GATE CS 2025 Set 1 Q.52: Intermediate Code Generation, Data Flow Analysis and Code Optimization

Refer to the given 3-address code sequence. This code sequence is split into basic blocks. The number of basic blocks is ________. (Answer in integer)

1001: i = 1
1002: j = 1
1003: t1 = 10*i
1004: t2 = t1+j
1005: t3 = 8*t2
1006: t4 = t3-88
1007: a[t4] = 0.0
1008: j = j+1
1009: if j <= 10 goto 1003
1010: i = i+1
1011: if i <= 10 goto 1002
1012: i = 1
1013: t5 = i-1
1014: t6 = 88*t5
1015: a[t6] = 1.0
1016: i = i+1
1017: if i <= 10 goto 1013

Your answer

Official answer and solution

Official answer: 6
From: Official GATE 2025 answer key

Solution

Identify all leader instructions (the first instruction, any target of a jump, and any instruction immediately following a jump).

By the standard basic-block partitioning algorithm, an instruction is a leader if it is:

The first instruction in the intermediate code: 1001.
The target of a conditional or unconditional goto: 1003 (from 1009), 1002 (from 1011), and 1013 (from 1017).
The instruction immediately following a conditional or unconditional goto: 1010 (after 1009) and 1012 (after 1011).

Thus the leaders are 1001, 1002, 1003, 1010, 1012, 1013, partitioning the code into 6 basic blocks:

$B_1$ : 1001
$B_2$ : 1002
$B_3$ : 1003..1009
$B_4$ : 1010..1011
$B_5$ : 1012
$B_6$ : 1013..1017

Final answer

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2025 Computer Science and Information Technology - Session 1 (CS1)
Question: 52 of 65
Section: Computer Science and Information Technology

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