1 /*
2 * Copyright (c) 2015, 2016, 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.org.objectweb.asm.ClassWriter;
29 import jdk.internal.org.objectweb.asm.Label;
30 import jdk.internal.org.objectweb.asm.MethodVisitor;
31 import jdk.internal.org.objectweb.asm.Opcodes;
32 import jdk.internal.vm.annotation.ForceInline;
33 import sun.misc.Unsafe;
34
35 import java.lang.invoke.MethodHandles.Lookup;
36 import java.security.AccessController;
37 import java.security.PrivilegedAction;
38 import java.util.*;
39 import java.util.concurrent.ConcurrentHashMap;
40 import java.util.concurrent.ConcurrentMap;
41 import java.util.function.Function;
42
43 import static jdk.internal.org.objectweb.asm.Opcodes.*;
44
45 /**
46 * <p>Methods to facilitate the creation of String concatenation methods, that
47 * can be used to efficiently concatenate a known number of arguments of known
48 * types, possibly after type adaptation and partial evaluation of arguments.
49 * These methods are typically used as <em>bootstrap methods</em> for {@code
50 * invokedynamic} call sites, to support the <em>string concatenation</em>
51 * feature of the Java Programming Language.
52 *
53 * <p>Indirect access to the behavior specified by the provided {@code
54 * MethodHandle} proceeds in order through two phases:
55 *
56 * <ol>
57 * <li><em>Linkage</em> occurs when the methods in this class are invoked.
58 * They take as arguments a method type describing the concatenated arguments
59 * count and types, and optionally the String <em>recipe</em>, plus the
60 * constants that participate in the String concatenation. The details on
61 * accepted recipe shapes are described further below. Linkage may involve
62 * dynamically loading a new class that implements the expected concatenation
63 * behavior. The {@code CallSite} holds the {@code MethodHandle} pointing to the
64 * exact concatenation method. The concatenation methods may be shared among
65 * different {@code CallSite}s, e.g. if linkage methods produce them as pure
66 * functions.</li>
67 *
68 * <li><em>Invocation</em> occurs when a generated concatenation method is
69 * invoked with the exact dynamic arguments. This may occur many times for a
70 * single concatenation method. The method referenced by the behavior {@code
71 * MethodHandle} is invoked with the static arguments and any additional dynamic
72 * arguments provided on invocation, as if by {@link MethodHandle#invoke(Object...)}.</li>
73 * </ol>
74 *
75 * <p> This class provides two forms of linkage methods: a simple version
76 * ({@link #makeConcat(java.lang.invoke.MethodHandles.Lookup, String,
77 * MethodType)}) using only the dynamic arguments, and an advanced version
78 * ({@link #makeConcatWithConstants(java.lang.invoke.MethodHandles.Lookup,
79 * String, MethodType, String, Object...)} using the advanced forms of capturing
80 * the constant arguments. The advanced strategy can produce marginally better
81 * invocation bytecode, at the expense of exploding the number of shapes of
82 * string concatenation methods present at runtime, because those shapes would
83 * include constant static arguments as well.
84 *
85 * @author Aleksey Shipilev
86 * @author Remi Forax
87 * @author Peter Levart
88 *
89 * @apiNote
90 * <p>There is a JVM limit (classfile structural constraint): no method
91 * can call with more than 255 slots. This limits the number of static and
92 * dynamic arguments one can pass to bootstrap method. Since there are potential
93 * concatenation strategies that use {@code MethodHandle} combinators, we need
94 * to reserve a few empty slots on the parameter lists to to capture the
95 * temporal results. This is why bootstrap methods in this factory do not accept
96 * more than 200 argument slots. Users requiring more than 200 argument slots in
97 * concatenation are expected to split the large concatenation in smaller
98 * expressions.
99 *
100 * @since 9
101 */
102 public final class StringConcatFactory {
103
104 /**
105 * Tag used to demarcate an ordinary argument.
106 */
107 private static final char TAG_ARG = '\u0001';
108
109 /**
110 * Tag used to demarcate a constant.
111 */
112 private static final char TAG_CONST = '\u0002';
113
114 /**
115 * Maximum number of argument slots in String Concat call.
116 *
117 * While the maximum number of argument slots that indy call can handle is 253,
118 * we do not use all those slots, to let the strategies with MethodHandle
119 * combinators to use some arguments.
120 */
121 private static final int MAX_INDY_CONCAT_ARG_SLOTS = 200;
122
123 /**
124 * Concatenation strategy to use. See {@link Strategy} for possible options.
125 * This option is controllable with -Djava.lang.invoke.stringConcat JDK option.
126 */
127 private static final Strategy STRATEGY;
128
129 /**
130 * Default strategy to use for concatenation.
131 */
132 private static final Strategy DEFAULT_STRATEGY = Strategy.BC_SB;
133
134 private enum Strategy {
135 /**
136 * Bytecode generator, calling into {@link java.lang.StringBuilder}.
137 */
138 BC_SB,
139
140 /**
141 * Bytecode generator, calling into {@link java.lang.StringBuilder};
142 * but trying to estimate the required storage.
143 */
144 BC_SB_SIZED,
145
146 /**
147 * Bytecode generator, calling into {@link java.lang.StringBuilder};
148 * but computing the required storage exactly.
149 */
150 BC_SB_SIZED_EXACT,
151
152 /**
153 * MethodHandle-based generator, that in the end calls into {@link java.lang.StringBuilder}.
154 * This strategy also tries to estimate the required storage.
155 */
156 MH_SB_SIZED,
157
158 /**
159 * MethodHandle-based generator, that in the end calls into {@link java.lang.StringBuilder}.
160 * This strategy also estimate the required storage exactly.
161 */
162 MH_SB_SIZED_EXACT,
163
164 /**
165 * MethodHandle-based generator, that constructs its own byte[] array from
166 * the arguments. It computes the required storage exactly.
167 */
168 MH_INLINE_SIZED_EXACT
169 }
170
171 /**
172 * Enables debugging: this may print debugging messages, perform additional (non-neutral for performance)
173 * checks, etc.
174 */
175 private static final boolean DEBUG;
176
177 /**
178 * Enables caching of strategy stubs. This may improve the linkage time by reusing the generated
179 * code, at the expense of contaminating the profiles.
180 */
181 private static final boolean CACHE_ENABLE;
182
183 private static final ConcurrentMap<Key, MethodHandle> CACHE;
184
185 static {
186 // Poke the privileged block once, taking everything we need:
187 final Object[] values = new Object[3];
188 AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
189 values[0] = System.getProperty("java.lang.invoke.stringConcat");
190 values[1] = Boolean.getBoolean("java.lang.invoke.stringConcat.cache");
191 values[2] = Boolean.getBoolean("java.lang.invoke.stringConcat.debug");
192 return null;
193 });
194
195 final String strategy = (String) values[0];
196 CACHE_ENABLE = (Boolean) values[1];
197 DEBUG = (Boolean) values[2];
198
199 STRATEGY = (strategy == null) ? DEFAULT_STRATEGY : Strategy.valueOf(strategy);
200 CACHE = CACHE_ENABLE ? new ConcurrentHashMap<>() : null;
201 }
202
203 private static final class Key {
204 final MethodType mt;
205 final Recipe recipe;
206
207 public Key(MethodType mt, Recipe recipe) {
208 this.mt = mt;
209 this.recipe = recipe;
210 }
211
212 @Override
213 public boolean equals(Object o) {
214 if (this == o) return true;
215 if (o == null || getClass() != o.getClass()) return false;
216
217 Key key = (Key) o;
218
219 if (!mt.equals(key.mt)) return false;
220 if (!recipe.equals(key.recipe)) return false;
221 return true;
222 }
223
224 @Override
225 public int hashCode() {
226 int result = mt.hashCode();
227 result = 31 * result + recipe.hashCode();
228 return result;
229 }
230 }
231
232 /**
233 * Parses the recipe string, and produces the traversable collection of
234 * {@link java.lang.invoke.StringConcatFactory.RecipeElement}-s for generator
235 * strategies. Notably, this class parses out the constants from the recipe
236 * and from other static arguments.
237 */
238 private static final class Recipe {
239 private final List<RecipeElement> elements;
240 private final List<RecipeElement> elementsRev;
241
242 public Recipe(String src, Object[] constants) {
243 List<RecipeElement> el = new ArrayList<>();
244
245 int constC = 0;
246 int argC = 0;
247
248 StringBuilder acc = new StringBuilder();
249
250 for (int i = 0; i < src.length(); i++) {
251 char c = src.charAt(i);
252
253 if (c == TAG_CONST || c == TAG_ARG) {
254 // Detected a special tag, flush all accumulated characters
255 // as a constant first:
256 if (acc.length() > 0) {
257 el.add(new RecipeElement(acc.toString()));
258 acc.setLength(0);
259 }
260 if (c == TAG_CONST) {
261 Object cnst = constants[constC++];
262 el.add(new RecipeElement(cnst));
263 }
264 if (c == TAG_ARG) {
265 el.add(new RecipeElement(argC++));
266 }
267 } else {
268 // Not a special characters, this is a constant embedded into
269 // the recipe itself.
270 acc.append(c);
271 }
272 }
273
274 // Flush the remaining characters as constant:
275 if (acc.length() > 0) {
276 el.add(new RecipeElement(acc.toString()));
277 }
278
279 elements = new ArrayList<>(el);
280 Collections.reverse(el);
281 elementsRev = el;
282 }
283
284 public Collection<RecipeElement> getElements() {
285 return elements;
286 }
287
288 public Collection<RecipeElement> getElementsReversed() {
289 return elementsRev;
290 }
291
292 @Override
293 public boolean equals(Object o) {
294 if (this == o) return true;
295 if (o == null || getClass() != o.getClass()) return false;
296
297 Recipe recipe = (Recipe) o;
298 return elements.equals(recipe.elements);
299 }
300
301 @Override
302 public int hashCode() {
303 return elements.hashCode();
304 }
305 }
306
307 private static final class RecipeElement {
308 private final Object value;
309 private final int argPos;
310 private final Tag tag;
311
312 public RecipeElement(Object cnst) {
313 this.value = Objects.requireNonNull(cnst);
314 this.argPos = -1;
315 this.tag = Tag.CONST;
316 }
317
318 public RecipeElement(int arg) {
319 this.value = null;
320 this.argPos = arg;
321 this.tag = Tag.ARG;
322 }
323
324 public Object getValue() {
325 assert (tag == Tag.CONST);
326 return value;
327 }
328
329 public int getArgPos() {
330 assert (tag == Tag.ARG);
331 return argPos;
332 }
333
334 public Tag getTag() {
335 return tag;
336 }
337
338 @Override
339 public boolean equals(Object o) {
340 if (this == o) return true;
341 if (o == null || getClass() != o.getClass()) return false;
342
343 RecipeElement that = (RecipeElement) o;
344
345 if (tag != that.tag) return false;
346 if (tag == Tag.CONST && (!value.equals(that.value))) return false;
347 if (tag == Tag.ARG && (argPos != that.argPos)) return false;
348 return true;
349 }
350
351 @Override
352 public int hashCode() {
353 return tag.hashCode();
354 }
355 }
356
357 private enum Tag {
358 CONST, ARG
359 }
360
361 /**
362 * Facilitates the creation of optimized String concatenation methods, that
363 * can be used to efficiently concatenate a known number of arguments of
364 * known types, possibly after type adaptation and partial evaluation of
365 * arguments. Typically used as a <em>bootstrap method</em> for {@code
366 * invokedynamic} call sites, to support the <em>string concatenation</em>
367 * feature of the Java Programming Language.
368 *
369 * <p>When the target of the {@code CallSite} returned from this method is
370 * invoked, it returns the result of String concatenation, taking all
371 * function arguments passed to the linkage method as inputs for
372 * concatenation. The target signature is given by {@code concatType}.
373 * The arguments are concatenated as per requirements stated in JLS 15.18.1
374 * "String Concatenation Operator +". Notably, the inputs are converted as
375 * per JLS 5.1.11 "String Conversion", and combined from left to right.
376 *
377 * <p>Assume the linkage arguments are as follows:
378 *
379 * <ul>
380 * <li>{@code concatType}, describing the {@code CallSite} signature</li>
381 * </ul>
382 *
383 * <p>Then the following linkage invariants must hold:
384 *
385 * <ul>
386 * <li>The parameter count in {@code concatType} is less than or equal to 200</li>
387 *
388 * <li>The return type in {@code concatType} is assignable from {@link java.lang.String}</li>
389 * </ul>
390 *
391 * @param lookup Represents a lookup context with the accessibility
392 * privileges of the caller. When used with {@code
393 * invokedynamic}, this is stacked automatically by the VM.
394 * @param name The name of the method to implement. This name is
395 * arbitrary, and has no meaning for this linkage method.
396 * When used with {@code invokedynamic}, this is provided by
397 * the {@code NameAndType} of the {@code InvokeDynamic}
398 * structure and is stacked automatically by the VM.
399 * @param concatType The expected signature of the {@code CallSite}. The
400 * parameter types represent the types of concatenation
401 * arguments; the return type is always assignable from {@link
402 * java.lang.String}. When used with {@code invokedynamic},
403 * this is provided by the {@code NameAndType} of the {@code
404 * InvokeDynamic} structure and is stacked automatically by
405 * the VM.
406 * @return a CallSite whose target can be used to perform String
407 * concatenation, with dynamic concatenation arguments described by the given
408 * {@code concatType}.
409 * @throws StringConcatException If any of the linkage invariants described
410 * here are violated.
411 * @throws NullPointerException If any of the incoming arguments is null.
412 * This will never happen when a bootstrap method
413 * is called with invokedynamic.
414 *
415 * @jls 5.1.11 String Conversion
416 * @jls 15.18.1 String Concatenation Operator +
417 */
418 public static CallSite makeConcat(MethodHandles.Lookup lookup,
419 String name,
420 MethodType concatType) throws StringConcatException {
421 if (DEBUG) {
422 System.out.println("StringConcatFactory " + STRATEGY + " is here for " + concatType);
423 }
424
425 return doStringConcat(lookup, name, concatType, true, null);
426 }
427
428 /**
429 * Facilitates the creation of optimized String concatenation methods, that
430 * can be used to efficiently concatenate a known number of arguments of
431 * known types, possibly after type adaptation and partial evaluation of
432 * arguments. Typically used as a <em>bootstrap method</em> for {@code
433 * invokedynamic} call sites, to support the <em>string concatenation</em>
434 * feature of the Java Programming Language.
435 *
436 * <p>When the target of the {@code CallSite} returned from this method is
437 * invoked, it returns the result of String concatenation, taking all
438 * function arguments and constants passed to the linkage method as inputs for
439 * concatenation. The target signature is given by {@code concatType}, and
440 * does not include constants. The arguments are concatenated as per requirements
441 * stated in JLS 15.18.1 "String Concatenation Operator +". Notably, the inputs
442 * are converted as per JLS 5.1.11 "String Conversion", and combined from left
443 * to right.
444 *
445 * <p>The concatenation <em>recipe</em> is a String description for the way to
446 * construct a concatenated String from the arguments and constants. The
447 * recipe is processed from left to right, and each character represents an
448 * input to concatenation. Recipe characters mean:
449 *
450 * <ul>
451 *
452 * <li><em>\1 (Unicode point 0001)</em>: an ordinary argument. This
453 * input is passed through dynamic argument, and is provided during the
454 * concatenation method invocation. This input can be null.</li>
455 *
456 * <li><em>\2 (Unicode point 0002):</em> a constant. This input passed
457 * through static bootstrap argument. This constant can be any value
458 * representable in constant pool. If necessary, the factory would call
459 * {@code toString} to perform a one-time String conversion.</li>
460 *
461 * <li><em>Any other char value:</em> a single character constant.</li>
462 * </ul>
463 *
464 * <p>Assume the linkage arguments are as follows:
465 *
466 * <ul>
467 * <li>{@code concatType}, describing the {@code CallSite} signature</li>
468 * <li>{@code recipe}, describing the String recipe</li>
469 * <li>{@code constants}, the vararg array of constants</li>
470 * </ul>
471 *
472 * <p>Then the following linkage invariants must hold:
473 *
474 * <ul>
475 * <li>The parameter count in {@code concatType} is less than or equal to
476 * 200</li>
477 *
478 * <li>The parameter count in {@code concatType} equals to number of \1 tags
479 * in {@code recipe}</li>
480 *
481 * <li>The return type in {@code concatType} is assignable
482 * from {@link java.lang.String}, and matches the return type of the
483 * returned {@link MethodHandle}</li>
484 *
485 * <li>The number of elements in {@code constants} equals to number of \2
486 * tags in {@code recipe}</li>
487 * </ul>
488 *
489 * @param lookup Represents a lookup context with the accessibility
490 * privileges of the caller. When used with {@code
491 * invokedynamic}, this is stacked automatically by the
492 * VM.
493 * @param name The name of the method to implement. This name is
494 * arbitrary, and has no meaning for this linkage method.
495 * When used with {@code invokedynamic}, this is provided
496 * by the {@code NameAndType} of the {@code InvokeDynamic}
497 * structure and is stacked automatically by the VM.
498 * @param concatType The expected signature of the {@code CallSite}. The
499 * parameter types represent the types of dynamic concatenation
500 * arguments; the return type is always assignable from {@link
501 * java.lang.String}. When used with {@code
502 * invokedynamic}, this is provided by the {@code
503 * NameAndType} of the {@code InvokeDynamic} structure and
504 * is stacked automatically by the VM.
505 * @param recipe Concatenation recipe, described above.
506 * @param constants A vararg parameter representing the constants passed to
507 * the linkage method.
508 * @return a CallSite whose target can be used to perform String
509 * concatenation, with dynamic concatenation arguments described by the given
510 * {@code concatType}.
511 * @throws StringConcatException If any of the linkage invariants described
512 * here are violated.
513 * @throws NullPointerException If any of the incoming arguments is null, or
514 * any constant in {@code recipe} is null.
515 * This will never happen when a bootstrap method
516 * is called with invokedynamic.
517 * @apiNote Code generators have three distinct ways to process a constant
518 * string operand S in a string concatenation expression. First, S can be
519 * materialized as a reference (using ldc) and passed as an ordinary argument
520 * (recipe '\1'). Or, S can be stored in the constant pool and passed as a
521 * constant (recipe '\2') . Finally, if S contains neither of the recipe
522 * tag characters ('\1', '\2') then S can be interpolated into the recipe
523 * itself, causing its characters to be inserted into the result.
524 *
525 * @jls 5.1.11 String Conversion
526 * @jls 15.18.1 String Concatenation Operator +
527 */
528 public static CallSite makeConcatWithConstants(MethodHandles.Lookup lookup,
529 String name,
530 MethodType concatType,
531 String recipe,
532 Object... constants) throws StringConcatException {
533 if (DEBUG) {
534 System.out.println("StringConcatFactory " + STRATEGY + " is here for " + concatType + ", {" + recipe + "}, " + Arrays.toString(constants));
535 }
536
537 return doStringConcat(lookup, name, concatType, false, recipe, constants);
538 }
539
540 private static CallSite doStringConcat(MethodHandles.Lookup lookup,
541 String name,
542 MethodType concatType,
543 boolean generateRecipe,
544 String recipe,
545 Object... constants) throws StringConcatException {
546 Objects.requireNonNull(lookup, "Lookup is null");
547 Objects.requireNonNull(name, "Name is null");
548 Objects.requireNonNull(concatType, "Concat type is null");
549 Objects.requireNonNull(constants, "Constants are null");
550
551 for (Object o : constants) {
552 Objects.requireNonNull(o, "Cannot accept null constants");
553 }
554
555 int cCount = 0;
556 int oCount = 0;
557 if (generateRecipe) {
558 // Mock the recipe to reuse the concat generator code
559 char[] value = new char[concatType.parameterCount()];
560 Arrays.fill(value, TAG_ARG);
561 recipe = new String(value);
562 oCount = concatType.parameterCount();
563 } else {
564 Objects.requireNonNull(recipe, "Recipe is null");
565
566 for (int i = 0; i < recipe.length(); i++) {
567 char c = recipe.charAt(i);
568 if (c == TAG_CONST) cCount++;
569 if (c == TAG_ARG) oCount++;
570 }
571 }
572
573 if (oCount != concatType.parameterCount()) {
574 throw new StringConcatException(
575 "Mismatched number of concat arguments: recipe wants " +
576 oCount +
577 " arguments, but signature provides " +
578 concatType.parameterCount());
579 }
580
581 if (cCount != constants.length) {
582 throw new StringConcatException(
583 "Mismatched number of concat constants: recipe wants " +
584 cCount +
585 " constants, but only " +
586 constants.length +
587 " are passed");
588 }
589
590 if (!concatType.returnType().isAssignableFrom(String.class)) {
591 throw new StringConcatException(
592 "The return type should be compatible with String, but it is " +
593 concatType.returnType());
594 }
595
596 if (concatType.parameterCount() > MAX_INDY_CONCAT_ARG_SLOTS) {
597 throw new StringConcatException("Too many concat argument slots: " +
598 concatType.parameterCount() +
599 ", can only accept " +
600 MAX_INDY_CONCAT_ARG_SLOTS);
601 }
602
603 MethodType mt = adaptType(concatType);
604
605 Recipe rec = new Recipe(recipe, constants);
606
607 MethodHandle mh;
608 if (CACHE_ENABLE) {
609 Key key = new Key(mt, rec);
610 mh = CACHE.get(key);
611 if (mh == null) {
612 mh = generate(lookup, mt, rec);
613 CACHE.put(key, mh);
614 }
615 } else {
616 mh = generate(lookup, mt, rec);
617 }
618 return new ConstantCallSite(mh.asType(concatType));
619 }
620
621 /**
622 * Adapt method type to an API we are going to use.
623 *
624 * This strips the concrete classes from the signatures, thus preventing
625 * class leakage when we cache the concatenation stubs.
626 *
627 * @param args actual argument types
628 * @return argument types the strategy is going to use
629 */
630 private static MethodType adaptType(MethodType args) {
631 Class<?>[] ptypes = args.parameterArray();
632 boolean changed = false;
633 for (int i = 0; i < ptypes.length; i++) {
634 Class<?> ptype = ptypes[i];
635 if (!ptype.isPrimitive() &&
636 ptype != String.class &&
637 ptype != Object.class) { // truncate to Object
638 ptypes[i] = Object.class;
639 changed = true;
640 }
641 // else other primitives or String or Object (unchanged)
642 }
643 return changed
644 ? MethodType.methodType(args.returnType(), ptypes)
645 : args;
646 }
647
648 private static MethodHandle generate(Lookup lookup, MethodType mt, Recipe recipe) throws StringConcatException {
649 try {
650 switch (STRATEGY) {
651 case BC_SB:
652 return BytecodeStringBuilderStrategy.generate(lookup, mt, recipe, Mode.DEFAULT);
653 case BC_SB_SIZED:
654 return BytecodeStringBuilderStrategy.generate(lookup, mt, recipe, Mode.SIZED);
655 case BC_SB_SIZED_EXACT:
656 return BytecodeStringBuilderStrategy.generate(lookup, mt, recipe, Mode.SIZED_EXACT);
657 case MH_SB_SIZED:
658 return MethodHandleStringBuilderStrategy.generate(mt, recipe, Mode.SIZED);
659 case MH_SB_SIZED_EXACT:
660 return MethodHandleStringBuilderStrategy.generate(mt, recipe, Mode.SIZED_EXACT);
661 case MH_INLINE_SIZED_EXACT:
662 return MethodHandleInlineCopyStrategy.generate(mt, recipe);
663 default:
664 throw new StringConcatException("Concatenation strategy " + STRATEGY + " is not implemented");
665 }
666 } catch (Throwable t) {
667 throw new StringConcatException("Generator failed", t);
668 }
669 }
670
671 private enum Mode {
672 DEFAULT(false, false),
673 SIZED(true, false),
674 SIZED_EXACT(true, true);
675
676 private final boolean sized;
677 private final boolean exact;
678
679 Mode(boolean sized, boolean exact) {
680 this.sized = sized;
681 this.exact = exact;
682 }
683
684 boolean isSized() {
685 return sized;
686 }
687
688 boolean isExact() {
689 return exact;
690 }
691 }
692
693 /**
694 * Bytecode StringBuilder strategy.
695 *
696 * <p>This strategy operates in three modes, gated by {@link Mode}.
697 *
698 * <p><b>{@link Strategy#BC_SB}: "bytecode StringBuilder".</b>
699 *
700 * <p>This strategy spins up the bytecode that has the same StringBuilder
701 * chain javac would otherwise emit. This strategy uses only the public API,
702 * and comes as the baseline for the current JDK behavior. On other words,
703 * this strategy moves the javac generated bytecode to runtime. The
704 * generated bytecode is loaded via Unsafe.defineAnonymousClass, but with
705 * the caller class coming from the BSM -- in other words, the protection
706 * guarantees are inherited from the method where invokedynamic was
707 * originally called. This means, among other things, that the bytecode is
708 * verified for all non-JDK uses.
709 *
710 * <p><b>{@link Strategy#BC_SB_SIZED}: "bytecode StringBuilder, but
711 * sized".</b>
712 *
713 * <p>This strategy acts similarly to {@link Strategy#BC_SB}, but it also
714 * tries to guess the capacity required for StringBuilder to accept all
715 * arguments without resizing. This strategy only makes an educated guess:
716 * it only guesses the space required for known types (e.g. primitives and
717 * Strings), but does not otherwise convert arguments. Therefore, the
718 * capacity estimate may be wrong, and StringBuilder may have to
719 * transparently resize or trim when doing the actual concatenation. While
720 * this does not constitute a correctness issue (in the end, that what BC_SB
721 * has to do anyway), this does pose a potential performance problem.
722 *
723 * <p><b>{@link Strategy#BC_SB_SIZED_EXACT}: "bytecode StringBuilder, but
724 * sized exactly".</b>
725 *
726 * <p>This strategy improves on @link Strategy#BC_SB_SIZED}, by first
727 * converting all arguments to String in order to get the exact capacity
728 * StringBuilder should have. The conversion is done via the public
729 * String.valueOf and/or Object.toString methods, and does not touch any
730 * private String API.
731 */
732 private static final class BytecodeStringBuilderStrategy {
733 static final Unsafe UNSAFE = Unsafe.getUnsafe();
734 static final int CLASSFILE_VERSION = 52;
735 static final String NAME_FACTORY = "concat";
736 static final String CLASS_NAME = "java/lang/String$Concat";
737
738 private BytecodeStringBuilderStrategy() {
739 // no instantiation
740 }
741
742 private static MethodHandle generate(MethodHandles.Lookup lookup, MethodType args, Recipe recipe, Mode mode) throws Exception {
743 ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS + ClassWriter.COMPUTE_FRAMES);
744
745 cw.visit(CLASSFILE_VERSION,
746 ACC_SUPER + ACC_PUBLIC + ACC_FINAL + ACC_SYNTHETIC,
747 CLASS_NAME,
748 null,
749 "java/lang/Object",
750 null
751 );
752
753 MethodVisitor mv = cw.visitMethod(
754 ACC_PUBLIC + ACC_STATIC + ACC_FINAL,
755 NAME_FACTORY,
756 args.toMethodDescriptorString(),
757 null,
758 null);
759
760 mv.visitAnnotation("Ljdk/internal/vm/annotation/ForceInline;", true);
761 mv.visitCode();
762
763 Class<?>[] arr = args.parameterArray();
764 boolean[] guaranteedNonNull = new boolean[arr.length];
765
766 if (mode.isExact()) {
767 /*
768 In exact mode, we need to convert all arguments to their String representations,
769 as this allows to compute their String sizes exactly. We cannot use private
770 methods for primitives in here, therefore we need to convert those as well.
771
772 We also record what arguments are guaranteed to be non-null as the result
773 of the conversion. String.valueOf does the null checks for us. The only
774 corner case to take care of is String.valueOf(Object) returning null itself.
775
776 Also, if any conversion happened, then the slot indices in the incoming
777 arguments are not equal to the final local maps. The only case this may break
778 is when converting 2-slot long/double argument to 1-slot String. Therefore,
779 we get away with tracking modified offset, since no conversion can overwrite
780 the upcoming the argument.
781 */
782
783 int off = 0;
784 int modOff = 0;
785 for (int c = 0; c < arr.length; c++) {
786 Class<?> cl = arr[c];
787 if (cl == String.class) {
788 if (off != modOff) {
789 mv.visitIntInsn(getLoadOpcode(cl), off);
790 mv.visitIntInsn(ASTORE, modOff);
791 }
792 } else {
793 mv.visitIntInsn(getLoadOpcode(cl), off);
794 mv.visitMethodInsn(
795 INVOKESTATIC,
796 "java/lang/String",
797 "valueOf",
798 getStringValueOfDesc(cl),
799 false
800 );
801 mv.visitIntInsn(ASTORE, modOff);
802 arr[c] = String.class;
803 guaranteedNonNull[c] = cl.isPrimitive();
804 }
805 off += getParameterSize(cl);
806 modOff += getParameterSize(String.class);
807 }
808 }
809
810 if (mode.isSized()) {
811 /*
812 When operating in sized mode (this includes exact mode), it makes sense to make
813 StringBuilder append chains look familiar to OptimizeStringConcat. For that, we
814 need to do null-checks early, not make the append chain shape simpler.
815 */
816
817 int off = 0;
818 for (RecipeElement el : recipe.getElements()) {
819 switch (el.getTag()) {
820 case CONST: {
821 // Guaranteed non-null, no null check required.
822 break;
823 }
824 case ARG: {
825 // Null-checks are needed only for String arguments, and when a previous stage
826 // did not do implicit null-checks. If a String is null, we eagerly replace it
827 // with "null" constant. Note, we omit Objects here, because we don't call
828 // .length() on them down below.
829 int ac = el.getArgPos();
830 Class<?> cl = arr[ac];
831 if (cl == String.class && !guaranteedNonNull[ac]) {
832 Label l0 = new Label();
833 mv.visitIntInsn(ALOAD, off);
834 mv.visitJumpInsn(IFNONNULL, l0);
835 mv.visitLdcInsn("null");
836 mv.visitIntInsn(ASTORE, off);
837 mv.visitLabel(l0);
838 }
839 off += getParameterSize(cl);
840 break;
841 }
842 default:
843 throw new StringConcatException("Unhandled tag: " + el.getTag());
844 }
845 }
846 }
847
848 // Prepare StringBuilder instance
849 mv.visitTypeInsn(NEW, "java/lang/StringBuilder");
850 mv.visitInsn(DUP);
851
852 if (mode.isSized()) {
853 /*
854 Sized mode requires us to walk through the arguments, and estimate the final length.
855 In exact mode, this will operate on Strings only. This code would accumulate the
856 final length on stack.
857 */
858 int len = 0;
859 int off = 0;
860
861 mv.visitInsn(ICONST_0);
862
863 for (RecipeElement el : recipe.getElements()) {
864 switch (el.getTag()) {
865 case CONST: {
866 Object cnst = el.getValue();
867 len += cnst.toString().length();
868 break;
869 }
870 case ARG: {
871 /*
872 If an argument is String, then we can call .length() on it. Sized/Exact modes have
873 converted arguments for us. If an argument is primitive, we can provide a guess
874 for its String representation size.
875 */
876 Class<?> cl = arr[el.getArgPos()];
877 if (cl == String.class) {
878 mv.visitIntInsn(ALOAD, off);
879 mv.visitMethodInsn(
880 INVOKEVIRTUAL,
881 "java/lang/String",
882 "length",
883 "()I",
884 false
885 );
886 mv.visitInsn(IADD);
887 } else if (cl.isPrimitive()) {
888 len += estimateSize(cl);
889 }
890 off += getParameterSize(cl);
891 break;
892 }
893 default:
894 throw new StringConcatException("Unhandled tag: " + el.getTag());
895 }
896 }
897
898 // Constants have non-zero length, mix in
899 if (len > 0) {
900 iconst(mv, len);
901 mv.visitInsn(IADD);
902 }
903
904 mv.visitMethodInsn(
905 INVOKESPECIAL,
906 "java/lang/StringBuilder",
907 "<init>",
908 "(I)V",
909 false
910 );
911 } else {
912 mv.visitMethodInsn(
913 INVOKESPECIAL,
914 "java/lang/StringBuilder",
915 "<init>",
916 "()V",
917 false
918 );
919 }
920
921 // At this point, we have a blank StringBuilder on stack, fill it in with .append calls.
922 {
923 int off = 0;
924 for (RecipeElement el : recipe.getElements()) {
925 String desc;
926 switch (el.getTag()) {
927 case CONST: {
928 Object cnst = el.getValue();
929 mv.visitLdcInsn(cnst);
930 desc = getSBAppendDesc(cnst.getClass());
931 break;
932 }
933 case ARG: {
934 Class<?> cl = arr[el.getArgPos()];
935 mv.visitVarInsn(getLoadOpcode(cl), off);
936 off += getParameterSize(cl);
937 desc = getSBAppendDesc(cl);
938 break;
939 }
940 default:
941 throw new StringConcatException("Unhandled tag: " + el.getTag());
942 }
943 mv.visitMethodInsn(
944 INVOKEVIRTUAL,
945 "java/lang/StringBuilder",
946 "append",
947 desc,
948 false
949 );
950 }
951 }
952
953 if (DEBUG && mode.isExact()) {
954 /*
955 Exactness checks compare the final StringBuilder.capacity() with a resulting
956 String.length(). If these values disagree, that means StringBuilder had to perform
957 storage trimming, which defeats the purpose of exact strategies.
958 */
959
960 /*
961 The logic for this check is as follows:
962
963 Stack before: Op:
964 (SB) dup, dup
965 (SB, SB, SB) capacity()
966 (int, SB, SB) swap
967 (SB, int, SB) toString()
968 (S, int, SB) length()
969 (int, int, SB) if_icmpeq
970 (SB) <end>
971
972 Note that it leaves the same StringBuilder on exit, like the one on enter.
973 */
974
975 mv.visitInsn(DUP);
976 mv.visitInsn(DUP);
977
978 mv.visitMethodInsn(
979 INVOKEVIRTUAL,
980 "java/lang/StringBuilder",
981 "capacity",
982 "()I",
983 false
984 );
985
986 mv.visitInsn(SWAP);
987
988 mv.visitMethodInsn(
989 INVOKEVIRTUAL,
990 "java/lang/StringBuilder",
991 "toString",
992 "()Ljava/lang/String;",
993 false
994 );
995
996 mv.visitMethodInsn(
997 INVOKEVIRTUAL,
998 "java/lang/String",
999 "length",
1000 "()I",
1001 false
1002 );
1003
1004 Label l0 = new Label();
1005 mv.visitJumpInsn(IF_ICMPEQ, l0);
1006
1007 mv.visitTypeInsn(NEW, "java/lang/AssertionError");
1008 mv.visitInsn(DUP);
1009 mv.visitLdcInsn("Failed exactness check");
1010 mv.visitMethodInsn(INVOKESPECIAL,
1011 "java/lang/AssertionError",
1012 "<init>",
1013 "(Ljava/lang/Object;)V",
1014 false);
1015 mv.visitInsn(ATHROW);
1016
1017 mv.visitLabel(l0);
1018 }
1019
1020 mv.visitMethodInsn(
1021 INVOKEVIRTUAL,
1022 "java/lang/StringBuilder",
1023 "toString",
1024 "()Ljava/lang/String;",
1025 false
1026 );
1027
1028 mv.visitInsn(ARETURN);
1029
1030 mv.visitMaxs(-1, -1);
1031 mv.visitEnd();
1032 cw.visitEnd();
1033
1034 Class<?> targetClass = lookup.lookupClass();
1035 final byte[] classBytes = cw.toByteArray();
1036 final Class<?> innerClass = UNSAFE.defineAnonymousClass(targetClass, classBytes, null);
1037
1038 try {
1039 UNSAFE.ensureClassInitialized(innerClass);
1040 return lookup.findStatic(innerClass, NAME_FACTORY, args);
1041 } catch (ReflectiveOperationException e) {
1042 throw new StringConcatException("Exception finding constructor", e);
1043 }
1044 }
1045
1046 private static String getSBAppendDesc(Class<?> cl) {
1047 if (cl.isPrimitive()) {
1048 if (cl == Integer.TYPE || cl == Byte.TYPE || cl == Short.TYPE) {
1049 return "(I)Ljava/lang/StringBuilder;";
1050 } else if (cl == Boolean.TYPE) {
1051 return "(Z)Ljava/lang/StringBuilder;";
1052 } else if (cl == Character.TYPE) {
1053 return "(C)Ljava/lang/StringBuilder;";
1054 } else if (cl == Double.TYPE) {
1055 return "(D)Ljava/lang/StringBuilder;";
1056 } else if (cl == Float.TYPE) {
1057 return "(F)Ljava/lang/StringBuilder;";
1058 } else if (cl == Long.TYPE) {
1059 return "(J)Ljava/lang/StringBuilder;";
1060 } else {
1061 throw new IllegalStateException("Unhandled primitive StringBuilder.append: " + cl);
1062 }
1063 } else if (cl == String.class) {
1064 return "(Ljava/lang/String;)Ljava/lang/StringBuilder;";
1065 } else {
1066 return "(Ljava/lang/Object;)Ljava/lang/StringBuilder;";
1067 }
1068 }
1069
1070 private static String getStringValueOfDesc(Class<?> cl) {
1071 if (cl.isPrimitive()) {
1072 if (cl == Integer.TYPE || cl == Byte.TYPE || cl == Short.TYPE) {
1073 return "(I)Ljava/lang/String;";
1074 } else if (cl == Boolean.TYPE) {
1075 return "(Z)Ljava/lang/String;";
1076 } else if (cl == Character.TYPE) {
1077 return "(C)Ljava/lang/String;";
1078 } else if (cl == Double.TYPE) {
1079 return "(D)Ljava/lang/String;";
1080 } else if (cl == Float.TYPE) {
1081 return "(F)Ljava/lang/String;";
1082 } else if (cl == Long.TYPE) {
1083 return "(J)Ljava/lang/String;";
1084 } else {
1085 throw new IllegalStateException("Unhandled String.valueOf: " + cl);
1086 }
1087 } else if (cl == String.class) {
1088 return "(Ljava/lang/String;)Ljava/lang/String;";
1089 } else {
1090 return "(Ljava/lang/Object;)Ljava/lang/String;";
1091 }
1092 }
1093
1094 /**
1095 * The following method is copied from
1096 * org.objectweb.asm.commons.InstructionAdapter. Part of ASM: a very small
1097 * and fast Java bytecode manipulation framework.
1098 * Copyright (c) 2000-2005 INRIA, France Telecom All rights reserved.
1099 */
1100 private static void iconst(MethodVisitor mv, final int cst) {
1101 if (cst >= -1 && cst <= 5) {
1102 mv.visitInsn(Opcodes.ICONST_0 + cst);
1103 } else if (cst >= Byte.MIN_VALUE && cst <= Byte.MAX_VALUE) {
1104 mv.visitIntInsn(Opcodes.BIPUSH, cst);
1105 } else if (cst >= Short.MIN_VALUE && cst <= Short.MAX_VALUE) {
1106 mv.visitIntInsn(Opcodes.SIPUSH, cst);
1107 } else {
1108 mv.visitLdcInsn(cst);
1109 }
1110 }
1111
1112 private static int getLoadOpcode(Class<?> c) {
1113 if (c == Void.TYPE) {
1114 throw new InternalError("Unexpected void type of load opcode");
1115 }
1116 return ILOAD + getOpcodeOffset(c);
1117 }
1118
1119 private static int getOpcodeOffset(Class<?> c) {
1120 if (c.isPrimitive()) {
1121 if (c == Long.TYPE) {
1122 return 1;
1123 } else if (c == Float.TYPE) {
1124 return 2;
1125 } else if (c == Double.TYPE) {
1126 return 3;
1127 }
1128 return 0;
1129 } else {
1130 return 4;
1131 }
1132 }
1133
1134 private static int getParameterSize(Class<?> c) {
1135 if (c == Void.TYPE) {
1136 return 0;
1137 } else if (c == Long.TYPE || c == Double.TYPE) {
1138 return 2;
1139 }
1140 return 1;
1141 }
1142 }
1143
1144 /**
1145 * MethodHandle StringBuilder strategy.
1146 *
1147 * <p>This strategy operates in two modes, gated by {@link Mode}.
1148 *
1149 * <p><b>{@link Strategy#MH_SB_SIZED}: "MethodHandles StringBuilder,
1150 * sized".</b>
1151 *
1152 * <p>This strategy avoids spinning up the bytecode by building the
1153 * computation on MethodHandle combinators. The computation is built with
1154 * public MethodHandle APIs, resolved from a public Lookup sequence, and
1155 * ends up calling the public StringBuilder API. Therefore, this strategy
1156 * does not use any private API at all, even the Unsafe.defineAnonymousClass,
1157 * since everything is handled under cover by java.lang.invoke APIs.
1158 *
1159 * <p><b>{@link Strategy#MH_SB_SIZED_EXACT}: "MethodHandles StringBuilder,
1160 * sized exactly".</b>
1161 *
1162 * <p>This strategy improves on @link Strategy#MH_SB_SIZED}, by first
1163 * converting all arguments to String in order to get the exact capacity
1164 * StringBuilder should have. The conversion is done via the public
1165 * String.valueOf and/or Object.toString methods, and does not touch any
1166 * private String API.
1167 */
1168 private static final class MethodHandleStringBuilderStrategy {
1169
1170 private MethodHandleStringBuilderStrategy() {
1171 // no instantiation
1172 }
1173
1174 private static MethodHandle generate(MethodType mt, Recipe recipe, Mode mode) throws Exception {
1175 int pc = mt.parameterCount();
1176
1177 Class<?>[] ptypes = mt.parameterArray();
1178 MethodHandle[] filters = new MethodHandle[ptypes.length];
1179 for (int i = 0; i < ptypes.length; i++) {
1180 MethodHandle filter;
1181 switch (mode) {
1182 case SIZED:
1183 // In sized mode, we convert all references and floats/doubles
1184 // to String: there is no specialization for different
1185 // classes in StringBuilder API, and it will convert to
1186 // String internally anyhow.
1187 filter = Stringifiers.forMost(ptypes[i]);
1188 break;
1189 case SIZED_EXACT:
1190 // In exact mode, we convert everything to String:
1191 // this helps to compute the storage exactly.
1192 filter = Stringifiers.forAny(ptypes[i]);
1193 break;
1194 default:
1195 throw new StringConcatException("Not supported");
1196 }
1197 if (filter != null) {
1198 filters[i] = filter;
1199 ptypes[i] = filter.type().returnType();
1200 }
1201 }
1202
1203 List<Class<?>> ptypesList = Arrays.asList(ptypes);
1204 MethodHandle[] lengthers = new MethodHandle[pc];
1205
1206 // Figure out lengths: constants' lengths can be deduced on the spot.
1207 // All reference arguments were filtered to String in the combinators below, so we can
1208 // call the usual String.length(). Primitive values string sizes can be estimated.
1209 int initial = 0;
1210 for (RecipeElement el : recipe.getElements()) {
1211 switch (el.getTag()) {
1212 case CONST: {
1213 Object cnst = el.getValue();
1214 initial += cnst.toString().length();
1215 break;
1216 }
1217 case ARG: {
1218 final int i = el.getArgPos();
1219 Class<?> type = ptypesList.get(i);
1220 if (type.isPrimitive()) {
1221 MethodHandle est = MethodHandles.constant(int.class, estimateSize(type));
1222 est = MethodHandles.dropArguments(est, 0, type);
1223 lengthers[i] = est;
1224 } else {
1225 lengthers[i] = STRING_LENGTH;
1226 }
1227 break;
1228 }
1229 default:
1230 throw new StringConcatException("Unhandled tag: " + el.getTag());
1231 }
1232 }
1233
1234 // Create (StringBuilder, <args>) shape for appending:
1235 MethodHandle builder = MethodHandles.dropArguments(MethodHandles.identity(StringBuilder.class), 1, ptypesList);
1236
1237 // Compose append calls. This is done in reverse because the application order is
1238 // reverse as well.
1239 for (RecipeElement el : recipe.getElementsReversed()) {
1240 MethodHandle appender;
1241 switch (el.getTag()) {
1242 case CONST: {
1243 Object constant = el.getValue();
1244 MethodHandle mh = appender(adaptToStringBuilder(constant.getClass()));
1245 appender = MethodHandles.insertArguments(mh, 1, constant);
1246 break;
1247 }
1248 case ARG: {
1249 int ac = el.getArgPos();
1250 appender = appender(ptypesList.get(ac));
1251
1252 // Insert dummy arguments to match the prefix in the signature.
1253 // The actual appender argument will be the ac-ith argument.
1254 if (ac != 0) {
1255 appender = MethodHandles.dropArguments(appender, 1, ptypesList.subList(0, ac));
1256 }
1257 break;
1258 }
1259 default:
1260 throw new StringConcatException("Unhandled tag: " + el.getTag());
1261 }
1262 builder = MethodHandles.foldArguments(builder, appender);
1263 }
1264
1265 // Build the sub-tree that adds the sizes and produces a StringBuilder:
1266
1267 // a) Start with the reducer that accepts all arguments, plus one
1268 // slot for the initial value. Inject the initial value right away.
1269 // This produces (<ints>)int shape:
1270 MethodHandle sum = getReducerFor(pc + 1);
1271 MethodHandle adder = MethodHandles.insertArguments(sum, 0, initial);
1272
1273 // b) Apply lengthers to transform arguments to lengths, producing (<args>)int
1274 adder = MethodHandles.filterArguments(adder, 0, lengthers);
1275
1276 // c) Instantiate StringBuilder (<args>)int -> (<args>)StringBuilder
1277 MethodHandle newBuilder = MethodHandles.filterReturnValue(adder, NEW_STRING_BUILDER);
1278
1279 // d) Fold in StringBuilder constructor, this produces (<args>)StringBuilder
1280 MethodHandle mh = MethodHandles.foldArguments(builder, newBuilder);
1281
1282 // Convert non-primitive arguments to Strings
1283 mh = MethodHandles.filterArguments(mh, 0, filters);
1284
1285 // Convert (<args>)StringBuilder to (<args>)String
1286 if (DEBUG && mode.isExact()) {
1287 mh = MethodHandles.filterReturnValue(mh, BUILDER_TO_STRING_CHECKED);
1288 } else {
1289 mh = MethodHandles.filterReturnValue(mh, BUILDER_TO_STRING);
1290 }
1291
1292 return mh;
1293 }
1294
1295 private static MethodHandle getReducerFor(int cnt) {
1296 return SUMMERS.computeIfAbsent(cnt, SUMMER);
1297 }
1298
1299 private static MethodHandle appender(Class<?> appendType) {
1300 MethodHandle appender = lookupVirtual(MethodHandles.publicLookup(), StringBuilder.class, "append",
1301 StringBuilder.class, adaptToStringBuilder(appendType));
1302
1303 // appenders should return void, this would not modify the target signature during folding
1304 MethodType nt = MethodType.methodType(void.class, StringBuilder.class, appendType);
1305 return appender.asType(nt);
1306 }
1307
1308 private static String toStringChecked(StringBuilder sb) {
1309 String s = sb.toString();
1310 if (s.length() != sb.capacity()) {
1311 throw new AssertionError("Exactness check failed: result length = " + s.length() + ", buffer capacity = " + sb.capacity());
1312 }
1313 return s;
1314 }
1315
1316 private static int sum(int v1, int v2) {
1317 return v1 + v2;
1318 }
1319
1320 private static int sum(int v1, int v2, int v3) {
1321 return v1 + v2 + v3;
1322 }
1323
1324 private static int sum(int v1, int v2, int v3, int v4) {
1325 return v1 + v2 + v3 + v4;
1326 }
1327
1328 private static int sum(int v1, int v2, int v3, int v4, int v5) {
1329 return v1 + v2 + v3 + v4 + v5;
1330 }
1331
1332 private static int sum(int v1, int v2, int v3, int v4, int v5, int v6) {
1333 return v1 + v2 + v3 + v4 + v5 + v6;
1334 }
1335
1336 private static int sum(int v1, int v2, int v3, int v4, int v5, int v6, int v7) {
1337 return v1 + v2 + v3 + v4 + v5 + v6 + v7;
1338 }
1339
1340 private static int sum(int v1, int v2, int v3, int v4, int v5, int v6, int v7, int v8) {
1341 return v1 + v2 + v3 + v4 + v5 + v6 + v7 + v8;
1342 }
1343
1344 private static int sum(int initial, int[] vs) {
1345 int sum = initial;
1346 for (int v : vs) {
1347 sum += v;
1348 }
1349 return sum;
1350 }
1351
1352 private static final ConcurrentMap<Integer, MethodHandle> SUMMERS;
1353
1354 // This one is deliberately non-lambdified to optimize startup time:
1355 private static final Function<Integer, MethodHandle> SUMMER = new Function<Integer, MethodHandle>() {
1356 @Override
1357 public MethodHandle apply(Integer cnt) {
1358 if (cnt == 1) {
1359 return MethodHandles.identity(int.class);
1360 } else if (cnt <= 8) {
1361 // Variable-arity collectors are not as efficient as small-count methods,
1362 // unroll some initial sizes.
1363 Class<?>[] cls = new Class<?>[cnt];
1364 Arrays.fill(cls, int.class);
1365 return lookupStatic(Lookup.IMPL_LOOKUP, MethodHandleStringBuilderStrategy.class, "sum", int.class, cls);
1366 } else {
1367 return lookupStatic(Lookup.IMPL_LOOKUP, MethodHandleStringBuilderStrategy.class, "sum", int.class, int.class, int[].class)
1368 .asCollector(int[].class, cnt - 1);
1369 }
1370 }
1371 };
1372
1373 private static final MethodHandle NEW_STRING_BUILDER, STRING_LENGTH, BUILDER_TO_STRING, BUILDER_TO_STRING_CHECKED;
1374
1375 static {
1376 SUMMERS = new ConcurrentHashMap<>();
1377 Lookup publicLookup = MethodHandles.publicLookup();
1378 NEW_STRING_BUILDER = lookupConstructor(publicLookup, StringBuilder.class, int.class);
1379 STRING_LENGTH = lookupVirtual(publicLookup, String.class, "length", int.class);
1380 BUILDER_TO_STRING = lookupVirtual(publicLookup, StringBuilder.class, "toString", String.class);
1381 if (DEBUG) {
1382 BUILDER_TO_STRING_CHECKED = lookupStatic(MethodHandles.Lookup.IMPL_LOOKUP,
1383 MethodHandleStringBuilderStrategy.class, "toStringChecked", String.class, StringBuilder.class);
1384 } else {
1385 BUILDER_TO_STRING_CHECKED = null;
1386 }
1387 }
1388
1389 }
1390
1391
1392 /**
1393 * <p><b>{@link Strategy#MH_INLINE_SIZED_EXACT}: "MethodHandles inline,
1394 * sized exactly".</b>
1395 *
1396 * <p>This strategy replicates what StringBuilders are doing: it builds the
1397 * byte[] array on its own and passes that byte[] array to String
1398 * constructor. This strategy requires access to some private APIs in JDK,
1399 * most notably, the read-only Integer/Long.stringSize methods that measure
1400 * the character length of the integers, and the private String constructor
1401 * that accepts byte[] arrays without copying. While this strategy assumes a
1402 * particular implementation details for String, this opens the door for
1403 * building a very optimal concatenation sequence. This is the only strategy
1404 * that requires porting if there are private JDK changes occur.
1405 */
1406 private static final class MethodHandleInlineCopyStrategy {
1407
1408 private MethodHandleInlineCopyStrategy() {
1409 // no instantiation
1410 }
1411
1412 static MethodHandle generate(MethodType mt, Recipe recipe) throws Throwable {
1413
1414 // Create filters and obtain filtered parameter types. Filters would be used in the beginning
1415 // to convert the incoming arguments into the arguments we can process (e.g. Objects -> Strings).
1416 // The filtered argument type list is used all over in the combinators below.
1417 Class<?>[] ptypes = mt.parameterArray();
1418 MethodHandle[] filters = null;
1419 for (int i = 0; i < ptypes.length; i++) {
1420 MethodHandle filter = Stringifiers.forMost(ptypes[i]);
1421 if (filter != null) {
1422 if (filters == null) {
1423 filters = new MethodHandle[ptypes.length];
1424 }
1425 filters[i] = filter;
1426 ptypes[i] = filter.type().returnType();
1427 }
1428 }
1429 List<Class<?>> ptypesList = Arrays.asList(ptypes);
1430
1431 // Start building the combinator tree. The tree "starts" with (<parameters>)String, and "finishes"
1432 // with the (int, byte[], byte)String in String helper. The combinators are assembled bottom-up,
1433 // which makes the code arguably hard to read.
1434
1435 // Drop all remaining parameter types, leave only helper arguments:
1436 MethodHandle mh;
1437
1438 mh = MethodHandles.dropArguments(NEW_STRING, 2, ptypes);
1439 mh = MethodHandles.dropArguments(mh, 0, int.class);
1440
1441 // In debug mode, check that remaining index is zero.
1442 if (DEBUG) {
1443 mh = MethodHandles.filterArgument(mh, 0, CHECK_INDEX);
1444 }
1445
1446 // Mix in prependers. This happens when (int, byte[], byte) = (index, storage, coder) is already
1447 // known from the combinators below. We are assembling the string backwards, so "index" is the
1448 // *ending* index.
1449 for (RecipeElement el : recipe.getElements()) {
1450 MethodHandle prepender;
1451 switch (el.getTag()) {
1452 case CONST: {
1453 Object cnst = el.getValue();
1454 prepender = MethodHandles.insertArguments(prepender(cnst.getClass()), 3, cnst);
1455 break;
1456 }
1457 case ARG: {
1458 int pos = el.getArgPos();
1459 prepender = selectArgument(prepender(ptypesList.get(pos)), 3, ptypesList, pos);
1460 break;
1461 }
1462 default:
1463 throw new StringConcatException("Unhandled tag: " + el.getTag());
1464 }
1465
1466 // Remove "old" index from arguments
1467 mh = MethodHandles.dropArguments(mh, 1, int.class);
1468
1469 // Do the prepend, and put "new" index at index 0
1470 mh = MethodHandles.foldArguments(mh, prepender);
1471 }
1472
1473 // Prepare the argument list for prepending. The tree below would instantiate
1474 // the storage byte[] into argument 0, so we need to swap "storage" and "index".
1475 // The index at this point equals to "size", and resides at argument 1.
1476 {
1477 MethodType nmt = mh.type()
1478 .changeParameterType(0, byte[].class)
1479 .changeParameterType(1, int.class);
1480 mh = MethodHandles.permuteArguments(mh, nmt, swap10(nmt.parameterCount()));
1481 }
1482
1483 // Fold in byte[] instantiation at argument 0.
1484 MethodHandle combiner = MethodHandles.dropArguments(NEW_ARRAY, 2, ptypesList);
1485 mh = MethodHandles.foldArguments(mh, combiner);
1486
1487 // Start combining length and coder mixers.
1488 //
1489 // Length is easy: constant lengths can be computed on the spot, and all non-constant
1490 // shapes have been either converted to Strings, or explicit methods for getting the
1491 // string length out of primitives are provided.
1492 //
1493 // Coders are more interesting. Only Object, String and char arguments (and constants)
1494 // can have non-Latin1 encoding. It is easier to blindly convert constants to String,
1495 // and deduce the coder from there. Arguments would be either converted to Strings
1496 // during the initial filtering, or handled by primitive specializations in CODER_MIXERS.
1497 //
1498 // The method handle shape after all length and coder mixers is:
1499 // (int, byte, <args>)String = ("index", "coder", <args>)
1500 byte initialCoder = 0; // initial coder
1501 int initialLen = 0; // initial length, in characters
1502 for (RecipeElement el : recipe.getElements()) {
1503 switch (el.getTag()) {
1504 case CONST: {
1505 Object constant = el.getValue();
1506 String s = constant.toString();
1507 initialCoder = (byte) coderMixer(String.class).invoke(initialCoder, s);
1508 initialLen += s.length();
1509 break;
1510 }
1511 case ARG: {
1512 int ac = el.getArgPos();
1513
1514 Class<?> argClass = ptypesList.get(ac);
1515 MethodHandle lm = selectArgument(lengthMixer(argClass), 1, ptypesList, ac);
1516 lm = MethodHandles.dropArguments(lm, 0, byte.class); // (*)
1517 lm = MethodHandles.dropArguments(lm, 2, byte.class);
1518
1519 MethodHandle cm = selectArgument(coderMixer(argClass), 1, ptypesList, ac);
1520 cm = MethodHandles.dropArguments(cm, 0, int.class); // (**)
1521
1522 // Read this bottom up:
1523
1524 // 4. Drop old index and coder, producing ("new-index", "new-coder", <args>)
1525 mh = MethodHandles.dropArguments(mh, 2, int.class, byte.class);
1526
1527 // 3. Compute "new-index", producing ("new-index", "new-coder", "old-index", "old-coder", <args>)
1528 // Length mixer ignores both "new-coder" and "old-coder" due to dropArguments above (*)
1529 mh = MethodHandles.foldArguments(mh, lm);
1530
1531 // 2. Compute "new-coder", producing ("new-coder", "old-index", "old-coder", <args>)
1532 // Coder mixer ignores the "old-index" arg due to dropArguments above (**)
1533 mh = MethodHandles.foldArguments(mh, cm);
1534
1535 // 1. The mh shape here is ("old-index", "old-coder", <args>)
1536 break;
1537 }
1538 default:
1539 throw new StringConcatException("Unhandled tag: " + el.getTag());
1540 }
1541 }
1542
1543 // Insert initial lengths and coders here.
1544 // The method handle shape here is (<args>).
1545 mh = MethodHandles.insertArguments(mh, 0, initialLen, initialCoder);
1546
1547 // Apply filters, converting the arguments:
1548 if (filters != null) {
1549 mh = MethodHandles.filterArguments(mh, 0, filters);
1550 }
1551
1552 return mh;
1553 }
1554
1555 private static int[] swap10(int count) {
1556 int[] perm = new int[count];
1557 perm[0] = 1;
1558 perm[1] = 0;
1559 for (int i = 2; i < count; i++) {
1560 perm[i] = i;
1561 }
1562 return perm;
1563 }
1564
1565 // Adapts: (...prefix..., parameter[pos])R -> (...prefix..., ...parameters...)R
1566 private static MethodHandle selectArgument(MethodHandle mh, int prefix, List<Class<?>> ptypes, int pos) {
1567 if (pos == 0) {
1568 return MethodHandles.dropArguments(mh, prefix + 1, ptypes.subList(1, ptypes.size()));
1569 } else if (pos == ptypes.size() - 1) {
1570 return MethodHandles.dropArguments(mh, prefix, ptypes.subList(0, ptypes.size() - 1));
1571 } else { // 0 < pos < ptypes.size() - 1
1572 MethodHandle t = MethodHandles.dropArguments(mh, prefix, ptypes.subList(0, pos));
1573 return MethodHandles.dropArguments(t, prefix + 1 + pos, ptypes.subList(pos + 1, ptypes.size()));
1574 }
1575 }
1576
1577 @ForceInline
1578 private static byte[] newArray(int length, byte coder) {
1579 return new byte[length << coder];
1580 }
1581
1582 @ForceInline
1583 private static int checkIndex(int index) {
1584 if (index != 0) {
1585 throw new AssertionError("Exactness check failed: " + index + " characters left in the buffer.");
1586 }
1587 return index;
1588 }
1589
1590 private static MethodHandle prepender(Class<?> cl) {
1591 return PREPENDERS.computeIfAbsent(cl, PREPEND);
1592 }
1593
1594 private static MethodHandle coderMixer(Class<?> cl) {
1595 return CODER_MIXERS.computeIfAbsent(cl, CODER_MIX);
1596 }
1597
1598 private static MethodHandle lengthMixer(Class<?> cl) {
1599 return LENGTH_MIXERS.computeIfAbsent(cl, LENGTH_MIX);
1600 }
1601
1602 // This one is deliberately non-lambdified to optimize startup time:
1603 private static final Function<Class<?>, MethodHandle> PREPEND = new Function<Class<?>, MethodHandle>() {
1604 @Override
1605 public MethodHandle apply(Class<?> c) {
1606 return lookupStatic(Lookup.IMPL_LOOKUP, STRING_HELPER, "prepend", int.class, int.class, byte[].class, byte.class, c);
1607 }
1608 };
1609
1610 // This one is deliberately non-lambdified to optimize startup time:
1611 private static final Function<Class<?>, MethodHandle> CODER_MIX = new Function<Class<?>, MethodHandle>() {
1612 @Override
1613 public MethodHandle apply(Class<?> c) {
1614 return lookupStatic(Lookup.IMPL_LOOKUP, STRING_HELPER, "mixCoder", byte.class, byte.class, c);
1615 }
1616 };
1617
1618 // This one is deliberately non-lambdified to optimize startup time:
1619 private static final Function<Class<?>, MethodHandle> LENGTH_MIX = new Function<Class<?>, MethodHandle>() {
1620 @Override
1621 public MethodHandle apply(Class<?> c) {
1622 return lookupStatic(Lookup.IMPL_LOOKUP, STRING_HELPER, "mixLen", int.class, int.class, c);
1623 }
1624 };
1625
1626 private static final MethodHandle NEW_STRING;
1627 private static final MethodHandle CHECK_INDEX;
1628 private static final MethodHandle NEW_ARRAY;
1629 private static final ConcurrentMap<Class<?>, MethodHandle> PREPENDERS;
1630 private static final ConcurrentMap<Class<?>, MethodHandle> LENGTH_MIXERS;
1631 private static final ConcurrentMap<Class<?>, MethodHandle> CODER_MIXERS;
1632 private static final Class<?> STRING_HELPER;
1633
1634 static {
1635 try {
1636 STRING_HELPER = Class.forName("java.lang.StringConcatHelper");
1637 } catch (ClassNotFoundException e) {
1638 throw new AssertionError(e);
1639 }
1640
1641 PREPENDERS = new ConcurrentHashMap<>();
1642 LENGTH_MIXERS = new ConcurrentHashMap<>();
1643 CODER_MIXERS = new ConcurrentHashMap<>();
1644
1645 NEW_STRING = lookupStatic(Lookup.IMPL_LOOKUP, STRING_HELPER, "newString", String.class, byte[].class, byte.class);
1646 NEW_ARRAY = lookupStatic(Lookup.IMPL_LOOKUP, MethodHandleInlineCopyStrategy.class, "newArray", byte[].class, int.class, byte.class);
1647
1648 if (DEBUG) {
1649 CHECK_INDEX = lookupStatic(Lookup.IMPL_LOOKUP, MethodHandleInlineCopyStrategy.class, "checkIndex", int.class, int.class);
1650 } else {
1651 CHECK_INDEX = null;
1652 }
1653 }
1654 }
1655
1656 /**
1657 * Public gateways to public "stringify" methods. These methods have the form String apply(T obj), and normally
1658 * delegate to {@code String.valueOf}, depending on argument's type.
1659 */
1660 private static final class Stringifiers {
1661 private Stringifiers() {
1662 // no instantiation
1663 }
1664
1665 // This one is deliberately non-lambdified to optimize startup time:
1666 private static final Function<Class<?>, MethodHandle> MOST = new Function<Class<?>, MethodHandle>() {
1667 @Override
1668 public MethodHandle apply(Class<?> cl) {
1669 MethodHandle mhObject = lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, Object.class);
1670
1671 // We need the additional conversion here, because String.valueOf(Object) may return null.
1672 // String conversion rules in Java state we need to produce "null" String in this case.
1673 // It can be easily done with applying valueOf the second time.
1674 MethodHandle mhObjectNoNulls = MethodHandles.filterReturnValue(mhObject,
1675 mhObject.asType(MethodType.methodType(String.class, String.class)));
1676
1677 if (cl == String.class) {
1678 return mhObject;
1679 } else if (cl == float.class) {
1680 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, float.class);
1681 } else if (cl == double.class) {
1682 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, double.class);
1683 } else if (!cl.isPrimitive()) {
1684 return mhObjectNoNulls;
1685 }
1686
1687 return null;
1688 }
1689 };
1690
1691 // This one is deliberately non-lambdified to optimize startup time:
1692 private static final Function<Class<?>, MethodHandle> ANY = new Function<Class<?>, MethodHandle>() {
1693 @Override
1694 public MethodHandle apply(Class<?> cl) {
1695 MethodHandle mh = MOST.apply(cl);
1696 if (mh != null) {
1697 return mh;
1698 }
1699
1700 if (cl == byte.class || cl == short.class || cl == int.class) {
1701 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, int.class);
1702 } else if (cl == boolean.class) {
1703 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, boolean.class);
1704 } else if (cl == char.class) {
1705 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, char.class);
1706 } else if (cl == long.class) {
1707 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, long.class);
1708 } else {
1709 throw new IllegalStateException("Unknown class: " + cl);
1710 }
1711 }
1712 };
1713
1714 private static final ConcurrentMap<Class<?>, MethodHandle> STRINGIFIERS_MOST = new ConcurrentHashMap<>();
1715 private static final ConcurrentMap<Class<?>, MethodHandle> STRINGIFIERS_ANY = new ConcurrentHashMap<>();
1716
1717 /**
1718 * Returns a stringifier for references and floats/doubles only.
1719 * Always returns null for other primitives.
1720 *
1721 * @param t class to stringify
1722 * @return stringifier; null, if not available
1723 */
1724 static MethodHandle forMost(Class<?> t) {
1725 return STRINGIFIERS_MOST.computeIfAbsent(t, MOST);
1726 }
1727
1728 /**
1729 * Returns a stringifier for any type. Never returns null.
1730 *
1731 * @param t class to stringify
1732 * @return stringifier
1733 */
1734 static MethodHandle forAny(Class<?> t) {
1735 return STRINGIFIERS_ANY.computeIfAbsent(t, ANY);
1736 }
1737 }
1738
1739 /* ------------------------------- Common utilities ------------------------------------ */
1740
1741 private static MethodHandle lookupStatic(Lookup lookup, Class<?> refc, String name, Class<?> rtype, Class<?>... ptypes) {
1742 try {
1743 return lookup.findStatic(refc, name, MethodType.methodType(rtype, ptypes));
1744 } catch (NoSuchMethodException | IllegalAccessException e) {
1745 throw new AssertionError(e);
1746 }
1747 }
1748
1749 private static MethodHandle lookupVirtual(Lookup lookup, Class<?> refc, String name, Class<?> rtype, Class<?>... ptypes) {
1750 try {
1751 return lookup.findVirtual(refc, name, MethodType.methodType(rtype, ptypes));
1752 } catch (NoSuchMethodException | IllegalAccessException e) {
1753 throw new AssertionError(e);
1754 }
1755 }
1756
1757 private static MethodHandle lookupConstructor(Lookup lookup, Class<?> refc, Class<?> ptypes) {
1758 try {
1759 return lookup.findConstructor(refc, MethodType.methodType(void.class, ptypes));
1760 } catch (NoSuchMethodException | IllegalAccessException e) {
1761 throw new AssertionError(e);
1762 }
1763 }
1764
1765 private static int estimateSize(Class<?> cl) {
1766 if (cl == Integer.TYPE) {
1767 return 11; // "-2147483648"
1768 } else if (cl == Boolean.TYPE) {
1769 return 5; // "false"
1770 } else if (cl == Byte.TYPE) {
1771 return 4; // "-128"
1772 } else if (cl == Character.TYPE) {
1773 return 1; // duh
1774 } else if (cl == Short.TYPE) {
1775 return 6; // "-32768"
1776 } else if (cl == Double.TYPE) {
1777 return 26; // apparently, no larger than this, see FloatingDecimal.BinaryToASCIIBuffer.buffer
1778 } else if (cl == Float.TYPE) {
1779 return 26; // apparently, no larger than this, see FloatingDecimal.BinaryToASCIIBuffer.buffer
1780 } else if (cl == Long.TYPE) {
1781 return 20; // "-9223372036854775808"
1782 } else {
1783 throw new IllegalArgumentException("Cannot estimate the size for " + cl);
1784 }
1785 }
1786
1787 private static Class<?> adaptToStringBuilder(Class<?> c) {
1788 if (c.isPrimitive()) {
1789 if (c == Byte.TYPE || c == Short.TYPE) {
1790 return int.class;
1791 }
1792 } else {
1793 if (c != String.class) {
1794 return Object.class;
1795 }
1796 }
1797 return c;
1798 }
1799
1800 private StringConcatFactory() {
1801 // no instantiation
1802 }
1803
1804 }