1 /*
   2  * Copyright (c) 2011, 2025, 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 java.lang.classfile.TypeKind;
  29 import jdk.internal.perf.PerfCounter;
  30 import jdk.internal.vm.annotation.AOTSafeClassInitializer;
  31 import jdk.internal.vm.annotation.DontInline;
  32 import jdk.internal.vm.annotation.Hidden;
  33 import jdk.internal.vm.annotation.Stable;
  34 import sun.invoke.util.Wrapper;
  35 
  36 import java.lang.annotation.ElementType;
  37 import java.lang.annotation.Retention;
  38 import java.lang.annotation.RetentionPolicy;
  39 import java.lang.annotation.Target;
  40 import java.lang.reflect.Method;
  41 import java.util.Arrays;
  42 import java.util.HashMap;
  43 
  44 import static java.lang.invoke.LambdaForm.BasicType.*;
  45 import static java.lang.invoke.MethodHandleNatives.Constants.*;
  46 import static java.lang.invoke.MethodHandleStatics.*;
  47 
  48 /**
  49  * The symbolic, non-executable form of a method handle's invocation semantics.
  50  * It consists of a series of names.
  51  * The first N (N=arity) names are parameters,
  52  * while any remaining names are temporary values.
  53  * Each temporary specifies the application of a function to some arguments.
  54  * The functions are method handles, while the arguments are mixes of
  55  * constant values and local names.
  56  * The result of the lambda is defined as one of the names, often the last one.
  57  * <p>
  58  * Here is an approximate grammar:
  59  * <blockquote><pre>{@code
  60  * LambdaForm = "(" ArgName* ")=>{" TempName* Result "}"
  61  * ArgName = "a" N ":" T
  62  * TempName = "t" N ":" T "=" Function "(" Argument* ");"
  63  * Function = ConstantValue
  64  * Argument = NameRef | ConstantValue
  65  * Result = NameRef | "void"
  66  * NameRef = "a" N | "t" N
  67  * N = (any whole number)
  68  * T = "L" | "I" | "J" | "F" | "D" | "V"
  69  * }</pre></blockquote>
  70  * Names are numbered consecutively from left to right starting at zero.
  71  * (The letters are merely a taste of syntax sugar.)
  72  * Thus, the first temporary (if any) is always numbered N (where N=arity).
  73  * Every occurrence of a name reference in an argument list must refer to
  74  * a name previously defined within the same lambda.
  75  * A lambda has a void result if and only if its result index is -1.
  76  * If a temporary has the type "V", it cannot be the subject of a NameRef,
  77  * even though possesses a number.
  78  * Note that all reference types are erased to "L", which stands for {@code Object}.
  79  * All subword types (boolean, byte, short, char) are erased to "I" which is {@code int}.
  80  * The other types stand for the usual primitive types.
  81  * <p>
  82  * Function invocation closely follows the static rules of the Java verifier.
  83  * Arguments and return values must exactly match when their "Name" types are
  84  * considered.
  85  * Conversions are allowed only if they do not change the erased type.
  86  * <ul>
  87  * <li>L = Object: casts are used freely to convert into and out of reference types
  88  * <li>I = int: subword types are forcibly narrowed when passed as arguments (see {@code explicitCastArguments})
  89  * <li>J = long: no implicit conversions
  90  * <li>F = float: no implicit conversions
  91  * <li>D = double: no implicit conversions
  92  * <li>V = void: a function result may be void if and only if its Name is of type "V"
  93  * </ul>
  94  * Although implicit conversions are not allowed, explicit ones can easily be
  95  * encoded by using temporary expressions which call type-transformed identity functions.
  96  * <p>
  97  * Examples:
  98  * <blockquote><pre>{@code
  99  * (a0:J)=>{ a0 }
 100  *     == identity(long)
 101  * (a0:I)=>{ t1:V = System.out#println(a0); void }
 102  *     == System.out#println(int)
 103  * (a0:L)=>{ t1:V = System.out#println(a0); a0 }
 104  *     == identity, with printing side-effect
 105  * (a0:L, a1:L)=>{ t2:L = BoundMethodHandle#argument(a0);
 106  *                 t3:L = BoundMethodHandle#target(a0);
 107  *                 t4:L = MethodHandle#invoke(t3, t2, a1); t4 }
 108  *     == general invoker for unary insertArgument combination
 109  * (a0:L, a1:L)=>{ t2:L = FilterMethodHandle#filter(a0);
 110  *                 t3:L = MethodHandle#invoke(t2, a1);
 111  *                 t4:L = FilterMethodHandle#target(a0);
 112  *                 t5:L = MethodHandle#invoke(t4, t3); t5 }
 113  *     == general invoker for unary filterArgument combination
 114  * (a0:L, a1:L)=>{ ...(same as previous example)...
 115  *                 t5:L = MethodHandle#invoke(t4, t3, a1); t5 }
 116  *     == general invoker for unary/unary foldArgument combination
 117  * (a0:L, a1:I)=>{ t2:I = identity(long).asType((int)->long)(a1); t2 }
 118  *     == invoker for identity method handle which performs i2l
 119  * (a0:L, a1:L)=>{ t2:L = BoundMethodHandle#argument(a0);
 120  *                 t3:L = Class#cast(t2,a1); t3 }
 121  *     == invoker for identity method handle which performs cast
 122  * }</pre></blockquote>
 123  * <p>
 124  * @author John Rose, JSR 292 EG
 125  */
 126 @AOTSafeClassInitializer
 127 class LambdaForm {
 128     final int arity;
 129     final int result;
 130     final boolean forceInline;
 131     final MethodHandle customized;
 132     @Stable final Name[] names;
 133     final Kind kind;
 134     MemberName vmentry;   // low-level behavior, or null if not yet prepared
 135     private boolean isCompiled;
 136 
 137     // Either a LambdaForm cache (managed by LambdaFormEditor) or a link to uncustomized version (for customized LF)
 138     volatile Object transformCache;
 139 
 140     public static final int VOID_RESULT = -1, LAST_RESULT = -2;
 141 
 142     /// Represents the "basic" types that exist in the JVM linkage and stack/locals.
 143     /// All objects are erased to a reference.
 144     /// All subwords (boolean, byte, char, short) are promoted to int.
 145     enum BasicType {
 146         L_TYPE('L', Object.class, Wrapper.OBJECT, TypeKind.REFERENCE),
 147         I_TYPE('I', int.class,    Wrapper.INT,    TypeKind.INT),
 148         J_TYPE('J', long.class,   Wrapper.LONG,   TypeKind.LONG),
 149         F_TYPE('F', float.class,  Wrapper.FLOAT,  TypeKind.FLOAT),
 150         D_TYPE('D', double.class, Wrapper.DOUBLE, TypeKind.DOUBLE),  // end arg types
 151         V_TYPE('V', void.class,   Wrapper.VOID,   TypeKind.VOID);    // only valid in method return
 152 
 153         static final @Stable BasicType[] ALL_TYPES = BasicType.values();
 154         static final @Stable BasicType[] ARG_TYPES = Arrays.copyOf(ALL_TYPES, ALL_TYPES.length-1);
 155 
 156         static final int ARG_TYPE_LIMIT = ARG_TYPES.length;
 157         static final int TYPE_LIMIT = ALL_TYPES.length;
 158 
 159         final char btChar;
 160         final Class<?> btClass;
 161         final Wrapper btWrapper;
 162         final TypeKind btKind;
 163 
 164         private BasicType(char btChar, Class<?> btClass, Wrapper wrapper, TypeKind typeKind) {
 165             this.btChar = btChar;
 166             this.btClass = btClass;
 167             this.btWrapper = wrapper;
 168             this.btKind = typeKind;
 169         }
 170 
 171         char basicTypeChar() {
 172             return btChar;
 173         }
 174         Class<?> basicTypeClass() {
 175             return btClass;
 176         }
 177         Wrapper basicTypeWrapper() {
 178             return btWrapper;
 179         }
 180         TypeKind basicTypeKind() {
 181             return btKind;
 182         }
 183         int basicTypeSlots() {
 184             return btWrapper.stackSlots();
 185         }
 186 
 187         static BasicType basicType(byte type) {
 188             return ALL_TYPES[type];
 189         }
 190         static BasicType basicType(char type) {
 191             return switch (type) {
 192                 case 'L' -> L_TYPE;
 193                 case 'I' -> I_TYPE;
 194                 case 'J' -> J_TYPE;
 195                 case 'F' -> F_TYPE;
 196                 case 'D' -> D_TYPE;
 197                 case 'V' -> V_TYPE;
 198                 // all subword types are represented as ints
 199                 case 'Z', 'B', 'S', 'C' -> I_TYPE;
 200                 default -> throw newInternalError("Unknown type char: '" + type + "'");
 201             };
 202         }
 203         static BasicType basicType(Class<?> type) {
 204             return basicType(Wrapper.basicTypeChar(type));
 205         }
 206         static int[] basicTypeOrds(BasicType[] types) {
 207             if (types == null) {
 208                 return null;
 209             }
 210             int[] a = new int[types.length];
 211             for(int i = 0; i < types.length; ++i) {
 212                 a[i] = types[i].ordinal();
 213             }
 214             return a;
 215         }
 216 
 217         static char basicTypeChar(Class<?> type) {
 218             return basicType(type).btChar;
 219         }
 220 
 221         static int[] basicTypesOrd(Class<?>[] types) {
 222             int[] ords = new int[types.length];
 223             for (int i = 0; i < ords.length; i++) {
 224                 ords[i] = basicType(types[i]).ordinal();
 225             }
 226             return ords;
 227         }
 228 
 229         static boolean isBasicTypeChar(char c) {
 230             return "LIJFDV".indexOf(c) >= 0;
 231         }
 232         static boolean isArgBasicTypeChar(char c) {
 233             return "LIJFD".indexOf(c) >= 0;
 234         }
 235 
 236         static { assert(checkBasicType()); }
 237         private static boolean checkBasicType() {
 238             for (int i = 0; i < ARG_TYPE_LIMIT; i++) {
 239                 assert ARG_TYPES[i].ordinal() == i;
 240                 assert ARG_TYPES[i] == ALL_TYPES[i];
 241             }
 242             for (int i = 0; i < TYPE_LIMIT; i++) {
 243                 assert ALL_TYPES[i].ordinal() == i;
 244             }
 245             assert ALL_TYPES[TYPE_LIMIT - 1] == V_TYPE;
 246             assert !Arrays.asList(ARG_TYPES).contains(V_TYPE);
 247             return true;
 248         }
 249     }
 250 
 251     enum Kind {
 252         GENERIC("invoke"),
 253         IDENTITY("identity"),
 254         CONSTANT("constant"),
 255         BOUND_REINVOKER("BMH.reinvoke", "reinvoke"),
 256         REINVOKER("MH.reinvoke", "reinvoke"),
 257         DELEGATE("MH.delegate", "delegate"),
 258         EXACT_LINKER("MH.invokeExact_MT", "invokeExact_MT"),
 259         EXACT_INVOKER("MH.exactInvoker", "exactInvoker"),
 260         GENERIC_LINKER("MH.invoke_MT", "invoke_MT"),
 261         GENERIC_INVOKER("MH.invoker", "invoker"),
 262         LINK_TO_TARGET_METHOD("linkToTargetMethod"),
 263         LINK_TO_CALL_SITE("linkToCallSite"),
 264         DIRECT_INVOKE_VIRTUAL("DMH.invokeVirtual", "invokeVirtual"),
 265         DIRECT_INVOKE_SPECIAL("DMH.invokeSpecial", "invokeSpecial"),
 266         DIRECT_INVOKE_SPECIAL_IFC("DMH.invokeSpecialIFC", "invokeSpecialIFC"),
 267         DIRECT_INVOKE_STATIC("DMH.invokeStatic", "invokeStatic"),
 268         DIRECT_NEW_INVOKE_SPECIAL("DMH.newInvokeSpecial", "newInvokeSpecial"),
 269         DIRECT_INVOKE_INTERFACE("DMH.invokeInterface", "invokeInterface"),
 270         DIRECT_INVOKE_STATIC_INIT("DMH.invokeStaticInit", "invokeStaticInit"),
 271         FIELD_ACCESS("fieldAccess"),
 272         FIELD_ACCESS_INIT("fieldAccessInit"),
 273         VOLATILE_FIELD_ACCESS("volatileFieldAccess"),
 274         VOLATILE_FIELD_ACCESS_INIT("volatileFieldAccessInit"),
 275         FIELD_ACCESS_B("fieldAccessB"),
 276         FIELD_ACCESS_INIT_B("fieldAccessInitB"),
 277         VOLATILE_FIELD_ACCESS_B("volatileFieldAccessB"),
 278         VOLATILE_FIELD_ACCESS_INIT_B("volatileFieldAccessInitB"),
 279         FIELD_ACCESS_C("fieldAccessC"),
 280         FIELD_ACCESS_INIT_C("fieldAccessInitC"),
 281         VOLATILE_FIELD_ACCESS_C("volatileFieldAccessC"),
 282         VOLATILE_FIELD_ACCESS_INIT_C("volatileFieldAccessInitC"),
 283         FIELD_ACCESS_S("fieldAccessS"),
 284         FIELD_ACCESS_INIT_S("fieldAccessInitS"),
 285         VOLATILE_FIELD_ACCESS_S("volatileFieldAccessS"),
 286         VOLATILE_FIELD_ACCESS_INIT_S("volatileFieldAccessInitS"),
 287         FIELD_ACCESS_Z("fieldAccessZ"),
 288         FIELD_ACCESS_INIT_Z("fieldAccessInitZ"),
 289         VOLATILE_FIELD_ACCESS_Z("volatileFieldAccessZ"),
 290         VOLATILE_FIELD_ACCESS_INIT_Z("volatileFieldAccessInitZ"),
 291         FIELD_ACCESS_CAST("fieldAccessCast"),
 292         FIELD_ACCESS_INIT_CAST("fieldAccessInitCast"),
 293         VOLATILE_FIELD_ACCESS_CAST("volatileFieldAccessCast"),
 294         VOLATILE_FIELD_ACCESS_INIT_CAST("volatileFieldAccessInitCast"),
 295         TRY_FINALLY("tryFinally"),
 296         TABLE_SWITCH("tableSwitch"),
 297         COLLECTOR("collector"),
 298         LOOP("loop"),
 299         GUARD("guard"),
 300         GUARD_WITH_CATCH("guardWithCatch"),
 301         VARHANDLE_EXACT_INVOKER("VH.exactInvoker"),
 302         VARHANDLE_INVOKER("VH.invoker", "invoker"),
 303         VARHANDLE_LINKER("VH.invoke_MT", "invoke_MT");
 304 
 305         final String defaultLambdaName;
 306         final String methodName;
 307 
 308         private Kind(String defaultLambdaName) {
 309             this(defaultLambdaName, defaultLambdaName);
 310         }
 311 
 312         private Kind(String defaultLambdaName, String methodName) {
 313             this.defaultLambdaName = defaultLambdaName;
 314             this.methodName = methodName;
 315         }
 316     }
 317 
 318     // private version that doesn't do checks or defensive copies
 319     private LambdaForm(int arity, int result, boolean forceInline, MethodHandle customized, Name[] names, Kind kind) {
 320         this.arity = arity;
 321         this.result = result;
 322         this.forceInline = forceInline;
 323         this.customized = customized;
 324         this.names = names;
 325         this.kind = kind;
 326         this.vmentry = null;
 327         this.isCompiled = false;
 328     }
 329 
 330     // root factory pre/post processing and calls simple constructor
 331     private static LambdaForm create(int arity, Name[] names, int result, boolean forceInline, MethodHandle customized, Kind kind) {
 332         names = names.clone();
 333         assert(namesOK(arity, names));
 334         result = fixResult(result, names);
 335 
 336         boolean canInterpret = normalizeNames(arity, names);
 337         LambdaForm form = new LambdaForm(arity, result, forceInline, customized, names, kind);
 338         assert(form.nameRefsAreLegal());
 339         if (!canInterpret) {
 340             form.compileToBytecode();
 341         }
 342         return form;
 343     }
 344 
 345     // derived factories with defaults
 346     private static final int DEFAULT_RESULT = LAST_RESULT;
 347     private static final boolean DEFAULT_FORCE_INLINE = true;
 348     private static final MethodHandle DEFAULT_CUSTOMIZED = null;
 349     private static final Kind DEFAULT_KIND = Kind.GENERIC;
 350 
 351     static LambdaForm create(int arity, Name[] names, int result) {
 352         return create(arity, names, result, DEFAULT_FORCE_INLINE, DEFAULT_CUSTOMIZED, DEFAULT_KIND);
 353     }
 354     static LambdaForm create(int arity, Name[] names, int result, Kind kind) {
 355         return create(arity, names, result, DEFAULT_FORCE_INLINE, DEFAULT_CUSTOMIZED, kind);
 356     }
 357     static LambdaForm create(int arity, Name[] names) {
 358         return create(arity, names, DEFAULT_RESULT, DEFAULT_FORCE_INLINE, DEFAULT_CUSTOMIZED, DEFAULT_KIND);
 359     }
 360     static LambdaForm create(int arity, Name[] names, Kind kind) {
 361         return create(arity, names, DEFAULT_RESULT, DEFAULT_FORCE_INLINE, DEFAULT_CUSTOMIZED, kind);
 362     }
 363     static LambdaForm create(int arity, Name[] names, boolean forceInline, Kind kind) {
 364         return create(arity, names, DEFAULT_RESULT, forceInline, DEFAULT_CUSTOMIZED, kind);
 365     }
 366 
 367     private static int fixResult(int result, Name[] names) {
 368         if (result == LAST_RESULT)
 369             result = names.length - 1;  // might still be void
 370         if (result >= 0 && names[result].type == V_TYPE)
 371             result = VOID_RESULT;
 372         return result;
 373     }
 374 
 375     static boolean debugNames() {
 376         return DEBUG_NAME_COUNTERS != null;
 377     }
 378 
 379     static void associateWithDebugName(LambdaForm form, String name) {
 380         assert (debugNames());
 381         synchronized (DEBUG_NAMES) {
 382             DEBUG_NAMES.put(form, name);
 383         }
 384     }
 385 
 386     String lambdaName() {
 387         if (DEBUG_NAMES != null) {
 388             synchronized (DEBUG_NAMES) {
 389                 String name = DEBUG_NAMES.get(this);
 390                 if (name == null) {
 391                     name = generateDebugName();
 392                 }
 393                 return name;
 394             }
 395         }
 396         return kind.defaultLambdaName;
 397     }
 398 
 399     private String generateDebugName() {
 400         assert (debugNames());
 401         String debugNameStem = kind.defaultLambdaName;
 402         Integer ctr = DEBUG_NAME_COUNTERS.getOrDefault(debugNameStem, 0);
 403         DEBUG_NAME_COUNTERS.put(debugNameStem, ctr + 1);
 404         StringBuilder buf = new StringBuilder(debugNameStem);
 405         int leadingZero = buf.length();
 406         buf.append((int) ctr);
 407         for (int i = buf.length() - leadingZero; i < 3; i++) {
 408             buf.insert(leadingZero, '0');
 409         }
 410         buf.append('_');
 411         buf.append(basicTypeSignature());
 412         String name = buf.toString();
 413         associateWithDebugName(this, name);
 414         return name;
 415     }
 416 
 417     private static boolean namesOK(int arity, Name[] names) {
 418         for (int i = 0; i < names.length; i++) {
 419             Name n = names[i];
 420             assert(n != null) : "n is null";
 421             if (i < arity)
 422                 assert( n.isParam()) : n + " is not param at " + i;
 423             else
 424                 assert(!n.isParam()) : n + " is param at " + i;
 425         }
 426         return true;
 427     }
 428 
 429     /** Customize LambdaForm for a particular MethodHandle */
 430     LambdaForm customize(MethodHandle mh) {
 431         if (customized == mh) {
 432             return this;
 433         }
 434         LambdaForm customForm = LambdaForm.create(arity, names, result, forceInline, mh, kind);
 435         if (COMPILE_THRESHOLD >= 0 && isCompiled) {
 436             // If shared LambdaForm has been compiled, compile customized version as well.
 437             customForm.compileToBytecode();
 438         }
 439         customForm.transformCache = this; // LambdaFormEditor should always use uncustomized form.
 440         return customForm;
 441     }
 442 
 443     /** Get uncustomized flavor of the LambdaForm */
 444     LambdaForm uncustomize() {
 445         if (customized == null) {
 446             return this;
 447         }
 448         assert(transformCache != null); // Customized LambdaForm should always has a link to uncustomized version.
 449         LambdaForm uncustomizedForm = (LambdaForm)transformCache;
 450         if (COMPILE_THRESHOLD >= 0 && isCompiled) {
 451             // If customized LambdaForm has been compiled, compile uncustomized version as well.
 452             uncustomizedForm.compileToBytecode();
 453         }
 454         return uncustomizedForm;
 455     }
 456 
 457     /** Renumber and/or replace params so that they are interned and canonically numbered.
 458      *  @return true if we can interpret
 459      */
 460     private static boolean normalizeNames(int arity, Name[] names) {
 461         Name[] oldNames = names.clone();
 462         int maxOutArity = 0;
 463         for (int i = 0; i < names.length; i++) {
 464             Name n = names[i];
 465             names[i] = n.withIndex(i);
 466             if (n.arguments != null && maxOutArity < n.arguments.length)
 467                 maxOutArity = n.arguments.length;
 468         }
 469         if (oldNames != null) {
 470             for (int i = Math.max(1, arity); i < names.length; i++) {
 471                 Name fixed = names[i].replaceNames(oldNames, names, 0, i);
 472                 names[i] = fixed.withIndex(i);
 473             }
 474         }
 475         int maxInterned = Math.min(arity, INTERNED_ARGUMENT_LIMIT);
 476         boolean needIntern = false;
 477         for (int i = 0; i < maxInterned; i++) {
 478             Name n = names[i], n2 = internArgument(n);
 479             if (n != n2) {
 480                 names[i] = n2;
 481                 needIntern = true;
 482             }
 483         }
 484         if (needIntern) {
 485             for (int i = arity; i < names.length; i++) {
 486                 names[i].internArguments();
 487             }
 488         }
 489 
 490         // return true if we can interpret
 491         if (maxOutArity > MethodType.MAX_MH_INVOKER_ARITY) {
 492             // Cannot use LF interpreter on very high arity expressions.
 493             assert(maxOutArity <= MethodType.MAX_JVM_ARITY);
 494             return false;
 495         }
 496         return true;
 497     }
 498 
 499     /**
 500      * Check that all embedded Name references are localizable to this lambda,
 501      * and are properly ordered after their corresponding definitions.
 502      * <p>
 503      * Note that a Name can be local to multiple lambdas, as long as
 504      * it possesses the same index in each use site.
 505      * This allows Name references to be freely reused to construct
 506      * fresh lambdas, without confusion.
 507      */
 508     boolean nameRefsAreLegal() {
 509         assert(arity >= 0 && arity <= names.length);
 510         assert(result >= -1 && result < names.length);
 511         // Do all names possess an index consistent with their local definition order?
 512         for (int i = 0; i < arity; i++) {
 513             Name n = names[i];
 514             assert(n.index() == i) : Arrays.asList(n.index(), i);
 515             assert(n.isParam());
 516         }
 517         // Also, do all local name references
 518         for (int i = arity; i < names.length; i++) {
 519             Name n = names[i];
 520             assert(n.index() == i);
 521             for (Object arg : n.arguments) {
 522                 if (arg instanceof Name n2) {
 523                     int i2 = n2.index;
 524                     assert(0 <= i2 && i2 < names.length) : n.debugString() + ": 0 <= i2 && i2 < names.length: 0 <= " + i2 + " < " + names.length;
 525                     assert(names[i2] == n2) : Arrays.asList("-1-", i, "-2-", n.debugString(), "-3-", i2, "-4-", n2.debugString(), "-5-", names[i2].debugString(), "-6-", this);
 526                     assert(i2 < i);  // ref must come after def!
 527                 }
 528             }
 529         }
 530         return true;
 531     }
 532 
 533     // /** Invoke this form on the given arguments. */
 534     // final Object invoke(Object... args) throws Throwable {
 535     //     // NYI: fit this into the fast path?
 536     //     return interpretWithArguments(args);
 537     // }
 538 
 539     /** Report the return type. */
 540     BasicType returnType() {
 541         if (result < 0)  return V_TYPE;
 542         Name n = names[result];
 543         return n.type;
 544     }
 545 
 546     /** Report the N-th argument type. */
 547     BasicType parameterType(int n) {
 548         return parameter(n).type;
 549     }
 550 
 551     /** Report the N-th argument name. */
 552     Name parameter(int n) {
 553         Name param = names[n];
 554         assert(n < arity && param.isParam());
 555         return param;
 556     }
 557 
 558     /** Report the N-th argument type constraint. */
 559     Object parameterConstraint(int n) {
 560         return parameter(n).constraint;
 561     }
 562 
 563     /** Report the arity. */
 564     int arity() {
 565         return arity;
 566     }
 567 
 568     /** Report the number of expressions (non-parameter names). */
 569     int expressionCount() {
 570         return names.length - arity;
 571     }
 572 
 573     /** Return the method type corresponding to my basic type signature. */
 574     MethodType methodType() {
 575         Class<?>[] ptypes = new Class<?>[arity];
 576         for (int i = 0; i < arity; ++i) {
 577             ptypes[i] = parameterType(i).btClass;
 578         }
 579         return MethodType.methodType(returnType().btClass, ptypes, true);
 580     }
 581 
 582     /** Return ABC_Z, where the ABC are parameter type characters, and Z is the return type character. */
 583     final String basicTypeSignature() {
 584         StringBuilder buf = new StringBuilder(arity() + 3);
 585         for (int i = 0, a = arity(); i < a; i++)
 586             buf.append(parameterType(i).basicTypeChar());
 587         return buf.append('_').append(returnType().basicTypeChar()).toString();
 588     }
 589     static int signatureArity(String sig) {
 590         assert(isValidSignature(sig));
 591         return sig.indexOf('_');
 592     }
 593     static boolean isValidSignature(String sig) {
 594         int arity = sig.indexOf('_');
 595         if (arity < 0)  return false;  // must be of the form *_*
 596         int siglen = sig.length();
 597         if (siglen != arity + 2)  return false;  // *_X
 598         for (int i = 0; i < siglen; i++) {
 599             if (i == arity)  continue;  // skip '_'
 600             char c = sig.charAt(i);
 601             if (c == 'V')
 602                 return (i == siglen - 1 && arity == siglen - 2);
 603             if (!isArgBasicTypeChar(c))  return false; // must be [LIJFD]
 604         }
 605         return true;  // [LIJFD]*_[LIJFDV]
 606     }
 607 
 608     /**
 609      * Check if i-th name is a call to MethodHandleImpl.selectAlternative.
 610      */
 611     boolean isSelectAlternative(int pos) {
 612         // selectAlternative idiom:
 613         //   t_{n}:L=MethodHandleImpl.selectAlternative(...)
 614         //   t_{n+1}:?=MethodHandle.invokeBasic(t_{n}, ...)
 615         if (pos+1 >= names.length)  return false;
 616         Name name0 = names[pos];
 617         Name name1 = names[pos+1];
 618         return name0.refersTo(MethodHandleImpl.class, "selectAlternative") &&
 619                 name1.isInvokeBasic() &&
 620                 name1.lastUseIndex(name0) == 0 && // t_{n+1}:?=MethodHandle.invokeBasic(t_{n}, ...)
 621                 lastUseIndex(name0) == pos+1;     // t_{n} is local: used only in t_{n+1}
 622     }
 623 
 624     private boolean isMatchingIdiom(int pos, String idiomName, int nArgs) {
 625         if (pos+2 >= names.length)  return false;
 626         Name name0 = names[pos];
 627         Name name1 = names[pos+1];
 628         Name name2 = names[pos+2];
 629         return name1.refersTo(MethodHandleImpl.class, idiomName) &&
 630                 name0.isInvokeBasic() &&
 631                 name2.isInvokeBasic() &&
 632                 name1.lastUseIndex(name0) == nArgs && // t_{n+1}:L=MethodHandleImpl.<invoker>(<args>, t_{n});
 633                 lastUseIndex(name0) == pos+1 &&       // t_{n} is local: used only in t_{n+1}
 634                 name2.lastUseIndex(name1) == 1 &&     // t_{n+2}:?=MethodHandle.invokeBasic(*, t_{n+1})
 635                 lastUseIndex(name1) == pos+2;         // t_{n+1} is local: used only in t_{n+2}
 636     }
 637 
 638     /**
 639      * Check if i-th name is a start of GuardWithCatch idiom.
 640      */
 641     boolean isGuardWithCatch(int pos) {
 642         // GuardWithCatch idiom:
 643         //   t_{n}:L=MethodHandle.invokeBasic(...)
 644         //   t_{n+1}:L=MethodHandleImpl.guardWithCatch(*, *, *, t_{n});
 645         //   t_{n+2}:?=MethodHandle.invokeBasic(*, t_{n+1})
 646         return isMatchingIdiom(pos, "guardWithCatch", 3);
 647     }
 648 
 649     /**
 650      * Check if i-th name is a start of the tryFinally idiom.
 651      */
 652     boolean isTryFinally(int pos) {
 653         // tryFinally idiom:
 654         //   t_{n}:L=MethodHandle.invokeBasic(...)
 655         //   t_{n+1}:L=MethodHandleImpl.tryFinally(*, *, t_{n})
 656         //   t_{n+2}:?=MethodHandle.invokeBasic(*, t_{n+1})
 657         return isMatchingIdiom(pos, "tryFinally", 2);
 658     }
 659 
 660     /**
 661      * Check if i-th name is a start of the tableSwitch idiom.
 662      */
 663     boolean isTableSwitch(int pos) {
 664         // tableSwitch idiom:
 665         //   t_{n}:L=MethodHandle.invokeBasic(...)     // args
 666         //   t_{n+1}:L=MethodHandleImpl.tableSwitch(*, *, *, t_{n})
 667         //   t_{n+2}:?=MethodHandle.invokeBasic(*, t_{n+1})
 668         if (pos + 2 >= names.length)  return false;
 669 
 670         final int POS_COLLECT_ARGS = pos;
 671         final int POS_TABLE_SWITCH = pos + 1;
 672         final int POS_UNBOX_RESULT = pos + 2;
 673 
 674         Name collectArgs = names[POS_COLLECT_ARGS];
 675         Name tableSwitch = names[POS_TABLE_SWITCH];
 676         Name unboxResult = names[POS_UNBOX_RESULT];
 677         return tableSwitch.refersTo(MethodHandleImpl.class, "tableSwitch") &&
 678                 collectArgs.isInvokeBasic() &&
 679                 unboxResult.isInvokeBasic() &&
 680                 tableSwitch.lastUseIndex(collectArgs) == 3 &&     // t_{n+1}:L=MethodHandleImpl.<invoker>(*, *, *, t_{n});
 681                 lastUseIndex(collectArgs) == POS_TABLE_SWITCH &&  // t_{n} is local: used only in t_{n+1}
 682                 unboxResult.lastUseIndex(tableSwitch) == 1 &&     // t_{n+2}:?=MethodHandle.invokeBasic(*, t_{n+1})
 683                 lastUseIndex(tableSwitch) == POS_UNBOX_RESULT;    // t_{n+1} is local: used only in t_{n+2}
 684     }
 685 
 686     /**
 687      * Check if i-th name is a start of the loop idiom.
 688      */
 689     boolean isLoop(int pos) {
 690         // loop idiom:
 691         //   t_{n}:L=MethodHandle.invokeBasic(...)
 692         //   t_{n+1}:L=MethodHandleImpl.loop(types, *, t_{n})
 693         //   t_{n+2}:?=MethodHandle.invokeBasic(*, t_{n+1})
 694         return isMatchingIdiom(pos, "loop", 2);
 695     }
 696 
 697     /*
 698      * Code generation issues:
 699      *
 700      * Compiled LFs should be reusable in general.
 701      * The biggest issue is how to decide when to pull a name into
 702      * the bytecode, versus loading a reified form from the MH data.
 703      *
 704      * For example, an asType wrapper may require execution of a cast
 705      * after a call to a MH.  The target type of the cast can be placed
 706      * as a constant in the LF itself.  This will force the cast type
 707      * to be compiled into the bytecodes and native code for the MH.
 708      * Or, the target type of the cast can be erased in the LF, and
 709      * loaded from the MH data.  (Later on, if the MH as a whole is
 710      * inlined, the data will flow into the inlined instance of the LF,
 711      * as a constant, and the end result will be an optimal cast.)
 712      *
 713      * This erasure of cast types can be done with any use of
 714      * reference types.  It can also be done with whole method
 715      * handles.  Erasing a method handle might leave behind
 716      * LF code that executes correctly for any MH of a given
 717      * type, and load the required MH from the enclosing MH's data.
 718      * Or, the erasure might even erase the expected MT.
 719      *
 720      * Also, for direct MHs, the MemberName of the target
 721      * could be erased, and loaded from the containing direct MH.
 722      * As a simple case, a LF for all int-valued non-static
 723      * field getters would perform a cast on its input argument
 724      * (to non-constant base type derived from the MemberName)
 725      * and load an integer value from the input object
 726      * (at a non-constant offset also derived from the MemberName).
 727      * Such MN-erased LFs would be inlinable back to optimized
 728      * code, whenever a constant enclosing DMH is available
 729      * to supply a constant MN from its data.
 730      *
 731      * The main problem here is to keep LFs reasonably generic,
 732      * while ensuring that hot spots will inline good instances.
 733      * "Reasonably generic" means that we don't end up with
 734      * repeated versions of bytecode or machine code that do
 735      * not differ in their optimized form.  Repeated versions
 736      * of machine would have the undesirable overheads of
 737      * (a) redundant compilation work and (b) extra I$ pressure.
 738      * To control repeated versions, we need to be ready to
 739      * erase details from LFs and move them into MH data,
 740      * whenever those details are not relevant to significant
 741      * optimization.  "Significant" means optimization of
 742      * code that is actually hot.
 743      *
 744      * Achieving this may require dynamic splitting of MHs, by replacing
 745      * a generic LF with a more specialized one, on the same MH,
 746      * if (a) the MH is frequently executed and (b) the MH cannot
 747      * be inlined into a containing caller, such as an invokedynamic.
 748      *
 749      * Compiled LFs that are no longer used should be GC-able.
 750      * If they contain non-BCP references, they should be properly
 751      * interlinked with the class loader(s) that their embedded types
 752      * depend on.  This probably means that reusable compiled LFs
 753      * will be tabulated (indexed) on relevant class loaders,
 754      * or else that the tables that cache them will have weak links.
 755      */
 756 
 757     /**
 758      * Make this LF directly executable, as part of a MethodHandle.
 759      * Invariant:  Every MH which is invoked must prepare its LF
 760      * before invocation.
 761      * (In principle, the JVM could do this very lazily,
 762      * as a sort of pre-invocation linkage step.)
 763      */
 764     public void prepare() {
 765         if (COMPILE_THRESHOLD == 0 && !forceInterpretation() && !isCompiled) {
 766             compileToBytecode();
 767         }
 768         if (this.vmentry != null) {
 769             // already prepared (e.g., a primitive DMH invoker form)
 770             return;
 771         }
 772         MethodType mtype = methodType();
 773         MethodTypeForm form = mtype.form();
 774 
 775         MemberName entry = form.cachedInterpretEntry();
 776         if (entry == null) {
 777             assert (isValidSignature(basicTypeSignature()));
 778             entry = InvokerBytecodeGenerator.generateLambdaFormInterpreterEntryPoint(mtype);
 779             entry = form.setCachedInterpretEntry(entry);
 780         }
 781         this.vmentry = entry;
 782         // TO DO: Maybe add invokeGeneric, invokeWithArguments
 783     }
 784 
 785     private static @Stable PerfCounter LF_FAILED;
 786 
 787     private static PerfCounter failedCompilationCounter() {
 788         if (LF_FAILED == null) {
 789             LF_FAILED = PerfCounter.newPerfCounter("java.lang.invoke.failedLambdaFormCompilations");
 790         }
 791         return LF_FAILED;
 792     }
 793 
 794     /** Generate optimizable bytecode for this form. */
 795     void compileToBytecode() {
 796         if (forceInterpretation()) {
 797             return; // this should not be compiled
 798         }
 799         if (vmentry != null && isCompiled) {
 800             return;  // already compiled somehow
 801         }
 802 
 803         // Obtain the invoker MethodType outside of the following try block.
 804         // This ensures that an IllegalArgumentException is directly thrown if the
 805         // type would have 256 or more parameters
 806         MethodType invokerType = methodType();
 807         assert(vmentry == null || vmentry.getMethodType().basicType().equals(invokerType));
 808         try {
 809             vmentry = InvokerBytecodeGenerator.generateCustomizedCode(this, invokerType);
 810             if (TRACE_INTERPRETER)
 811                 traceInterpreter("compileToBytecode", this);
 812             isCompiled = true;
 813         } catch (InvokerBytecodeGenerator.BytecodeGenerationException bge) {
 814             // bytecode generation failed - mark this LambdaForm as to be run in interpretation mode only
 815             invocationCounter = -1;
 816             failedCompilationCounter().increment();
 817             if (LOG_LF_COMPILATION_FAILURE) {
 818                 System.out.println("LambdaForm compilation failed: " + this);
 819                 bge.printStackTrace(System.out);
 820             }
 821         } catch (Error e) {
 822             // Pass through any error
 823             throw e;
 824         } catch (Exception e) {
 825             // Wrap any exception
 826             throw newInternalError(this.toString(), e);
 827         }
 828     }
 829 
 830     // The next few routines are called only from assert expressions
 831     // They verify that the built-in invokers process the correct raw data types.
 832     private static boolean argumentTypesMatch(String sig, Object[] av) {
 833         int arity = signatureArity(sig);
 834         assert(av.length == arity) : "av.length == arity: av.length=" + av.length + ", arity=" + arity;
 835         assert(av[0] instanceof MethodHandle) : "av[0] not instance of MethodHandle: " + av[0];
 836         MethodHandle mh = (MethodHandle) av[0];
 837         MethodType mt = mh.type();
 838         assert(mt.parameterCount() == arity-1);
 839         for (int i = 0; i < av.length; i++) {
 840             Class<?> pt = (i == 0 ? MethodHandle.class : mt.parameterType(i-1));
 841             assert(valueMatches(basicType(sig.charAt(i)), pt, av[i]));
 842         }
 843         return true;
 844     }
 845     private static boolean valueMatches(BasicType tc, Class<?> type, Object x) {
 846         // The following line is needed because (...)void method handles can use non-void invokers
 847         if (type == void.class)  tc = V_TYPE;   // can drop any kind of value
 848         assert tc == basicType(type) : tc + " == basicType(" + type + ")=" + basicType(type);
 849         switch (tc) {
 850         case I_TYPE: assert checkInt(type, x)   : "checkInt(" + type + "," + x +")";   break;
 851         case J_TYPE: assert x instanceof Long   : "instanceof Long: " + x;             break;
 852         case F_TYPE: assert x instanceof Float  : "instanceof Float: " + x;            break;
 853         case D_TYPE: assert x instanceof Double : "instanceof Double: " + x;           break;
 854         case L_TYPE: assert checkRef(type, x)   : "checkRef(" + type + "," + x + ")";  break;
 855         case V_TYPE: break;  // allow anything here; will be dropped
 856         default:  assert(false);
 857         }
 858         return true;
 859     }
 860     private static boolean checkInt(Class<?> type, Object x) {
 861         assert(x instanceof Integer);
 862         if (type == int.class)  return true;
 863         Wrapper w = Wrapper.forBasicType(type);
 864         assert(w.isSubwordOrInt());
 865         Object x1 = Wrapper.INT.wrap(w.wrap(x));
 866         return x.equals(x1);
 867     }
 868     private static boolean checkRef(Class<?> type, Object x) {
 869         assert(!type.isPrimitive());
 870         if (x == null)  return true;
 871         if (type.isInterface())  return true;
 872         return type.isInstance(x);
 873     }
 874 
 875     /** If the invocation count hits the threshold we spin bytecodes and call that subsequently. */
 876     private static final int COMPILE_THRESHOLD;
 877     static {
 878         COMPILE_THRESHOLD = Math.max(-1, MethodHandleStatics.COMPILE_THRESHOLD);
 879     }
 880     private int invocationCounter = 0; // a value of -1 indicates LambdaForm interpretation mode forever
 881 
 882     private boolean forceInterpretation() {
 883         return invocationCounter == -1;
 884     }
 885 
 886     /** Interpretively invoke this form on the given arguments. */
 887     @Hidden
 888     @DontInline
 889     Object interpretWithArguments(Object... argumentValues) throws Throwable {
 890         if (TRACE_INTERPRETER)
 891             return interpretWithArgumentsTracing(argumentValues);
 892         checkInvocationCounter();
 893         assert(arityCheck(argumentValues));
 894         Object[] values = Arrays.copyOf(argumentValues, names.length);
 895         for (int i = argumentValues.length; i < values.length; i++) {
 896             values[i] = interpretName(names[i], values);
 897         }
 898         Object rv = (result < 0) ? null : values[result];
 899         assert(resultCheck(argumentValues, rv));
 900         return rv;
 901     }
 902 
 903     /** Evaluate a single Name within this form, applying its function to its arguments. */
 904     @Hidden
 905     @DontInline
 906     Object interpretName(Name name, Object[] values) throws Throwable {
 907         if (TRACE_INTERPRETER)
 908             traceInterpreter("| interpretName", name.debugString(), (Object[]) null);
 909         Object[] arguments = Arrays.copyOf(name.arguments, name.arguments.length, Object[].class);
 910         for (int i = 0; i < arguments.length; i++) {
 911             Object a = arguments[i];
 912             if (a instanceof Name n) {
 913                 int i2 = n.index();
 914                 assert(names[i2] == a);
 915                 a = values[i2];
 916                 arguments[i] = a;
 917             }
 918         }
 919         return name.function.invokeWithArguments(arguments);
 920     }
 921 
 922     private void checkInvocationCounter() {
 923         if (COMPILE_THRESHOLD != 0 &&
 924             !forceInterpretation() && invocationCounter < COMPILE_THRESHOLD) {
 925             invocationCounter++;  // benign race
 926             if (invocationCounter >= COMPILE_THRESHOLD) {
 927                 // Replace vmentry with a bytecode version of this LF.
 928                 compileToBytecode();
 929             }
 930         }
 931     }
 932     Object interpretWithArgumentsTracing(Object... argumentValues) throws Throwable {
 933         traceInterpreter("[ interpretWithArguments", this, argumentValues);
 934         if (!forceInterpretation() && invocationCounter < COMPILE_THRESHOLD) {
 935             int ctr = invocationCounter++;  // benign race
 936             traceInterpreter("| invocationCounter", ctr);
 937             if (invocationCounter >= COMPILE_THRESHOLD) {
 938                 compileToBytecode();
 939             }
 940         }
 941         Object rval;
 942         try {
 943             assert(arityCheck(argumentValues));
 944             Object[] values = Arrays.copyOf(argumentValues, names.length);
 945             for (int i = argumentValues.length; i < values.length; i++) {
 946                 values[i] = interpretName(names[i], values);
 947             }
 948             rval = (result < 0) ? null : values[result];
 949         } catch (Throwable ex) {
 950             traceInterpreter("] throw =>", ex);
 951             throw ex;
 952         }
 953         traceInterpreter("] return =>", rval);
 954         return rval;
 955     }
 956 
 957     static void traceInterpreter(String event, Object obj, Object... args) {
 958         if (TRACE_INTERPRETER) {
 959             System.out.println("LFI: "+event+" "+(obj != null ? obj : "")+(args != null && args.length != 0 ? Arrays.asList(args) : ""));
 960         }
 961     }
 962     static void traceInterpreter(String event, Object obj) {
 963         traceInterpreter(event, obj, (Object[])null);
 964     }
 965     private boolean arityCheck(Object[] argumentValues) {
 966         assert(argumentValues.length == arity) : arity+"!="+Arrays.asList(argumentValues)+".length";
 967         // also check that the leading (receiver) argument is somehow bound to this LF:
 968         assert(argumentValues[0] instanceof MethodHandle) : "not MH: " + argumentValues[0];
 969         MethodHandle mh = (MethodHandle) argumentValues[0];
 970         assert(mh.internalForm() == this);
 971         // note:  argument #0 could also be an interface wrapper, in the future
 972         argumentTypesMatch(basicTypeSignature(), argumentValues);
 973         return true;
 974     }
 975     private boolean resultCheck(Object[] argumentValues, Object result) {
 976         MethodHandle mh = (MethodHandle) argumentValues[0];
 977         MethodType mt = mh.type();
 978         assert(valueMatches(returnType(), mt.returnType(), result));
 979         return true;
 980     }
 981 
 982     public String toString() {
 983         return debugString(-1);
 984     }
 985 
 986     String debugString(int indentLevel) {
 987         String prefix = MethodHandle.debugPrefix(indentLevel);
 988         String lambdaName = lambdaName();
 989         StringBuilder buf = new StringBuilder(lambdaName);
 990         buf.append("=Lambda(");
 991         for (int i = 0; i < names.length; i++) {
 992             if (i == arity)  buf.append(")=>{");
 993             Name n = names[i];
 994             if (i >= arity)  buf.append("\n    ").append(prefix);
 995             buf.append(n.paramString());
 996             if (i < arity) {
 997                 if (i+1 < arity)  buf.append(",");
 998                 continue;
 999             }
1000             buf.append("=").append(n.exprString());
1001             buf.append(";");
1002         }
1003         if (arity == names.length)  buf.append(")=>{");
1004         buf.append(result < 0 ? "void" : names[result]).append("}");
1005         if (TRACE_INTERPRETER) {
1006             // Extra verbosity:
1007             buf.append(":").append(basicTypeSignature());
1008             buf.append("/").append(vmentry);
1009         }
1010         return buf.toString();
1011     }
1012 
1013     @Override
1014     public boolean equals(Object obj) {
1015         return obj instanceof LambdaForm lf && equals(lf);
1016     }
1017     public boolean equals(LambdaForm that) {
1018         if (this.result != that.result)  return false;
1019         return Arrays.equals(this.names, that.names);
1020     }
1021     public int hashCode() {
1022         return result + 31 * Arrays.hashCode(names);
1023     }
1024     LambdaFormEditor editor() {
1025         return LambdaFormEditor.lambdaFormEditor(this);
1026     }
1027 
1028     boolean contains(Name name) {
1029         int pos = name.index();
1030         if (pos >= 0) {
1031             return pos < names.length && name.equals(names[pos]);
1032         }
1033         for (int i = arity; i < names.length; i++) {
1034             if (name.equals(names[i]))
1035                 return true;
1036         }
1037         return false;
1038     }
1039 
1040     @AOTSafeClassInitializer
1041     static class NamedFunction {
1042         final MemberName member;
1043         private @Stable MethodHandle resolvedHandle;
1044         private @Stable MethodType type;
1045 
1046         NamedFunction(MethodHandle resolvedHandle) {
1047             this(resolvedHandle.internalMemberName(), resolvedHandle);
1048         }
1049         NamedFunction(MemberName member, MethodHandle resolvedHandle) {
1050             this.member = member;
1051             this.resolvedHandle = resolvedHandle;
1052              // The following assert is almost always correct, but will fail for corner cases, such as PrivateInvokeTest.
1053              //assert(!isInvokeBasic(member));
1054         }
1055         NamedFunction(MethodType basicInvokerType) {
1056             assert(basicInvokerType == basicInvokerType.basicType()) : basicInvokerType;
1057             if (basicInvokerType.parameterSlotCount() < MethodType.MAX_MH_INVOKER_ARITY) {
1058                 this.resolvedHandle = basicInvokerType.invokers().basicInvoker();
1059                 this.member = resolvedHandle.internalMemberName();
1060             } else {
1061                 // necessary to pass BigArityTest
1062                 this.member = Invokers.invokeBasicMethod(basicInvokerType);
1063             }
1064             assert(isInvokeBasic(member));
1065         }
1066 
1067         private static boolean isInvokeBasic(MemberName member) {
1068             return member != null &&
1069                    member.getDeclaringClass() == MethodHandle.class &&
1070                   "invokeBasic".equals(member.getName());
1071         }
1072 
1073         // The next 2 constructors are used to break circular dependencies on MH.invokeStatic, etc.
1074         // Any LambdaForm containing such a member is not interpretable.
1075         // This is OK, since all such LFs are prepared with special primitive vmentry points.
1076         // And even without the resolvedHandle, the name can still be compiled and optimized.
1077         NamedFunction(Method method) {
1078             this(new MemberName(method));
1079         }
1080         NamedFunction(MemberName member) {
1081             this(member, null);
1082         }
1083 
1084         MethodHandle resolvedHandle() {
1085             if (resolvedHandle == null)  resolve();
1086             return resolvedHandle;
1087         }
1088 
1089         synchronized void resolve() {
1090             if (resolvedHandle == null) {
1091                 resolvedHandle = DirectMethodHandle.make(member);
1092             }
1093         }
1094 
1095         @Override
1096         public boolean equals(Object other) {
1097             if (this == other) return true;
1098             if (other == null) return false;
1099             return (other instanceof NamedFunction that)
1100                     && this.member != null
1101                     && this.member.equals(that.member);
1102         }
1103 
1104         @Override
1105         public int hashCode() {
1106             if (member != null)
1107                 return member.hashCode();
1108             return super.hashCode();
1109         }
1110 
1111         static final MethodType INVOKER_METHOD_TYPE =
1112             MethodType.methodType(Object.class, MethodHandle.class, Object[].class);
1113 
1114         private static MethodHandle computeInvoker(MethodTypeForm typeForm) {
1115             typeForm = typeForm.basicType().form();  // normalize to basic type
1116             MethodHandle mh = typeForm.cachedMethodHandle(MethodTypeForm.MH_NF_INV);
1117             if (mh != null)  return mh;
1118             MemberName invoker = InvokerBytecodeGenerator.generateNamedFunctionInvoker(typeForm);  // this could take a while
1119             mh = DirectMethodHandle.make(invoker);
1120             MethodHandle mh2 = typeForm.cachedMethodHandle(MethodTypeForm.MH_NF_INV);
1121             if (mh2 != null)  return mh2;  // benign race
1122             if (!mh.type().equals(INVOKER_METHOD_TYPE))
1123                 throw newInternalError(mh.debugString());
1124             return typeForm.setCachedMethodHandle(MethodTypeForm.MH_NF_INV, mh);
1125         }
1126 
1127         @Hidden
1128         Object invokeWithArguments(Object... arguments) throws Throwable {
1129             // If we have a cached invoker, call it right away.
1130             // NOTE: The invoker always returns a reference value.
1131             if (TRACE_INTERPRETER)  return invokeWithArgumentsTracing(arguments);
1132             return invoker().invokeBasic(resolvedHandle(), arguments);
1133         }
1134 
1135         @Hidden
1136         Object invokeWithArgumentsTracing(Object[] arguments) throws Throwable {
1137             Object rval;
1138             try {
1139                 traceInterpreter("[ call", this, arguments);
1140                 // resolvedHandle might be uninitialized, ok for tracing
1141                 if (resolvedHandle == null) {
1142                     traceInterpreter("| resolve", this);
1143                     resolvedHandle();
1144                 }
1145                 rval = invoker().invokeBasic(resolvedHandle(), arguments);
1146             } catch (Throwable ex) {
1147                 traceInterpreter("] throw =>", ex);
1148                 throw ex;
1149             }
1150             traceInterpreter("] return =>", rval);
1151             return rval;
1152         }
1153 
1154         private MethodHandle invoker() {
1155             return computeInvoker(methodType().form());
1156         }
1157 
1158         MethodType methodType() {
1159             MethodType type = this.type;
1160             if (type == null) {
1161                 this.type = type = calculateMethodType(member, resolvedHandle);
1162             }
1163             return type;
1164         }
1165 
1166         private static MethodType calculateMethodType(MemberName member, MethodHandle resolvedHandle) {
1167             if (resolvedHandle != null) {
1168                 return resolvedHandle.type();
1169             } else {
1170                 // only for certain internal LFs during bootstrapping
1171                 return member.getInvocationType();
1172             }
1173         }
1174 
1175         MemberName member() {
1176             assert(assertMemberIsConsistent());
1177             return member;
1178         }
1179 
1180         // Called only from assert.
1181         private boolean assertMemberIsConsistent() {
1182             if (resolvedHandle instanceof DirectMethodHandle) {
1183                 MemberName m = resolvedHandle.internalMemberName();
1184                 assert(m.equals(member));
1185             }
1186             return true;
1187         }
1188 
1189         Class<?> memberDeclaringClassOrNull() {
1190             return (member == null) ? null : member.getDeclaringClass();
1191         }
1192 
1193         BasicType returnType() {
1194             return basicType(methodType().returnType());
1195         }
1196 
1197         BasicType parameterType(int n) {
1198             return basicType(methodType().parameterType(n));
1199         }
1200 
1201         int arity() {
1202             return methodType().parameterCount();
1203         }
1204 
1205         public String toString() {
1206             if (member == null)  return String.valueOf(resolvedHandle);
1207             return member.getDeclaringClass().getSimpleName()+"."+member.getName();
1208         }
1209 
1210         public boolean isIdentity() {
1211             return this.equals(identity(returnType()));
1212         }
1213 
1214         public MethodHandleImpl.Intrinsic intrinsicName() {
1215             return resolvedHandle != null
1216                 ? resolvedHandle.intrinsicName()
1217                 : MethodHandleImpl.Intrinsic.NONE;
1218         }
1219 
1220         public Object intrinsicData() {
1221             return resolvedHandle != null
1222                 ? resolvedHandle.intrinsicData()
1223                 : null;
1224         }
1225     }
1226 
1227     public static String basicTypeSignature(MethodType type) {
1228         int params = type.parameterCount();
1229         char[] sig = new char[params + 2];
1230         int sigp = 0;
1231         while (sigp < params) {
1232             sig[sigp] = basicTypeChar(type.parameterType(sigp++));
1233         }
1234         sig[sigp++] = '_';
1235         sig[sigp++] = basicTypeChar(type.returnType());
1236         assert(sigp == sig.length);
1237         return String.valueOf(sig);
1238     }
1239 
1240     /** Hack to make signatures more readable when they show up in method names.
1241      * Signature should start with a sequence of uppercase ASCII letters.
1242      * Runs of three or more are replaced by a single letter plus a decimal repeat count.
1243      * A tail of anything other than uppercase ASCII is passed through unchanged.
1244      * @param signature sequence of uppercase ASCII letters with possible repetitions
1245      * @return same sequence, with repetitions counted by decimal numerals
1246      */
1247     public static String shortenSignature(String signature) {
1248         final int NO_CHAR = -1, MIN_RUN = 3;
1249         int c0, c1 = NO_CHAR, c1reps = 0;
1250         StringBuilder buf = null;
1251         int len = signature.length();
1252         if (len < MIN_RUN)  return signature;
1253         for (int i = 0; i <= len; i++) {
1254             if (c1 != NO_CHAR && !('A' <= c1 && c1 <= 'Z')) {
1255                 // wrong kind of char; bail out here
1256                 if (buf != null) {
1257                     buf.append(signature, i - c1reps, len);
1258                 }
1259                 break;
1260             }
1261             // shift in the next char:
1262             c0 = c1; c1 = (i == len ? NO_CHAR : signature.charAt(i));
1263             if (c1 == c0) { ++c1reps; continue; }
1264             // shift in the next count:
1265             int c0reps = c1reps; c1reps = 1;
1266             // end of a  character run
1267             if (c0reps < MIN_RUN) {
1268                 if (buf != null) {
1269                     while (--c0reps >= 0)
1270                         buf.append((char)c0);
1271                 }
1272                 continue;
1273             }
1274             // found three or more in a row
1275             if (buf == null)
1276                 buf = new StringBuilder().append(signature, 0, i - c0reps);
1277             buf.append((char)c0).append(c0reps);
1278         }
1279         return (buf == null) ? signature : buf.toString();
1280     }
1281 
1282     static final class Name {
1283         final BasicType type;
1284         final short index;
1285         final NamedFunction function;
1286         final Object constraint;  // additional type information, if not null
1287         @Stable final Object[] arguments;
1288 
1289         private static final Object[] EMPTY_ARGS = new Object[0];
1290 
1291         private Name(int index, BasicType type, NamedFunction function, Object[] arguments, Object constraint) {
1292             this.index = (short)index;
1293             this.type = type;
1294             this.function = function;
1295             this.arguments = arguments;
1296             this.constraint = constraint;
1297             assert(this.index == index && typesMatch(function, arguments));
1298             assert(constraint == null || isParam());  // only params have constraints
1299             assert(constraint == null || constraint instanceof ClassSpecializer.SpeciesData || constraint instanceof Class);
1300         }
1301 
1302         Name(MethodHandle function, Object... arguments) {
1303             this(new NamedFunction(function), arguments);
1304         }
1305         Name(MethodType functionType, Object... arguments) {
1306             this(new NamedFunction(functionType), arguments);
1307             assert(arguments[0] instanceof Name name && name.type == L_TYPE);
1308         }
1309         Name(MemberName function, Object... arguments) {
1310             this(new NamedFunction(function), arguments);
1311         }
1312         Name(NamedFunction function) {
1313             this(-1, function.returnType(), function, EMPTY_ARGS, null);
1314         }
1315         Name(NamedFunction function, Object arg) {
1316             this(-1, function.returnType(), function, new Object[] { arg }, null);
1317         }
1318         Name(NamedFunction function, Object arg0, Object arg1) {
1319             this(-1, function.returnType(), function, new Object[] { arg0, arg1 }, null);
1320         }
1321         Name(NamedFunction function, Object... arguments) {
1322             this(-1, function.returnType(), function, Arrays.copyOf(arguments, arguments.length, Object[].class), null);
1323         }
1324         /** Create a raw parameter of the given type, with an expected index. */
1325         Name(int index, BasicType type) {
1326             this(index, type, null, null, null);
1327         }
1328         /** Create a raw parameter of the given type. */
1329         Name(BasicType type) { this(-1, type); }
1330 
1331         BasicType type() { return type; }
1332         int index() { return index; }
1333 
1334         char typeChar() {
1335             return type.btChar;
1336         }
1337 
1338         Name withIndex(int i) {
1339             if (i == this.index) return this;
1340             return new Name(i, type, function, arguments, constraint);
1341         }
1342 
1343         Name withConstraint(Object constraint) {
1344             if (constraint == this.constraint)  return this;
1345             return new Name(index, type, function, arguments, constraint);
1346         }
1347 
1348         Name replaceName(Name oldName, Name newName) {  // FIXME: use replaceNames uniformly
1349             if (oldName == newName)  return this;
1350             @SuppressWarnings("LocalVariableHidesMemberVariable")
1351             Object[] arguments = this.arguments;
1352             if (arguments == null)  return this;
1353             boolean replaced = false;
1354             for (int j = 0; j < arguments.length; j++) {
1355                 if (arguments[j] == oldName) {
1356                     if (!replaced) {
1357                         replaced = true;
1358                         arguments = arguments.clone();
1359                     }
1360                     arguments[j] = newName;
1361                 }
1362             }
1363             if (!replaced)  return this;
1364             return new Name(function, arguments);
1365         }
1366         /** In the arguments of this Name, replace oldNames[i] pairwise by newNames[i].
1367          *  Limit such replacements to {@code start<=i<end}.  Return possibly changed self.
1368          */
1369         Name replaceNames(Name[] oldNames, Name[] newNames, int start, int end) {
1370             if (start >= end)  return this;
1371             @SuppressWarnings("LocalVariableHidesMemberVariable")
1372             Object[] arguments = this.arguments;
1373             boolean replaced = false;
1374         eachArg:
1375             for (int j = 0; j < arguments.length; j++) {
1376                 if (arguments[j] instanceof Name n) {
1377                     int check = n.index;
1378                     // harmless check to see if the thing is already in newNames:
1379                     if (check >= 0 && check < newNames.length && n == newNames[check])
1380                         continue eachArg;
1381                     // n might not have the correct index: n != oldNames[n.index].
1382                     for (int i = start; i < end; i++) {
1383                         if (n == oldNames[i]) {
1384                             if (n == newNames[i])
1385                                 continue eachArg;
1386                             if (!replaced) {
1387                                 replaced = true;
1388                                 arguments = arguments.clone();
1389                             }
1390                             arguments[j] = newNames[i];
1391                             continue eachArg;
1392                         }
1393                     }
1394                 }
1395             }
1396             if (!replaced)  return this;
1397             return new Name(function, arguments);
1398         }
1399         void internArguments() {
1400             @SuppressWarnings("LocalVariableHidesMemberVariable")
1401             Object[] arguments = this.arguments;
1402             for (int j = 0; j < arguments.length; j++) {
1403                 if (arguments[j] instanceof Name n) {
1404                     if (n.isParam() && n.index < INTERNED_ARGUMENT_LIMIT)
1405                         arguments[j] = internArgument(n);
1406                 }
1407             }
1408         }
1409         boolean isParam() {
1410             return function == null;
1411         }
1412 
1413         boolean refersTo(Class<?> declaringClass, String methodName) {
1414             return function != null &&
1415                     function.member() != null && function.member().refersTo(declaringClass, methodName);
1416         }
1417 
1418         /**
1419          * Check if MemberName is a call to MethodHandle.invokeBasic.
1420          */
1421         boolean isInvokeBasic() {
1422             if (function == null)
1423                 return false;
1424             if (arguments.length < 1)
1425                 return false;  // must have MH argument
1426             MemberName member = function.member();
1427             return member != null && member.refersTo(MethodHandle.class, "invokeBasic") &&
1428                     !member.isPublic() && !member.isStatic();
1429         }
1430 
1431         /**
1432          * Check if MemberName is a call to MethodHandle.linkToStatic, etc.
1433          */
1434         boolean isLinkerMethodInvoke() {
1435             if (function == null)
1436                 return false;
1437             if (arguments.length < 1)
1438                 return false;  // must have MH argument
1439             MemberName member = function.member();
1440             return member != null &&
1441                     member.getDeclaringClass() == MethodHandle.class &&
1442                     !member.isPublic() && member.isStatic() &&
1443                     member.getName().startsWith("linkTo");
1444         }
1445 
1446         public String toString() {
1447             return (isParam()?"a":"t")+(index >= 0 ? index : System.identityHashCode(this))+":"+typeChar();
1448         }
1449         public String debugString() {
1450             String s = paramString();
1451             return (function == null) ? s : s + "=" + exprString();
1452         }
1453         public String paramString() {
1454             String s = toString();
1455             Object c = constraint;
1456             if (c == null)
1457                 return s;
1458             if (c instanceof Class<?> cl)  c = cl.getSimpleName();
1459             return s + "/" + c;
1460         }
1461         public String exprString() {
1462             if (function == null)  return toString();
1463             StringBuilder buf = new StringBuilder(function.toString());
1464             buf.append("(");
1465             String cma = "";
1466             for (Object a : arguments) {
1467                 buf.append(cma); cma = ",";
1468                 if (a instanceof Name || a instanceof Integer)
1469                     buf.append(a);
1470                 else
1471                     buf.append("(").append(a).append(")");
1472             }
1473             buf.append(")");
1474             return buf.toString();
1475         }
1476 
1477         private boolean typesMatch(NamedFunction function, Object ... arguments) {
1478             if (arguments == null) {
1479                 assert(function == null);
1480                 return true;
1481             }
1482             assert(arguments.length == function.arity()) : "arity mismatch: arguments.length=" + arguments.length + " == function.arity()=" + function.arity() + " in " + debugString();
1483             for (int i = 0; i < arguments.length; i++) {
1484                 assert (typesMatch(function.parameterType(i), arguments[i])) : "types don't match: function.parameterType(" + i + ")=" + function.parameterType(i) + ", arguments[" + i + "]=" + arguments[i] + " in " + debugString();
1485             }
1486             return true;
1487         }
1488 
1489         private static boolean typesMatch(BasicType parameterType, Object object) {
1490             if (object instanceof Name name) {
1491                 return name.type == parameterType;
1492             }
1493             switch (parameterType) {
1494                 case I_TYPE:  return object instanceof Integer;
1495                 case J_TYPE:  return object instanceof Long;
1496                 case F_TYPE:  return object instanceof Float;
1497                 case D_TYPE:  return object instanceof Double;
1498             }
1499             assert(parameterType == L_TYPE);
1500             return true;
1501         }
1502 
1503         /** Return the index of the last occurrence of n in the argument array.
1504          *  Return -1 if the name is not used.
1505          */
1506         int lastUseIndex(Name n) {
1507             Object[] arguments = this.arguments;
1508             if (arguments == null)  return -1;
1509             for (int i = arguments.length; --i >= 0; ) {
1510                 if (arguments[i] == n)  return i;
1511             }
1512             return -1;
1513         }
1514 
1515         public boolean equals(Name that) {
1516             if (this == that)  return true;
1517             if (isParam())
1518                 // each parameter is a unique atom
1519                 return false;  // this != that
1520             return
1521                 //this.index == that.index &&
1522                 this.type == that.type &&
1523                 this.function.equals(that.function) &&
1524                 Arrays.equals(this.arguments, that.arguments);
1525         }
1526         @Override
1527         public boolean equals(Object x) {
1528             return x instanceof Name n && equals(n);
1529         }
1530         @Override
1531         public int hashCode() {
1532             if (isParam())
1533                 return index | (type.ordinal() << 8);
1534             return function.hashCode() ^ Arrays.hashCode(arguments);
1535         }
1536     }
1537 
1538     /** Return the index of the last name which contains n as an argument.
1539      *  Return -1 if the name is not used.  Return names.length if it is the return value.
1540      */
1541     int lastUseIndex(Name n) {
1542         int ni = n.index, nmax = names.length;
1543         assert(names[ni] == n);
1544         if (result == ni)  return nmax;  // live all the way beyond the end
1545         for (int i = nmax; --i > ni; ) {
1546             if (names[i].lastUseIndex(n) >= 0)
1547                 return i;
1548         }
1549         return -1;
1550     }
1551 
1552     /** Return the number of times n is used as an argument or return value. */
1553     int useCount(Name n) {
1554         int count = (result == n.index) ? 1 : 0;
1555         int i = Math.max(n.index + 1, arity);
1556         Name[] names = this.names;
1557         while (i < names.length) {
1558             Object[] arguments = names[i++].arguments;
1559             if (arguments != null) {
1560                 for (Object argument : arguments) {
1561                     if (argument == n) {
1562                         count++;
1563                     }
1564                 }
1565             }
1566         }
1567         return count;
1568     }
1569 
1570     static Name argument(int which, BasicType type) {
1571         if (which >= INTERNED_ARGUMENT_LIMIT)
1572             return new Name(which, type);
1573         return INTERNED_ARGUMENTS[type.ordinal()][which];
1574     }
1575     static Name internArgument(Name n) {
1576         assert(n.isParam()) : "not param: " + n;
1577         assert(n.index < INTERNED_ARGUMENT_LIMIT);
1578         if (n.constraint != null)  return n;
1579         return argument(n.index, n.type);
1580     }
1581     static Name[] arguments(int extra, MethodType types) {
1582         int length = types.parameterCount();
1583         Name[] names = new Name[length + extra];
1584         for (int i = 0; i < length; i++)
1585             names[i] = argument(i, basicType(types.parameterType(i)));
1586         return names;
1587     }
1588 
1589     static Name[] invokeArguments(int extra, MethodType types) {
1590         int length = types.parameterCount();
1591         Name[] names = new Name[length + extra + 1];
1592         names[0] = argument(0, L_TYPE);
1593         for (int i = 0; i < length; i++)
1594             names[i + 1] = argument(i + 1, basicType(types.parameterType(i)));
1595         return names;
1596     }
1597 
1598     static final int INTERNED_ARGUMENT_LIMIT = 10;
1599     private static final Name[][] INTERNED_ARGUMENTS
1600             = new Name[ARG_TYPE_LIMIT][INTERNED_ARGUMENT_LIMIT];
1601     static {
1602         for (BasicType type : BasicType.ARG_TYPES) {
1603             int ord = type.ordinal();
1604             for (int i = 0; i < INTERNED_ARGUMENTS[ord].length; i++) {
1605                 INTERNED_ARGUMENTS[ord][i] = new Name(i, type);
1606             }
1607         }
1608     }
1609 
1610     private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
1611 
1612     static LambdaForm identityForm(BasicType type) {
1613         int ord = type.ordinal();
1614         LambdaForm form = LF_identity[ord];
1615         if (form != null) {
1616             return form;
1617         }
1618         createIdentityForm(type);
1619         return LF_identity[ord];
1620     }
1621 
1622     static NamedFunction identity(BasicType type) {
1623         int ord = type.ordinal();
1624         NamedFunction function = NF_identity[ord];
1625         if (function != null) {
1626             return function;
1627         }
1628         createIdentityForm(type);
1629         return NF_identity[ord];
1630     }
1631 
1632     static LambdaForm constantForm(BasicType type) {
1633         assert type != null && type != V_TYPE : type;
1634         var cached = LF_constant[type.ordinal()];
1635         if (cached != null)
1636             return cached;
1637         return createConstantForm(type);
1638     }
1639 
1640     private static LambdaForm createConstantForm(BasicType type) {
1641         UNSAFE.ensureClassInitialized(BoundMethodHandle.class); // defend access to SimpleMethodHandle
1642         var species = SimpleMethodHandle.BMH_SPECIES.extendWith(type);
1643         var carrier = argument(0, L_TYPE).withConstraint(species); // BMH bound with data
1644         Name[] constNames = new Name[] { carrier, new Name(species.getterFunction(0), carrier) };
1645         return LF_constant[type.ordinal()] = create(1, constNames, Kind.CONSTANT);
1646     }
1647 
1648     private static final @Stable LambdaForm[] LF_identity = new LambdaForm[TYPE_LIMIT];
1649     private static final @Stable NamedFunction[] NF_identity = new NamedFunction[TYPE_LIMIT];
1650     private static final @Stable LambdaForm[] LF_constant = new LambdaForm[ARG_TYPE_LIMIT]; // no void
1651 
1652     private static final Object createIdentityFormLock = new Object();
1653     private static void createIdentityForm(BasicType type) {
1654         // Avoid racy initialization during bootstrap
1655         UNSAFE.ensureClassInitialized(BoundMethodHandle.class);
1656         synchronized (createIdentityFormLock) {
1657             final int ord = type.ordinal();
1658             LambdaForm idForm = LF_identity[ord];
1659             if (idForm != null) {
1660                 return;
1661             }
1662             char btChar = type.basicTypeChar();
1663             boolean isVoid = (type == V_TYPE);
1664             Class<?> btClass = type.btClass;
1665             MethodType idType = (isVoid) ? MethodType.methodType(btClass) : MethodType.methodType(btClass, btClass);
1666 
1667             // Look up symbolic names.  It might not be necessary to have these,
1668             // but if we need to emit direct references to bytecodes, it helps.
1669             MemberName idMem = new MemberName(LambdaForm.class, "identity_"+btChar, idType, REF_invokeStatic);
1670             try {
1671                 idMem = IMPL_NAMES.resolveOrFail(REF_invokeStatic, idMem, null, LM_TRUSTED, NoSuchMethodException.class);
1672             } catch (IllegalAccessException|NoSuchMethodException ex) {
1673                 throw newInternalError(ex);
1674             }
1675 
1676             NamedFunction idFun;
1677 
1678             // Create the LFs and NamedFunctions. Precompiling LFs to byte code is needed to break circular
1679             // bootstrap dependency on this method in case we're interpreting LFs
1680             if (isVoid) {
1681                 Name[] idNames = new Name[] { argument(0, L_TYPE) };
1682                 idForm = LambdaForm.create(1, idNames, VOID_RESULT, Kind.IDENTITY);
1683                 idForm.compileToBytecode();
1684                 idFun = new NamedFunction(idMem, SimpleMethodHandle.make(idMem.getInvocationType(), idForm));
1685             } else {
1686                 Name[] idNames = new Name[] { argument(0, L_TYPE), argument(1, type) };
1687                 idForm = LambdaForm.create(2, idNames, 1, Kind.IDENTITY);
1688                 idForm.compileToBytecode();
1689                 idFun = new NamedFunction(idMem, MethodHandleImpl.makeIntrinsic(idMem.getInvocationType(), idForm,
1690                             MethodHandleImpl.Intrinsic.IDENTITY));
1691             }
1692 
1693             LF_identity[ord] = idForm;
1694             NF_identity[ord] = idFun;
1695 
1696             assert(idFun.isIdentity());
1697         }
1698     }
1699 
1700     // Avoid appealing to ValueConversions at bootstrap time:
1701     private static int identity_I(int x) { return x; }
1702     private static long identity_J(long x) { return x; }
1703     private static float identity_F(float x) { return x; }
1704     private static double identity_D(double x) { return x; }
1705     private static Object identity_L(Object x) { return x; }
1706     private static void identity_V() { return; }
1707     /**
1708      * Internal marker for byte-compiled LambdaForms.
1709      */
1710     /*non-public*/
1711     @Target(ElementType.METHOD)
1712     @Retention(RetentionPolicy.RUNTIME)
1713     @interface Compiled {
1714     }
1715 
1716     private static final HashMap<String,Integer> DEBUG_NAME_COUNTERS;
1717     private static final HashMap<LambdaForm,String> DEBUG_NAMES;
1718     static {
1719         if (debugEnabled()) {
1720             DEBUG_NAME_COUNTERS = new HashMap<>();
1721             DEBUG_NAMES = new HashMap<>();
1722         } else {
1723             DEBUG_NAME_COUNTERS = null;
1724             DEBUG_NAMES = null;
1725         }
1726     }
1727 
1728     static {
1729         // The Holder class will contain pre-generated forms resolved
1730         // using MemberName.getFactory(). However, that doesn't initialize the
1731         // class, which subtly breaks inlining etc. By forcing
1732         // initialization of the Holder class we avoid these issues.
1733         UNSAFE.ensureClassInitialized(Holder.class);
1734     }
1735 
1736     /// Holds pre-generated bytecode for common lambda forms.
1737     ///
1738     /// This class may be substituted in the JDK's modules image, or in an AOT
1739     /// cache, by a version generated by [GenerateJLIClassesHelper].
1740     ///
1741     /// The method names of this class are internal tokens recognized by
1742     /// [InvokerBytecodeGenerator#lookupPregenerated] and are subject to change.
1743     @AOTSafeClassInitializer
1744     final class Holder {}
1745 
1746     // The following hack is necessary in order to suppress TRACE_INTERPRETER
1747     // during execution of the static initializes of this class.
1748     // Turning on TRACE_INTERPRETER too early will cause
1749     // stack overflows and other misbehavior during attempts to trace events
1750     // that occur during LambdaForm.<clinit>.
1751     // Therefore, do not move this line higher in this file, and do not remove.
1752     private static final boolean TRACE_INTERPRETER = MethodHandleStatics.TRACE_INTERPRETER;
1753 }