GATE CSE 2023 | Question: 1

Question

Consider the following statements regarding the front-end and back-end of a compiler.

S1: The front-end includes phases that are independent of the target hardware.
S2: The back-end includes phases that are specific to the target hardware.
S3: The back-end includes phases that are specific to the programming language used in the source code.

Identify the CORRECT option.

• A. Only $\mathbf{S 1}$ is TRUE.
• B. Only $\mathbf{S 1}$ and $\mathbf{S 2}$ are TRUE.
• C. $\mathbf{S 1}, \mathbf{S 2}$, and $\mathbf{S 3}$ are all TRUE.
• D. Only $\mathbf{S 1}$ and $\mathbf{S 3}$ are TRUE.

Answer 1

Answer: Option B.

A compiler is a program that takes as input a program written in one language (the source language) and translates it into a functionally equivalent program in another language (the target language) without changing the meaning of the code.

Compiler process goes through lexical, syntax, and semantic analysis at the front end, and code generation and optimization at a back-end.

Front end and Back end of compiler:

The front end of a compiler is the part that takes the source language and produces an intermediate representation. This stage of compilation aims to detect any programmatic errors with the source code. It does this by performing lexical analysis, parsing (or syntax analysis) and semantic analysis. The output of the front end is an intermediate representation of the code, which can be passed to the middle end. The front end is also called analysis.

The back end is designed to produce a program for a target computer from the intermediate representation. It includes the code optimization phase and final code generation phase, along with the necessary error handling and symbol table operations. Back end phase of the compiler consists of those phases which depend on the target machine and are independent of the source program.

So, answer is Option B.

Comments

“Back end phase of compiler consists of those phases which depend on the target machine and are independent of the source program.” is a wrong statement.

The back end actually has an IR optimization phase that does not depend on the target machine, which is why it is also called a machine-independent optimizer which I guess is implemented differently for different programming languages from the source code. This is the reason why S3 is right.

So, to sum it up, if different programming languages use the same machine-independent optimizer then only S1 and S2 are true or else all three are right. 

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@jomboy IR optimisations don’t have any programming language specific quirks. For example, if you take the example of LLVM, once the frontend lowers things to the LLVM IR, the optimisations are language agnostic.

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@goxul

I don’t know compilers in depth but I thought machine-independent optimizers in complex programming languages(ex: C++, and Java) have more details to consider during optimization than those in simple programming languages(ex: C). So they are implemented differently for different programming languages. I could be wrong.

Answer 2

 

S1: The Front-End Phase of the compiler doesn’t contain any hardware specific process. So, the front-end phases of the compiler are independent of target hardware. So, S1 is true.

S2 : The Target Code Generation phase of back-end is hardware specific. So, S2 is also true.

S3 : It’s front-end which convert the programming code into Intermediate code. The back-end phase of the compiler has nothing to do with programming language. It is Independent of programming language. So, S3 is false.

Only S1 & S2 are true. Hence, B is correct answer.

Answer 3

The correct option is:

B. Only S1 and S2 are TRUE.

Here's the explanation for each statement:

S1: The front-end includes phases that are independent of the target hardware.
- This statement is true. The front-end of a compiler is responsible for tasks like lexical analysis, syntax analysis, and semantic analysis, which are independent of the target hardware.

S2: The back-end includes phases that are specific to the target hardware.
- This statement is true. The back-end of a compiler is responsible for tasks like code generation and optimization, which are specific to the target hardware platform.

S3: The back-end includes phases that are specific to the programming language used in the source code.
- This statement is not generally true. The phases in the back-end of a compiler are primarily concerned with generating efficient code for the target hardware. While the choice of programming language can influence some aspects of code generation, it's not a phase specific to the programming language itself. Most of the language-specific tasks are handled in the front-end.

So, only statements S1 and S2 are true, making option B the correct choice.

Answer 4

Option(B) is correct.