Chapter 2Language Processors

Fall 2013

Chart 2

Translators and Compilers Interpreters Real and Abstract Machines Interpretive Compilers Portable Compilers Bootstrapping Case Study: The Triangle Language

Processor

Chart 3

Translator: a program that accepts any text expressed in one language (the translator’s source language), and generates a semantically-equivalent text expressed in another language (its target language)o Chinese-into-Englisho Java-into-Co Java-into-x86o X86 assembler

Chart 4

Assembler: translates from an assembly language into the corresponding machine codeo Generates one machine code instruction per source

instruction Compiler: translates from a high-level language

into a low-level languageo Generates several machine-code instructions per source

command.

Chart 5

Disassembler: translates a machine code into the corresponding assembly language

Decompiler: translates a low-level language into a high-level language

Question: Why would you want a disassembler or decompiler?

Chart 6

Source Program: the source language text Object Program: the target language text

Compiler

ObjectProgram

Syntax Check

Context Constraints

Generate Object Code

Semantic Analysis

SourceProgram

• Object program semantically equivalent to source program If source program is well-formed

Chart 7

Why would you want to do:o Java-into-C translatoro C-into-Java translatoro Assembly-language-into-Pascal decompiler

Chart 8

M

P

L

P

L

M

P = Program NameL = Implementation Language

M = Target Machine

For this to work, L must equal M, that is, the implementation language must be the same as the machine language

S T

L

S = Source LanguageT = Target LanguageL = Translator’s Implementation Language

S-into-T Translator is itself a program that runs on machine L

Chart 9

• Translating a source program P • Expressed in language T, • Using an S-into-T translator • Running on machine M

P

S

M

S T

M

P

T

Chart 10

• Translating a source program sort • Expressed in language Java, • Using a Java-into-x86 translator • Running on an x86 machine

sort

Java

x86

Java x86

x86

sort

x86

The object program is running on the same machine as the compiler

sort

x86

x86

Chart 11

sort

Java

x86

Java PPC

x86

sort

PPC

Cross Compiler: The object program is running on a different machine than the compiler

sort

PPC

PPC

download

• Translating a source program sort • Expressed in language Java, • Using a Java-into-PPC translator • Running on an x86 machine• Downloaded to a PPC machine

Chart 12

sortJava

x86

Java C

x86

sort

C

Two-stage Compiler: The source program is translated to another language before being translated into the object program

sort

x86

x86

• Translating a source program sort • Expressed in language Java, • Using a Java-into-C translator • Running on an x86 machine

x86

x86

x86

sort

x86C

• Then translating the C program• Using an C-into x86 compiler• Running on an x86 machine• Into x86 object program

Chart 13

Translator Ruleso Can run on machine M only if it is expressed in machine

code Mo Source program must be expressed in translator’s

source language So Object program is expressed in the translator’s target

language To Object program is semantically equivalent to the source

program

Chart 14

Accepts any program (source program) expressed in a particular language (source language) and runs that source program immediatelyo Does not translate the source program into object code

prior to execution

Chart 15

Interpreter

Program Complete

Fetch Instruction

Analyze Instruction

Execute Instruction

SourceProgram

• Source program starts to run as soon as the first instruction is analyzed

Chart 16

When to Use Interpretationo Interactive mode – want to see results of instruction

before entering next instructiono Only use program onceo Each instruction expected to be executed only onceo Instructions have simple formats

Disadvantageso Slow: up to 100 times slower than in machine code

Chart 17

Exampleso Basico Lispo Unix Command Language (shell)o SQL

Chart 18

SL S interpreter expressed in language L

SM

P

S

M

Program P expressed in language S, using Interpreter S, running on machine M

Basicx86

graph

Basic

x86

Program graph written in Basic running on a Basic interpreter executed on an x86 machine

Chart 19

Hardware emulation: Using software to execute one set of machine code on another machineo Can measure everything about the new machine except

its speedo Abstract machine: emulatoro Real machine: actual hardware

An abstract machine is functionally equivalent to a real machine if they both implement the same language L

Chart 20

nmiC

M

C M

M

New Machine Instruction (nmi) interpreter written in C

nmiC

nmiM

The nmi interpreter is translated into machine code M using the C compiler

Compiler to translate C program into M machine code

nmi interpreter written in C nmi interpreter expressed in machine code M

nmiM

P

nmi

M

P

nmi

nmi

Chart 21

Combination of compiler and interpretero Translate source program into an intermediate languageo It is intermediate in level between the source language

and ordinary machine codeo Its instructions have simple formats, and therefore can be

analyzed easily and quicklyo Translation from the source language into the

intermediate language is easy and fast

An interpretive compiler combines fast compilation with tolerable running speed

Chart 22

Java JVM

M

JVMM

Java into JVM translator running on machine M

JVM code interpreter running on machine M

Java JVM

M

P

Java

P

JVM

M

P

JVM

M

JVMM

A Java program P is first translated into JVM-code, and then the JVM-code object program is interpreted

Chart 23

A program is portable if it can be compiled and run on any machine, without changeo A portable program is more valuable than an unportable

one, because its development cost can be spread over more copies

o Portability is measured by the proportion of code that remains unchanged when it is moved to a dissimilar machine

• Language affects portability• Assembly language: 0% portable• High level language: approaches 100% portability

Chart 24

Language Processorso Valuable and widely used programso Typically written in high-level language

• Pascal, C, Javao Part of language processor is machine dependent

• Code generation part• Language processor is only about 50% portable

o Compiler that generates intermediate code is more portable than a compiler that generates machine code

Chart 25

Java JVM

JavaJVMJava

Java JVM

JVM

P

Java

P

JVM

M

P

JVM

M

JVMM

JVMC

Java JVM

JVM

2. Rewrite interpreter in C

C M

M

M

JVMC

JVMM

JVMM

Note: C M Compiler exists; rewrite JVM interpreter from Java to C

1. Start with the following

3. Compile the compiler 4. Java program P is translated into JVM program P and run using ghe JVM intrepreter

Chart 26

The language processor is used to process itselfo Implementation language is the source language

Bootstrapping a portable compilero A portable compiler can be bootstrapped to make a true

compiler – one that generates machine code – by writing an intermediate-language-into-machine-code translator

Full bootstrapo Writing the compiler in itselfo Using the latest version to upgrade the next version

Half bootstrapo Compiler expressed in itself but targeted for another

machine Bootstrapping to improve efficiency

o Upgrade the compiler to optimize code generation as well as to improve compile efficiency

Chart 27

Bootstrap an interpretive compiler to generate machine code

JVM M

Java

M

JVMM

JVM M

Java Java JVM

JVM

JVM M

JVM

M

JVMM

JVM M

JVM JVM M

JVM

JVM M

M

M

Java JVM

JVM JVM M

M

Java JVM

MJava JVM

M

M

JVM M

M

M

P

Java

P

JVMP

M

1, First, write a JVM-coded-into-M translator in Java

2. Next, compile translator using existing interpreter

3. Use translator to translate itself

4. Translate Java-into-JVM-code translator into machine code

5. Two stage Java-into-M compiler

Chart 28

Full bootstrapAda-S M

C

v1

Ada-S M

C C M

M

Ada-S M

M

M

v1 v1

Ada-S M

Ada-S

v2

Ada-S M

Ada-S Ada-S M

M

Ada-S M

M

M

v2 v2

v1 Ada M

Ada-S Ada-S M

M

Ada M

M

M

v3 v3

v2

Ada M

Ada-S

v3

5. Extend Ada-S compiler to (full) Ada compiler

3. Convert the C version of Ada-S into Ada-S version of Ada-S

1. Write Ada-S compiler in C 2. Compile v1

using the C compiler

4. Use v1 to compile v2 6. Compile full version of Ada using Ada-S compiler

Chart 29

Half bootstrapAda HM

Ada

Ada HM

HM

Ada TM

Ada

Ada TM

Ada Ada HM

HM

HM

Ada TM

HMP

Ada Ada TM

HM

P

TMP

TM

TM

Ada TM

Ada Ada TM

HM

HM

Ada TM

TM

2. Ada compiler that generates machine code for machine H expressed in HM

1. Ada compiler that generates machine code for machine H expressed in Ada

3.Rewrite Ada compiler that generates HM code to Ada compiler that generates machine code for machine TM

5. Make sure the compiler works properly

6. Use the compiler to compile itself. Now have an Ada compiler that generates TM code that runs on machine TM

4. Use existing Ada compiler fro HM to compile the Ada compiler that run on HM but generates code for TM

Chart 30

Bootstrap to improve efficiency

Ada Ms

Ms

v1

Ada Ms

Ada

v1Ada Mf

Ada

v2

Ada Mf

Ada

v2

Ada Ms

Ms

v1 Ada Mf

Ms

v2

M

Ada Mf

Ms

v2P

Ada

1. Start with v1 targeted to M-slow written in Ada and compiled to run on M-slow

2. Rewrite v1 to run on M-fast in Ada

3. Use v1 to compile v2

P

Mf

P

Mf

M

4. Compile a program using v2; it will compile slow but run fast

Ada Mf

Ada

v2

Ada Ms

Ms

v2 Ada Mf

Mf

v3

M5. Use v2 to compile v2 to produce v3

which will be the fast compiler.