GATE CS 2025 Set 2 — Question 21

MCQ+1 / -0.33EasyBackpatchingIntermediate Code GenerationCompiler Design

Compiler Design → Intermediate Code Generation → Backpatching

Last updated 5 September 2026

Question

Consider the following statements about the use of backpatching in a compiler for intermediate code generation: (I) Backpatching can be used to generate code for Boolean expression in one pass. (II) Backpatching can be used to generate code for flow-of-control statements in one pass. Which ONE of the following options is CORRECT?

Correct answer (C) Both (I) and (II) are correct. Solution Backpatching is a technique used in the intermediate code generation phase of a compiler. It is primarily used to generate code for boolean expressions and flow-of-control statements in a single pass. When generating code for boolean expressions (like a < b or A || B) and control flow statements (like if, while), the compiler often needs to generate jump instructions. In a single-pass compiler, the target address (label) of a forward jump is not known at the moment the jump instruction is generated. Backpatching solves this by generating the jump instruction with an empty or placeholder target and adding the location of this instruction to a list. Later, when the target label is determined, the compiler goes back and fills in (backpatches) the correct address in all the instructions on the list. Therefore: (I) is TRUE: Backpatching allows single-pass generation for Boolean expressions (short-circuit evaluation involves jumps). (II) is TRUE: Backpatching allows single-pass generation for flow-of-control statements. Hence, both statements are correct. Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (C) Both (I) and (II) are correct. Solution Backpatching is a technique used in the intermediate code generation phase of a compiler. It is primarily used to generate code for boolean expressions and flow-of-control statements in a single pass. When generating code for boolean expressions (like a < b or A || B) and control flow statements (like if, while), the compiler often needs to generate jump instructions. In a single-pass compiler, the target address (label) of a forward jump is not known at the moment the jump instruction is generated. Backpatching solves this by generating the jump instruction with an empty or placeholder target and adding the location of this instruction to a list. Later, when the target label is determined, the compiler goes back and fills in (backpatches) the correct address in all the instructions on the list. Therefore: (I) is TRUE: Backpatching allows single-pass generation for Boolean expressions (short-circuit evaluation involves jumps). (II) is TRUE: Backpatching allows single-pass generation for flow-of-control statements. Hence, both statements are correct.

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