Examples of java.lang.invoke.LambdaForm$NamedFunction

java.lang.invoke.LambdaForm
The symbolic, non-executable form of a method handle's invocation semantics. It consists of a series of names. The first N (N=arity) names are parameters, while any remaining names are temporary values. Each temporary specifies the application of a function to some arguments. The functions are method handles, while the arguments are mixes of constant values and local names. The result of the lambda is defined as one of the names, often the last one.
Here is an approximate grammar:
```
 {@code}LambdaForm = "(" ArgName* ")=> " TempName* Result "}" ArgName = "a" N ":" T TempName = "t" N ":" T "=" Function "(" Argument* ");" Function = ConstantValue Argument = NameRef | ConstantValue Result = NameRef | "void" NameRef = "a" N | "t" N N = (any whole number) T = "L" | "I" | "J" | "F" | "D" | "V" }
```
Names are numbered consecutively from left to right starting at zero. (The letters are merely a taste of syntax sugar.) Thus, the first temporary (if any) is always numbered N (where N=arity). Every occurrence of a name reference in an argument list must refer to a name previously defined within the same lambda. A lambda has a void result if and only if its result index is -1. If a temporary has the type "V", it cannot be the subject of a NameRef, even though possesses a number. Note that all reference types are erased to "L", which stands for {@code Object}. All subword types (boolean, byte, short, char) are erased to "I" which is {@code int}. The other types stand for the usual primitive types.
Function invocation closely follows the static rules of the Java verifier. Arguments and return values must exactly match when their "Name" types are considered. Conversions are allowed only if they do not change the erased type.
- L = Object: casts are used freely to convert into and out of reference types
- I = int: subword types are forcibly narrowed when passed as arguments (see {@code explicitCastArguments})
- J = long: no implicit conversions
- F = float: no implicit conversions
- D = double: no implicit conversions
- V = void: a function result may be void if and only if its Name is of type "V"
Although implicit conversions are not allowed, explicit ones can easily be encoded by using temporary expressions which call type-transformed identity functions.
Examples:
```
 {@code}(a0:J)=> a0 } == identity(long) (a0:I)=>{ t1:V = System.out#println(a0); void } == System.out#println(int) (a0:L)=>{ t1:V = System.out#println(a0); a0 } == identity, with printing side-effect (a0:L, a1:L)=>{ t2:L = BoundMethodHandle#argument(a0); t3:L = BoundMethodHandle#target(a0); t4:L = MethodHandle#invoke(t3, t2, a1); t4 } == general invoker for unary insertArgument combination (a0:L, a1:L)=>{ t2:L = FilterMethodHandle#filter(a0); t3:L = MethodHandle#invoke(t2, a1); t4:L = FilterMethodHandle#target(a0); t5:L = MethodHandle#invoke(t4, t3); t5 } == general invoker for unary filterArgument combination (a0:L, a1:L)=>{ ...(same as previous example)... t5:L = MethodHandle#invoke(t4, t3, a1); t5 } == general invoker for unary/unary foldArgument combination (a0:L, a1:I)=>{ t2:I = identity(long).asType((int)->long)(a1); t2 } == invoker for identity method handle which performs i2l (a0:L, a1:L)=>{ t2:L = BoundMethodHandle#argument(a0); t3:L = Class#cast(t2,a1); t3 } == invoker for identity method handle which performs cast }
```
@author John Rose, JSR 292 EG


    private MethodHandle makeExactOrGeneralInvoker(boolean isExact) {
        MethodType mtype = targetType;
        MethodType invokerType = mtype.invokerType();
        int which = (isExact ? MethodTypeForm.LF_EX_INVOKER : MethodTypeForm.LF_GEN_INVOKER);
        LambdaForm lform = invokeHandleForm(mtype, false, which);
        MethodHandle invoker = BoundMethodHandle.bindSingle(invokerType, lform, mtype);
        String whichName = (isExact ? "invokeExact" : "invoke");
        invoker = invoker.withInternalMemberName(MemberName.makeMethodHandleInvoke(whichName, mtype));
        assert(checkInvoker(invoker));
        maybeCompileToBytecode(invoker);

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        switch (name) {
        case "invokeExact":  which = MethodTypeForm.LF_EX_LINKER; break;
        case "invoke":       which = MethodTypeForm.LF_GEN_LINKER; break;
        default:             throw new InternalError("not invoker: "+name);
        }
        LambdaForm lform;
        if (mtype.parameterSlotCount() <= MethodType.MAX_MH_ARITY - MH_LINKER_ARG_APPENDED) {
            lform = invokeHandleForm(mtype, false, which);
            appendixResult[0] = mtype;
        } else {
            lform = invokeHandleForm(mtype, true, which);

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        case MethodTypeForm.LF_EX_INVOKER:  isLinker = false; isGeneric = false; debugName = "exactInvoker"; break;
        case MethodTypeForm.LF_GEN_LINKER:  isLinker = true;  isGeneric = true;  debugName = "invoke_MT"; break;
        case MethodTypeForm.LF_GEN_INVOKER: isLinker = false; isGeneric = true;  debugName = "invoker"; break;
        default: throw new InternalError();
        }
        LambdaForm lform;
        if (isCached) {
            lform = mtype.form().cachedLambdaForm(which);
            if (lform != null)  return lform;
        }
        // exactInvokerForm (Object,Object)Object
        //   link with java.lang.invoke.MethodHandle.invokeBasic(MethodHandle,Object,Object)Object/invokeSpecial
        final int THIS_MH      = 0;
        final int CALL_MH      = THIS_MH + (isLinker ? 0 : 1);
        final int ARG_BASE     = CALL_MH + 1;
        final int OUTARG_LIMIT = ARG_BASE + mtype.parameterCount();
        final int INARG_LIMIT  = OUTARG_LIMIT + (isLinker && !customized ? 1 : 0);
        int nameCursor = OUTARG_LIMIT;
        final int MTYPE_ARG    = customized ? -1 : nameCursor++;  // might be last in-argument
        final int CHECK_TYPE   = nameCursor++;
        final int LINKER_CALL  = nameCursor++;
        MethodType invokerFormType = mtype.invokerType();
        if (isLinker) {
            if (!customized)
                invokerFormType = invokerFormType.appendParameterTypes(MemberName.class);
        } else {
            invokerFormType = invokerFormType.invokerType();
        }
        Name[] names = arguments(nameCursor - INARG_LIMIT, invokerFormType);
        assert(names.length == nameCursor)
                : Arrays.asList(mtype, customized, which, nameCursor, names.length);
        if (MTYPE_ARG >= INARG_LIMIT) {
            assert(names[MTYPE_ARG] == null);
            NamedFunction getter = BoundMethodHandle.getSpeciesData("L").getterFunction(0);
            names[MTYPE_ARG] = new Name(getter, names[THIS_MH]);
            // else if isLinker, then MTYPE is passed in from the caller (e.g., the JVM)
        }


        // Make the final call.  If isGeneric, then prepend the result of type checking.
        MethodType outCallType = mtype.basicType();
        Object[] outArgs = Arrays.copyOfRange(names, CALL_MH, OUTARG_LIMIT, Object[].class);
        Object mtypeArg = (customized ? mtype : names[MTYPE_ARG]);
        if (!isGeneric) {
            names[CHECK_TYPE] = new Name(NF_checkExactType, names[CALL_MH], mtypeArg);
            // mh.invokeExact(a*):R => checkExactType(mh, TYPEOF(a*:R)); mh.invokeBasic(a*)
        } else {
            names[CHECK_TYPE] = new Name(NF_checkGenericType, names[CALL_MH], mtypeArg);
            // mh.invokeGeneric(a*):R => checkGenericType(mh, TYPEOF(a*:R)).invokeBasic(a*)
            outArgs[0] = names[CHECK_TYPE];
        }
        names[LINKER_CALL] = new Name(outCallType, outArgs);
        lform = new LambdaForm(debugName, INARG_LIMIT, names);
        if (isLinker)
            lform.compileToBytecode();  // JVM needs a real methodOop
        if (isCached)
            lform = mtype.form().setCachedLambdaForm(which, lform);
        return lform;
    }

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         *  => MH.asType(MT0).invokeBasic(A*)
         */
    }


    static MemberName linkToCallSiteMethod(MethodType mtype) {
        LambdaForm lform = callSiteForm(mtype, false);
        return lform.vmentry;
    }

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        LambdaForm lform = callSiteForm(mtype, false);
        return lform.vmentry;
    }


    static MemberName linkToTargetMethod(MethodType mtype) {
        LambdaForm lform = callSiteForm(mtype, true);
        return lform.vmentry;
    }

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    // skipCallSite is true if we are optimizing a ConstantCallSite
    private static LambdaForm callSiteForm(MethodType mtype, boolean skipCallSite) {
        mtype = mtype.basicType();  // normalize Z to I, String to Object, etc.
        final int which = (skipCallSite ? MethodTypeForm.LF_MH_LINKER : MethodTypeForm.LF_CS_LINKER);
        LambdaForm lform = mtype.form().cachedLambdaForm(which);
        if (lform != null)  return lform;
        // exactInvokerForm (Object,Object)Object
        //   link with java.lang.invoke.MethodHandle.invokeBasic(MethodHandle,Object,Object)Object/invokeSpecial
        final int ARG_BASE     = 0;
        final int OUTARG_LIMIT = ARG_BASE + mtype.parameterCount();
        final int INARG_LIMIT  = OUTARG_LIMIT + 1;
        int nameCursor = OUTARG_LIMIT;
        final int APPENDIX_ARG = nameCursor++;  // the last in-argument
        final int CSITE_ARG    = skipCallSite ? -1 : APPENDIX_ARG;
        final int CALL_MH      = skipCallSite ? APPENDIX_ARG : nameCursor++;  // result of getTarget
        final int LINKER_CALL  = nameCursor++;
        MethodType invokerFormType = mtype.appendParameterTypes(skipCallSite ? MethodHandle.class : CallSite.class);
        Name[] names = arguments(nameCursor - INARG_LIMIT, invokerFormType);
        assert(names.length == nameCursor);
        assert(names[APPENDIX_ARG] != null);
        if (!skipCallSite)
            names[CALL_MH] = new Name(NF_getCallSiteTarget, names[CSITE_ARG]);
        // (site.)invokedynamic(a*):R => mh = site.getTarget(); mh.invokeBasic(a*)
        final int PREPEND_MH = 0, PREPEND_COUNT = 1;
        Object[] outArgs = Arrays.copyOfRange(names, ARG_BASE, OUTARG_LIMIT + PREPEND_COUNT, Object[].class);
        // prepend MH argument:
        System.arraycopy(outArgs, 0, outArgs, PREPEND_COUNT, outArgs.length - PREPEND_COUNT);
        outArgs[PREPEND_MH] = names[CALL_MH];
        names[LINKER_CALL] = new Name(mtype, outArgs);
        lform = new LambdaForm((skipCallSite ? "linkToTargetMethod" : "linkToCallSite"), INARG_LIMIT, names);
        lform.compileToBytecode();  // JVM needs a real methodOop
        lform = mtype.form().setCachedLambdaForm(which, lform);
        return lform;
    }

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            mtype = mtype.insertParameterTypes(0, receiver);
        }
        if (!member.isField()) {
            if (refKind == REF_invokeSpecial) {
                member = member.asSpecial();
                LambdaForm lform = preparedLambdaForm(member);
                return new Special(mtype, lform, member);
            } else {
                LambdaForm lform = preparedLambdaForm(member);
                return new DirectMethodHandle(mtype, lform, member);
            }
        } else {
            LambdaForm lform = preparedFieldLambdaForm(member);
            if (member.isStatic()) {
                long offset = MethodHandleNatives.staticFieldOffset(member);
                Object base = MethodHandleNatives.staticFieldBase(member);
                return new StaticAccessor(mtype, lform, member, base, offset);
            } else {

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        assert(ctor.isConstructor() && ctor.getName().equals("<init>"));
        Class<?> instanceClass = ctor.getDeclaringClass();
        ctor = ctor.asConstructor();
        assert(ctor.isConstructor() && ctor.getReferenceKind() == REF_newInvokeSpecial) : ctor;
        MethodType mtype = ctor.getMethodType().changeReturnType(instanceClass);
        LambdaForm lform = preparedLambdaForm(ctor);
        MemberName init = ctor.asSpecial();
        assert(init.getMethodType().returnType() == void.class);
        return new Constructor(mtype, lform, ctor, init, instanceClass);
    }

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        if (which == LF_INVSTATIC && shouldBeInitialized(m)) {
            // precompute the barrier-free version:
            preparedLambdaForm(mtype, which);
            which = LF_INVSTATIC_INIT;
        }
        LambdaForm lform = preparedLambdaForm(mtype, which);
        maybeCompile(lform, m);
        assert(lform.methodType().dropParameterTypes(0, 1)
                .equals(m.getInvocationType().basicType()))
                : Arrays.asList(m, m.getInvocationType().basicType(), lform, lform.methodType());
        return lform;
    }

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                : Arrays.asList(m, m.getInvocationType().basicType(), lform, lform.methodType());
        return lform;
    }


    private static LambdaForm preparedLambdaForm(MethodType mtype, int which) {
        LambdaForm lform = mtype.form().cachedLambdaForm(which);
        if (lform != null)  return lform;
        lform = makePreparedLambdaForm(mtype, which);
        return mtype.form().setCachedLambdaForm(which, lform);
    }

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