What are common examiner traps in Code Generation?

Failing to mark a variable as dead immediately after its final read in the code sequence. Assuming variables live into one branch must remain live through the alternative branch when both branches don't use them. Counting total unique variables in the snippet instead of the maximum simultaneously live variables. Overlooking that newly generated temporary values occupy a register concurrently with remaining live operands.

GATE CSE Code Generation PYQs

Standard yield1.5% of Compiler Design

In Code Generation, GATE tests machine-level resource management, specifically register allocation and the minimum number of registers required to evaluate a co… Read the guide

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Questions: 1
Asked: 2013
Total marks: 2
Marks / paper: 0.1

1 GATE CSE Code Generation PYQs with solutions, from Compiler Design. Browse all GATE CSE PYQs.

Questions

Every official paper that asked this topic, newest first.

GATE CSE 2013 · Q49Common Data for Questions 48 and 49: The following code segment is executed on a processor which allows only register operands in its instructions. Each instruction can have atmost two source operands and one destination operand. Assume that all variables are dead after this code segment.c = a + b; d = c * a; e = c + a; x = c * c; if (x > a) { y = a * a; } else { d = d * d; e = e * e; }…MCQ2 marksMediumSolve

What GATE tests in Code Generation

Concepts, patterns, formulas and traps distilled from past papers.

In Code Generation, GATE tests machine-level resource management, specifically register allocation and the minimum number of registers required to evaluate a code block without memory spilling. Questions evaluate students on identifying live ranges of variables across basic blocks and control-flow branches under explicit instruction set architecture (ISA) constraints.

Core concepts

Liveness analysis at program points
Live ranges and register interference
Register allocation without spilling
Register-register (load-store / 3-address) ISA execution constraints
Handling branching and conditional execution in liveness analysis

Recurring question patterns

Minimum Register Allocation without Spilling
RareMCQ2 marks2013
Given a straight-line or simple branching code snippet, determine the minimum number of CPU registers required to execute the snippet without spilling any variables to memory, based on live variable analysis at each program point.

Formulas GATE uses

Minimum Registers without Spilling

R_{\min} = \max_{p \in \text{Program Points}} |\text{LiveVariables}(p)|

Used to find the minimum number of machine registers required to execute a sequence of instructions without saving/restoring (spilling) variables to memory when register re-use is allowed.

Examiner traps in Code Generation

Failing to mark a variable as dead immediately after its final read in the code sequence.
Assuming variables live into one branch must remain live through the alternative branch when both branches don't use them.
Counting total unique variables in the snippet instead of the maximum simultaneously live variables.
Overlooking that newly generated temporary values occupy a register concurrently with remaining live operands.

How questions are asked

Find the minimum number of CPU registers needed to compile/execute a code segment without spilling

Paper trends

Tested via a 2-mark question focusing on live variable analysis and register allocation without spilling in an explicit register-only ISA with simple branching.
2013

Difficulty notes

Medium questions present a straight-line or simple if-else segment with 5–8 instructions where students compute the intersection of live ranges step-by-step. Harder variations could involve loops or complex DAG-based register evaluation trees (e.g., Ershov numbers / Sethi-Ullman algorithm).