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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package jdk.nashorn.internal.codegen;

import static jdk.nashorn.internal.codegen.CompilerConstants.virtualCallNoLookup;
import static jdk.nashorn.internal.runtime.linker.NashornCallSiteDescriptor.CALLSITE_OPTIMISTIC;

import java.util.Arrays;
import java.util.EnumSet;
import jdk.nashorn.internal.codegen.types.Type;
import jdk.nashorn.internal.ir.Symbol;
import jdk.nashorn.internal.runtime.ScriptObject;
import jdk.nashorn.internal.runtime.UnwarrantedOptimismException;
import jdk.nashorn.internal.runtime.options.Options;

A scope call or get operation that can be shared by several call sites. This generates a static
method that wraps the invokedynamic instructions to get or call scope variables.
The reason for this is to reduce memory footprint and initial linking overhead of huge scripts.
Static methods generated by this class expect three parameters in addition to the parameters of the
function call: The current scope object, the depth of the target scope relative to the scope argument,
and the program point in case the target operation is optimistic.
Optimistic operations are called with program point 0. If an UnwarrentedOptimismException
is thrown, it is caught by the shared call method and rethrown with the program point of the invoking call site.
Shared scope calls are not used if the scope contains a with statement or a call to
eval.
/**
 * A scope call or get operation that can be shared by several call sites. This generates a static
 * method that wraps the invokedynamic instructions to get or call scope variables.
 * The reason for this is to reduce memory footprint and initial linking overhead of huge scripts.
 *
 * <p>Static methods generated by this class expect three parameters in addition to the parameters of the
 * function call: The current scope object, the depth of the target scope relative to the scope argument,
 * and the program point in case the target operation is optimistic.</p>
 *
 * <p>Optimistic operations are called with program point <code>0</code>. If an <code>UnwarrentedOptimismException</code>
 * is thrown, it is caught by the shared call method and rethrown with the program point of the invoking call site.</p>
 *
 * <p>Shared scope calls are not used if the scope contains a <code>with</code> statement or a call to
 * <code>eval</code>.</p>
 */
class SharedScopeCall {

    
Threshold for using shared scope function calls.
/**
     * Threshold for using shared scope function calls.
     */
    public static final int SHARED_CALL_THRESHOLD =
            Options.getIntProperty("nashorn.shared.scope.call.threshold", 5);
    
Threshold for using shared scope variable getter. This is higher than for calls as lower values
degrade performance on many scripts.
/**
     * Threshold for using shared scope variable getter. This is higher than for calls as lower values
     * degrade performance on many scripts.
     */
    public static final int SHARED_GET_THRESHOLD  =
            Options.getIntProperty("nashorn.shared.scope.get.threshold", 100);

    private static final CompilerConstants.Call REPLACE_PROGRAM_POINT = virtualCallNoLookup(
                    UnwarrantedOptimismException.class, "replaceProgramPoint",
                    UnwarrantedOptimismException.class, int.class);

    
Number of fixed parameters /** Number of fixed parameters */
    private static final int FIXED_PARAM_COUNT = 3;

    private final Type valueType;
    private final Symbol symbol;
    private final Type returnType;
    private final Type[] paramTypes;
    private final int flags;
    private final boolean isCall;
    private final boolean isOptimistic;
    private CompileUnit compileUnit;
    private String methodName;
    private String staticSignature;

    
Constructor.
Params:
symbol – the symbol
valueType – the type of the value
returnType – the return type
paramTypes – the function parameter types
flags – the callsite flags
isOptimistic – whether target call is optimistic and we need to handle UnwarrentedOptimismException/**
     * Constructor.
     *
     * @param symbol the symbol
     * @param valueType the type of the value
     * @param returnType the return type
     * @param paramTypes the function parameter types
     * @param flags the callsite flags
     * @param isOptimistic whether target call is optimistic and we need to handle UnwarrentedOptimismException
     */
    SharedScopeCall(final Symbol symbol, final Type valueType, final Type returnType, final Type[] paramTypes,
                    final int flags, final boolean isOptimistic) {
        this.symbol = symbol;
        this.valueType = valueType;
        this.returnType = returnType;
        this.paramTypes = paramTypes;
        this.flags = flags;
        this.isCall = paramTypes != null; // If paramTypes is not null this is a call, otherwise it's just a get.
        this.isOptimistic = isOptimistic;
    }

    @Override
    public int hashCode() {
        return symbol.hashCode() ^ returnType.hashCode() ^ Arrays.hashCode(paramTypes) ^ flags ^ Boolean.hashCode(isOptimistic);
    }

    @Override
    public boolean equals(final Object obj) {
        if (obj instanceof SharedScopeCall) {
            final SharedScopeCall c = (SharedScopeCall) obj;
            return symbol.equals(c.symbol)
                    && flags == c.flags
                    && returnType.equals(c.returnType)
                    && Arrays.equals(paramTypes, c.paramTypes)
                    && isOptimistic == c.isOptimistic;
        }
        return false;
    }

    
Set the compile unit and method name.
Params:
compileUnit – the compile unit
methodName – the method name/**
     * Set the compile unit and method name.
     * @param compileUnit the compile unit
     * @param methodName the method name
     */
    protected void setClassAndName(final CompileUnit compileUnit, final String methodName) {
        this.compileUnit = compileUnit;
        this.methodName  = methodName;
    }

    
Generate the invoke instruction for this shared scope call.
Params:
method – the method emitter/**
     * Generate the invoke instruction for this shared scope call.
     * @param method the method emitter
     */
    public void generateInvoke(final MethodEmitter method) {
        method.invokestatic(compileUnit.getUnitClassName(), methodName, getStaticSignature());
    }

    
Generate the method that implements the scope get or call.
/**
     * Generate the method that implements the scope get or call.
     */
    protected void generateScopeCall() {
        final ClassEmitter classEmitter = compileUnit.getClassEmitter();
        final EnumSet<ClassEmitter.Flag> methodFlags = EnumSet.of(ClassEmitter.Flag.STATIC);

        // This method expects two fixed parameters in addition to any parameters that may be
        // passed on to the function: A ScriptObject representing the caller's current scope object,
        // and an int specifying the distance to the target scope containing the symbol we want to
        // access, or -1 if this is not known at compile time (e.g. because of a "with" or "eval").

        final MethodEmitter method = classEmitter.method(methodFlags, methodName, getStaticSignature());
        method.begin();

        // Load correct scope by calling getProto(int) on the scope argument with the supplied depth argument
        method.load(Type.OBJECT, 0);
        method.load(Type.INT, 1);
        method.invoke(ScriptObject.GET_PROTO_DEPTH);

        assert !isCall || valueType.isObject(); // Callables are always loaded as object

        // Labels for catch of UnsupportedOptimismException
        final Label beginTry;
        final Label endTry;
        final Label catchLabel;

        if(isOptimistic) {
            beginTry = new Label("begin_try");
            endTry = new Label("end_try");
            catchLabel = new Label("catch_label");
            method.label(beginTry);
            method._try(beginTry, endTry, catchLabel, UnwarrantedOptimismException.class, false);
        } else {
            beginTry = endTry = catchLabel = null;
        }

        // If this is an optimistic get we set the optimistic flag but don't set the program point,
        // which implies a program point of 0. If optimism fails we'll replace it with the actual
        // program point which caller supplied as third argument.
        final int getFlags = isOptimistic && !isCall ? flags | CALLSITE_OPTIMISTIC : flags;
        method.dynamicGet(valueType, symbol.getName(), getFlags, isCall, false);

        // If this is a get we're done, otherwise call the value as function.
        if (isCall) {
            method.convert(Type.OBJECT);
            // ScriptFunction will see CALLSITE_SCOPE and will bind scope accordingly.
            method.loadUndefined(Type.OBJECT);
            int slot = FIXED_PARAM_COUNT;
            for (final Type type : paramTypes) {
                method.load(type, slot);
                slot += type.getSlots();
            }

            // Same as above, set optimistic flag but leave program point as 0.
            final int callFlags = isOptimistic ? flags | CALLSITE_OPTIMISTIC : flags;

            method.dynamicCall(returnType, 2 + paramTypes.length, callFlags, symbol.getName());

        }

        if (isOptimistic) {
            method.label(endTry);
        }

        method._return(returnType);

        if (isOptimistic) {
            // We caught a UnwarrantedOptimismException, replace 0 program point with actual program point
            method._catch(catchLabel);
            method.load(Type.INT, 2);
            method.invoke(REPLACE_PROGRAM_POINT);
            method.athrow();
        }

        method.end();
    }

    private String getStaticSignature() {
        if (staticSignature == null) {
            if (paramTypes == null) {
                staticSignature = Type.getMethodDescriptor(returnType, Type.typeFor(ScriptObject.class), Type.INT, Type.INT);
            } else {
                final Type[] params = new Type[paramTypes.length + FIXED_PARAM_COUNT];
                params[0] = Type.typeFor(ScriptObject.class);
                params[1] = Type.INT;
                params[2] = Type.INT;
                System.arraycopy(paramTypes, 0, params, FIXED_PARAM_COUNT, paramTypes.length);
                staticSignature = Type.getMethodDescriptor(returnType, params);
            }
        }
        return staticSignature;
    }

    @Override
    public String toString() {
        return methodName + " " + staticSignature;
    }

}