Code Generation and Optimization · Compiler Design · GATE CSE

In the context of compilers, which of the following is/are NOT an intermediate representation of the source program?

Consider the following statements.

I. Symbol table is accessed only during lexical analysis and syntax analysis.

II. Compilers for programming languages that support recursion necessarily need heap storage for memory allocation in the run-time environment.

III. Errors violating the condition ‘any variable must be declared before its use’ are detected during syntax analysis.

Which of the above statements is/are TRUE?

Which one of the following is FALSE?

Which languages necessarily need heap allocation in the runtime environment?

Some code optimizations are carried out on the intermediate code because

Consider the grammar rule $$E \to {E_1} - {E_2}$$ for arithmetic expressions. The code generated is targeted to a CPU having a single user register. The subtraction operation requires the first operand to be in the register. If E₁ and E₂ do not have any common sub-expression, in order to get the shortest possible code.

Match the followings:

Group-I

(a) Pointer data type
(b) Activation Record
(c) Repeat -Until
(d) Coercion

Group-II

(p) Type Conversion
(q) Dynamic Data Structure
(r) Recursion
(s) Nondeterministic loop

Consider the following pseudo-code.

L1: t1 = -1
L2: t2 = 0
L3: t3 = 0
L4: t4 = 4 * t3
L5: t5 = 4 * t2
L6: t6 = t5 * M
L7: t7 = t4 + t6
L8: t8 = a[t7]
L9: if t8 <= max goto L11
L10: t1 = t8
L11: t3 = t3 + 1
L12: if t3 < M goto L4
L13: t2 = t2 + 1
L14: if t2 < N goto L3
L15: max = t1

Which one of the following options CORRECTLY specifies the number of basic blocks and the number of instructions in the largest basic block, respectively ?

Consider the control flow graph shown.

Which one of the following choices correctly lists the set of live variables at the exit point of each basic block?

Consider the following ANSI C code segment:

z = x + 3 + y -> f1 + y -> f2;

for (i = 0; i < 200; i = i + 2){

if (z > i) {

P = p + x + 3;

q = q + y -> f2;

} else {

p = p + y -> f2;

q = q + x + 3;

}

}

Assume that the variable y points to a struct (allocated on the heap) containing two fields f1 and f2, and the local variables x, y, z, p, g, and i are allotted registers. Common sub-expression elimination (CSE) optimization is applied on the code. The number of addition and dereference operations (of the form y -> f1 or y -> f2 ) in the optimized code, respectively, are:  

For a statement S in a program, in the context of liveness analysis, the following sets are defined:

USE(S): the set of variables used in S

IN(S): the set of variables that are live at the entry of S

OUT(S): the set of variables that are live at the exit of S

Consider a basic block that consists of two statements, S₁ followed by S₂.

Which one of the following statements is correct?

A variable x is said to be live at a statement $${S_i}$$ in a programif the following three conditions hold simultaneously:

i. There exists a statement $${S_j}$$ that uses x
ii. There is a path from $${S_i}$$ to $${S_j}$$ in the flow graph corresponding to the program
iii. The path has no intervening assignment to x including at $${S_i}$$ and $${S_j}$$

The variables which are live both at the statement in basic block 2 and at the statement in basic block 3 of the above control flow graph are

The least number of temporary variables required to create a three-address code in static single assignment form for the expression $$q + r / 3 + s - t * 5 + u * v/w$$ is _______________.

Consider the intermediate code given below.

(1)  i = 1
(2)  j = 1
(3)  t1 = 5 ∗ i
(4)  t2 = t1 + j
(5)  t3 = 4 ∗ t2
(6)  t4 = t3
(7)  a[t4] = -1
(8)  j = j + 1
(9)  if j<=5 goto (3)
(10) i=i+1
(11) if i<5 goto (2)

The number of nodes and edges in the control-flow-graph constructed for the above code, respectively, are

For a C program accessing X[ i ] [ j ] [ k ], the following intermediate code is generated by a compiler. Assume that the size of an integer is 32 bits and the size of a character is 8 bits.

t0 = i * 1024 
t1 = j * 32 
t2 = k * 4 
t3 = t1 + t0 
t4 = t3 + t2 
t5 = X[t4] 

Which one of the following statements about the source code for the C program is CORRECT?

Consider the following C code segment.

for (i = 0; i < n; i++) 
  { 
      for (j=0; j < n; j++) 
      { 
          if (i%2) 
          { 
           x += (4*j + 5*i); 
           y += (7 + 4*j); 
          } 
       } 
  } 

Which one of the following is false?

Consider the following translation scheme.

$$\eqalign{ & S \to ER \cr & R \to *E\left\{ {pr{\mathop{\rm int}} ('*');} \right\}R\,|\,\varepsilon \cr & E \to F + E\left\{ {pr{\mathop{\rm int}} (' + ');} \right\}\,|\,F \cr & F \to S\,|\,id\,\left\{ {pr{\mathop{\rm int}} (id.value);} \right\} \cr} $$

Here id is a token that represents an integer and id.value represents the corresponding integer value. For an input '2 * 3 + 4' this translation scheme prints

Consider line number 3 of the following C - program.

int main ( ) {              /* Line 1 */ 
int I, N;                   /* Line 2 */ 
fro (I = 0, I < N, I++);    /* Line 3 */ 
} 

Identify the compiler's response about this line while creating the object-module

Which of the following is NOT an advantage of using shared, dynamically linked libraries as opposed to using statically linked libraries?

Consider the syntax directed definition shown below.

Here, gen is a function that generates the output code, and newtemp is a function that returns the name of a new temporary variable on every call. Assume that ti's are the temporary variable names generated by newtemp. For the statement 'X : = Y + Z', the 3-address code sequence generated by this definition is