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Tutorial Code GenerationCompiler Construction

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S C I E N C E ■ P A S S I O N ■ T E C H N O L O G Y

u www.tugraz.at

Tutorial 3: Code Generation

Univ.-Prof. Dr. Franz Wotawa, DI Roxane Koitz,Stephan Frühwirt, Christopher Liebmann

Institute for Software Technology


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Jova Input Program

Java Byte Code

Compiler Phases


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Jova Input Program

Java Byte Code

Compiler Phases


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Jova Input Program

Java Byte Code

Compiler Phases


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Jova Input Program

Java Byte Code

Compiler Phases


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Source Code(*.jova file) Syntax tree

Grammar(Jova.g4)

ANTLRLexer and Parser

Lexical and syntactical errors

Symbol table

ANTLRvisitor / listener

Type checking errors

Debugging output

Debugging output

Workflow (1/2)


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Syntax tree

Symbol table

Workflow (2/2)

Jasmin code(.j file)

Byte code(.class file)

Jasmin


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What is Jasmin?

• Assembler for Java bytecode• Input: <filename>.j file

• contains assembly of the original code• written in Jasmin assembler language

• Output: executable Java .class file


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Pipeline

CreateAssembly

• Produce jasmin assembly• Result: <filename>.j

Convert

• Invoke “java –jar jasmin.jar <filename>.j“• Result: <filename>.class

Execute

• Invoke “java <filename>“• Result: executes main method of class


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• One statement per line• Inline comments, initiated by ‘;‘• Assembly setup:

• Required options• Method 1• Method 2• …• Method n

Jasmin syntax


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Required Options

▪ .source: Source of assembly▪ e.g.: .source MyClass.jova

▪ .class: Resulting java class description

▪e.g.: .class public MyClass▪ .super: Superclass of resulting java class

▪always: .super java/lang/Object

… unless you’ve implemented inheritance▪ .field: Specify fields of class

▪e.g.: .field public my_field I


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Default Constructor

▪ needs to be defined for every class

▪ since Jova does not have Constructors you can use the same definition for every class:.method public <init>()V.limit stack 1.limit locals 1aload_0

invokespecial java/lang/Object/<init>()Vreturn.end method


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.method <method signature>e.g. .method public myMethod(I)V

.limit stack nn: choose realistic number

.limit locals nn = #parameters + #local_vars + #temp_var

<instructions>

returnrequires matching type on top-of-stack for non-void returns

(e.g. ireturn).end method

Methode structure


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Example: DoNix

File: DoNix.j.source noSource.class public DoNix.super java/lang/Object

.method public static main([Ljava/lang/String;)V

.limit stack 0

.limit locals 1;nothing to do herereturn.end method


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• Two data structures per method• Stack• Locals array

• Operations to manipulate both• Build-in datatypes

• Primitives• Arrays• Objects

Data Management


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• Each method has its own operand stack • Size is definable per method

(just assume a realistic number)

• LIFO• Stack operations

• Push values onto stack• Pop/Fetch values from stack• Instructions which require one or multiple values

on stack (order does matter!)

Data Management: Stack


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• Each method has its own locals array• Definable size for each method (0-based indices)• Typing

• Can store arbitrary types• Items need to be initialized before read access

• Contains• Method parameters (stored in lowest indices)• At index 0 the ‘this’ reference

Data Management: Locals Array


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Data Managment: Types

▪ … a few primitives▪Integer indicated by letter I▪Void indicated by letter V▪Boolean indicated by letter Z

▪ Objects following the format “package/Classname;“▪e.g. Ljava/lang/String; String object

▪ Array indicated by a leading [▪e.g. [Ljava/lang/String; array of Strings


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Instructions

▪ One instruction per line▪ Can involve stack and locals array▪ May require a specific number/type of elements

present▪ Order for binary instructions like 4 – 2:1. bipush 4 ;push 4 on stack2. bipush 2 ;push 2 on stack 3. isub ;pop both and push

value of

;4 - 21. result is now on top of stack


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Instructions: Stack - locals interaction

▪ iload n pushes integer, stored in index n oflocals array, onto stack

▪ istore n pops integer from stack and stores itinto index n of locals array

▪ aload n pushes object, stored in index n oflocals array, onto stack

▪ astore n pops object from stack and stores itinto index n of locals array


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Instructions: Constants

▪ sipush n / bipush n▪Pushes integer constant onto stack▪E.g. sipush 10▪For -1 - 5 you can also use iconst_<n>

▪ ldc “<string>”▪Pushes string constant <string> onto stack▪E.g. ldc “Hello World”▪Note: Strings are Objects (variable access with astore/aload)


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Instructions: Arithmetic Operators

▪ ineg toggles sign of int on top of stack▪ iadd add two integers▪ isub subtract two integers▪ imul multiply two integers▪ idiv divide two integers▪ irem modulo division of two integers


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Instructions: Logic Operators

▪ iand bitwise and of two integers▪ ior bitwise or of two integers▪ inot does not exist!

▪Note: Needs to be assembled using custom labels and conditional jump operations


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Example: BasicInstructions

File: BasicInstructions.j.source noSource.class public BasicInstructions.super java/lang/Object


.limit stack 5

.limit locals 3sipush 5 ;push integer 5 onto stack istore 0 ;pop integer 5 and store in index 0ldc "Hello World" ;push string Hello World onto stackastore 1 ;store string in index 1

iload 0 ;load 5dup ;duplicate stack entry 5sipush 2 ;push integer 2 onto stackisub ;pop 5 and 2 and store result 3 onto stackiadd ;pop 5 and 3 and store result 8 onto stackistore 0 ;store result 8 in index 0

return.end method


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Instructions: Relation Operators

▪ Do not exist!▪ Need to be assembled using custom labels and

conditional jump operations


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Instructions: Labels and Jumps

▪ <labelname>:▪makes a label in the assembly

▪ goto <labelname>▪continues execution of current method at position of the label <labelname>

▪ if_icmpXX <labelname>▪pops two elements of the stack, relates them and jumps to <labelname> if comparison computes to true


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Instructions: if_icmp variations

▪ if_icmplt relation using <▪ if_icmple relation using <=▪ if_icmpge relation using >=▪ if_icmpgt relation using >▪ if_icmpeq relation using ==▪ if_icmpne relation using !=


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Example: LabelsAndJumpsFile: LabelsAndJumps.j

.source noSource

.class public LabelsAndJumps

.super java/lang/Object


.limit stack 5

.limit locals 3sipush 10istore 0 ;store 10 in index 0goto label_skip_redefinitionsipush 20istore 0 ;store 20 to index 0 - skippedlabel_skip_redefinition:iload 0 ;push value of index 0: 10sipush 15 ;push 15 if_icmplt label_is_lesserldc "greater" ;push string to stack - skippedgoto label_endlabel_is_lesser:ldc "lesser" ;push string to stacklabel_end:; result: string "lesser" on top of stackreturn.end method


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Instructions: field access

▪ Call put-/getfield of object on stack▪ Call using

putfield <class ID>/<field ID> <type>getfield <class ID>/<field ID> <type>

▪ Requires value and object on stack▪ Example

▪field: public int my_field▪signature: myClass/my_field I▪assembly: putfield myClass/my_field I


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Instructions: non-static method calls

▪ Call method of object on stack▪ Call using

invokevirtual <class ID>/<method signature>

▪ Requires parameters and object on stack▪ Example

▪method: public int myMethod(int a)▪signature: myMethod(I)I▪invokation: invokevirtual MyClass/myMethod(I)I


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Instructions: print

▪ Based on virtual invokation▪ How to:

1. Push PrintStream object onto stackgetstatic java/lang/System/out Ljava/io/PrintStream;

2. Push value onto stack (iload, aload, etc.)3. Invoke matching PrintStream method

invokevirtual java/io/PrintStream/print(I)V

invokevirtual java/io/PrintStream/print(Ljava/lang/String;)V


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Hints

▪ Try and write some simple Jasmin code yourselves▪ Use aload_0 to get ‘this’ reference▪ Number your labels ▪ Map Jova/internal variables to locals array indices▪ Instruction swap may be useful in some cases▪ Use the online documentation to find additional

instructions/explanations▪ When in doubt: model a problem in Java - compile it -

and use javap -c <Class> to decompile the .class files


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Questions?

tutorial 3: code generation - graz university of technology · tutorial code generation compiler...

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