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Issue 6811012: Remove some dead code. (Closed) Base URL: https://v8.googlecode.com/svn/branches/bleeding_edge
Patch Set: Created 9 years, 8 months ago
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1 // Copyright 2008 the V8 project authors. All rights reserved.
2 // Redistribution and use in source and binary forms, with or without
3 // modification, are permitted provided that the following conditions are
4 // met:
5 //
6 // * Redistributions of source code must retain the above copyright
7 // notice, this list of conditions and the following disclaimer.
8 // * Redistributions in binary form must reproduce the above
9 // copyright notice, this list of conditions and the following
10 // disclaimer in the documentation and/or other materials provided
11 // with the distribution.
12 // * Neither the name of Google Inc. nor the names of its
13 // contributors may be used to endorse or promote products derived
14 // from this software without specific prior written permission.
15 //
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27
28 #include "v8.h"
29
30 #if defined(V8_TARGET_ARCH_IA32)
31
32 #include "codegen-inl.h"
33 #include "jump-target-inl.h"
34 #include "register-allocator-inl.h"
35 #include "virtual-frame-inl.h"
36
37 namespace v8 {
38 namespace internal {
39
40 // -------------------------------------------------------------------------
41 // JumpTarget implementation.
42
43 #define __ ACCESS_MASM(cgen()->masm())
44
45 void JumpTarget::DoJump() {
46 ASSERT(cgen()->has_valid_frame());
47 // Live non-frame registers are not allowed at unconditional jumps
48 // because we have no way of invalidating the corresponding results
49 // which are still live in the C++ code.
50 ASSERT(cgen()->HasValidEntryRegisters());
51
52 if (is_bound()) {
53 // Backward jump. There is an expected frame to merge to.
54 ASSERT(direction_ == BIDIRECTIONAL);
55 cgen()->frame()->PrepareMergeTo(entry_frame_);
56 cgen()->frame()->MergeTo(entry_frame_);
57 cgen()->DeleteFrame();
58 __ jmp(&entry_label_);
59 } else if (entry_frame_ != NULL) {
60 // Forward jump with a preconfigured entry frame. Assert the
61 // current frame matches the expected one and jump to the block.
62 ASSERT(cgen()->frame()->Equals(entry_frame_));
63 cgen()->DeleteFrame();
64 __ jmp(&entry_label_);
65 } else {
66 // Forward jump. Remember the current frame and emit a jump to
67 // its merge code.
68 AddReachingFrame(cgen()->frame());
69 RegisterFile empty;
70 cgen()->SetFrame(NULL, &empty);
71 __ jmp(&merge_labels_.last());
72 }
73 }
74
75
76 void JumpTarget::DoBranch(Condition cc, Hint hint) {
77 ASSERT(cgen() != NULL);
78 ASSERT(cgen()->has_valid_frame());
79
80 if (is_bound()) {
81 ASSERT(direction_ == BIDIRECTIONAL);
82 // Backward branch. We have an expected frame to merge to on the
83 // backward edge.
84
85 // Swap the current frame for a copy (we do the swapping to get
86 // the off-frame registers off the fall through) to use for the
87 // branch.
88 VirtualFrame* fall_through_frame = cgen()->frame();
89 VirtualFrame* branch_frame = new VirtualFrame(fall_through_frame);
90 RegisterFile non_frame_registers;
91 cgen()->SetFrame(branch_frame, &non_frame_registers);
92
93 // Check if we can avoid merge code.
94 cgen()->frame()->PrepareMergeTo(entry_frame_);
95 if (cgen()->frame()->Equals(entry_frame_)) {
96 // Branch right in to the block.
97 cgen()->DeleteFrame();
98 __ j(cc, &entry_label_, hint);
99 cgen()->SetFrame(fall_through_frame, &non_frame_registers);
100 return;
101 }
102
103 // Check if we can reuse existing merge code.
104 for (int i = 0; i < reaching_frames_.length(); i++) {
105 if (reaching_frames_[i] != NULL &&
106 cgen()->frame()->Equals(reaching_frames_[i])) {
107 // Branch to the merge code.
108 cgen()->DeleteFrame();
109 __ j(cc, &merge_labels_[i], hint);
110 cgen()->SetFrame(fall_through_frame, &non_frame_registers);
111 return;
112 }
113 }
114
115 // To emit the merge code here, we negate the condition and branch
116 // around the merge code on the fall through path.
117 Label original_fall_through;
118 __ j(NegateCondition(cc), &original_fall_through, NegateHint(hint));
119 cgen()->frame()->MergeTo(entry_frame_);
120 cgen()->DeleteFrame();
121 __ jmp(&entry_label_);
122 cgen()->SetFrame(fall_through_frame, &non_frame_registers);
123 __ bind(&original_fall_through);
124
125 } else if (entry_frame_ != NULL) {
126 // Forward branch with a preconfigured entry frame. Assert the
127 // current frame matches the expected one and branch to the block.
128 ASSERT(cgen()->frame()->Equals(entry_frame_));
129 // Explicitly use the macro assembler instead of __ as forward
130 // branches are expected to be a fixed size (no inserted
131 // coverage-checking instructions please). This is used in
132 // Reference::GetValue.
133 cgen()->masm()->j(cc, &entry_label_, hint);
134
135 } else {
136 // Forward branch. A copy of the current frame is remembered and
137 // a branch to the merge code is emitted. Explicitly use the
138 // macro assembler instead of __ as forward branches are expected
139 // to be a fixed size (no inserted coverage-checking instructions
140 // please). This is used in Reference::GetValue.
141 AddReachingFrame(new VirtualFrame(cgen()->frame()));
142 cgen()->masm()->j(cc, &merge_labels_.last(), hint);
143 }
144 }
145
146
147 void JumpTarget::Call() {
148 // Call is used to push the address of the catch block on the stack as
149 // a return address when compiling try/catch and try/finally. We
150 // fully spill the frame before making the call. The expected frame
151 // at the label (which should be the only one) is the spilled current
152 // frame plus an in-memory return address. The "fall-through" frame
153 // at the return site is the spilled current frame.
154 ASSERT(cgen() != NULL);
155 ASSERT(cgen()->has_valid_frame());
156 // There are no non-frame references across the call.
157 ASSERT(cgen()->HasValidEntryRegisters());
158 ASSERT(!is_linked());
159
160 cgen()->frame()->SpillAll();
161 VirtualFrame* target_frame = new VirtualFrame(cgen()->frame());
162 target_frame->Adjust(1);
163 // We do not expect a call with a preconfigured entry frame.
164 ASSERT(entry_frame_ == NULL);
165 AddReachingFrame(target_frame);
166 __ call(&merge_labels_.last());
167 }
168
169
170 void JumpTarget::DoBind() {
171 ASSERT(cgen() != NULL);
172 ASSERT(!is_bound());
173
174 // Live non-frame registers are not allowed at the start of a basic
175 // block.
176 ASSERT(!cgen()->has_valid_frame() || cgen()->HasValidEntryRegisters());
177
178 // Fast case: the jump target was manually configured with an entry
179 // frame to use.
180 if (entry_frame_ != NULL) {
181 // Assert no reaching frames to deal with.
182 ASSERT(reaching_frames_.is_empty());
183 ASSERT(!cgen()->has_valid_frame());
184
185 RegisterFile empty;
186 if (direction_ == BIDIRECTIONAL) {
187 // Copy the entry frame so the original can be used for a
188 // possible backward jump.
189 cgen()->SetFrame(new VirtualFrame(entry_frame_), &empty);
190 } else {
191 // Take ownership of the entry frame.
192 cgen()->SetFrame(entry_frame_, &empty);
193 entry_frame_ = NULL;
194 }
195 __ bind(&entry_label_);
196 return;
197 }
198
199 if (!is_linked()) {
200 ASSERT(cgen()->has_valid_frame());
201 if (direction_ == FORWARD_ONLY) {
202 // Fast case: no forward jumps and no possible backward jumps.
203 // The stack pointer can be floating above the top of the
204 // virtual frame before the bind. Afterward, it should not.
205 VirtualFrame* frame = cgen()->frame();
206 int difference = frame->stack_pointer_ - (frame->element_count() - 1);
207 if (difference > 0) {
208 frame->stack_pointer_ -= difference;
209 __ add(Operand(esp), Immediate(difference * kPointerSize));
210 }
211 } else {
212 ASSERT(direction_ == BIDIRECTIONAL);
213 // Fast case: no forward jumps, possible backward ones. Remove
214 // constants and copies above the watermark on the fall-through
215 // frame and use it as the entry frame.
216 cgen()->frame()->MakeMergable();
217 entry_frame_ = new VirtualFrame(cgen()->frame());
218 }
219 __ bind(&entry_label_);
220 return;
221 }
222
223 if (direction_ == FORWARD_ONLY &&
224 !cgen()->has_valid_frame() &&
225 reaching_frames_.length() == 1) {
226 // Fast case: no fall-through, a single forward jump, and no
227 // possible backward jumps. Pick up the only reaching frame, take
228 // ownership of it, and use it for the block about to be emitted.
229 VirtualFrame* frame = reaching_frames_[0];
230 RegisterFile empty;
231 cgen()->SetFrame(frame, &empty);
232 reaching_frames_[0] = NULL;
233 __ bind(&merge_labels_[0]);
234
235 // The stack pointer can be floating above the top of the
236 // virtual frame before the bind. Afterward, it should not.
237 int difference = frame->stack_pointer_ - (frame->element_count() - 1);
238 if (difference > 0) {
239 frame->stack_pointer_ -= difference;
240 __ add(Operand(esp), Immediate(difference * kPointerSize));
241 }
242
243 __ bind(&entry_label_);
244 return;
245 }
246
247 // If there is a current frame, record it as the fall-through. It
248 // is owned by the reaching frames for now.
249 bool had_fall_through = false;
250 if (cgen()->has_valid_frame()) {
251 had_fall_through = true;
252 AddReachingFrame(cgen()->frame()); // Return value ignored.
253 RegisterFile empty;
254 cgen()->SetFrame(NULL, &empty);
255 }
256
257 // Compute the frame to use for entry to the block.
258 ComputeEntryFrame();
259
260 // Some moves required to merge to an expected frame require purely
261 // frame state changes, and do not require any code generation.
262 // Perform those first to increase the possibility of finding equal
263 // frames below.
264 for (int i = 0; i < reaching_frames_.length(); i++) {
265 if (reaching_frames_[i] != NULL) {
266 reaching_frames_[i]->PrepareMergeTo(entry_frame_);
267 }
268 }
269
270 if (is_linked()) {
271 // There were forward jumps. Handle merging the reaching frames
272 // to the entry frame.
273
274 // Loop over the (non-null) reaching frames and process any that
275 // need merge code. Iterate backwards through the list to handle
276 // the fall-through frame first. Set frames that will be
277 // processed after 'i' to NULL if we want to avoid processing
278 // them.
279 for (int i = reaching_frames_.length() - 1; i >= 0; i--) {
280 VirtualFrame* frame = reaching_frames_[i];
281
282 if (frame != NULL) {
283 // Does the frame (probably) need merge code?
284 if (!frame->Equals(entry_frame_)) {
285 // We could have a valid frame as the fall through to the
286 // binding site or as the fall through from a previous merge
287 // code block. Jump around the code we are about to
288 // generate.
289 if (cgen()->has_valid_frame()) {
290 cgen()->DeleteFrame();
291 __ jmp(&entry_label_);
292 }
293 // Pick up the frame for this block. Assume ownership if
294 // there cannot be backward jumps.
295 RegisterFile empty;
296 if (direction_ == BIDIRECTIONAL) {
297 cgen()->SetFrame(new VirtualFrame(frame), &empty);
298 } else {
299 cgen()->SetFrame(frame, &empty);
300 reaching_frames_[i] = NULL;
301 }
302 __ bind(&merge_labels_[i]);
303
304 // Loop over the remaining (non-null) reaching frames,
305 // looking for any that can share merge code with this one.
306 for (int j = 0; j < i; j++) {
307 VirtualFrame* other = reaching_frames_[j];
308 if (other != NULL && other->Equals(cgen()->frame())) {
309 // Set the reaching frame element to null to avoid
310 // processing it later, and then bind its entry label.
311 reaching_frames_[j] = NULL;
312 __ bind(&merge_labels_[j]);
313 }
314 }
315
316 // Emit the merge code.
317 cgen()->frame()->MergeTo(entry_frame_);
318 } else if (i == reaching_frames_.length() - 1 && had_fall_through) {
319 // If this is the fall through frame, and it didn't need
320 // merge code, we need to pick up the frame so we can jump
321 // around subsequent merge blocks if necessary.
322 RegisterFile empty;
323 cgen()->SetFrame(frame, &empty);
324 reaching_frames_[i] = NULL;
325 }
326 }
327 }
328
329 // The code generator may not have a current frame if there was no
330 // fall through and none of the reaching frames needed merging.
331 // In that case, clone the entry frame as the current frame.
332 if (!cgen()->has_valid_frame()) {
333 RegisterFile empty;
334 cgen()->SetFrame(new VirtualFrame(entry_frame_), &empty);
335 }
336
337 // There may be unprocessed reaching frames that did not need
338 // merge code. They will have unbound merge labels. Bind their
339 // merge labels to be the same as the entry label and deallocate
340 // them.
341 for (int i = 0; i < reaching_frames_.length(); i++) {
342 if (!merge_labels_[i].is_bound()) {
343 reaching_frames_[i] = NULL;
344 __ bind(&merge_labels_[i]);
345 }
346 }
347
348 // There are non-NULL reaching frames with bound labels for each
349 // merge block, but only on backward targets.
350 } else {
351 // There were no forward jumps. There must be a current frame and
352 // this must be a bidirectional target.
353 ASSERT(reaching_frames_.length() == 1);
354 ASSERT(reaching_frames_[0] != NULL);
355 ASSERT(direction_ == BIDIRECTIONAL);
356
357 // Use a copy of the reaching frame so the original can be saved
358 // for possible reuse as a backward merge block.
359 RegisterFile empty;
360 cgen()->SetFrame(new VirtualFrame(reaching_frames_[0]), &empty);
361 __ bind(&merge_labels_[0]);
362 cgen()->frame()->MergeTo(entry_frame_);
363 }
364
365 __ bind(&entry_label_);
366 }
367
368
369 void BreakTarget::Jump() {
370 // Drop leftover statement state from the frame before merging, without
371 // emitting code.
372 ASSERT(cgen()->has_valid_frame());
373 int count = cgen()->frame()->height() - expected_height_;
374 cgen()->frame()->ForgetElements(count);
375 DoJump();
376 }
377
378
379 void BreakTarget::Jump(Result* arg) {
380 // Drop leftover statement state from the frame before merging, without
381 // emitting code.
382 ASSERT(cgen()->has_valid_frame());
383 int count = cgen()->frame()->height() - expected_height_;
384 cgen()->frame()->ForgetElements(count);
385 cgen()->frame()->Push(arg);
386 DoJump();
387 }
388
389
390 void BreakTarget::Bind() {
391 #ifdef DEBUG
392 // All the forward-reaching frames should have been adjusted at the
393 // jumps to this target.
394 for (int i = 0; i < reaching_frames_.length(); i++) {
395 ASSERT(reaching_frames_[i] == NULL ||
396 reaching_frames_[i]->height() == expected_height_);
397 }
398 #endif
399 // Drop leftover statement state from the frame before merging, even on
400 // the fall through. This is so we can bind the return target with state
401 // on the frame.
402 if (cgen()->has_valid_frame()) {
403 int count = cgen()->frame()->height() - expected_height_;
404 cgen()->frame()->ForgetElements(count);
405 }
406 DoBind();
407 }
408
409
410 void BreakTarget::Bind(Result* arg) {
411 #ifdef DEBUG
412 // All the forward-reaching frames should have been adjusted at the
413 // jumps to this target.
414 for (int i = 0; i < reaching_frames_.length(); i++) {
415 ASSERT(reaching_frames_[i] == NULL ||
416 reaching_frames_[i]->height() == expected_height_ + 1);
417 }
418 #endif
419 // Drop leftover statement state from the frame before merging, even on
420 // the fall through. This is so we can bind the return target with state
421 // on the frame.
422 if (cgen()->has_valid_frame()) {
423 int count = cgen()->frame()->height() - expected_height_;
424 cgen()->frame()->ForgetElements(count);
425 cgen()->frame()->Push(arg);
426 }
427 DoBind();
428 *arg = cgen()->frame()->Pop();
429 }
430
431
432 #undef __
433
434
435 } } // namespace v8::internal
436
437 #endif // V8_TARGET_ARCH_IA32
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