3/24/2004COSC4301 assignment 31 Compiler, Interpreter, and Bootstrapping Motivation: When we are asked to write a Compiler for a complex source language.

3/24/2004 COSC4301 assignment 3 1

Compiler, Interpreter, and Bootstrapping

Motivation:When we are asked to write a

Compiler for a complex source language or Interpreter for a low level intermediate

language or Emulator for a new virtual machine

Our strategy?


Motivation continued

Strategy:

o machine code VS high level language

o scratch VS improve existing code

We introduce some basic concepts and give

some examples to make stuff clear.


Terminology

• Q: Which programming languages play a role in this picture?

input translator output

source program expressed in the target

(expressed in the implementation language

source language) language


Tombstone Diagram

Program P implemented in L

LP S -> T

L

Translator implemented in L

M

Machine implemented in hardware

ML

Language interpreter in L


Tombstone diagram: Combination rules

M

MP

SP P

TS -> T

M

M

LP

S -> T

MM

LP

ok ok

Wrong!Wrong!


Compiler Basics

Host compiler and Cross compiler:Host compiler and Cross compiler:


Compiler Basics continued• Two stage compiler:

• Compile a translator implemented in high level language:

Output of the first compiler is the input of the second one


Interpreter

• A language process accept source code and executes it directly


Interpreters versus Compilers• Each faction hold the inverted set of advantages against

the other.• This part covered in previous presentation.• A comprise exists between two extremes to achieve

reasonable compilation and acceptable run time performance.

• Define an intermediate language

more high-level than machine code => easier to compile to

more low-level than source language => easy to implement as an interpreter


Interpretive CompilersHybrid of compilation and interpretationPascal/Java 2-stage compiler is good examplescompile source into machine independent low-level representation P-code/Byte codeinterpret P-code through machine dependent interpreter/JVM

Machine independent Machine dependent


Portable Compilers

JVMM

Java->JVM

JVM

JVMM

Java->JVM

M

For ideal portability, compilers areFor ideal portability, compilers are

. developed in modules for easy exchange.. developed in modules for easy exchange.

. implemented in high level language.. implemented in high level language.

Given 2 kits, which one is more portable?Given 2 kits, which one is more portable?

k1

k2


Portable Compilers continued

Suppose we have following modules (high level).

We have no way to run Pascal program, why?


Portable Compilers continue

• We need a interpreter

re-implement

We can expect a fairly easy implantation using high level language implementation


Portable Compilers continued

• Now, we can run our Pascal program smoothly

• Note here interpreter plays a dual role in both compiling and execution.


Bootstrapping

• a number of techniques which rely on partial/inefficient compiler version to create a full/better version

• often compiling a translator expressed in its own language


Full Bootstrapping

• A full bootstrap is necessary when we are building a new compiler from scratch.

• Example:• We want to implement an Ada compiler for

machine M. We don’t currently have access to any Ada compiler (not on M, nor on any other machine).

• Idea: Ada is very large, we will implement the compiler in a subset of Ada and bootstrap it from a subset of Ada compiler in another language. (e.g. C)


Full Bootstrapping continued

• Step 1: build a compiler for Ada-S in another language

Ada-S ->M

C

v1

Ada-S ->M

C

v1

Step 1a: build a compiler (v1) for Ada-S in another language.


Full bootstrapping continued

Ada-S ->MC

v1

MAda-S->M

v1

Step 1b: Compile v1 compiler on M

M

C->MM

This compiler can be used for bootstrapping on machine M but we do not want to rely on it permanently!



Ada-S ->M

Ada-S

v2

Step 2a: Implement v2 of Ada-S compiler in Ada-S

Ada-S ->M

Ada-S

v2

M

M

Ada-S->Mv2

Step 2b: Compile v2 compiler with v1 compiler

Ada-S ->M

M

v1

We are now no longer dependent on the availability of a C compiler!



Step 3a: Build a full Ada compiler in Ada-S

Ada->M

Ada-S

v3

Step 3b: Compile with v2 compiler

M

Ada->Mv3

Ada-S ->M

M

v2Ada->M

Ada-S

v3

M

From this point on we can maintain the compiler in Ada. Subsequent versions v4,v5,... of the compiler in Ada and compile each with the the previous version.


Half BootstrappingWe discussed full bootstrapping which is required when we have no access to a compiler for our language at all.

Q: What if we have access to an compiler for our language on a different machine HM but want to develop one for TM ?

Ada->HM

HM

Ada->HM

Ada

Ada->TM

TM

We have We want

Idea: we can use cross compilation from HM to TM to bootstrap the TM compiler


Half Bootstrapping continued

Step 1: Implement Ada->TM compiler in Ada

Ada->TM

Ada

Step 2: Compile on HM

Ada->TM

Ada

HM

Ada->HM

HM

Ada->TM Cross compiler: running on HM but

emits TM codeHM


Half Bootstrapping continued

Step 3: Cross compile our TM compiler.

Ada->TM

Ada Ada->TM

HM

HM

TMDONE!

From now on we can develop subsequent versions of the compiler completely on TM

Ada->TM


Bootstrap to improve efficiency

The efficiency of programs and compilers:Efficiency of programs:

- memory usage- runtime

Efficiency of compilers: - Efficiency of the compiler itself- Efficiency of the emitted code

Idea: We start from a simple compiler (generating inefficient code) and develop more sophisticated version of it. We can then use bootstrapping to improve performance of the compiler.



Ada->Mslow

Ada

Ada-> Mslow

Mslow

Ada->Mfast

Ada

Ada->Mfast

Ada

M

Ada->Mfast

Mslow

Step 1

Ada-> Mslow

Mslow

We have We want



Step 2 Ada->Mfast

Ada

M

Ada->Mfast

MfastAda-> Mfast

Mslow

Fast compiler that emits fast code!


Conclusion

• To write a good compiler you may be writing several simpler ones first

• You have to think about the source language, the target language and the implementation language.

• The work of a compiler writer is never finished, there is always version 1.x and version 2.0 and …

3/24/2004COSC4301 assignment 31 Compiler, Interpreter, and Bootstrapping Motivation: When we are asked to write a Compiler for a complex source language.

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