Tue, 11 Nov 2014 11:05:41 +0100
8056071: compiler/whitebox/IsMethodCompilableTest.java fails with 'method() is not compilable after 3 iterations'
Summary: Always use MDO if valid and always compile trivial methods with C1 if available.
Reviewed-by: kvn, iveresov
1 /*
2 * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
25 #include "precompiled.hpp"
26 #include "classfile/javaClasses.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "classfile/vmSymbols.hpp"
29 #include "code/codeCache.hpp"
30 #include "code/debugInfoRec.hpp"
31 #include "code/nmethod.hpp"
32 #include "code/pcDesc.hpp"
33 #include "code/scopeDesc.hpp"
34 #include "interpreter/interpreter.hpp"
35 #include "interpreter/oopMapCache.hpp"
36 #include "memory/resourceArea.hpp"
37 #include "oops/instanceKlass.hpp"
38 #include "oops/oop.inline.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/objectMonitor.hpp"
41 #include "runtime/objectMonitor.inline.hpp"
42 #include "runtime/signature.hpp"
43 #include "runtime/stubRoutines.hpp"
44 #include "runtime/synchronizer.hpp"
45 #include "runtime/vframe.hpp"
46 #include "runtime/vframeArray.hpp"
47 #include "runtime/vframe_hp.hpp"
49 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
51 vframe::vframe(const frame* fr, const RegisterMap* reg_map, JavaThread* thread)
52 : _reg_map(reg_map), _thread(thread) {
53 assert(fr != NULL, "must have frame");
54 _fr = *fr;
55 }
57 vframe::vframe(const frame* fr, JavaThread* thread)
58 : _reg_map(thread), _thread(thread) {
59 assert(fr != NULL, "must have frame");
60 _fr = *fr;
61 }
63 vframe* vframe::new_vframe(const frame* f, const RegisterMap* reg_map, JavaThread* thread) {
64 // Interpreter frame
65 if (f->is_interpreted_frame()) {
66 return new interpretedVFrame(f, reg_map, thread);
67 }
69 // Compiled frame
70 CodeBlob* cb = f->cb();
71 if (cb != NULL) {
72 if (cb->is_nmethod()) {
73 nmethod* nm = (nmethod*)cb;
74 return new compiledVFrame(f, reg_map, thread, nm);
75 }
77 if (f->is_runtime_frame()) {
78 // Skip this frame and try again.
79 RegisterMap temp_map = *reg_map;
80 frame s = f->sender(&temp_map);
81 return new_vframe(&s, &temp_map, thread);
82 }
83 }
85 // External frame
86 return new externalVFrame(f, reg_map, thread);
87 }
89 vframe* vframe::sender() const {
90 RegisterMap temp_map = *register_map();
91 assert(is_top(), "just checking");
92 if (_fr.is_entry_frame() && _fr.is_first_frame()) return NULL;
93 frame s = _fr.real_sender(&temp_map);
94 if (s.is_first_frame()) return NULL;
95 return vframe::new_vframe(&s, &temp_map, thread());
96 }
98 vframe* vframe::top() const {
99 vframe* vf = (vframe*) this;
100 while (!vf->is_top()) vf = vf->sender();
101 return vf;
102 }
105 javaVFrame* vframe::java_sender() const {
106 vframe* f = sender();
107 while (f != NULL) {
108 if (f->is_java_frame()) return javaVFrame::cast(f);
109 f = f->sender();
110 }
111 return NULL;
112 }
114 // ------------- javaVFrame --------------
116 GrowableArray<MonitorInfo*>* javaVFrame::locked_monitors() {
117 assert(SafepointSynchronize::is_at_safepoint() || JavaThread::current() == thread(),
118 "must be at safepoint or it's a java frame of the current thread");
120 GrowableArray<MonitorInfo*>* mons = monitors();
121 GrowableArray<MonitorInfo*>* result = new GrowableArray<MonitorInfo*>(mons->length());
122 if (mons->is_empty()) return result;
124 bool found_first_monitor = false;
125 ObjectMonitor *pending_monitor = thread()->current_pending_monitor();
126 ObjectMonitor *waiting_monitor = thread()->current_waiting_monitor();
127 oop pending_obj = (pending_monitor != NULL ? (oop) pending_monitor->object() : (oop) NULL);
128 oop waiting_obj = (waiting_monitor != NULL ? (oop) waiting_monitor->object() : (oop) NULL);
130 for (int index = (mons->length()-1); index >= 0; index--) {
131 MonitorInfo* monitor = mons->at(index);
132 if (monitor->eliminated() && is_compiled_frame()) continue; // skip eliminated monitor
133 oop obj = monitor->owner();
134 if (obj == NULL) continue; // skip unowned monitor
135 //
136 // Skip the monitor that the thread is blocked to enter or waiting on
137 //
138 if (!found_first_monitor && (obj == pending_obj || obj == waiting_obj)) {
139 continue;
140 }
141 found_first_monitor = true;
142 result->append(monitor);
143 }
144 return result;
145 }
147 static void print_locked_object_class_name(outputStream* st, Handle obj, const char* lock_state) {
148 if (obj.not_null()) {
149 st->print("\t- %s <" INTPTR_FORMAT "> ", lock_state, (address)obj());
150 if (obj->klass() == SystemDictionary::Class_klass()) {
151 Klass* target_klass = java_lang_Class::as_Klass(obj());
152 st->print_cr("(a java.lang.Class for %s)", InstanceKlass::cast(target_klass)->external_name());
153 } else {
154 Klass* k = obj->klass();
155 st->print_cr("(a %s)", k->external_name());
156 }
157 }
158 }
160 void javaVFrame::print_lock_info_on(outputStream* st, int frame_count) {
161 ResourceMark rm;
163 // If this is the first frame, and java.lang.Object.wait(...) then print out the receiver.
164 if (frame_count == 0) {
165 if (method()->name() == vmSymbols::wait_name() &&
166 method()->method_holder()->name() == vmSymbols::java_lang_Object()) {
167 StackValueCollection* locs = locals();
168 if (!locs->is_empty()) {
169 StackValue* sv = locs->at(0);
170 if (sv->type() == T_OBJECT) {
171 Handle o = locs->at(0)->get_obj();
172 print_locked_object_class_name(st, o, "waiting on");
173 }
174 }
175 } else if (thread()->current_park_blocker() != NULL) {
176 oop obj = thread()->current_park_blocker();
177 Klass* k = obj->klass();
178 st->print_cr("\t- %s <" INTPTR_FORMAT "> (a %s)", "parking to wait for ", (address)obj, k->external_name());
179 }
180 }
183 // Print out all monitors that we have locked or are trying to lock
184 GrowableArray<MonitorInfo*>* mons = monitors();
185 if (!mons->is_empty()) {
186 bool found_first_monitor = false;
187 for (int index = (mons->length()-1); index >= 0; index--) {
188 MonitorInfo* monitor = mons->at(index);
189 if (monitor->eliminated() && is_compiled_frame()) { // Eliminated in compiled code
190 if (monitor->owner_is_scalar_replaced()) {
191 Klass* k = java_lang_Class::as_Klass(monitor->owner_klass());
192 st->print("\t- eliminated <owner is scalar replaced> (a %s)", k->external_name());
193 } else {
194 oop obj = monitor->owner();
195 if (obj != NULL) {
196 print_locked_object_class_name(st, obj, "eliminated");
197 }
198 }
199 continue;
200 }
201 if (monitor->owner() != NULL) {
202 // the monitor is associated with an object, i.e., it is locked
204 // First, assume we have the monitor locked. If we haven't found an
205 // owned monitor before and this is the first frame, then we need to
206 // see if we have completed the lock or we are blocked trying to
207 // acquire it - we can only be blocked if the monitor is inflated
209 const char *lock_state = "locked"; // assume we have the monitor locked
210 if (!found_first_monitor && frame_count == 0) {
211 markOop mark = monitor->owner()->mark();
212 if (mark->has_monitor() &&
213 ( // we have marked ourself as pending on this monitor
214 mark->monitor() == thread()->current_pending_monitor() ||
215 // we are not the owner of this monitor
216 !mark->monitor()->is_entered(thread())
217 )) {
218 lock_state = "waiting to lock";
219 }
220 }
222 found_first_monitor = true;
223 print_locked_object_class_name(st, monitor->owner(), lock_state);
224 }
225 }
226 }
227 }
229 // ------------- interpretedVFrame --------------
231 u_char* interpretedVFrame::bcp() const {
232 return fr().interpreter_frame_bcp();
233 }
235 void interpretedVFrame::set_bcp(u_char* bcp) {
236 fr().interpreter_frame_set_bcp(bcp);
237 }
239 intptr_t* interpretedVFrame::locals_addr_at(int offset) const {
240 assert(fr().is_interpreted_frame(), "frame should be an interpreted frame");
241 return fr().interpreter_frame_local_at(offset);
242 }
245 GrowableArray<MonitorInfo*>* interpretedVFrame::monitors() const {
246 GrowableArray<MonitorInfo*>* result = new GrowableArray<MonitorInfo*>(5);
247 for (BasicObjectLock* current = (fr().previous_monitor_in_interpreter_frame(fr().interpreter_frame_monitor_begin()));
248 current >= fr().interpreter_frame_monitor_end();
249 current = fr().previous_monitor_in_interpreter_frame(current)) {
250 result->push(new MonitorInfo(current->obj(), current->lock(), false, false));
251 }
252 return result;
253 }
255 int interpretedVFrame::bci() const {
256 return method()->bci_from(bcp());
257 }
259 Method* interpretedVFrame::method() const {
260 return fr().interpreter_frame_method();
261 }
263 static StackValue* create_stack_value_from_oop_map(const InterpreterOopMap& oop_mask,
264 int index,
265 const intptr_t* const addr) {
267 assert(index >= 0 &&
268 index < oop_mask.number_of_entries(), "invariant");
270 // categorize using oop_mask
271 if (oop_mask.is_oop(index)) {
272 // reference (oop) "r"
273 Handle h(addr != NULL ? (*(oop*)addr) : (oop)NULL);
274 return new StackValue(h);
275 }
276 // value (integer) "v"
277 return new StackValue(addr != NULL ? *addr : 0);
278 }
280 static bool is_in_expression_stack(const frame& fr, const intptr_t* const addr) {
281 assert(addr != NULL, "invariant");
283 // Ensure to be 'inside' the expresion stack (i.e., addr >= sp for Intel).
284 // In case of exceptions, the expression stack is invalid and the sp
285 // will be reset to express this condition.
286 if (frame::interpreter_frame_expression_stack_direction() > 0) {
287 return addr <= fr.interpreter_frame_tos_address();
288 }
290 return addr >= fr.interpreter_frame_tos_address();
291 }
293 static void stack_locals(StackValueCollection* result,
294 int length,
295 const InterpreterOopMap& oop_mask,
296 const frame& fr) {
298 assert(result != NULL, "invariant");
300 for (int i = 0; i < length; ++i) {
301 const intptr_t* const addr = fr.interpreter_frame_local_at(i);
302 assert(addr != NULL, "invariant");
303 assert(addr >= fr.sp(), "must be inside the frame");
305 StackValue* const sv = create_stack_value_from_oop_map(oop_mask, i, addr);
306 assert(sv != NULL, "sanity check");
308 result->add(sv);
309 }
310 }
312 static void stack_expressions(StackValueCollection* result,
313 int length,
314 int max_locals,
315 const InterpreterOopMap& oop_mask,
316 const frame& fr) {
318 assert(result != NULL, "invariant");
320 for (int i = 0; i < length; ++i) {
321 const intptr_t* addr = fr.interpreter_frame_expression_stack_at(i);
322 assert(addr != NULL, "invariant");
323 if (!is_in_expression_stack(fr, addr)) {
324 // Need to ensure no bogus escapes.
325 addr = NULL;
326 }
328 StackValue* const sv = create_stack_value_from_oop_map(oop_mask,
329 i + max_locals,
330 addr);
331 assert(sv != NULL, "sanity check");
333 result->add(sv);
334 }
335 }
337 StackValueCollection* interpretedVFrame::locals() const {
338 return stack_data(false);
339 }
341 StackValueCollection* interpretedVFrame::expressions() const {
342 return stack_data(true);
343 }
345 /*
346 * Worker routine for fetching references and/or values
347 * for a particular bci in the interpretedVFrame.
348 *
349 * Returns data for either "locals" or "expressions",
350 * using bci relative oop_map (oop_mask) information.
351 *
352 * @param expressions bool switch controlling what data to return
353 (false == locals / true == expressions)
354 *
355 */
356 StackValueCollection* interpretedVFrame::stack_data(bool expressions) const {
358 InterpreterOopMap oop_mask;
359 // oopmap for current bci
360 if (TraceDeoptimization && Verbose) {
361 methodHandle m_h(Thread::current(), method());
362 OopMapCache::compute_one_oop_map(m_h, bci(), &oop_mask);
363 } else {
364 method()->mask_for(bci(), &oop_mask);
365 }
367 const int mask_len = oop_mask.number_of_entries();
369 // If the method is native, method()->max_locals() is not telling the truth.
370 // For our purposes, max locals instead equals the size of parameters.
371 const int max_locals = method()->is_native() ?
372 method()->size_of_parameters() : method()->max_locals();
374 assert(mask_len >= max_locals, "invariant");
376 const int length = expressions ? mask_len - max_locals : max_locals;
377 assert(length >= 0, "invariant");
379 StackValueCollection* const result = new StackValueCollection(length);
381 if (0 == length) {
382 return result;
383 }
385 if (expressions) {
386 stack_expressions(result, length, max_locals, oop_mask, fr());
387 } else {
388 stack_locals(result, length, oop_mask, fr());
389 }
391 assert(length == result->size(), "invariant");
393 return result;
394 }
396 void interpretedVFrame::set_locals(StackValueCollection* values) const {
397 if (values == NULL || values->size() == 0) return;
399 // If the method is native, max_locals is not telling the truth.
400 // maxlocals then equals the size of parameters
401 const int max_locals = method()->is_native() ?
402 method()->size_of_parameters() : method()->max_locals();
404 assert(max_locals == values->size(), "Mismatch between actual stack format and supplied data");
406 // handle locals
407 for (int i = 0; i < max_locals; i++) {
408 // Find stack location
409 intptr_t *addr = locals_addr_at(i);
411 // Depending on oop/int put it in the right package
412 const StackValue* const sv = values->at(i);
413 assert(sv != NULL, "sanity check");
414 if (sv->type() == T_OBJECT) {
415 *(oop *) addr = (sv->get_obj())();
416 } else { // integer
417 *addr = sv->get_int();
418 }
419 }
420 }
422 // ------------- cChunk --------------
424 entryVFrame::entryVFrame(const frame* fr, const RegisterMap* reg_map, JavaThread* thread)
425 : externalVFrame(fr, reg_map, thread) {}
428 void vframeStreamCommon::found_bad_method_frame() {
429 // 6379830 Cut point for an assertion that occasionally fires when
430 // we are using the performance analyzer.
431 // Disable this assert when testing the analyzer with fastdebug.
432 // -XX:SuppressErrorAt=vframe.cpp:XXX (XXX=following line number)
433 assert(false, "invalid bci or invalid scope desc");
434 }
436 // top-frame will be skipped
437 vframeStream::vframeStream(JavaThread* thread, frame top_frame,
438 bool stop_at_java_call_stub) : vframeStreamCommon(thread) {
439 _stop_at_java_call_stub = stop_at_java_call_stub;
441 // skip top frame, as it may not be at safepoint
442 _frame = top_frame.sender(&_reg_map);
443 while (!fill_from_frame()) {
444 _frame = _frame.sender(&_reg_map);
445 }
446 }
449 // Step back n frames, skip any pseudo frames in between.
450 // This function is used in Class.forName, Class.newInstance, Method.Invoke,
451 // AccessController.doPrivileged.
452 void vframeStreamCommon::security_get_caller_frame(int depth) {
453 assert(depth >= 0, err_msg("invalid depth: %d", depth));
454 for (int n = 0; !at_end(); security_next()) {
455 if (!method()->is_ignored_by_security_stack_walk()) {
456 if (n == depth) {
457 // We have reached the desired depth; return.
458 return;
459 }
460 n++; // this is a non-skipped frame; count it against the depth
461 }
462 }
463 // NOTE: At this point there were not enough frames on the stack
464 // to walk to depth. Callers of this method have to check for at_end.
465 }
468 void vframeStreamCommon::security_next() {
469 if (method()->is_prefixed_native()) {
470 skip_prefixed_method_and_wrappers(); // calls next()
471 } else {
472 next();
473 }
474 }
477 void vframeStreamCommon::skip_prefixed_method_and_wrappers() {
478 ResourceMark rm;
479 HandleMark hm;
481 int method_prefix_count = 0;
482 char** method_prefixes = JvmtiExport::get_all_native_method_prefixes(&method_prefix_count);
483 KlassHandle prefixed_klass(method()->method_holder());
484 const char* prefixed_name = method()->name()->as_C_string();
485 size_t prefixed_name_len = strlen(prefixed_name);
486 int prefix_index = method_prefix_count-1;
488 while (!at_end()) {
489 next();
490 if (method()->method_holder() != prefixed_klass()) {
491 break; // classes don't match, can't be a wrapper
492 }
493 const char* name = method()->name()->as_C_string();
494 size_t name_len = strlen(name);
495 size_t prefix_len = prefixed_name_len - name_len;
496 if (prefix_len <= 0 || strcmp(name, prefixed_name + prefix_len) != 0) {
497 break; // prefixed name isn't prefixed version of method name, can't be a wrapper
498 }
499 for (; prefix_index >= 0; --prefix_index) {
500 const char* possible_prefix = method_prefixes[prefix_index];
501 size_t possible_prefix_len = strlen(possible_prefix);
502 if (possible_prefix_len == prefix_len &&
503 strncmp(possible_prefix, prefixed_name, prefix_len) == 0) {
504 break; // matching prefix found
505 }
506 }
507 if (prefix_index < 0) {
508 break; // didn't find the prefix, can't be a wrapper
509 }
510 prefixed_name = name;
511 prefixed_name_len = name_len;
512 }
513 }
516 void vframeStreamCommon::skip_reflection_related_frames() {
517 while (!at_end() &&
518 (JDK_Version::is_gte_jdk14x_version() && UseNewReflection &&
519 (method()->method_holder()->is_subclass_of(SystemDictionary::reflect_MethodAccessorImpl_klass()) ||
520 method()->method_holder()->is_subclass_of(SystemDictionary::reflect_ConstructorAccessorImpl_klass())))) {
521 next();
522 }
523 }
526 #ifndef PRODUCT
527 void vframe::print() {
528 if (WizardMode) _fr.print_value_on(tty,NULL);
529 }
532 void vframe::print_value() const {
533 ((vframe*)this)->print();
534 }
537 void entryVFrame::print_value() const {
538 ((entryVFrame*)this)->print();
539 }
541 void entryVFrame::print() {
542 vframe::print();
543 tty->print_cr("C Chunk inbetween Java");
544 tty->print_cr("C link " INTPTR_FORMAT, _fr.link());
545 }
548 // ------------- javaVFrame --------------
550 static void print_stack_values(const char* title, StackValueCollection* values) {
551 if (values->is_empty()) return;
552 tty->print_cr("\t%s:", title);
553 values->print();
554 }
557 void javaVFrame::print() {
558 ResourceMark rm;
559 vframe::print();
560 tty->print("\t");
561 method()->print_value();
562 tty->cr();
563 tty->print_cr("\tbci: %d", bci());
565 print_stack_values("locals", locals());
566 print_stack_values("expressions", expressions());
568 GrowableArray<MonitorInfo*>* list = monitors();
569 if (list->is_empty()) return;
570 tty->print_cr("\tmonitor list:");
571 for (int index = (list->length()-1); index >= 0; index--) {
572 MonitorInfo* monitor = list->at(index);
573 tty->print("\t obj\t");
574 if (monitor->owner_is_scalar_replaced()) {
575 Klass* k = java_lang_Class::as_Klass(monitor->owner_klass());
576 tty->print("( is scalar replaced %s)", k->external_name());
577 } else if (monitor->owner() == NULL) {
578 tty->print("( null )");
579 } else {
580 monitor->owner()->print_value();
581 tty->print("(" INTPTR_FORMAT ")", (address)monitor->owner());
582 }
583 if (monitor->eliminated() && is_compiled_frame())
584 tty->print(" ( lock is eliminated )");
585 tty->cr();
586 tty->print("\t ");
587 monitor->lock()->print_on(tty);
588 tty->cr();
589 }
590 }
593 void javaVFrame::print_value() const {
594 Method* m = method();
595 InstanceKlass* k = m->method_holder();
596 tty->print_cr("frame( sp=" INTPTR_FORMAT ", unextended_sp=" INTPTR_FORMAT ", fp=" INTPTR_FORMAT ", pc=" INTPTR_FORMAT ")",
597 _fr.sp(), _fr.unextended_sp(), _fr.fp(), _fr.pc());
598 tty->print("%s.%s", k->internal_name(), m->name()->as_C_string());
600 if (!m->is_native()) {
601 Symbol* source_name = k->source_file_name();
602 int line_number = m->line_number_from_bci(bci());
603 if (source_name != NULL && (line_number != -1)) {
604 tty->print("(%s:%d)", source_name->as_C_string(), line_number);
605 }
606 } else {
607 tty->print("(Native Method)");
608 }
609 // Check frame size and print warning if it looks suspiciously large
610 if (fr().sp() != NULL) {
611 RegisterMap map = *register_map();
612 uint size = fr().frame_size(&map);
613 #ifdef _LP64
614 if (size > 8*K) warning("SUSPICIOUSLY LARGE FRAME (%d)", size);
615 #else
616 if (size > 4*K) warning("SUSPICIOUSLY LARGE FRAME (%d)", size);
617 #endif
618 }
619 }
622 bool javaVFrame::structural_compare(javaVFrame* other) {
623 // Check static part
624 if (method() != other->method()) return false;
625 if (bci() != other->bci()) return false;
627 // Check locals
628 StackValueCollection *locs = locals();
629 StackValueCollection *other_locs = other->locals();
630 assert(locs->size() == other_locs->size(), "sanity check");
631 int i;
632 for(i = 0; i < locs->size(); i++) {
633 // it might happen the compiler reports a conflict and
634 // the interpreter reports a bogus int.
635 if ( is_compiled_frame() && locs->at(i)->type() == T_CONFLICT) continue;
636 if (other->is_compiled_frame() && other_locs->at(i)->type() == T_CONFLICT) continue;
638 if (!locs->at(i)->equal(other_locs->at(i)))
639 return false;
640 }
642 // Check expressions
643 StackValueCollection* exprs = expressions();
644 StackValueCollection* other_exprs = other->expressions();
645 assert(exprs->size() == other_exprs->size(), "sanity check");
646 for(i = 0; i < exprs->size(); i++) {
647 if (!exprs->at(i)->equal(other_exprs->at(i)))
648 return false;
649 }
651 return true;
652 }
655 void javaVFrame::print_activation(int index) const {
656 // frame number and method
657 tty->print("%2d - ", index);
658 ((vframe*)this)->print_value();
659 tty->cr();
661 if (WizardMode) {
662 ((vframe*)this)->print();
663 tty->cr();
664 }
665 }
668 void javaVFrame::verify() const {
669 }
672 void interpretedVFrame::verify() const {
673 }
676 // ------------- externalVFrame --------------
678 void externalVFrame::print() {
679 _fr.print_value_on(tty,NULL);
680 }
683 void externalVFrame::print_value() const {
684 ((vframe*)this)->print();
685 }
686 #endif // PRODUCT