language levels and translation

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Language Levelsand Translation

http://www.pds.ewi.tudelft.nl/~iosup/Courses/2011_ti1400_11.ppt

See also: Blackboard >> Course Material >> Reader (Dictaat)http://www.pds.ewi.tudelft.nl/vakken/in1705/cos2007.pdf

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IT Industry Competitiveness

Source: The Economist, Benchmarking IT industry competitiveness 2009 http://portal.bsa.org/2009eiu/study/2009_eiu_global.pdf

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The Netherlands: A Top IT Industry

Source: The Economist, Benchmarking IT industry competitiveness 2009 http://portal.bsa.org/2009eiu/study/2009_eiu_global.pdf

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But … Where’s the Human Capital?

“A longer-term challenge for some European countries is encouraging more graduates to choose science-related subjects.”- NL is 27th in HC

Source: The Economist, Benchmarking IT industry competitiveness 2009

Q: Good/Bad news for you?

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The Simplest(?) Problem: How to Program Computers?

• So far- Design them from scratch

- Assembly

• This lecture- Language levels

- Translation

- The compiler sequence

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Language levels

• A computer has several language levels:

- machine language

- assembler language (e.g., Intel/Pentium

assembler)

- higher-level language (e.g., Java)

- application-specific language (e.g., MatLab)

• Close the gap between problem

description and machine program

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Program transformations

• Need for program transformations

• Semantics of programs must remain the same

• Two ways of transformation:

1. compilation: first translate, then execute

2. interpretation: interleave translation and execution

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Type of translators

Java

machineinstructions

Java

IA-32assembler

machineinstructions

Java

IA-32assembler

machineinstructions

JVMcompile tomachinelanguage

interpretbyte codecompile to

assembler

compile

assembleassemble

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Types of interpreters

programPC

program

inter-preter

IPC

PC

program

run-timesystem/OS

(I)PC

PC

many steps of PC for one step of IPC

combination:interpretsystem calls

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Compilation versus Interpretation

• Advantages interpretation- Direct edit/execution cycle

- Debugging on the level of interpreted language

- Less memory requirements for programs

• Advantage compilation- Faster execution (factor of 50-100)

- Semantic checks during compilation process

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Simulation versus Emulation

• Mimicking of hardware or software

• Through program: simulation

• Through hardware: emulation

• Example:- PowerPC simulation on Intel Pentium

- Virtual machines such as KVM and VMware

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Programs and machines

• In exchanging programs and machines three notions are relevant:

1. Compatibility

2. Portability

3. Conversion

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Compatibility

• Compatibility: functionality of system is

independent of implementation

- machine versions with same instruction set

• Upward (FWD) compatibility: new version of

system incorporates functionality of old system

- Code compiled on old system will run on new system

- CDs are FWD-compatible with DVD readers

- (DVD readers are backwards-compatible with CDs)

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Portability (1)

• Portability is the ease of transferring a program to different machines and operating systems.

• Problems:- Different machine instructions- Different OS calls- Other compiler with deviating

conventions

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Portability (3)

• Steps:- making readable on new system

- adapt to new OS

- recompile

• Performance characteristics can change

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Conversion

• Conversion is adaptation of applications to a different language or (operating) system- Faster code execution

• Conversion problems:- expressiveness of new language

- different operating systems

- different network environment

- different machine precision

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Portability/Conversion Cost

• An example- Mid-size game studio has 25+ game titles

- 4 languages, 25 x 4 = 100 releases

- 100 platforms (mobiles etc.)

- $1,000/release x 100 x 100 = $10,000,000 all

Q: How would you address this situation?

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Outsourcing: The Dutch Market Story

0-49k

50-199k

200-499k

500k+Outsourcing

Web

Java Ent.

Mobile

Services

Embedded

Stop0-1yr

1-2yr2+yr

Source: European IT Outsourcing Intelligence Report 2011: The Netherlands http://www.itsourcing-europe.com/uploads/Dutch_ITO_Intelligence_Report_2011.pdf

Q: Good/Bad news for you?

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Levels of abstraction

Language level

Machine-program level

Microprogram level

Assembler level

Digital logic level

Operating System

.......

interpret

translate

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Virtual machines (1)

Virtual machine Mn with machine language Ln

Virtual machine M3 with machine language L3

Virtual machine M2 with machine language L2

Real machine M1 with machine language L1

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Virtual machines (2)

• A language defines a virtual machine

• The machines M2,...,Mn are virtual

• Machine M1 is real

• At Mi we need an interpreter or a compiler

to translate programs written in Li+1 to Li

• Hardware and software are equivalent

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Compiler structure

Source program

Lexicographical analysis

Syntactic analysis

Semantic analysis

Intermediate-codegeneration

Code optimization

Code generation

Target program

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Lexicographical analysis (1)

Goal: reading program text and group characters into tokens

int SUM = 0;

i n t S U M = 0 ;

int SUM = 0 ;

10 characters

5 tokens

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Lexicographical analysis (2)

Tokens are classified:• Keywords (for, if,....)• Identifiers (SUM, ...)• Constants (0, 3.14, “char”)• Delimiters ({,;)• Operators (+, =, ...)

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Lexicographical analysis (3)

• Identifiers and constants are stored in the symbol table:

entry name kind type value.. .. .. .. ..100 SUM ident int .... .. .. .. ..200 PI const real 3.1415

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Syntactic analysis

• Check of correctness of program with respect to the grammar of the language

• Also called parsing• Building of so called parse tree

total = 3 + (2*5)

=

+

*

52

3

total

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Semantic analysis

• Static semantics- (part of) type checking

- illegal statements

• Dynamic semantics- done at run-time

- remainder of type checking

- operator exceptions (e.g., division by 0)

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Intermediate code (1)

• Reasons for intermediate code level:1. simplify compilation process

2. reuse parts of compiler for different architectures

• In intermediate code:- a single operation at a time

- test on only one condition at a time

- while loops replaced by test and branch instructions, and labels

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Intermediate code (2): Example

while ( (a>b) && (a <= c+d) )

a = a*b;

translated into:

L1: if (a>b) goto L2

goto L3L2: h1 = c+d

if (a <= h1) goto L4goto L3

L4: a = a*bgoto L1

L3:

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Code generation (1)

MOV EAX, <RHS >(0)MOV <LHS >, EAXMOV EAX, 3ADD EAX, <2*5 >

MOV EAX, 2MOV EBX, 5IMUL EAX, EBX

=

3 + <2*5>

2*5

<LHS> = “total”

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Code generation (2)

MOV EAX, 2 load 2 in EAXMOV EBX, 5 load 5 in EBXIMUL EAX,EBX multiplyPUSH EAX push result on stack

MOV EAX, 3 load 3 in EAXPOP EBX pop from stackADD EAX,EBX additionPUSH EAX push result on stack

POP EAX pop from stackMOV total(0),EAX do final assignment

communication via stack

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Code optimization

MOV EAX, 2 load 2 in EAXMOV EBX, 5 load 5 in EBXIMUL EAX,EBX multiply

MOV EBX, 3 load 3 in EBXADD EAX, EBX addition

STW total(0), EAX do final assignment

omit communication via stack