MadeEasy Test Series: Compiler Design - Compilation Phases

Question

Which of the following is true?

A)  Symbol table is constructed during the analysis part of compiler i.e., (front end

B)  Type checking is done during syntax analysis phase.

C)  SDD with only synthesised attribute, always have a order of evaluation.

D)   Both (a) and (c)

Answer 1

A) Symbol table is constructed in the lexical analysis phase which is in end so A is true

    The front end includes all analysis phases end the intermediate code generator.

    The back end includes the code optimization phase and final code generation phase.

B) Type checking is done during semantic analysis phase and syntax analysis is used to generate parse trees.                                    eg int a = "world" . Hence false

C) Yes we can use post order traversal for evaluation when there are only synthesized attributes.

http://www.cse.iitm.ac.in/~rupesh/teaching/compiler/aug15/schedule/4-sdt.pdf

Hence A and C are true.

Therefore, D is the answer.

Comments

I am confused in 2nd statement ... can u plz explain the working of each phase?

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All  phases: -

1. Lexical Analysis:

Lexeme - a basic lexical unit of language consisting of one word or several words. eg. if , else

Main task of lexical analyzer is to read the input characters of the source program, group them into lexemes, and produce as output a sequence of token for each lexeme in the source program. Then this stream of tokens is sent to the parser for syntax analysis.

When the lexical analyzer discovers a lexeme constituting an identifier, it needs to enter that lexeme into symbol table.

tasks performed by lexical analyzer: removing comments, white spaces(blank, new line, tab). Expansion of macros, it also keep the track of number of newline character seen and hence error detection is possible.

2. Syntax analysis - Parsing:

It is used to generate syntax tree based on the lexemes provided by the lexical analysis phase. It takes help of symbol table. It involves parsers.

3. Semantic analysis :

Here you check the parse tree which is generated by the syntax analysis is meaningful or not. Type checking is also performed in this stage. Here we use semantic rules with grammar to generate syntax directed translation. There are 2 attributed SDT - S and L, where in S we use only synthesized attribute whose evaluation can be done using post order traversal.

4. Intermediate code generation:

It is used to generate three address code.

5. Code optimization

 Reduces same repeating lines in a code and optimizes based on usage of variables.

6. Target code generation

It is used to generated assembly code