GATE CS 2024 Set 2 Q.43: Intermediate Code Generation, Data Flow Analysis and Code Optimization

Consider the following expression: $x[i] = (p + r) * -s[i] + u/w$ . The following sequence shows the list of triples representing the given expression, with entries missing for triples (1), (3), and (6).

Triple	Op	Arg 1	Arg 2
(0)	`+`	$p$	$r$
(1)
(2)	`uminus`	(1)
(3)
(4)	`/`	$u$	$w$
(5)	`+`	(3)	(4)
(6)
(7)	`=`	(6)	(5)

Which one of the following options fills in the missing entries CORRECTLY?

(1) =[] $s$ $i$ (3) * (0) (2) (6) []= $x$ $i$

(1) []= $s$ $i$ (3) - (0) (2) (6) =[] $x$ (5)

(1) =[] $s$ $i$ (3) * (0) (2) (6) []= $x$ (5)

(1) []= $s$ $i$ (3) - (0) (2) (6) =[] $x$ $i$

Official answer and solution

Official answer: A
From: Official GATE 2024 answer key

Solution

Trace the subexpressions of $x[i] = (p + r) * (-s[i]) + u / w$ and distinguish r-value array read (=[] s i) from l-value indexed target ([]= x i).

Triple (1): Triple (2) applies unary minus (uminus) to (1), so (1) must fetch the r-value of $s[i]$ , represented as =[] s i.
Triple (3): Multiplies (0) ( $p + r$ ) and (2) ( $-s[i]$ ), represented as * (0) (2).
Triple (6): Triple (7) assigns (5) (the entire RHS value) to the target (6), so (6) represents the l-value array reference $x[i]$ , written as []= x i.

Hence (A) is the correct combination.

Final answer

Option (A)

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

Source

Paper: GATE 2024 Computer Science and Information Technology - Set 2 (CS2)
Question: 43 of 65
Section: Computer Science and Information Technology

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