lookup.
122 fieldDescriptor field_desc;
123 klassOop canonical_holder =
124 loaded_decl_holder->find_field(name(), signature(), &field_desc);
125 if (canonical_holder == NULL) {
126 // Field lookup failed. Will be detected by will_link.
127 _holder = declared_holder;
128 _offset = -1;
129 _is_constant = false;
130 return;
131 }
132
133 assert(canonical_holder == field_desc.field_holder(), "just checking");
134 initialize_from(&field_desc);
135 }
136
137 ciField::ciField(fieldDescriptor *fd): _known_to_link_with(NULL) {
138 ASSERT_IN_VM;
139
140 _cp_index = -1;
141
142 // Get the field's name, signature, and type.
143 ciEnv* env = CURRENT_ENV;
144 _name = env->get_object(fd->name())->as_symbol();
145 _signature = env->get_object(fd->signature())->as_symbol();
146
147 BasicType field_type = fd->field_type();
148
149 // If the field is a pointer type, get the klass of the
150 // field.
151 if (field_type == T_OBJECT || field_type == T_ARRAY) {
152 _type = NULL; // must call compute_type on first access
153 } else {
154 _type = ciType::make(field_type);
155 }
156
157 initialize_from(fd);
158
159 // Either (a) it is marked shared, or else (b) we are done bootstrapping.
160 assert(is_shared() || ciObjectFactory::is_initialized(),
161 "bootstrap classes must not create & cache unshared fields");
162 }
163
164 static bool trust_final_non_static_fields(ciInstanceKlass* holder) {
165 if (holder == NULL)
166 return false;
167 if (holder->name() == ciSymbol::java_lang_System())
168 // Never trust strangely unstable finals: System.out, etc.
169 return false;
170 // Even if general trusting is disabled, trust system-built closures in these packages.
171 if (holder->is_in_package("java/dyn") || holder->is_in_package("sun/dyn"))
172 return true;
173 return TrustFinalNonStaticFields;
174 }
175
176 void ciField::initialize_from(fieldDescriptor* fd) {
177 // Get the flags, offset, and canonical holder of the field.
178 _flags = ciFlags(fd->access_flags());
179 _offset = fd->offset();
180 _holder = CURRENT_ENV->get_object(fd->field_holder())->as_instance_klass();
181
182 // Check to see if the field is constant.
183 if (_holder->is_initialized() && this->is_final()) {
184 if (!this->is_static()) {
185 // A field can be constant if it's a final static field or if it's
186 // a final non-static field of a trusted class ({java,sun}.dyn).
187 if (trust_final_non_static_fields(_holder)) {
188 _is_constant = true;
189 return;
190 }
191 _is_constant = false;
192 return;
193 }
194
195 // This field just may be constant. The only cases where it will
196 // not be constant are:
197 //
198 // 1. The field holds a non-perm-space oop. The field is, strictly
199 // speaking, constant but we cannot embed non-perm-space oops into
200 // generated code. For the time being we need to consider the
201 // field to be not constant.
202 // 2. The field is a *special* static&final field whose value
203 // may change. The three examples are java.lang.System.in,
204 // java.lang.System.out, and java.lang.System.err.
205
206 klassOop k = _holder->get_klassOop();
207 assert( SystemDictionary::System_klass() != NULL, "Check once per vm");
208 if( k == SystemDictionary::System_klass() ) {
209 // Check offsets for case 2: System.in, System.out, or System.err
210 if( _offset == java_lang_System::in_offset_in_bytes() ||
211 _offset == java_lang_System::out_offset_in_bytes() ||
212 _offset == java_lang_System::err_offset_in_bytes() ) {
213 _is_constant = false;
214 return;
215 }
216 }
217
218 _is_constant = true;
219 switch(type()->basic_type()) {
220 case T_BYTE:
221 _constant_value = ciConstant(type()->basic_type(), k->byte_field(_offset));
222 break;
223 case T_CHAR:
224 _constant_value = ciConstant(type()->basic_type(), k->char_field(_offset));
225 break;
226 case T_SHORT:
227 _constant_value = ciConstant(type()->basic_type(), k->short_field(_offset));
228 break;
229 case T_BOOLEAN:
230 _constant_value = ciConstant(type()->basic_type(), k->bool_field(_offset));
231 break;
232 case T_INT:
233 _constant_value = ciConstant(type()->basic_type(), k->int_field(_offset));
234 break;
235 case T_FLOAT:
236 _constant_value = ciConstant(k->float_field(_offset));
237 break;
238 case T_DOUBLE:
239 _constant_value = ciConstant(k->double_field(_offset));
240 break;
241 case T_LONG:
242 _constant_value = ciConstant(k->long_field(_offset));
243 break;
244 case T_OBJECT:
245 case T_ARRAY:
246 {
247 oop o = k->obj_field(_offset);
248
249 // A field will be "constant" if it is known always to be
250 // a non-null reference to an instance of a particular class,
251 // or to a particular array. This can happen even if the instance
252 // or array is not perm. In such a case, an "unloaded" ciArray
253 // or ciInstance is created. The compiler may be able to use
254 // information about the object's class (which is exact) or length.
255
256 if (o == NULL) {
257 _constant_value = ciConstant(type()->basic_type(), ciNullObject::make());
258 } else {
259 _constant_value = ciConstant(type()->basic_type(), CURRENT_ENV->get_object(o));
260 assert(_constant_value.as_object() == CURRENT_ENV->get_object(o), "check interning");
261 }
262 }
263 }
264 } else {
265 _is_constant = false;
266 }
267 }
268
269 // ------------------------------------------------------------------
270 // ciField::compute_type
271 //
272 // Lazily compute the type, if it is an instance klass.
273 ciType* ciField::compute_type() {
274 GUARDED_VM_ENTRY(return compute_type_impl();)
275 }
276
277 ciType* ciField::compute_type_impl() {
278 ciKlass* type = CURRENT_ENV->get_klass_by_name_impl(_holder, _signature, false);
279 if (!type->is_primitive_type() && is_shared()) {
280 // We must not cache a pointer to an unshared type, in a shared field.
281 bool type_is_also_shared = false;
282 if (type->is_type_array_klass()) {
283 type_is_also_shared = true; // int[] etc. are explicitly bootstrapped
284 } else if (type->is_instance_klass()) {
285 type_is_also_shared = type->as_instance_klass()->is_shared();
286 } else {
287 // Currently there is no 'shared' query for array types.
288 type_is_also_shared = !ciObjectFactory::is_initialized();
289 }
290 if (!type_is_also_shared)
291 return type; // Bummer.
292 }
293 _type = type;
294 return type;
295 }
296
297
298 // ------------------------------------------------------------------
299 // ciField::will_link
300 //
301 // Can a specific access to this field be made without causing
302 // link errors?
303 bool ciField::will_link(ciInstanceKlass* accessing_klass,
304 Bytecodes::Code bc) {
305 VM_ENTRY_MARK;
306 if (_offset == -1) {
307 // at creation we couldn't link to our holder so we need to
308 // maintain that stance, otherwise there's no safe way to use this
309 // ciField.
310 return false;
311 }
312
313 if (_known_to_link_with == accessing_klass) {
314 return true;
315 }
316
317 FieldAccessInfo result;
318 constantPoolHandle c_pool(THREAD,
319 accessing_klass->get_instanceKlass()->constants());
320 LinkResolver::resolve_field(result, c_pool, _cp_index,
321 Bytecodes::java_code(bc),
322 true, false, KILL_COMPILE_ON_FATAL_(false));
323
324 // update the hit-cache, unless there is a problem with memory scoping:
325 if (accessing_klass->is_shared() || !is_shared())
326 _known_to_link_with = accessing_klass;
327
328 return true;
329 }
330
331 // ------------------------------------------------------------------
332 // ciField::print
333 void ciField::print() {
334 tty->print("<ciField ");
335 _holder->print_name();
336 tty->print(".");
337 _name->print_symbol();
338 tty->print(" offset=%d type=", _offset);
339 if (_type != NULL) _type->print_name();
340 else tty->print("(reference)");
341 tty->print(" is_constant=%s", bool_to_str(_is_constant));
342 if (_is_constant && is_static()) {
343 tty->print(" constant_value=");
344 _constant_value.print();
345 }
346 tty->print(">");
347 }
348
349 // ------------------------------------------------------------------
350 // ciField::print_name_on
351 //
352 // Print the name of this field
353 void ciField::print_name_on(outputStream* st) {
354 name()->print_symbol_on(st);
355 }