ChocoPy/src/main/java/chocopy/common/codegen/CodeGenBase.java

package chocopy.common.codegen;

import chocopy.common.analysis.AbstractNodeAnalyzer;
import chocopy.common.analysis.SymbolTable;
import chocopy.common.analysis.types.Type;
import chocopy.common.analysis.types.ValueType;
import chocopy.common.astnodes.*;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import static chocopy.common.Utils.*;
import static chocopy.common.codegen.RiscVBackend.Register.*;

/**
 * The code generator for a ChocoPy program.
 *
 * <p>This class implements logic to analyze all declarations in a program and create descriptors
 * for classes, functions, methods, variables (global and local), and attributes. This logic also
 * builds symbol tables for globals and individual functions.
 *
 * <p>This class also implements logic to emit global variables, object prototypes and dispatch
 * tables, as well as int/str/bool constants.
 *
 * <p>However, this class is abstract because it does not implement logic for emitting executable
 * code in bodies of user-defined functions as well as in top-level statements. This class should be
 * extended with implementations for such logic.
 *
 * <p>All non-public members of this class are `protected`, and can be overridden by sub-classes to
 * extend change functionality.
 *
 * <p>The SymbolInfo classes can also be overridden. If say you want to use your own extended
 * FuncInfo called MyFuncInfo (that extends FuncInfo), then override the makeFuncInfo() method of
 * this class to `return new MyFuncInfo(...)` instead. This is probably not needed, though.
 */
public abstract class CodeGenBase {

    /** The location of the text resources containing common library code. */
    protected static final String LIBRARY_CODE_DIR = "chocopy/common/";

    /** The backend that emits assembly. */
    protected final RiscVBackend backend;

    /** Convenience variable: the word size for the current back end. */
    protected final int wordSize;

    /** A counter for generating unique class type tags. */
    protected int nextTypeTag = 0;

    /** A counter used to generate unique local label names. */
    protected int nextLabelSuffix = 0;

    /**
     * Predefined classes. The list "class" is a fake class; we use it only to emit a prototype
     * object for empty lists.
     */
    protected ClassInfo objectClass, intClass, boolClass, strClass, listClass;

    /** Predefined functions. */
    protected FuncInfo printFunc, lenFunc, inputFunc;

    /** A list of global variables, whose initial values are emitted in the backend. */
    protected final List<GlobalVarInfo> globalVars = new ArrayList<>();

    /**
     * A list of program classes, whose prototype objects and dispatch tables are emitted in the
     * backend.
     */
    protected final List<ClassInfo> classes = new ArrayList<>();

    /**
     * A list of functions (including methods and nested functions) whose bodies are emitted in the
     * backend.
     */
    protected final List<FuncInfo> functions = new ArrayList<>();

    /** Label for built-in routine: alloc. */
    protected final Label objectAllocLabel = new Label("alloc");

    /** Label for built-in routine: alloc2. */
    protected final Label objectAllocResizeLabel = new Label("alloc2");

    /** Label for built-in routine: abort. */
    protected final Label abortLabel = new Label("abort");

    /** Label for built-in routine: heap.init. */
    protected final Label heapInitLabel = new Label("heap.init");

    /** Error codes. */
    protected final int ERROR_ARG = 1,
            ERROR_DIV_ZERO = 2,
            ERROR_OOB = 3,
            ERROR_NONE = 4,
            ERROR_OOM = 5,
            ERROR_NYI = 6;

    /** Size of heap memory. */
    protected final int HEAP_SIZE_BYTES = 1024 * 1024 * 32;

    /** Ecall numbers for intrinsic routines. */
    protected final int EXIT_ECALL = 10,
            EXIT2_ECALL = 17,
            PRINT_STRING_ECALL = 4,
            PRINT_CHAR_ECALL = 11,
            PRINT_INT_ECALL = 1,
            READ_STRING_ECALL = 8,
            FILL_LINE_BUFFER__ECALL = 18,
            SBRK_ECALL = 9;

    /**
     * The symbol table that maps global names to information about the bound global variables,
     * global functions, or classes.
     */
    protected final SymbolTable<SymbolInfo> globalSymbols = new SymbolTable<>();

    /** A utility for caching constants and generating labels for constants. */
    protected final Constants constants = new Constants();

    /** The object header size, in words (includes type tag, size, and dispatch table pointer). */
    public static final int HEADER_SIZE = 3;

    /**
     * Initializes a code generator for ChocoPy that uses BACKEND to emit assembly code.
     *
     * <p>The constructor creates Info objects for predefined functions, classes, methods, and
     * built-in routines.
     */
    public CodeGenBase(RiscVBackend backend) {
        this.backend = backend;
        wordSize = backend.getWordSize();

        initClasses();
        initFunctions();
        initAsmConstants();
    }

    /** Return a fresh type tag. */
    protected int getNextTypeTag() {
        return nextTypeTag++;
    }

    /** Returns the next unique label suffix. */
    protected int getNextLabelSuffix() {
        return nextLabelSuffix++;
    }

    /**
     * Return a fresh label.
     *
     * <p>This label is guaranteed to be unique amongst labels generated by invoking this method.
     * All such labels have a prefix of `label_`.
     *
     * <p>This is useful to generate local labels in function bodies (e.g. for targets of jumps),
     * where the name does not matter in general.
     */
    protected Label generateLocalLabel() {
        return new Label(String.format("label_%d", getNextLabelSuffix()));
    }

    /**
     * Generates assembly code for PROGRAM.
     *
     * <p>This is the main driver that calls internal methods for emitting DATA section (globals,
     * constants, prototypes, etc) as well as the the CODE section (predefined functions, built-in
     * routines, and user-defined functions).
     */
    public void generate(Program program) {
        analyzeProgram(program);

        backend.startData();

        for (ClassInfo classInfo : this.classes) {
            emitPrototype(classInfo);
        }

        for (ClassInfo classInfo : this.classes) {
            emitDispatchTable(classInfo);
        }

        for (GlobalVarInfo global : this.globalVars) {
            backend.emitGlobalLabel(global.getLabel());
            emitConstant(
                    global.getInitialValue(),
                    global.getVarType(),
                    String.format("Initial value of global var: %s", global.getVarName()));
        }

        backend.startCode();

        Label mainLabel = new Label("main");
        backend.emitGlobalLabel(mainLabel);
        backend.emitLUI(A0, HEAP_SIZE_BYTES >> 12, "Initialize heap size (in multiples of 4KB)");
        backend.emitADD(S11, S11, A0, "Save heap size");
        backend.emitJAL(heapInitLabel, "Call heap.init routine");
        backend.emitMV(GP, A0, "Initialize heap pointer");
        backend.emitMV(S10, GP, "Set beginning of heap");
        backend.emitADD(S11, S10, S11, "Set end of heap (= start of heap + heap size)");
        backend.emitMV(RA, ZERO, "No normal return from main program.");
        backend.emitMV(FP, ZERO, "No preceding frame.");

        emitTopLevel(program.statements);

        for (FuncInfo funcInfo : this.functions) {
            funcInfo.emitBody();
        }

        emitStdFunc("alloc");
        emitStdFunc("alloc2");
        emitStdFunc("abort");
        emitStdFunc("heap.init");

        emitCustomCode();

        backend.startData();
        emitConstants();
    }

    /** Create descriptors and symbols for builtin classes and methods. */
    protected void initClasses() {
        FuncInfo objectInit =
                makeFuncInfo(
                        "object.__init__",
                        0,
                        Type.NONE_TYPE,
                        globalSymbols,
                        null,
                        this::emitStdFunc);
        objectInit.addParam(makeStackVarInfo("self", Type.OBJECT_TYPE, null, objectInit));
        functions.add(objectInit);

        objectClass = makeClassInfo("object", getNextTypeTag(), null);
        objectClass.addMethod(objectInit);
        classes.add(objectClass);
        globalSymbols.put(objectClass.getClassName(), objectClass);

        intClass = makeClassInfo("int", getNextTypeTag(), objectClass);
        intClass.addAttribute(makeAttrInfo("__int__", null, null));
        classes.add(intClass);
        globalSymbols.put(intClass.getClassName(), intClass);

        boolClass = makeClassInfo("bool", getNextTypeTag(), objectClass);
        boolClass.addAttribute(makeAttrInfo("__bool__", null, null));
        classes.add(boolClass);
        globalSymbols.put(boolClass.getClassName(), boolClass);

        strClass = makeClassInfo("str", getNextTypeTag(), objectClass);
        strClass.addAttribute(
                makeAttrInfo("__len__", Type.INT_TYPE, new IntegerLiteral(null, null, 0)));
        strClass.addAttribute(makeAttrInfo("__str__", null, null));
        classes.add(strClass);
        globalSymbols.put(strClass.getClassName(), strClass);

        listClass = makeClassInfo(".list", -1, objectClass);
        listClass.addAttribute(
                makeAttrInfo("__len__", Type.INT_TYPE, new IntegerLiteral(null, null, 0)));
        classes.add(listClass);
        listClass.dispatchTableLabel = null;
    }

    /** Create descriptors and symbols for builtin functions. */
    protected void initFunctions() {
        printFunc =
                makeFuncInfo("print", 0, Type.NONE_TYPE, globalSymbols, null, this::emitStdFunc);
        printFunc.addParam(makeStackVarInfo("arg", Type.OBJECT_TYPE, null, printFunc));
        functions.add(printFunc);
        globalSymbols.put(printFunc.getBaseName(), printFunc);

        lenFunc = makeFuncInfo("len", 0, Type.INT_TYPE, globalSymbols, null, this::emitStdFunc);
        lenFunc.addParam(makeStackVarInfo("arg", Type.OBJECT_TYPE, null, lenFunc));
        functions.add(lenFunc);
        globalSymbols.put(lenFunc.getBaseName(), lenFunc);

        inputFunc = makeFuncInfo("input", 0, Type.STR_TYPE, globalSymbols, null, this::emitStdFunc);
        functions.add(inputFunc);
        globalSymbols.put(inputFunc.getBaseName(), inputFunc);
    }

    /* Symbolic assembler constants defined here (to add others, override
     * initAsmConstants in an extension of CodeGenBase):
     * ecalls:
     *   @sbrk
     *   @fill_line_buffer
     *   @read_string
     *   @print_string
     *   @print_char
     *   @print_int
     *   @exit2
     * Exit codes:
     *   @error_div_zero: Division by 0.
     *   @error_arg: Bad argument.
     *   @error_oob: Out of bounds.
     *   @error_none: Attempt to access attribute of None.
     *   @error_oom: Out of memory.
     *   @error_nyi: Unimplemented operation.
     * Data-structure byte offsets:
     *   @.__obj_size__: Offset of size of object.
     *   @.__len__: Offset of length in chars or words.
     *   @.__str__: Offset of string data.
     *   @.__elts__: Offset of first list item.
     *   @.__int__: Offset of integer value.
     *   @.__bool__: Offset of boolean (1/0) value.
     */

    /** Define @-constants to be used in assembly code. */
    protected void initAsmConstants() {
        backend.defineSym("sbrk", SBRK_ECALL);
        backend.defineSym("print_string", PRINT_STRING_ECALL);
        backend.defineSym("print_char", PRINT_CHAR_ECALL);
        backend.defineSym("print_int", PRINT_INT_ECALL);
        backend.defineSym("exit2", EXIT2_ECALL);
        backend.defineSym("read_string", READ_STRING_ECALL);
        backend.defineSym("fill_line_buffer", FILL_LINE_BUFFER__ECALL);

        backend.defineSym(".__obj_size__", 4);
        backend.defineSym(".__len__", 12);
        backend.defineSym(".__int__", 12);
        backend.defineSym(".__bool__", 12);
        backend.defineSym(".__str__", 16);
        backend.defineSym(".__elts__", 16);

        backend.defineSym("error_div_zero", ERROR_DIV_ZERO);
        backend.defineSym("error_arg", ERROR_ARG);
        backend.defineSym("error_oob", ERROR_OOB);
        backend.defineSym("error_none", ERROR_NONE);
        backend.defineSym("error_oom", ERROR_OOM);
        backend.defineSym("error_nyi", ERROR_NYI);
    }

    /*-----------------------------------------------------------*/
    /*                                                           */
    /*          FACTORY METHODS TO CREATE INFO OBJECTS           */
    /*                                                           */
    /*-----------------------------------------------------------*/

    /**
     * A factory method that returns a descriptor for function or method FUNCNAME returning type
     * RETURNTYPE at nesting level DEPTH in the region corresponding to PARENTSYMBOLTABLE.
     *
     * <p>PARENTFUNCINFO is a descriptor of the enclosing function and is null for global functions
     * and methods.
     *
     * <p>EMITTER is a method that emits the function's body (usually a generic emitter for
     * user-defined functions/methods, and a special emitter for pre-defined functions/methods).
     *
     * <p>Sub-classes of CodeGenBase can override this method if they wish to use a sub-class of
     * FuncInfo with more functionality.
     */
    protected FuncInfo makeFuncInfo(
            String funcName,
            int depth,
            ValueType returnType,
            SymbolTable<SymbolInfo> parentSymbolTable,
            FuncInfo parentFuncInfo,
            Consumer<FuncInfo> emitter) {
        return new FuncInfo(
                funcName, depth, returnType, parentSymbolTable, parentFuncInfo, emitter);
    }

    /**
     * Return a descriptor for a class named CLASSNAME having type tag TYPETAG and superclass
     * SUPERCLASSINFO (null for `object' only).
     *
     * <p>Sub-classes of CodeGenBase can override this method if they wish to use a sub-class of
     * ClassInfo with more functionality.
     */
    public ClassInfo makeClassInfo(String className, int typeTag, ClassInfo superClassInfo) {
        return new ClassInfo(className, typeTag, superClassInfo);
    }

    /**
     * A factory method that returns a descriptor for an attribute named ATTRNAME of type ATTRTYPE
     * and with an initial value specified by INITIALVALUE, which may be null to indicate a default
     * initialization.
     *
     * <p>Sub-classes of CodeGenBase can override this method if they wish to use a sub-class of
     * AttrInfo with more functionality.
     */
    public AttrInfo makeAttrInfo(String attrName, ValueType attrType, Literal initialValue) {
        return new AttrInfo(attrName, attrType, initialValue);
    }

    /**
     * A factory method that returns a descriptor for a local variable or parameter named VARNAME of
     * type VARTYPE, whose initial value is specified by INITIALVALUE (if non-null) and which is
     * defined immediately within the function given by FUNCINFO.
     *
     * <p>These variables are allocated on the stack in activation frames.
     *
     * <p>Sub-classes of CodeGenBase can override this method if they wish to use a sub-class of
     * StackVarInfo with more functionality.
     */
    public StackVarInfo makeStackVarInfo(
            String varName, ValueType varType, Literal initialValue, FuncInfo funcInfo) {
        return new StackVarInfo(varName, varType, initialValue, funcInfo);
    }

    /**
     * A factory method that returns a descriptor for a global variable with name VARNAME and type
     * VARTYPE, whose initial value is specified by INITIALVALUE (if non-null).
     *
     * <p>Sub-classes of CodeGenBase can override this method if they wish to use a sub-class of
     * GlobalVarInfo with more functionality.
     */
    public GlobalVarInfo makeGlobalVarInfo(
            String varName, ValueType varType, Literal initialValue) {
        return new GlobalVarInfo(varName, varType, initialValue);
    }

    /*-----------------------------------------------------------*
     *                                                           *
     *             ANALYSIS OF AST INTO INFO OBJECTS             *
     *   (Students can ignore these methods as all the work has  *
     *    been done and does not need to be modified/extended)   *
     *                                                           *
     *-----------------------------------------------------------*/

    /** Analyze PROGRAM, creating Info objects for all symbols. Populate the global symbol table. */
    protected void analyzeProgram(Program program) {
        /* Proceed in phases:
         * 1. Analyze all global variable declarations.
         *    Do this first so that global variables are in the symbol
         *    table before we encounter `global x` declarations.
         * 2. Analyze classes and global functions now that global variables
         *    are in the symbol table.
         */
        for (Declaration decl : program.declarations) {
            if (decl instanceof VarDef) {
                VarDef varDef = (VarDef) decl;
                ValueType varType = ValueType.annotationToValueType(varDef.var.type);
                GlobalVarInfo globalVar =
                        makeGlobalVarInfo(varDef.var.identifier.name, varType, varDef.value);

                this.globalVars.add(globalVar);

                this.globalSymbols.put(globalVar.getVarName(), globalVar);
            }
        }

        for (Declaration decl : program.declarations) {
            if (decl instanceof ClassDef) {
                ClassDef classDef = (ClassDef) decl;
                ClassInfo classInfo = analyzeClass(classDef);

                this.classes.add(classInfo);

                this.globalSymbols.put(classInfo.getClassName(), classInfo);
            } else if (decl instanceof FuncDef) {
                FuncDef funcDef = (FuncDef) decl;
                FuncInfo funcInfo = analyzeFunction(null, funcDef, 0, globalSymbols, null);

                this.functions.add(funcInfo);

                this.globalSymbols.put(funcInfo.getBaseName(), funcInfo);
            }
        }
    }

    /**
     * Analyze a class definition CLASSDEF and return the resulting Info object. Also creates Info
     * objects for attributes/methods and stores them in the ClassInfo. Methods are recursively
     * analyzed using analyzeFunction().
     */
    protected ClassInfo analyzeClass(ClassDef classDef) {
        String className = classDef.name.name;
        String superClassName = classDef.superClass.name;
        SymbolInfo superSymbolInfo = globalSymbols.get(superClassName);
        assert superSymbolInfo instanceof ClassInfo
                : "Semantic analysis should ensure that super-class is defined";
        ClassInfo superClassInfo = (ClassInfo) superSymbolInfo;
        ClassInfo classInfo = makeClassInfo(className, getNextTypeTag(), superClassInfo);

        for (Declaration decl : classDef.declarations) {
            if (decl instanceof VarDef) {
                VarDef attrDef = (VarDef) decl;
                ValueType attrType = ValueType.annotationToValueType(attrDef.var.type);
                AttrInfo attrInfo =
                        makeAttrInfo(attrDef.var.identifier.name, attrType, attrDef.value);

                classInfo.addAttribute(attrInfo);
            } else if (decl instanceof FuncDef) {
                FuncDef funcDef = (FuncDef) decl;
                FuncInfo methodInfo = analyzeFunction(className, funcDef, 0, globalSymbols, null);

                this.functions.add(methodInfo);

                classInfo.addMethod(methodInfo);
            }
        }

        return classInfo;
    }

    /**
     * Analyze a function or method definition FUNCDEF at nesting depth DEPTH and return the
     * resulting Info object. Analyze any nested functions recursively. The FuncInfo's symbol table
     * is completely populated by analyzing all the params, local vars, global and nonlocal var
     * declarations.
     *
     * <p>CONTAINER is the fully qualified name of the containing function/class, or null for global
     * functions. PARENTSYMBOLTABLE symbol table contains symbols inherited from outer regions (that
     * of the containing function/method for nested function definitions, and the global symbol
     * table for global function / method definitions). PARENTFUNCINFO is the Info object for the
     * parent function/method if this definition is nested, and otherwise null.
     */
    protected FuncInfo analyzeFunction(
            String container,
            FuncDef funcDef,
            int depth,
            SymbolTable<SymbolInfo> parentSymbolTable,
            FuncInfo parentFuncInfo) {
        /* We proceed in three steps.
         *  1. Create the FuncInfo object to be returned.
         *  2. Populate it by analyzing all the parameters and local var
         *     definitions.
         *  3. Now that the function's symbol table is built up, analyze
         *     nested function definitions.
         *  4. Add the body to the function descriptor for code gen.
         */

        String funcBaseName = funcDef.name.name;
        String funcQualifiedName =
                container != null ? String.format("%s.%s", container, funcBaseName) : funcBaseName;

        FuncInfo funcInfo =
                makeFuncInfo(
                        funcQualifiedName,
                        depth,
                        ValueType.annotationToValueType(funcDef.returnType),
                        parentSymbolTable,
                        parentFuncInfo,
                        this::emitUserDefinedFunction);

        for (TypedVar param : funcDef.params) {
            ValueType paramType = ValueType.annotationToValueType(param.type);

            StackVarInfo paramInfo =
                    makeStackVarInfo(param.identifier.name, paramType, null, funcInfo);

            funcInfo.addParam(paramInfo);
        }

        LocalDeclAnalyzer localDefs = new LocalDeclAnalyzer(funcInfo);

        for (Declaration decl : funcDef.declarations) {
            decl.dispatch(localDefs);
        }

        NestedFuncAnalyzer nestedFuncs = new NestedFuncAnalyzer(funcInfo);

        for (Declaration decl : funcDef.declarations) {
            decl.dispatch(nestedFuncs);
        }

        funcInfo.addBody(funcDef.statements);
        return funcInfo;
    }

    /** Analyzer for local variable declarations in a function. */
    protected class LocalDeclAnalyzer extends AbstractNodeAnalyzer<Void> {
        /** The descriptor for the function being analyzed. */
        private final FuncInfo funcInfo;

        /** A new analyzer for a function with descriptor FUNCINFO0. */
        protected LocalDeclAnalyzer(FuncInfo funcInfo0) {
            funcInfo = funcInfo0;
        }

        @Override
        public Void analyze(VarDef localVarDef) {
            ValueType localVarType = ValueType.annotationToValueType(localVarDef.var.type);
            StackVarInfo localVar =
                    makeStackVarInfo(
                            localVarDef.var.identifier.name,
                            localVarType,
                            localVarDef.value,
                            funcInfo);
            funcInfo.addLocal(localVar);
            return null;
        }

        @Override
        public Void analyze(GlobalDecl decl) {
            SymbolInfo symInfo = globalSymbols.get(decl.getIdentifier().name);
            assert symInfo instanceof GlobalVarInfo
                    : "Semantic analysis should ensure that global var exists";
            GlobalVarInfo globalVar = (GlobalVarInfo) symInfo;
            funcInfo.getSymbolTable().put(globalVar.getVarName(), globalVar);
            return null;
        }

        @Override
        public Void analyze(NonLocalDecl decl) {
            assert funcInfo.getSymbolTable().get(decl.getIdentifier().name) instanceof StackVarInfo
                    : "Semantic analysis should ensure nonlocal var exists";
            return null;
        }
    }

    /** Analyzer for nested function declarations in a function. */
    protected class NestedFuncAnalyzer extends AbstractNodeAnalyzer<Void> {
        /** Descriptor for the function being analyzed. */
        private final FuncInfo funcInfo;

        /** A new analyzer for a function with descriptor FUNCINFO0. */
        protected NestedFuncAnalyzer(FuncInfo funcInfo0) {
            funcInfo = funcInfo0;
        }

        @Override
        public Void analyze(FuncDef nestedFuncDef) {
            FuncInfo nestedFuncInfo =
                    analyzeFunction(
                            funcInfo.getFuncName(),
                            nestedFuncDef,
                            funcInfo.getDepth() + 1,
                            funcInfo.getSymbolTable(),
                            funcInfo);

            functions.add(nestedFuncInfo);

            funcInfo.getSymbolTable().put(nestedFuncInfo.getBaseName(), nestedFuncInfo);
            return null;
        }
    }

    /*------------------------------------------------------------*
     *                                                            *
     *  EMITING DATA SECTION FOR GLOBALS+PROTOTYPES+CONSTANTS     *
     *   (Students can ignore these methods as all the work has   *
     *    been done and does not need to be modified/extended)    *
     *                                                            *
     *------------------------------------------------------------*/

    /** Emit code to align next data item to word boundary. */
    protected void alignObject() {
        int wordSizeLog2 = 31 - Integer.numberOfLeadingZeros(wordSize);
        backend.alignNext(wordSizeLog2);
    }

    /** Emit the constant section containing the prototype FOR the class defined by CLASSINFO. */
    protected void emitPrototype(ClassInfo classInfo) {
        backend.emitGlobalLabel(classInfo.getPrototypeLabel());
        backend.emitWordLiteral(
                classInfo.getTypeTag(),
                String.format("Type tag for class: %s", classInfo.getClassName()));
        backend.emitWordLiteral(classInfo.attributes.size() + HEADER_SIZE, "Object size");
        backend.emitWordAddress(classInfo.getDispatchTableLabel(), "Pointer to dispatch table");
        for (VarInfo attr : classInfo.attributes) {
            String cmnt = String.format("Initial value of attribute: %s", attr.getVarName());
            emitConstant(attr.getInitialValue(), attr.getVarType(), cmnt);
        }
        alignObject();
    }

    /** Emit a word containing a constant int representing VALUE */
    protected void emitConstantInt(int value, String comment) {
        backend.emitWordLiteral(value, comment);
    }

    /** Emit a word containing a constant bool representing VALUE */
    protected void emitConstantBool(boolean value, String comment) {
        backend.emitWordLiteral(value ? 1 : 0, comment);
    }

    /**
     * Emit a word containing a constant representing VALUE, assuming that it will be interpreted as
     * a value of static type TYPE. VALUE may be null, indicating None. TYPE may be null, indicating
     * object. COMMENT is an optional comment.
     */
    protected void emitConstant(Literal value, ValueType type, String comment) {
        if (type != null && type.equals(Type.INT_TYPE)) {
            this.emitConstantInt(((IntegerLiteral) value).value, comment);
        } else if (type != null && type.equals(Type.BOOL_TYPE)) {
            this.emitConstantBool(((BooleanLiteral) value).value, comment);
        } else {
            backend.emitWordAddress(constants.fromLiteral(value), comment);
        }
    }

    /** Emit code for all constants. */
    protected void emitConstants() {
        backend.emitGlobalLabel(constants.falseConstant);
        backend.emitWordLiteral(boolClass.getTypeTag(), "Type tag for class: bool");
        backend.emitWordLiteral(boolClass.attributes.size() + HEADER_SIZE, "Object size");
        backend.emitWordAddress(boolClass.getDispatchTableLabel(), "Pointer to dispatch table");
        backend.emitWordLiteral(0, "Constant value of attribute: __bool__");
        alignObject();

        backend.emitGlobalLabel(constants.trueConstant);
        backend.emitWordLiteral(boolClass.getTypeTag(), "Type tag for class: bool");
        backend.emitWordLiteral(boolClass.attributes.size() + HEADER_SIZE, "Object size");
        backend.emitWordAddress(boolClass.getDispatchTableLabel(), "Pointer to dispatch table");
        backend.emitWordLiteral(1, "Constant value of attribute: __bool__");
        alignObject();

        for (Map.Entry<String, Label> e : constants.strConstants.entrySet()) {
            String value = e.getKey();
            Label label = e.getValue();
            int numWordsForCharacters = value.length() / wordSize + 1;
            backend.emitGlobalLabel(label);
            backend.emitWordLiteral(strClass.getTypeTag(), "Type tag for class: str");
            backend.emitWordLiteral(3 + 1 + numWordsForCharacters, "Object size");
            backend.emitWordAddress(strClass.getDispatchTableLabel(), "Pointer to dispatch table");
            this.emitConstantInt(value.length(), "Constant value of attribute: __len__");
            backend.emitString(value, "Constant value of attribute: __str__");
            alignObject();
        }

        for (Map.Entry<Integer, Label> e : constants.intConstants.entrySet()) {
            Integer value = e.getKey();
            Label label = e.getValue();
            backend.emitGlobalLabel(label);
            backend.emitWordLiteral(intClass.getTypeTag(), "Type tag for class: int");
            backend.emitWordLiteral(intClass.attributes.size() + HEADER_SIZE, "Object size");
            backend.emitWordAddress(intClass.getDispatchTableLabel(), "Pointer to dispatch table");
            backend.emitWordLiteral(value, "Constant value of attribute: __int__");
            alignObject();
        }
    }

    /** Emit the method dispatching table for CLASSINFO. */
    protected void emitDispatchTable(ClassInfo classInfo) {
        Label dispatchTableLabel = classInfo.getDispatchTableLabel();
        if (dispatchTableLabel == null) {
            return;
        }
        backend.emitGlobalLabel(dispatchTableLabel);
        for (FuncInfo method : classInfo.methods) {
            String cmnt =
                    String.format(
                            "Implementation for method: %s.%s",
                            classInfo.getClassName(), method.getBaseName());
            backend.emitWordAddress(method.getCodeLabel(), cmnt);
        }
    }

    /*------------------------------------------------------------*
     *                                                            *
     *   UTILITY METHODS TO GET BYTE OFFSETS IN OBJECT LAYOUT     *
     *   (Students will find these methods helpful to use in      *
     *   their sub-class when generating code for expressions)    *
     *                                                            *
     *------------------------------------------------------------*/

    /** Return offset of the type-tag field in an object. */
    protected int getTypeTagOffset() {
        return 0 * wordSize;
    }

    /** Return offset of the size field in an object. */
    protected int getObjectSizeOffset() {
        return 1 * wordSize;
    }

    /** Return offset of the start of the pointer to the method-dispatching table in an object. */
    protected int getDispatchTableOffset() {
        return 2 * wordSize;
    }

    /** Return the offset of the ATTRNAME attribute of an object of type described by CLASSINFO. */
    protected int getAttrOffset(ClassInfo classInfo, String attrName) {
        int attrIndex = classInfo.getAttributeIndex(attrName);
        assert attrIndex >= 0 : "Type checker ensures that attributes are valid";
        return wordSize * (HEADER_SIZE + attrIndex);
    }

    /**
     * Return the offset of the method named METHODNAME in the method-dispatching table for the
     * class described by CLASSINFO.
     */
    protected int getMethodOffset(ClassInfo classInfo, String methodName) {
        int methodIndex = classInfo.getMethodIndex(methodName);
        assert methodIndex >= 0 : "Type checker ensures that attributes are valid";
        return wordSize * methodIndex;
    }

    /*------------------------------------------------------------*
     *                                                            *
     *        UNIMPLEMENTED METHODS (should be extended)          *
     *                                                            *
     *------------------------------------------------------------*/

    /** Emits code for STATEMENTS, assumed to be at the top level. */
    protected abstract void emitTopLevel(List<Stmt> statements);

    /** Emits code for the body of user-defined function FUNCINFO. */
    protected abstract void emitUserDefinedFunction(FuncInfo funcInfo);

    /**
     * Emits code outside the ChocoPy program.
     *
     * <p>Custom assembly routines (that may be jumpable from program statements) can be emitted
     * here.
     */
    protected abstract void emitCustomCode();

    /*------------------------------------------------------------*
     *                                                            *
     *             PREDEFINED FUNCTIONS AND ROUTINES              *
     *   (Students may find a cursory read of these methods to    *
     *    be useful to get an idea for how code can be emitted)   *
     *                                                            *
     *------------------------------------------------------------*/

    /**
     * Return Risc V assembler code for function NAME from directory LIB, or null if it does not
     * exist. LIB must end in '/'.
     */
    protected String getStandardLibraryCode(String name, String lib) {
        String simpleName = name.replace("$", "") + ".s";
        return getResourceFileAsString(lib + simpleName);
    }

    /**
     * Emit label and body for the function LABEL, taking the source from directory LIB (must end in
     * '/').
     */
    protected void emitStdFunc(Label label, String lib) {
        emitStdFunc(label, label.toString(), lib);
    }

    /**
     * Emit label and body for the function LABEL, taking the source from SOURCEFILE.s in directory
     * LIB (must end in '/').
     */
    protected void emitStdFunc(Label label, String sourceFile, String lib) {
        String source = getStandardLibraryCode(sourceFile, lib);
        if (source == null) {
            throw fatal("Code for %s is missing.", sourceFile);
        }
        backend.emitGlobalLabel(label);
        backend.emit(convertLiterals(source));
    }

    /**
     * Emit label and body for the function LABEL, taking the source from from the default library
     * directory.
     */
    protected void emitStdFunc(Label label) {
        emitStdFunc(label, LIBRARY_CODE_DIR);
    }

    /**
     * Emit label and body for the function NAME, taking the source from from the default library
     * directory.
     */
    protected void emitStdFunc(String name) {
        emitStdFunc(new Label(name));
    }

    /**
     * Emit label and body for the function described by FUNCINFO, taking the source from from the
     * default library directory.
     */
    protected void emitStdFunc(FuncInfo funcInfo) {
        emitStdFunc(funcInfo.getCodeLabel());
    }

    /** Pattern matching STRING["..."]. */
    private static final Pattern STRING_LITERAL_PATN = Pattern.compile("STRING\\[\"(.*?)\"\\]");

    /**
     * Return result of converting STRING["..."] notations in SOURCE to labels of string constants,
     * adding those constants to the pool.
     */
    private String convertLiterals(String source) {
        Matcher matcher = STRING_LITERAL_PATN.matcher(source);
        StringBuffer result = new StringBuffer();
        while (matcher.find()) {
            String r = constants.getStrConstant(matcher.group(1)).toString();
            matcher.appendReplacement(
                    result, pad(r, ' ', matcher.end(0) - matcher.start(0), false));
        }
        return matcher.appendTail(result).toString();
    }
}