Code Generation Questions and Answers

Q: Which of the following is/are type of data supported/added by/in typical object file formats in code generation phase of a compiler ?(i) Data segment(ii) Block started by symbol(iii) Text segment

All three are supported, so the answer is (i), (ii) and (iii) only.Typical object file formats (such as ELF or COFF) produced by a compiler's code generation phase contain a text segment holding the machine code, a data segment holding initialised global and static data, and a BSS segment ('block started by symbol') recording the size of uninitialised data, which takes no space in the file and is zeroed at load time.Each narrower option leaves out one of these standard sections.

Q: Which one of the following cannot be the input to the code generation process ?

The answer is Machine code.Code generation is the final phase of a compiler: it takes the program in an earlier form and produces target code. Machine code is what comes out of the process, so it cannot be its input.The code generator normally works on the intermediate code; the source program is what that intermediate code was made from and is the input to the translation as a whole; and an assembly program is translated into machine code by an assembler. Each can stand at the input side of code generation, while machine code never does.

71.

Consider the following statements about code generation.
1. Instruction selection depends on the target instruction set.
2. Register allocation depends on the number of machine registers.
3. Both are independent of the source language being compiled.

A.1 only
B.Only 4
C.All of them
D.None of them

Answer: C

All three hold. The back end sees only the intermediate representation and the machine description, which is precisely what allows one back end to serve several source languages. The machine description is the only thing that changes between targets.

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72.

Optimal code generation in the general case is

A.achieved routinely by every production compiler
B.impossible because the machine is not known at compile time
C.unnecessary because all instruction sequences cost the same
D.intractable, so heuristics are used throughout the back end

Answer: D

Correct answer: intractable, so heuristics are used throughout the back end

Instruction selection over a graph, register allocation by colouring, and instruction scheduling are each NP-hard on their own, and they interact so that solving one well can worsen another. Every production compiler therefore uses heuristics, and the quality of its code is the quality of those heuristics.

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73.

A code generator emitting assembly rather than machine code gains

A.output that is readable and can be assembled separately
B.faster compilation because assembly is smaller
C.the ability to skip the register allocation stage entirely
D.protection against errors in the generated code

Answer: A

Readability greatly eases development and debugging of the compiler itself. The cost is an extra assembly step, which matters mainly for compilation speed. Most production compilers still take that cost for the sake of maintainability.

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74.

The final quality of generated code depends most on

A.the parsing method the front end happened to use
B.how well selection, allocation and scheduling work together
C.the number of passes the compiler happens to make over the source
D.the size of the symbol table built during compilation

Answer: B

The three decisions interact, and a good result requires them to be coordinated rather than each optimised in isolation. The front end has almost no bearing on the outcome. This is why back end work dominates the effort in an optimising compiler.

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75.

Which of the following is/are type of data supported/added by/in typical object file formats in code generation phase of a compiler ?

(i) Data segment
(ii) Block started by symbol
(iii) Text segment

A.(i) only
B.(ii) and (iii) only
C.(i), (ii) and (iii) only
D.(i) and (iii) only

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: C

All three are supported, so the answer is (i), (ii) and (iii) only.

Typical object file formats (such as ELF or COFF) produced by a compiler's code generation phase contain a text segment holding the machine code, a data segment holding initialised global and static data, and a BSS segment ('block started by symbol') recording the size of uninitialised data, which takes no space in the file and is zeroed at load time.

Each narrower option leaves out one of these standard sections.

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76.

Which one of the following cannot be the input to the code generation process ?

A.Source program
B.Intermediate code
C.Assembly program
D.Machine code

Exam Year(s)

Tripura Public Service Commission - 2019,

Answer: D

The answer is Machine code.

Code generation is the final phase of a compiler: it takes the program in an earlier form and produces target code. Machine code is what comes out of the process, so it cannot be its input.

The code generator normally works on the intermediate code; the source program is what that intermediate code was made from and is the input to the translation as a whole; and an assembly program is translated into machine code by an assembler. Each can stand at the input side of code generation, while machine code never does.

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