36 // the entry layout is shared and looks as follows: |
36 // the entry layout is shared and looks as follows: |
37 // |
37 // |
38 // bit number |31 0| |
38 // bit number |31 0| |
39 // bit length |-8--|-8--|---16----| |
39 // bit length |-8--|-8--|---16----| |
40 // -------------------------------- |
40 // -------------------------------- |
41 // _indices [ b2 | b1 | index ] |
41 // _indices [ b2 | b1 | index ] index = constant_pool_index (!= 0, normal entries only) |
42 // _f1 [ entry specific ] |
42 // _indices [ index | 00000 ] index = main_entry_index (secondary entries only) |
43 // _f2 [ entry specific ] |
43 // _f1 [ entry specific ] method, klass, or oop (MethodType or CallSite) |
44 // _flags [t|f|vf|v|m|h|unused|field_index] (for field entries) |
44 // _f2 [ entry specific ] vtable index or vfinal method |
45 // bit length |4|1|1 |1|1|0|---7--|----16-----] |
45 // _flags [tos|0|00|00|00|f|v|f2|unused|field_index] (for field entries) |
46 // _flags [t|f|vf|v|m|h|unused|eidx|psze] (for method entries) |
46 // bit length [ 4 |1|1 |1 | 1|1|1| 1|---5--|----16-----] |
47 // bit length |4|1|1 |1|1|1|---7--|-8--|-8--] |
47 // _flags [tos|M|vf|fv|ea|f|0|f2|unused|00000|psize] (for method entries) |
|
48 // bit length [ 4 |1|1 |1 | 1|1|1| 1|---5--|--8--|--8--] |
48 |
49 |
49 // -------------------------------- |
50 // -------------------------------- |
50 // |
51 // |
51 // with: |
52 // with: |
52 // index = original constant pool index |
53 // index = original constant pool index |
53 // b1 = bytecode 1 |
54 // b1 = bytecode 1 |
54 // b2 = bytecode 2 |
55 // b2 = bytecode 2 |
55 // psze = parameters size (method entries only) |
56 // psize = parameters size (method entries only) |
56 // eidx = interpreter entry index (method entries only) |
|
57 // field_index = index into field information in holder instanceKlass |
57 // field_index = index into field information in holder instanceKlass |
58 // The index max is 0xffff (max number of fields in constant pool) |
58 // The index max is 0xffff (max number of fields in constant pool) |
59 // and is multiplied by (instanceKlass::next_offset) when accessing. |
59 // and is multiplied by (instanceKlass::next_offset) when accessing. |
60 // t = TosState (see below) |
60 // t = TosState (see below) |
61 // f = field is marked final (see below) |
61 // f = field is marked final (see below) |
62 // vf = virtual, final (method entries only : is_vfinal()) |
62 // f2 = virtual but final (method entries only: is_vfinal()) |
63 // v = field is volatile (see below) |
63 // v = field is volatile (see below) |
64 // m = invokeinterface used for method in class Object (see below) |
64 // m = invokeinterface used for method in class Object (see below) |
65 // h = RedefineClasses/Hotswap bit (see below) |
65 // h = RedefineClasses/Hotswap bit (see below) |
66 // |
66 // |
67 // The flags after TosState have the following interpretation: |
67 // The flags after TosState have the following interpretation: |
68 // bit 27: f flag true if field is marked final |
68 // bit 27: 0 for fields, 1 for methods |
69 // bit 26: vf flag true if virtual final method |
69 // f flag true if field is marked final |
70 // bit 25: v flag true if field is volatile (only for fields) |
70 // v flag true if field is volatile (only for fields) |
71 // bit 24: m flag true if invokeinterface used for method in class Object |
71 // f2 flag true if f2 contains an oop (e.g., virtual final method) |
72 // bit 23: 0 for fields, 1 for methods |
72 // fv flag true if invokeinterface used for method in class Object |
73 // |
73 // |
74 // The flags 31, 30, 29, 28 together build a 4 bit number 0 to 8 with the |
74 // The flags 31, 30, 29, 28 together build a 4 bit number 0 to 8 with the |
75 // following mapping to the TosState states: |
75 // following mapping to the TosState states: |
76 // |
76 // |
77 // btos: 0 |
77 // btos: 0 |
84 // atos: 7 |
84 // atos: 7 |
85 // vtos: 8 |
85 // vtos: 8 |
86 // |
86 // |
87 // Entry specific: field entries: |
87 // Entry specific: field entries: |
88 // _indices = get (b1 section) and put (b2 section) bytecodes, original constant pool index |
88 // _indices = get (b1 section) and put (b2 section) bytecodes, original constant pool index |
89 // _f1 = field holder |
89 // _f1 = field holder (as a java.lang.Class, not a klassOop) |
90 // _f2 = field offset in words |
90 // _f2 = field offset in bytes |
91 // _flags = field type information, original field index in field holder |
91 // _flags = field type information, original FieldInfo index in field holder |
92 // (field_index section) |
92 // (field_index section) |
93 // |
93 // |
94 // Entry specific: method entries: |
94 // Entry specific: method entries: |
95 // _indices = invoke code for f1 (b1 section), invoke code for f2 (b2 section), |
95 // _indices = invoke code for f1 (b1 section), invoke code for f2 (b2 section), |
96 // original constant pool index |
96 // original constant pool index |
97 // _f1 = method for all but virtual calls, unused by virtual calls |
97 // _f1 = methodOop for non-virtual calls, unused by virtual calls. |
98 // (note: for interface calls, which are essentially virtual, |
98 // for interface calls, which are essentially virtual but need a klass, |
99 // contains klassOop for the corresponding interface. |
99 // contains klassOop for the corresponding interface. |
100 // for invokedynamic, f1 contains the CallSite object for the invocation |
100 // for invokedynamic, f1 contains a site-specific CallSite object (as an appendix) |
101 // _f2 = method/vtable index for virtual calls only, unused by all other |
101 // for invokehandle, f1 contains a site-specific MethodType object (as an appendix) |
102 // calls. The vf flag indicates this is a method pointer not an |
102 // (upcoming metadata changes will move the appendix to a separate array) |
103 // index. |
103 // _f2 = vtable/itable index (or final methodOop) for virtual calls only, |
104 // _flags = field type info (f section), |
104 // unused by non-virtual. The is_vfinal flag indicates this is a |
105 // virtual final entry (vf), |
105 // method pointer for a final method, not an index. |
106 // interpreter entry index (eidx section), |
106 // _flags = method type info (t section), |
107 // parameter size (psze section) |
107 // virtual final bit (vfinal), |
|
108 // parameter size (psize section) |
108 // |
109 // |
109 // Note: invokevirtual & invokespecial bytecodes can share the same constant |
110 // Note: invokevirtual & invokespecial bytecodes can share the same constant |
110 // pool entry and thus the same constant pool cache entry. All invoke |
111 // pool entry and thus the same constant pool cache entry. All invoke |
111 // bytecodes but invokevirtual use only _f1 and the corresponding b1 |
112 // bytecodes but invokevirtual use only _f1 and the corresponding b1 |
112 // bytecode, while invokevirtual uses only _f2 and the corresponding |
113 // bytecode, while invokevirtual uses only _f2 and the corresponding |
136 void set_f1(oop f1) { |
137 void set_f1(oop f1) { |
137 oop existing_f1 = _f1; // read once |
138 oop existing_f1 = _f1; // read once |
138 assert(existing_f1 == NULL || existing_f1 == f1, "illegal field change"); |
139 assert(existing_f1 == NULL || existing_f1 == f1, "illegal field change"); |
139 oop_store(&_f1, f1); |
140 oop_store(&_f1, f1); |
140 } |
141 } |
141 void set_f1_if_null_atomic(oop f1); |
142 void release_set_f1(oop f1); |
142 void set_f2(intx f2) { assert(_f2 == 0 || _f2 == f2, "illegal field change"); _f2 = f2; } |
143 void set_f2(intx f2) { assert(_f2 == 0 || _f2 == f2, "illegal field change"); _f2 = f2; } |
143 int as_flags(TosState state, bool is_final, bool is_vfinal, bool is_volatile, |
144 void set_f2_as_vfinal_method(methodOop f2) { assert(_f2 == 0 || _f2 == (intptr_t) f2, "illegal field change"); assert(is_vfinal(), "flags must be set"); _f2 = (intptr_t) f2; } |
144 bool is_method_interface, bool is_method); |
145 int make_flags(TosState state, int option_bits, int field_index_or_method_params); |
145 void set_flags(intx flags) { _flags = flags; } |
146 void set_flags(intx flags) { _flags = flags; } |
|
147 bool init_flags_atomic(intx flags); |
|
148 void set_field_flags(TosState field_type, int option_bits, int field_index) { |
|
149 assert((field_index & field_index_mask) == field_index, "field_index in range"); |
|
150 set_flags(make_flags(field_type, option_bits | (1 << is_field_entry_shift), field_index)); |
|
151 } |
|
152 void set_method_flags(TosState return_type, int option_bits, int method_params) { |
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153 assert((method_params & parameter_size_mask) == method_params, "method_params in range"); |
|
154 set_flags(make_flags(return_type, option_bits, method_params)); |
|
155 } |
|
156 bool init_method_flags_atomic(TosState return_type, int option_bits, int method_params) { |
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157 assert((method_params & parameter_size_mask) == method_params, "method_params in range"); |
|
158 return init_flags_atomic(make_flags(return_type, option_bits, method_params)); |
|
159 } |
146 |
160 |
147 public: |
161 public: |
148 // specific bit values in flag field |
162 // specific bit definitions for the flags field: |
149 // Note: the interpreter knows this layout! |
163 // (Note: the interpreter must use these definitions to access the CP cache.) |
150 enum FlagBitValues { |
164 enum { |
151 hotSwapBit = 23, |
165 // high order bits are the TosState corresponding to field type or method return type |
152 methodInterface = 24, |
166 tos_state_bits = 4, |
153 volatileField = 25, |
167 tos_state_mask = right_n_bits(tos_state_bits), |
154 vfinalMethod = 26, |
168 tos_state_shift = BitsPerInt - tos_state_bits, // see verify_tos_state_shift below |
155 finalField = 27 |
169 // misc. option bits; can be any bit position in [16..27] |
|
170 is_vfinal_shift = 21, |
|
171 is_volatile_shift = 22, |
|
172 is_final_shift = 23, |
|
173 has_appendix_shift = 24, |
|
174 is_forced_virtual_shift = 25, |
|
175 is_field_entry_shift = 26, |
|
176 // low order bits give field index (for FieldInfo) or method parameter size: |
|
177 field_index_bits = 16, |
|
178 field_index_mask = right_n_bits(field_index_bits), |
|
179 parameter_size_bits = 8, // subset of field_index_mask, range is 0..255 |
|
180 parameter_size_mask = right_n_bits(parameter_size_bits), |
|
181 option_bits_mask = ~(((-1) << tos_state_shift) | (field_index_mask | parameter_size_mask)) |
156 }; |
182 }; |
157 |
183 |
158 enum { field_index_mask = 0xFFFF }; |
184 // specific bit definitions for the indices field: |
159 |
185 enum { |
160 // start of type bits in flags |
186 main_cp_index_bits = 2*BitsPerByte, |
161 // Note: the interpreter knows this layout! |
187 main_cp_index_mask = right_n_bits(main_cp_index_bits), |
162 enum FlagValues { |
188 bytecode_1_shift = main_cp_index_bits, |
163 tosBits = 28 |
189 bytecode_1_mask = right_n_bits(BitsPerByte), // == (u1)0xFF |
|
190 bytecode_2_shift = main_cp_index_bits + BitsPerByte, |
|
191 bytecode_2_mask = right_n_bits(BitsPerByte), // == (u1)0xFF |
|
192 // the secondary cp index overlaps with bytecodes 1 and 2: |
|
193 secondary_cp_index_shift = bytecode_1_shift, |
|
194 secondary_cp_index_bits = BitsPerInt - main_cp_index_bits |
164 }; |
195 }; |
|
196 |
165 |
197 |
166 // Initialization |
198 // Initialization |
167 void initialize_entry(int original_index); // initialize primary entry |
199 void initialize_entry(int original_index); // initialize primary entry |
168 void initialize_secondary_entry(int main_index); // initialize secondary entry |
200 void initialize_secondary_entry(int main_index); // initialize secondary entry |
169 |
201 |
187 void set_interface_call( |
219 void set_interface_call( |
188 methodHandle method, // Resolved method |
220 methodHandle method, // Resolved method |
189 int index // Method index into interface |
221 int index // Method index into interface |
190 ); |
222 ); |
191 |
223 |
|
224 void set_method_handle( |
|
225 methodHandle method, // adapter for invokeExact, etc. |
|
226 Handle appendix // stored in f1; could be a java.lang.invoke.MethodType |
|
227 ); |
|
228 |
192 void set_dynamic_call( |
229 void set_dynamic_call( |
193 Handle call_site, // Resolved java.lang.invoke.CallSite (f1) |
230 methodHandle method, // adapter for this call site |
194 methodHandle signature_invoker // determines signature information |
231 Handle appendix // stored in f1; could be a java.lang.invoke.CallSite |
195 ); |
232 ); |
196 |
233 |
197 methodOop get_method_if_resolved(Bytecodes::Code invoke_code, constantPoolHandle cpool); |
234 // Common code for invokedynamic and MH invocations. |
198 |
235 |
199 // For JVM_CONSTANT_InvokeDynamic cache entries: |
236 // The "appendix" is an optional call-site-specific parameter which is |
200 void initialize_bootstrap_method_index_in_cache(int bsm_cache_index); |
237 // pushed by the JVM at the end of the argument list. This argument may |
201 int bootstrap_method_index_in_cache(); |
238 // be a MethodType for the MH.invokes and a CallSite for an invokedynamic |
202 |
239 // instruction. However, its exact type and use depends on the Java upcall, |
203 void set_parameter_size(int value) { |
240 // which simply returns a compiled LambdaForm along with any reference |
204 assert(parameter_size() == 0 || parameter_size() == value, |
241 // that LambdaForm needs to complete the call. If the upcall returns a |
205 "size must not change"); |
242 // null appendix, the argument is not passed at all. |
206 // Setting the parameter size by itself is only safe if the |
243 // |
207 // current value of _flags is 0, otherwise another thread may have |
244 // The appendix is *not* represented in the signature of the symbolic |
208 // updated it and we don't want to overwrite that value. Don't |
245 // reference for the call site, but (if present) it *is* represented in |
209 // bother trying to update it once it's nonzero but always make |
246 // the methodOop bound to the site. This means that static and dynamic |
210 // sure that the final parameter size agrees with what was passed. |
247 // resolution logic needs to make slightly different assessments about the |
211 if (_flags == 0) { |
248 // number and types of arguments. |
212 Atomic::cmpxchg_ptr((value & 0xFF), &_flags, 0); |
249 void set_method_handle_common( |
213 } |
250 Bytecodes::Code invoke_code, // _invokehandle or _invokedynamic |
214 guarantee(parameter_size() == value, "size must not change"); |
251 methodHandle adapter, // invoker method (f2) |
215 } |
252 Handle appendix // appendix such as CallSite, MethodType, etc. (f1) |
|
253 ); |
|
254 |
|
255 methodOop method_if_resolved(constantPoolHandle cpool); |
|
256 |
|
257 void set_parameter_size(int value); |
216 |
258 |
217 // Which bytecode number (1 or 2) in the index field is valid for this bytecode? |
259 // Which bytecode number (1 or 2) in the index field is valid for this bytecode? |
218 // Returns -1 if neither is valid. |
260 // Returns -1 if neither is valid. |
219 static int bytecode_number(Bytecodes::Code code) { |
261 static int bytecode_number(Bytecodes::Code code) { |
220 switch (code) { |
262 switch (code) { |
221 case Bytecodes::_getstatic : // fall through |
263 case Bytecodes::_getstatic : // fall through |
222 case Bytecodes::_getfield : // fall through |
264 case Bytecodes::_getfield : // fall through |
223 case Bytecodes::_invokespecial : // fall through |
265 case Bytecodes::_invokespecial : // fall through |
224 case Bytecodes::_invokestatic : // fall through |
266 case Bytecodes::_invokestatic : // fall through |
225 case Bytecodes::_invokedynamic : // fall through |
|
226 case Bytecodes::_invokeinterface : return 1; |
267 case Bytecodes::_invokeinterface : return 1; |
227 case Bytecodes::_putstatic : // fall through |
268 case Bytecodes::_putstatic : // fall through |
228 case Bytecodes::_putfield : // fall through |
269 case Bytecodes::_putfield : // fall through |
|
270 case Bytecodes::_invokehandle : // fall through |
|
271 case Bytecodes::_invokedynamic : // fall through |
229 case Bytecodes::_invokevirtual : return 2; |
272 case Bytecodes::_invokevirtual : return 2; |
230 default : break; |
273 default : break; |
231 } |
274 } |
232 return -1; |
275 return -1; |
233 } |
276 } |
240 } |
283 } |
241 return false; // default: not resolved |
284 return false; // default: not resolved |
242 } |
285 } |
243 |
286 |
244 // Accessors |
287 // Accessors |
245 bool is_secondary_entry() const { return (_indices & 0xFFFF) == 0; } |
288 bool is_secondary_entry() const { return (_indices & main_cp_index_mask) == 0; } |
246 int constant_pool_index() const { assert((_indices & 0xFFFF) != 0, "must be main entry"); |
289 int main_entry_index() const { assert(is_secondary_entry(), "must be secondary entry"); |
247 return (_indices & 0xFFFF); } |
290 return ((uintx)_indices >> secondary_cp_index_shift); } |
248 int main_entry_index() const { assert((_indices & 0xFFFF) == 0, "must be secondary entry"); |
291 int primary_entry_indices() const { assert(!is_secondary_entry(), "must be main entry"); |
249 return ((uintx)_indices >> 16); } |
292 return _indices; } |
250 Bytecodes::Code bytecode_1() const { return Bytecodes::cast((_indices >> 16) & 0xFF); } |
293 int constant_pool_index() const { return (primary_entry_indices() & main_cp_index_mask); } |
251 Bytecodes::Code bytecode_2() const { return Bytecodes::cast((_indices >> 24) & 0xFF); } |
294 Bytecodes::Code bytecode_1() const { return Bytecodes::cast((primary_entry_indices() >> bytecode_1_shift) |
252 volatile oop f1() const { return _f1; } |
295 & bytecode_1_mask); } |
253 bool is_f1_null() const { return (oop)_f1 == NULL; } // classifies a CPC entry as unbound |
296 Bytecodes::Code bytecode_2() const { return Bytecodes::cast((primary_entry_indices() >> bytecode_2_shift) |
254 intx f2() const { return _f2; } |
297 & bytecode_2_mask); } |
255 int field_index() const; |
298 methodOop f1_as_method() const { oop f1 = _f1; assert(f1 == NULL || f1->is_method(), ""); return methodOop(f1); } |
256 int parameter_size() const { return _flags & 0xFF; } |
299 klassOop f1_as_klass() const { oop f1 = _f1; assert(f1 == NULL || f1->is_klass(), ""); return klassOop(f1); } |
257 bool is_vfinal() const { return ((_flags & (1 << vfinalMethod)) == (1 << vfinalMethod)); } |
300 oop f1_as_klass_mirror() const { oop f1 = f1_as_instance(); return f1; } // i.e., return a java_mirror |
258 bool is_volatile() const { return ((_flags & (1 << volatileField)) == (1 << volatileField)); } |
301 oop f1_as_instance() const { oop f1 = _f1; assert(f1 == NULL || f1->is_instance() || f1->is_array(), ""); return f1; } |
259 bool is_methodInterface() const { return ((_flags & (1 << methodInterface)) == (1 << methodInterface)); } |
302 oop f1_appendix() const { assert(has_appendix(), ""); return f1_as_instance(); } |
260 bool is_byte() const { return (((uintx) _flags >> tosBits) == btos); } |
303 bool is_f1_null() const { oop f1 = _f1; return f1 == NULL; } // classifies a CPC entry as unbound |
261 bool is_char() const { return (((uintx) _flags >> tosBits) == ctos); } |
304 int f2_as_index() const { assert(!is_vfinal(), ""); return (int) _f2; } |
262 bool is_short() const { return (((uintx) _flags >> tosBits) == stos); } |
305 methodOop f2_as_vfinal_method() const { assert(is_vfinal(), ""); return methodOop(_f2); } |
263 bool is_int() const { return (((uintx) _flags >> tosBits) == itos); } |
306 int field_index() const { assert(is_field_entry(), ""); return (_flags & field_index_mask); } |
264 bool is_long() const { return (((uintx) _flags >> tosBits) == ltos); } |
307 int parameter_size() const { assert(is_method_entry(), ""); return (_flags & parameter_size_mask); } |
265 bool is_float() const { return (((uintx) _flags >> tosBits) == ftos); } |
308 bool is_volatile() const { return (_flags & (1 << is_volatile_shift)) != 0; } |
266 bool is_double() const { return (((uintx) _flags >> tosBits) == dtos); } |
309 bool is_final() const { return (_flags & (1 << is_final_shift)) != 0; } |
267 bool is_object() const { return (((uintx) _flags >> tosBits) == atos); } |
310 bool has_appendix() const { return (_flags & (1 << has_appendix_shift)) != 0; } |
268 TosState flag_state() const { assert( ( (_flags >> tosBits) & 0x0F ) < number_of_states, "Invalid state in as_flags"); |
311 bool is_forced_virtual() const { return (_flags & (1 << is_forced_virtual_shift)) != 0; } |
269 return (TosState)((_flags >> tosBits) & 0x0F); } |
312 bool is_vfinal() const { return (_flags & (1 << is_vfinal_shift)) != 0; } |
|
313 bool is_method_entry() const { return (_flags & (1 << is_field_entry_shift)) == 0; } |
|
314 bool is_field_entry() const { return (_flags & (1 << is_field_entry_shift)) != 0; } |
|
315 bool is_byte() const { return flag_state() == btos; } |
|
316 bool is_char() const { return flag_state() == ctos; } |
|
317 bool is_short() const { return flag_state() == stos; } |
|
318 bool is_int() const { return flag_state() == itos; } |
|
319 bool is_long() const { return flag_state() == ltos; } |
|
320 bool is_float() const { return flag_state() == ftos; } |
|
321 bool is_double() const { return flag_state() == dtos; } |
|
322 bool is_object() const { return flag_state() == atos; } |
|
323 TosState flag_state() const { assert((uint)number_of_states <= (uint)tos_state_mask+1, ""); |
|
324 return (TosState)((_flags >> tos_state_shift) & tos_state_mask); } |
270 |
325 |
271 // Code generation support |
326 // Code generation support |
272 static WordSize size() { return in_WordSize(sizeof(ConstantPoolCacheEntry) / HeapWordSize); } |
327 static WordSize size() { return in_WordSize(sizeof(ConstantPoolCacheEntry) / HeapWordSize); } |
273 static ByteSize size_in_bytes() { return in_ByteSize(sizeof(ConstantPoolCacheEntry)); } |
328 static ByteSize size_in_bytes() { return in_ByteSize(sizeof(ConstantPoolCacheEntry)); } |
274 static ByteSize indices_offset() { return byte_offset_of(ConstantPoolCacheEntry, _indices); } |
329 static ByteSize indices_offset() { return byte_offset_of(ConstantPoolCacheEntry, _indices); } |
297 // printed the klass name so that other routines in the adjust_* |
352 // printed the klass name so that other routines in the adjust_* |
298 // group don't print the klass name. |
353 // group don't print the klass name. |
299 bool adjust_method_entry(methodOop old_method, methodOop new_method, |
354 bool adjust_method_entry(methodOop old_method, methodOop new_method, |
300 bool * trace_name_printed); |
355 bool * trace_name_printed); |
301 bool is_interesting_method_entry(klassOop k); |
356 bool is_interesting_method_entry(klassOop k); |
302 bool is_field_entry() const { return (_flags & (1 << hotSwapBit)) == 0; } |
|
303 bool is_method_entry() const { return (_flags & (1 << hotSwapBit)) != 0; } |
|
304 |
357 |
305 // Debugging & Printing |
358 // Debugging & Printing |
306 void print (outputStream* st, int index) const; |
359 void print (outputStream* st, int index) const; |
307 void verify(outputStream* st) const; |
360 void verify(outputStream* st) const; |
308 |
361 |
309 static void verify_tosBits() { |
362 static void verify_tos_state_shift() { |
310 assert(tosBits == 28, "interpreter now assumes tosBits is 28"); |
363 // When shifting flags as a 32-bit int, make sure we don't need an extra mask for tos_state: |
|
364 assert((((u4)-1 >> tos_state_shift) & ~tos_state_mask) == 0, "no need for tos_state mask"); |
311 } |
365 } |
312 }; |
366 }; |
313 |
367 |
314 |
368 |
315 // A constant pool cache is a runtime data structure set aside to a constant pool. The cache |
369 // A constant pool cache is a runtime data structure set aside to a constant pool. The cache |