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Table of contents
1.
Introduction
2.
Compiler Design Interview Questions for Freshers
2.1.
1. What is a compiler?
2.2.
2. What is compiler design?
2.3.
3. Briefly explain parts of the compilation.
2.4.
4. What is an Assembler?
2.5.
5. Name some compiler construction tools.
2.6.
6. What is lexical analysis?
2.7.
7. What is Linker in Compiler Design?
2.8.
8. What is Garbage Collection?
2.9.
9. Name various storage allocation strategies.
2.10.
10. What is loop unrolling?
2.11.
11. What is tail recursion, and how is it optimised in compilers?
2.12.
12. What is the difference between a compiler and an interpreter?
2.13.
13. What is the difference between a front-end and a back-end compiler?
2.14.
14. Explain the backend phases of a compiler.
2.15.
15. What is just in time compiler?
2.16.
16. Name all error recovery strategies.
2.17.
17. What is an operator precedence parser?
2.18.
18. Define ambiguous grammar.
2.19.
19. What is profile-guided optimisation, and how is it used in compilers?
2.20.
20. What is a compiler front-end, and what are some of its key components?
3.
Compiler Design Interview Questions for Experienced
3.1.
21. Explain bootstrapping in compiler design.
3.2.
22. What is Relocatable Machine Code?
3.3.
23. What is the problem with top-down parsing?
3.4.
24. What is type checking, and why is it important?
3.5.
25. What is Yacc?
3.6.
26. What is a symbol table, and why is it important?
3.7.
27. What is a parse tree, and how is it different from an abstract syntax tree?
3.8.
28. Mention types of LR parsers.
3.9.
29. What is dead code elimination, and how does it work?
3.10.
30. What is register allocation, and how is it used in compiler design?
3.11.
31. What is handle pruning?
3.12.
32. List properties of LR parser.
3.13.
33. What are viable prefixes?
3.14.
34. What are the benefits of intermediate code generation?
3.15.
35. Define backpatching.
3.16.
36. Briefly explain the functions used in backpatching.
3.17.
37. Define Peephole optimization.
3.18.
38. List characteristics of peephole optimization.
3.19.
39. What is dynamic scoping?
3.20.
40. How does a compiler handle errors and warnings?
3.21.
41. What is loop optimization, and how is it used in compiler design?
3.22.
42. What is code generation, and how is it used in compiler design?
3.23.
43. What is a dynamic programming language, and how does it differ from a static one?
3.24.
44. What is a recursive descent parser, and how is it used in compiler design?
3.25.
45. What is a Three-Address Code (TAC) and its role in compiler design?
4.
Conclusion
Last Updated: May 16, 2024

Compiler Design Interview Questions

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Introduction

Compiler Design is a world of programming language creation and machine code generation. It is important to learn this because it gives you a different perspective while writing code. One understands how things work under the hood. In this article w have categorised the compiler design interview questions based on the following:

  • Compiler design interview questions for freshers
  • Compiler design interview questions for experienced

 

Compiler Design Interview Questions 

In this article, we'll go through some commonly asked Compiler Design Interview Questions.

Compiler Design Interview Questions for Freshers

1. What is a compiler?

A compiler is a software designed to read a program written in one language and change it to another. The translated program is equivalent to the original program. A compiler also throws errors, if there are any, present in the code.

2. What is compiler design?

Compiler Design focuses on the creation of programming language compilers. A compiler is software that is designed to read a program written in one language and change it to another language. It also covers error detection and recovery.

3. Briefly explain parts of the compilation.

The compiler consists of several phases: 

  • Lexical Analysis: This phase is also known as scanning. The source code is broken down into a sequence of tokens.
     
  • Syntax Analysis: This phase checks the grammar of the code. A parser reads the token generated by the scanner and builds an abstract syntax tree.
     
  • Semantic Analysis: It is also known as context analysis. The semantic analyzer reads the AST produced during syntax analysis. Then it performs type checking, scope analysis, and other error.
     
  • Code Optimization: This involves improving the final code, which is done by reducing file size, increasing speed, reducing power consumption, etc.
     
  • Code Generation: It involves generating machine code from the intermediate after all the phases.
     

4. What is an Assembler?

An assembler is a software program that converts assembly code to machine-readable code. Assembly language is a low-level programming language. It uses symbolic representations of machine instructions to make programming easier for programmers to write and comprehend. The CPU can directly execute the code generated by the assembler.

5. Name some compiler construction tools.

The following is a list of some compiler construction tools:

  • Parser generators
  • Scanner generators
  • Syntax-directed translation engines
  • Automatic code generators
  • Data-flow engines
     

6. What is lexical analysis?

Lexical analysis is also known as scanning. The compilation process begins by performing a lexical analysis. It collects updated source code from the language preprocessor that is written as sentences. A lexical analyser converts the source code into a list of tokens.

7. What is Linker in Compiler Design?

Linker is also known as a link editor or binder. It is a utility program in a system. Depending on the compiler, it takes single or multiple files and converts them into an executable file. Linking is the process of combing multiple object modules into a single object file.

8. What is Garbage Collection?

Using garbage collection, a program can automatically release no longer required memory. It is crucial to the design of compilers since it can aid in preventing memory leaks and other memory-related mistakes.

9. Name various storage allocation strategies.

There are name 3 storage allocation strategies: 

  • Static allocation
  • Stack allocation
  • Heap allocation
     

10. What is loop unrolling?

Loop unrolling is used to reduce the overhead caused by loop control structures. It entails repeating a loop's body a predetermined number of times, enhancing performance by limiting the number of instructions the loop executes.

11. What is tail recursion, and how is it optimised in compilers?

Tail recursion occurs when the function's final action is the recursive call. Using a process known as tail call optimisation, which substitutes a jump to the function's beginning for the recursive call, it is possible to speed up the execution of the function in compilers.

12. What is the difference between a compiler and an interpreter?

compiler goes through the entire source code at once and only executes in case of no error. In comparison, the interpreter executes the source code statement line by line. Another major difference is that the compiler links various files into an executable file. In comparison, the interpreter doesn’t require any linking.  

13. What is the difference between a front-end and a back-end compiler?

A back-end compiler converts the intermediate representation of the source code into machine code after a front-end compiler performs lexical, syntactic, and semantic analysis to create an intermediate representation of the source code.

14. Explain the backend phases of a compiler.

A compiler's backend phase converts a program's intermediate representation, commonly expressed as an abstract syntax tree or three-address code, into machine code that the target machine can execute. Each stage in the backend phase of the translation process—which comprises numerous stages—performs a particular function.

15. What is just in time compiler?

The JIT compiler transforms the translated code into executable machine code for the processor. Generated code can outperform interpretation alone because it can employ processor-specific optimisations like instruction pipelining or register allocation.

16. Name all error recovery strategies.

There are namely 5 error recovery strategies:

  • Panic Mode Recovery: This method is known as "panic mode" because the parser effectively panics and attempts to recover by tossing out input until it can locate a suitable point to restart parsing from.
     
  • Statement Mode recovery: In this approach, the parser looks for the shortest phrase or subexpression that can be changed to fix the problem before re-synchronizing the parsing at that location. Compared to panic mode recovery, this approach is more targeted and specific and may allow for more effective error recovery.
     
  • Error Productions: This method involves adding more errors to the grammar, allowing the parser to carry on even in the face of an error. The error productions specify the appropriate action for the parser to do in response to the error and often generate a synthesis or default value to replace the incorrect input.
     
  • Global Correction: With this approach, the parser tries to fix the issue by making broad adjustments to the input code, such as adding or removing tokens or switching the sequence of operations. Although this method is less accurate than phrase-level recovery, it can work well for some problems.
     
  • Using Symbol Table: The associated identifier is found in a symbol table when there are semantic errors. The compiler automatically performs type conversion if the data types of the two operands are incompatible.
     

17. What is an operator precedence parser?

An operator precedence parser is a form of the bottom-up parsing approach used in compiler design to examine and produce the intermediate representation of the input program. The parser scans the input from left to right while keeping a stack of terminals and non-terminals. Each token is scanned, pushed onto the stack, and the parser decides what to do next by looking at the top of the stack.

18. Define ambiguous grammar.

A Grammar G is called ambiguous grammar if a language sentence has more than one parse tree. That means both derivations are the same for the given sentence leftmost and rightmost.

19. What is profile-guided optimisation, and how is it used in compilers?

Profile-guided optimisation is a compiler optimisation approach where the compiler uses data about the program's behaviour during runtime to make optimisation decisions. To optimise the code for performance, this method entails executing the program while using a profiler to gather information about the sections of the code that are executed the most frequently.

20. What is a compiler front-end, and what are some of its key components?

The compiler front-end is the compiler part that examines the input program and generates a rough approximation of the program's syntax. The front end includes crucial components such as the lexer, parser, semantic analyzer, and type checker.

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Compiler Design Interview Questions for Experienced

21. Explain bootstrapping in compiler design.

Bootstrapping is leveraging an existing compiler or interpreter to develop a new version of the same compiler or interpreter. This is accomplished by first compiling or interpreting the compiler's or interpreter's source code using the current version and then compiling or interpreting the source code once more using the recently constructed version.

22. What is Relocatable Machine Code?

Relocatable machine code is a subset of machine code that can be loaded and run from several memory locations. It has memory locations that can be changed or relocated during loading or execution because they are not fixed addresses.

23. What is the problem with top-down parsing?

Various problems arise while top-down parsing:

  • Left recursion
  • Left factoring
  • Ambiguity
  • Backtracking
     

24. What is type checking, and why is it important?

Type checking is verifying the types of values used inside the program. Type checking involves checking that the variables, functions, and expressions are performing what they should be. Type-checking is important because issues can be discovered early in the development process before the code is executed. Typographical errors can be challenging to find and debug, which can cause erroneous program behaviour or crashes. By requiring type-checking, the compiler can ensure that the program behaves effectively and errors are found before they cause issues.

25. What is Yacc?

Yacc stands for yet another compiler compiler. It is a parser-generation tool to create parsers for programming languages and other formal languages. Yacc is built on a formal grammar of the parsed language, expressed in a unique notation known as the Backus-Naur Form (BNF). The grammar describes the language's syntax and the language constructions' structure.

26. What is a symbol table, and why is it important?

The symbol table records the names of variables, functions, and other program elements and their characteristics and qualities. It is crucial since it helps resolve references to these things and identify use issues.

27. What is a parse tree, and how is it different from an abstract syntax tree?

The parse tree serves as a representation of a program's syntactic structure. The parser creates it during the parsing process and depicts the hierarchical relationship between the program's constituent parts, including expressions, commands, and functions. The compiler uses the parse tree for type checking, semantic analysis, and code compilation.

28. Mention types of LR parsers.

Types of LR parsers:

  • SLR parser- simple LR parser
  • LALR parser-lookahead LR parser
  • Canonical LR parser
     

29. What is dead code elimination, and how does it work?

Dead codes are those which does not require the working of the main application. Dead code elimination is an optimisation technique which removes the unwanted code in the application. There is dead code even at the source code level. This happens while working on a large project. Dead codes are common.

30. What is register allocation, and how is it used in compiler design?

Register allocation allocates computer system program variables to the few immediately accessible CPU registers. Compilers use this important optimisation technique to reduce the number of memory accesses required by a program, which can improve speed. Register allocation techniques include graph colouring and linear scan, for instance.

31. What is handle pruning?

In compiler design, handle pruning minimises the size of a grammar's parsing table. The parser uses the parsing table, a data structure, to decide how to parse the input string. It assigns a production rule to each pairing of a non-terminal symbol and a lookahead token. Handle pruning deletes empty entries from the parsing table that would never be used. This can greatly reduce the parsing table's size, enhancing the parser's functionality.

32. List properties of LR parser.

Properties of LR(Left-to-right, Rightmost derivation in reverse) Parser: 

  • The class of grammars the LR parser can parse is a superset of the class of grammars that predictive parsers can parse.
  • For the majority of programming languages where context-free grammar can be expressed, LR parsers can be built.
  • Although LR parsers use a non-backtracking shift-reduce method, it is effective.
     

33. What are viable prefixes?

Viable prefixes are the right sentential form prefixes that can appear on a shift-reduce parser's stack. A prefix of a right sentential form that does not extend past the right end of that sentential form's rightmost handle is an equivalent definition of a viable prefix.

34. What are the benefits of intermediate code generation?

It is possible to optimize the code generation by applying a machine-independent code optimizer to intermediate code. By connecting the various back ends to the preexisting front ends of each machine, a Compiler can be made for various machines. It is possible to develop a compiler for several source languages by presenting various front ends for associated back ends of preexisting source languages.

35. Define backpatching.

During the code generation process, backpatching adds relevant semantic actions to labels with unspecified information. The routines mklist(i), merge_list(p1,p2), and backpatch(p, i) are utilized in the semantic activities.

36. Briefly explain the functions used in backpatching.

Functions used in backpatching: 

  • mklist(i): It creates a new list. Where i is the index of the array of quadruples.
  • merge_list(p1, p2): It merges two lists p1 and p2. It returns the pointer to the merged list.
  • backpatch(p, i): It inserts ‘i’ as the target label for the statement pointed by pointer p. 
     

37. Define Peephole optimization.

Peephole optimisation is a quick and efficient method for enhancing target code on the local level. By looking at the brief sequence of target instructions and swapping them out with shorter or quicker sequences, this technique helps the target program run more efficiently.

38. List characteristics of peephole optimization.

Here are some characteristics of peephole optimization:

  • Redundant instruction elimination 
  • The flow of control optimization Algebraic simplification
  • Use of machine idioms
     

39. What is dynamic scoping?

When referring to non-local data in dynamic scoping, "non-local variable" refers to non-local information declared in the most recently called and active method. As a result, fresh discoveries are established for local names known as procedures each time. Symbol tables may be needed during operation in dynamic scoping.

40. How does a compiler handle errors and warnings?

Errors are issues that stop the code from being compiled into an executable program. As opposed to errors, which obstruct the compilation of the code, warnings point out potential difficulties or problems. When handling errors and warnings, a compiler examines the source code and produces messages pointing out potential faults or problems. Depending on their seriousness, these notifications can be considered errors or warnings.

41. What is loop optimization, and how is it used in compiler design?

Compilers use loop optimisation techniques to enhance the efficiency of loops in programs. This incorporates different transformations, which can decrease the number of instructions performed and enhance cache performance, such as loop unrolling, loop fusion, loop exchange, and loop-invariant code mobility. The speed of programs with repeating computations can be enhanced using loop optimization, a key method.

42. What is code generation, and how is it used in compiler design?

Code generation is turning the intermediate code produced by the compiler into machine code that can be executed on a target computer system. This entails several phases, including instruction choice, register allocation, and code structure, which can impact the effectiveness and efficiency of the resulting code. The process of code generation, which comes after compilation, is in charge of creating the user-executable program.

43. What is a dynamic programming language, and how does it differ from a static one?

A dynamic programming language conducts type checking and further semantic analysis during runtime as opposed to during compilation. This enables programming techniques like dynamic type and runtime code evaluation, which are more adaptable and expressive. In contrast, type checking and other semantic analyses are carried out at compile time in a static programming language, which can lead to speedier and more dependable code. Python, Ruby, and JavaScript are dynamic programming languages, whereas C++, Java, and Go are static.

44. What is a recursive descent parser, and how is it used in compiler design?

Recursive descent parsers are a form of the top-down parser that analyze input programs using a collection of mutually recursive procedures. The parsing of the corresponding section of the input program is the responsibility of each function, which maps to a non-terminal in the grammar. Recursive descent parsers are simple to use and comprehend, but they may have issues with left-recursive grammar and input that is unclear.

45. What is a Three-Address Code (TAC) and its role in compiler design?

Compilers use Three-Address Code (TAC), a low-level intermediate representation of a program, to optimize and produce executable code. TAC represents expressions and statements as a set of three-address instructions that each carry out a single operation on two or three operands. Thanks to TAC, compilers can perform typical optimizations like constant folding, dead code elimination, and common subexpression elimination.

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Conclusion

This article covered some Compiler Design Interview Questions. Compiler Design Interview Questions are divided into 3 categories easy, medium, and hard.

After reading this blog, you will have a good idea about the kind of Compiler Design Interview Questions asked.

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