01 Introduction

Language Translators¶

You should know by this stage :/

If you don’t, refer this.

Programming Language Processing¶

flowchart LR
a(( )) -->
|Source<br/>Program| Preprocessor -->
|Modified<br/>Source<br/>Program| Compiler -->
|Target<br/>Assembly<br/>Code| Assembler -->
|Relocatable<br/>Machine<br/>Code| Linker/Loader -->
|Target<br/>Machine<br/>Code| b(( ))

Compiler outputs assembly code, as it is easier to

• produce as output
• debug

Linker resolves ext mem addresses, where code in one file may refer to location in another file.

Stages of Compiler¶

flowchart LR

a[/Input/] -->
|Char<br/>Stream| la

subgraph Analysis/Front End
la["Lexical<br/>Analysis<br/>(Scanning)"] -->
|Token<br/>Stream| sya["Syntax<br/>Analysis<br>(Parsing)"] -->
|Syntax<br/>Tree| sea[Semantic<br/>Analysis]
end

sea --> |Syntax<br/>Tree| icg

subgraph Synthesis/Back End
icg[Intermediate<br/>Code<br/>Generation] -->
|Intermediate<br/>Representation| mico[Machine-Independent<br/>Code Optimization] -->
|Intermediate<br/>Representation| c[Code<br/>Generator] -->
|Target<br/>Machine<br/>Code| mdco[Machine-Dependent<br/>Code Optimization]
end

mdco --> o[/Output/]

Error Detection & Reporting¶

At every phase, if any error is identified, it is reported and handled

Tasks¶

• Report the presence of errors clearly & accurately. One error can mask another & cause correct code to look faulty.
• Recover from each error quickly enough to detect subsequent errors
• Add minimal overhead to processing of correct programs

Types of Errors¶

Symbol-Table¶

Data structure (usually hash table - for efficiency) containing a record for each identifier (variables, constants, functions) with fields for the attributes of the identifier

It is accessed at every phase of compiler.

• Scanner, parser, and semantic analyzer put names of identifiers in symbol table.
• The semantic analyzer stores more information (e.g. types) in the table.
• The intermediate code generator, code optimizer and code generator use information in symbol table to generate appropriate code.

Contains¶

• Attributes of variables are name, type, scope, etc.
• Attributes of procedure names which provide info about
• no and types of its arguments
• method of passing each argument (call by value/reference)
• type returned

Passes¶

Several phases are sometimes combined into a single ‘pass’

A pass reads an input file process it and writes an output file

Normal Passes in Compilers¶

• Front-end phases are combined into a pass
• Code optimization is an optional pass
• Back-end phase can be made into a pass

Misc¶

Compilation Examples¶

C¶

cc gx.c
objdump -d a.out

Java¶

This command shows how your class file is treated

javac File.java
javap -c File.class

It is cross platform, as it executes as a station machine

Python¶

python file.py
python decompile file.py

Android SDK¶

How does it show how your java program will work on mobile, when mobile is ARM architecture, but your laptop is usually x86 architecture.

This is because java program is cross-platform, and the simulator simulates execution of the program as if it is executed on an ARM processor.

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