KIET Group of Institutions, Ghaziabad

Department of Computer Applications (NBA Accredited)

(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

Department of Computer Applications

COURSE MCA, IV SEM,
(2019-20) Even Semester
Compiler Design (RCA:404)

QUESTION BANK

UNIT I– GRAMMER AND AUTOMATON

1. Define regular expression?

It is built up out of simpler regular expression using a set of defining rules. Each
regular expression ‘r’ denotes a language L(r). The defining rules specify how
L(r) is formed by combining in various ways the languages denoted by the sub
expressions of r.

2. Give the precedence of regular expression operator?

i) The unary operator * has the highest precedence and is left
associative.
ii) Concatenation has the second highest precedence and is left
associative.
iii) / has the lowest precedence and is left associative.

3 Define the length of a string?

It is the number of occurrences of symbols in string,‘s’ denoted by |s|.
Example: s=abc, |s| =3.

4. Give the rules in regular expression?

1) € is a regular expression that denotes {€}, that is the set containing
the empty string.
2) If ‘a’ is a symbol in ∑ , then a is a regular expression that denoted
{a} , i.e., the set containing the string a.
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Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

3) Suppose r and s are regular expression denoting the languages L( r)

and L(s) .

5. Define regular set?

A language denoted by a regular expression is said to be a regular set.

6. Give the types of notational shorthand’s of RE?

 Zero or more instance
 One or more instance
 Character classes
 Character not in a given set and unary operator?

7. Define kleene closure or star closure and positive closure?

Star closure of L, denoted L*, is the set of those strings that can be formed by
taking any number of strings from L and concatenating all of them.
L* = Li

Positive closure of L ,denoted L+, is the set of those strings that can be
Formed by one or more concatenations of L
L+ = Li
8. Define character class with example.
The notation [abc] where a, b, c are alphabet symbols denotes the regular
expression a/b/c.
Example:
[A-z] = a | b | c | ------ | z
Regular expression for identifiers using character classes
[a – z A – Z] [A – Z a – z 0 – 9] *

9. Give the error recovery strategies in lexical analyzer.

 Deleting an extraneous character
 Inserting a missing character
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Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

 Replacing an incorrect character by a correct character

 Transposing of two adjacent character

10. Write the R.E. for the following language.

i. Set of statements over {a,b,c} that contain no two consecutive b’s
(B/c) (A/c/ab/cb) *
ii. Set of statements over {a,b,c} that contain an even no of a’s
((b/c)* a (b/c) * a)* (b/c)*

11. Describe the language denoted by the following R.E.

i. (0/1)*0(0/1)(0/1)
The set of all strings of 0’s and 1’s with the third symbol from
the right end is 0.
ii. 0(0/1)*0
The set of all strings of 0’s and 1’s starting and ending with 0.
iii. (00/11)*((01/10)(00/11)*(01/10)(00/11)*)
The set of all strings of 0’s and 1’s with even number of 0’s
and 1’s
12. Define
i. L.L* = L+
ii. 1.1* = 1+

13. What are the tasks in lexical analyzer?

 One task is stripping out from the source program comments and white
space in the form of blank, tab, new line characters.
 Another task is correlating error messages from the compiler with the
source program.

14. Define finite automata and its types with eg.

 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

A recognizer for a language is a program that takes as input a string x and answers
“yes” if x is a sentence of the language and “no” otherwise.
A better way to convert a regular expression to a recognizer is to construct a
generalized transition diagram from the expression. This diagram is called a finite
automation.
1. Deterministic (DFA)
2. Non-deterministic (NFA)

PART B:

1. Write a short note on token specification.

2. Write about R.E.
3. Explain in detail about input buffering.
4. For the R.E. (a/b)*a(a/b). Draw the NFA. Obtain DFA form NFA. Minimize
DFA using ∏new construction. Write down the algorithm wherever necessary.
a) (a/b)* abb
b) (a/b)* a (a/b).
c) (a/b)* a (a/b).
d) (a/b)* a(a/b) (a/b)
e) (a/b)* abb (a/b)*
5. Give the minimized DFA for the following expression (a/b)* abb (same as 4
question pbm.).
 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

COURSE MCA, IV SEM,

(2019-20) Even Semester

Compiler Design (RCA:404)
QUESTION BANK

UNIT II – INTRODUCTION TO COMPILING

1. Define compiler?
A compiler is a program that reads a program written in one language (source
language) and translates it into an equivalent program in another language (target
language) and the compiler reports to its user the presence of errors in the source
program.
2. What are the classifications of compiler?
i) Single pass compiler
ii) Multi pass compiler
iii) Load-and-go compiler
iv) Debugging or optimizing compiler
3. What are the phases of compiler?
i) Lexical analyzer
ii) Syntax analyzer
iii) Semantic analyzer
iv) Intermediate code generation
v) Code generation
vi) Code optimization
vii) Symbol table manager.
4. Define preprocessor & what are the functions of preprocessor?
Preprocessor produce input to the compilers (i.e.) the program will be divided in to
the modules. They may perform the following functions.
i) Macro processing
ii) File inclusion
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(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

iii) Rational preprocessor

iv) Language extension

5. What are the tools available in analysis phase?

i) Structure editors
ii) Pretty printer
iii) Static checkers
iv) Interpreters.

6. Define pretty printers?

A pretty printer analyzes a program and prints it in such a way that the structure of
the program becomes clearly visible. For the comments may appear with an amount
of indentation proportional to the depth of their nesting in the hierarchical
organization of the statements.

7. Define assembler and its types?

It is defined by the low level language is assembly language and high level language
is machine language is called assembler.
 One pass assembler
 Two pass assembler

8. Give the types of a language processing system?

a) Preprocessors
b) Compilers
c) Assembler
d) Loaders and link editors

9. What are the functions performed in analysis phase?

a. Lexical analysis or Linear analysis
b. Syntax analysis or hierarchical analysis
c. Semantic analysis
 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

10. What are the functions performed in synthesis phase?

i) Intermediate code generation
ii) Code generation
iii) Code optimization

11. Give the classification of processing performed by the semantic analysis?

a) Processing of declarative statements.
b) Processing of executable statements.

12. Give the properties of intermediate representation?

a) It should be easy to produce.

b) It should be easy to translate into the target program.

13. What are the two different parts of compilation?

a) Analysis phases of compilation
b) Synthesis phases of compilation

14. What is meant by lexical analysis?

It reads the characters in the program and groups them into tokens that are sequences
of characters having a collective meaning Such as an identifier, a keyword, a
punctuation, character or a multi-character operator like ++.

15. What is meant by syntax analysis?

It processes the string of descriptors, synthesized by the lexical analyzer, to determine
the syntactic structure of an input statement. This process is known as parsing. Output
of the parsing step is a representation of the syntactic structure of a statement. It is
represented in the form of syntax tree.
 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

16. What is meant by intermediate code generation?

After syntax and semantic analysis, some compilers generate an explicit intermediate
representation of the source program. It can have a variety of forms. This form called
three-address code. It consists of sequence of instructions, each of which has at most
three operands.

17. What is meant by semantic analysis?

This phase checks the source program for semantic errors and gathers type of
information for the subsequent phase.

18. What do you meant by interpreter?

Certain other translators transform a programming language into a simplified
language called intermediate code, which can directly executed using a program
called an interpreter.

19. What do you meant by phases?

Each of which transforms the source program one representation to another. A phase
is a logically cohesive operation that takes as input one representation of the source
program and produces as output another representation

20. Write short notes on symbol table manager?

The table management or bookkeeping portion of the compiler keeps track of the
names used by program and records essential information about each, such as its type
(int, real etc.,) the data structure used to record this information is called a symbol
table manger.

21. Write short notes on error handler?

The error handler is invoked when a flaw in the source program is detected. It must
warn the programmer by issuing a diagnostic, and adjust the information being
 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

passed from phase to phase so that each phase can proceed. So that as many errors as
possible can be detected in one compilation.

22. Mention some of the cousins of the compiler?

i) Preprocessors
ii) Assemblers
iii) Two pass assembly
iv) Loaders and Linker-editors.

23. What is front end and back end?

The phases are collected into a front end and a back end. The front end consists of
those phases or parts of phases, that depends primarily on the source language and is
largely independent of the target machine. The back ends that depend on the target
machine and generally these portions do not depend on the source language.

24. What do you meant by passes?

A pass reads the source program or the output of the previous pass, makes the
transformations specified by its phases and writes output into an intermediate file,
which may then be read by a subsequent pass. In an implementation of a compiler,
portions of one or more phases are combined into a module called pass.

25. List some compiler construction tools?

i) Parser generators
ii) Scanner generators
iii) Syntax-directed translation engine
iv) Automatic code generators
v) Data-flow engine.

26. Explain any one compiler construction tool?

 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

Scanner generators, these automatically generate lexical analyzers normally from a

specification based on regular expressions. The resulting of lexical analyzer is in
effect of finite automata.
27. What are issues available in lexical analysis?
i) Simpler design
ii) Compiler efficiency is improved by specialized buffering
techniques for reading input characters and processing tokens and
significantly speeds up the performance of a compiler.
iii) Compiler portability is enhanced.

28. Define patterns/lexeme/tokens?

A set of strings in the input for which the same token is produced as output. This
set of strings described by a rule called pattern associated with the token.
A lexeme is a sequence of characters in the source program that is matched by the
pattern for a token.
Token is a sequence of character that can be treated as a single logical entity.

29. Give the algebraic properties of regular expression?

AXIOM DESCRIPTION
i) r/s = s/r / is commutative
ii) r/(s/t)=(r/s)/t / is associative
iii) (rs)t=r(st) concatenation is associative
iv) r(s/t)=rs/rt concatenation distributes over /
v) r**=r* * is idempotent

30. What are the systems referred to data flow engine?

i) Compiler-compilers
ii) Compiler-generators
iii) Translator writing systems.

31. Give the parts of a string?

 KIET Group of Institutions, Ghaziabad
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Prefix of s, suffix of s, substring of s, proper prefix, proper suffix, proper substring

and subsequence of s.

32. What are the operations on language?

 Union
 Concatenation
 Kleene closure or star closure and
 Star closure.

33. Give the error recovery actions in lexical errors?

i) Deleting an extraneous character
ii) Inserting a missing character
iii) Replacing an incorrect character by a correct character.

34. What are the implementations of lexical analyzer?

a) Use a lexical analyzer generator, such as Lex compiler, to produce
the lexical analyzer from a regular expression based specification
b) Write the lexical analyzer in a conventional systems-programming
language using the I/O facilities of that language to read the input.
c) Write the lexical analyzer in assembly language and explicitly
manage the reading of input.

35. What are the three parts of lexical program?

 Declarations
%%
 Translation rules
%%
 Auxiliary procedures

36. What are the four functions of regular expression to DFA?

 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

 Nullable (n)
 Firstpos (n)
 Last (n)
 Followpos (n)

37. What are the models of LEX compiler?

 Lexeme
 FA simulator
 Transition table

PART-B

1. Explain the various phases of compiler in detail. Also write down the output
for the following expression after each phase a=b*c-d or a=b+c*50
2. Briefly explain the compiler construction tool.
3. Describe how various phases should be combined as a pass in a compiler.
4. Elaborate on grouping of phases in a compiler.
5. What are the phases of the compiler? Explain the phases in detail.
6. Write down the output of each phase for the expression a: = b + c * 50.
 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

Department of Computer Applications

COURSE MCA, IV SEM,
(2019-20) Even Semester
Compiler Design (RCA:404)
QUESTION BANK

UNIT III – SYNTAX ANALYSIS

1. What do u meant by parser and its types?

A parser for grammar G is a program that takes as input a string ‘w’ and produces
as output either a parse tree for’w’, if ‘w’ is a sentence of G, or an error message
indicating that w is not a sentence of G. it obtains a string of tokens from the
lexical analyzer, verifies that the string generated by the grammar for the source
language.
a) Top down parsing
b) Bottom up parsing

2. What are the different levels of syntax error handler?

a) Lexical, such as misspelling an identifier, keyword, or operator.
b) Syntactic, such as an arithmetic expression with unbalanced
parentheses
c) Semantic, such as operator applied to an incompatible operand
d) Logical, such as an infinitely recursive call.

3. What are the goals of error handler in a parser?

i) It should report the presence of errors clearly and
accurately
ii) It should recover from each error quickly enough to be able
to detect subsequent errors
iii) It should not significantly slow down the processing of
correct programs.
 KIET Group of Institutions, Ghaziabad
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(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

4. What are error recovery strategies in parser?

a) Panic mode
b) Phrase level
c) Error productions
d) Global corrections

5. Define CFG?
Many programming language has rules that prescribe the syntactic structure of
well-formed programs. The syntax of programming language constructs can be
described by CFG. Conditional statement defined by a rule such as; If S1 and S2
are statements and E is an expression, then
“If E then S1 else S2” is a statement.

6. Define derivations. Give an example and its types?

We apply the productions of a CFG to infer that certain strings are in the language
of a certain variable. There are two approaches (a) derivations (b) recursive
inference or reduction. Then derivation uses the production from head to body. A
replacement according to a production is known as as derivation
i) Left most derivation
ii) Right most derivation or canonical derivations
E E+Eid+Eid+(E)
 id+(E+E)id+(id*E)
 id+(id*id)

7. Define ambiguity?
A grammar that produces more than one parse tree for some sentences is
said to be ambiguous.

8. Define sentential form?

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If G = (V, T, P, S) is a CFG, then any string ‘α’ in (VUT)* such that S* α
is a sentential form.

9. Define yield of the string?

A string that is derived from the root variable is called the yield of the tree.

10. Give the several reasons for writing a grammar?

a) The lexical rules of a language are frequently quite simple and to
describe them we do not need a notation as powerful as grammars.
b) R.E generally provides a more concise and easier to understand
notation for token than grammars.
c) More efficient lexical analyzers can be constructed automatically from
R.E than from arbitrary grammars.
d) Separating the syntactic structure of a language into lexical and
nonlexical parts provides a convenient way of modularizing the front
end of a compiler into two manageable-sized components.

11. Define left factoring?

The process of factoring out of common prefixes of alternates is called as left
factoring.

12. What are the difficulties with top down parsing?

a) Left recursion
b) Backtracking
c) The order in which alternates are tried can affect the language
accepted
d) When failure is reported. We have very little idea where the error
actually occurred.

13.What is meant by recursive-descent parser?

 KIET Group of Institutions, Ghaziabad
Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

A parser that uses a set of recursive procedures to recognize its input with no
backtracking is called a recursive-descent parser. To avoid the necessity of a
recursive language, we shall also consider a tabular implementation of recursive
descent called predictive parsing.

14.Define top down parsing?

It can be viewed as an attempt to find the left most derivation for an input string. It
can be viewed as attempting to construct a parse tree for the input starting from
the root and creating the nodes of the parse tree in preorder.

15. Define LL (1) grammar?

A grammar G is LL (1) if and only if, whenever A α / β are two distinct
productions of G of the following conditions
a) For no terminal ‘a’ do both α and β derive strings beginning with α.
b) At most one of α and β can derive the empty string.
c) If β* e then α does not derive any string beginning with a
terminal in FOLLOW (A).

16. What are the possibilities of non-recursive predictive parsing?

a) If X = a = $ the parser halts and announces successful completion of
parsing
b) If X = a = $ the parser pops X off the stack and advances the input pointer
to the next symbol
c) If X is a nonterminal, the program consults entry M[X,a] of the parsing
table M. this entry will be either an X-production of the grammar or an
error entry.
17. What are the actions available in shift reduce parser?
a) Shift
b) Reduce
c) Accept
d) Error
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Department of Computer Applications (NBA Accredited)
(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

18. Define handle?

A handle of a string is a substring that matches the right side of a production, and
whose reduction to the non-terminal on the left side of the production represents
one step along the reverse of a right most derivation.

19. Define viable prefixes?

The set of prefixes of right sentential forms that can appear on the stack of a shift
reduce parser are called viable prefixes.

20.What are the two common ways of determining precedence relations

should hold between a pair of terminals?
a) Based on associative and precedence of operators.
b) Construct an unambiguous grammar for the language, a grammar that
reflects the correct associativity and precedence in its parse tree.

21. Define operator grammar?

A grammar with the property that no production right side is £ or has two adjacent
non-terminals are called an operator grammar.

22. Define LR parser?

LR parsers can be used to parse a large class of context free grammars. The
technique is called LR (K) parsing.
“L” denotes that input sequence is processed from left to right
“R” denotes that the right most derivation is performed
“K” denotes that at most K symbols of the sequence are used to make a
decision.

23.What are the drawbacks of LR parser?

a) Parsing tables are too complicated to be generated by hand, need an
automated parser generator.
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b) Cannot handle ambiguous grammar without special tricks.

24. Give the reasons for LR parser?

a) LR parsers can handle a large class of CF languages
b) An LR parser can detect syntax errors as soon as they occur
c) The LR parsing method is the most general non-back tracking shift
reduce parsing method
d) LR parsers can handle all language recognizable by LL(1).

25. What are the techniques for producing LR parsing Table?

1) Shift s, where s is a state
2) Reduce by a grammar production A β
3) Accept and
4) Error

26. Define augmented grammar?

If G is a grammar with start symbol S, then G’ the augmented grammar for G, is
G with a new start symbol S’ and production S’S. the purpose of this new
starting production is to indicate to the parser when it should stop parsing and
announce acceptance of the input.

27. Define LR (0) items?

LR (0) item for a grammar G is a production of G with a dot at some position of
the right side. Thus production AXYZ yields the four items.
A.XYZ, AX.YZ, AXY.Z, AXYZ.

28. What are the two functions of LR parsing algorithm?

a) Action function
b) GOTO function

29. What are the three types of YACC?

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a) Declarations
b) Translation rules
c) supporting c-routines

30. Give note about semantic actions?

It is a sequence of c statements. In a semantic action, the symbol $$ refers to the
attribute value associated with the NT on the left, and $i refers to the value
associated with the ith grammar symbol on the right. It is called semantic action.

31. Define SLR parser?

The parsing table consisting of the parsing action and goto function determined by
constructing an SLR parsing table algorithm is called SLR(1) table. An LR parser
using the SLR (1) table is called SLR (1) parser. A grammar having an SLR (1)
parsing table is called SLR (1) grammar.

32. Give the two optional sections in the declarations parts?

a) Ordinary ‘c’ declarations
Delimited by % {and %}, a temporary variables used by the
translation rules or procedures.
b) Declarations of grammar tokens.

33. What are two classes of items in LR parser?

a) Kernel items, which include the initial item, S’.S, and all items
whose dots are not at the left end.
b) Non-Kernel items, which have their dots at the left end.

34. What are the three techniques for constructing LR parsing table?
a) SLR (simple LR)
b) Canonical LR
c) LALR (Look ahead LR)
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(An ISO – 9001: 2015 Certified & ‘A’ Grade accredited Institution by NAAC

35. Define bottom up parsing?

It attempts to construct a parse tree for an input string is beginning at leaves and
working up towards the root (i.e.) reducing a string ‘w’ to the start symbol of a
grammar. At each reduction step, a particular substring matching the right side of a
production is replaced by the symbol on the left of that production. It is a
rightmost derivation and it’s also known as shifts reduce parsing.

36. Define LALR grammar?

Last parser construction method, the LALR technique. This method is often used
in practice because the tables obtained by it are considerably smaller than the
canonical LR tables, yet most common syntactic constructs of programming
language can be expressed conveniently by an LALR grammar. If there are no
parsing action conflicts, then the given grammar is said to be an LALR (1)
grammar. The collection of sets of items constructed is called LALR (1)
collections.

37. Define operator precedence grammar?

It is an £-free operator grammar in which the precedence relations <., =., and .>
constructed as above are disjoint. That is for any pair of terminals a and b, never
more than one of the relations a<.b, a=.b, and a.>b is true.

38. Define handle pruning?

Reducing β to A in αβw is called handle pruning, i.e., removing the children of A
from the parse tree.

39. Eliminate left recursion from the grammar.

S Aa / b, AAc / Sd/e?

Replaced as AbdA’ / A’
A’cA’/ adA’/ £
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Finally we obtain
SAa / b,
AbdA’ / A’,
A’cA’ / adA’ / £

40. Define left recursion. Give an example?

A grammar is left recursive if it has a nonterminal ‘A’ such that there is a
derivation A+ Aα for some strings α.
Example: Pair of productions AAα/β.
Replaced by nonterminal productions
AβA’ and AαA’€E

PART B:

1. What is FIRST and FOLLOW? Explain in detail with an example.

Write down the necessary algorithm.
First and Follow:
1. E->E+T/T
T->T*F/F
F-> (E)/id

2. S-> (L)/a
L->L, S/a

3. E->E’|’T/T
T->T&F/F
F->! F/ (E)/1/0
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Top down parsing:

1. S->a/^/ (T)
T->T, S/S

2. S->a/^/(R)
T->S, T/S
R->T
Input for both problem for 1 and 2 : ( a, (a, a))
(((a, a), ^, (a)), (a))
Shift reduce parsing

1. S-> (L)/a
L->L, S/a
Input :( a, (a, a))
(a,((a, a),(a, a)))

2. S->ΑaZ
A->ΒbY
B->X
Input: αβXYZ

3. E->E+E/E*E/id/ (E)/-E
Input: id+id*id

4. S->aABe
A->Abc/b
B->d
Input: abbcde

5. S->ictS/ictSeS/a
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C->b
Input: ibtibtaea

6. S->a/^/ (T)
T->T, S / S

7.S->a/^/(R)
T->S, T/S
R->T
Input for both 6 & 7 problem :( a, (a, a))
(((a, a), ^, (a)), (a))
8.E->E+E/T
T->T*F/F
F-> (E)/id
Input: id+ (id+id)
id*(id+id)

Operator precedence parsing:

1. E->E+E/E*E/id
Input: id+id*id
id*id+id

2. E->E+E/T
T->T*F/F
F-> (E)/id
Input: id+ (id+id)
id*(id+id)

3. S-> (L)/a
L->L, S/S
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Input: (a, a)
(a, (a, a))
(a, ((a, a),(a, a)))

4. id+id*id

5. id*(id^id)-id/id

6. id+ (id*id)

LR (0):
1. E->E+E/T
T->T*F/F
F-> (E)/id

2. E->E’|’T/T
T->T&F/F
F->! F/ (E)/1/0

3. S->iSeS/iS/a

4. E->E+E/ E*E/(E)/id

5. E->EsubEsupE
->EsubE
->EsupE
-> {E}/c

LL (1):
1. S->AaAb/BbBa
A->ε
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B->ε
Check whether the grammar is LL (1) but not SLR (1)

LR (1):
1. S->CC
C->Cc
C->d

2. S->Aa/bAc/Bc/bBa
A->d
B->d
Check whether the grammar is LR (1) but not LALR (1)

LALR:
1. S->CC
C->Cc
C->d

2. S->Aa/bAc/dc/bda
A->d
Check whether the grammar is LALR (1) but not SLR (1)
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COURSE MCA, IV SEM,

(2019-20) Even Semester
Compiler Design (RCA:404)
QUESTION BANK

UNIT IV– INTERMEDIATE CODE GENERATION

.
1. What are the advantages of generating an intermediate representation?
i) Ease of conversion from the source program to the
intermediate code.
ii) Ease with which subsequent processing can be performed
from the intermediate code.

2. Define a syntax-directed translation?

Syntax-directed translation specifies the translation of a construct in terms
of Attributes associated with its syntactic components. Syntax-directed
translation uses a context free grammar to specify the syntactic structure of the
input. It is an input- output mapping.

3. Define an attribute. Give the types of an attribute?

An attribute may represent any quantity, with each grammar symbol, it associates
a set of attributes and with each production, a set of semantic rules for computing
values of the attributes associated with the symbols appearing in that production.
Example: a type, a value, a memory location etc.,
i) Synthesized attributes.
ii) Inherited attributes.

4. Define annotated parse tree?

A parse tree showing the values of attributes at each node is called an annotated
parse tree. The process of computing an attribute values at the nodes is called
annotating parse tree.
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Example: an annotated parse tree for the input 3*5+4n.

5. Define dependency graph?

The interdependencies among the inherited and synthesized attributes at the nodes
in a parse tree can be depicted by a directed graph is called a dependency graph.
Example: Production E E1 + E2
Semantic Rule E.val:= E1.va; + E2.val

6. Define syntax tree. Give an example?

An (abstract) syntax tree is a condensed form of parse tree useful for representing
language constructs.
Example: syntax tree for a – 4 + c
+

- c

a 4

7. What are the functions used to create the nodes of syntax trees?
i) Mknode (op, left, right)
ii) Mkleaf (id,entry)
iii) Mkleaf (num, val)

8. What are the functions for constructing syntax trees for expressions?
i) The construction of a syntax tree for an expression is
similar to the translation of the expression into postfix form.
ii) Each node in a syntax tree can be implemented as a record
with several fields.
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9. Define DAG. Give an example?

DAG is a directed acyclic graph for an expression identifies the common sub
expression in the expression.

Example: DAG for the expression a- 4 *c

P1 = mkleaf(id,a) P2 = mknum(num,4)
P3 = mkleaf(id,c) P4 = mknode(‘*’,p2,p3)
P5 = mknode(‘-‘,p1,p4)

10. What are the three kinds of intermediate representations?

i) Syntax trees.
ii) Postfix notation.
iii) Three address code.

11. Define postfix notation?

Postfix notation is a linearized representation of a syntax tree. It is a list of the
nodes of the tree in which a node appears immediately after its children.
The syntax tree is, a: = b*-c
The postfix notation for the syntax tree is, abc-*c

12. Define three-address code?

Three address code is a sequence of statements of the form x: = y op z. where x, y,
z are names, constants, or compiler generated temporaries, op stand for any type
of operator. Since a statement involves not more than three references it is called
three-address statement, and hence a sequence of such statement is called three
address codes.

13. What are the types of three address statements?

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Assignment statements, assignment instruction, copy statements, conditional

jump, address-address statements, indexed assignment statements, address and
pointer statements.

14. What are the three types of implementations of three-address statements?

i) Quadruples
ii) Triples
iii) Indirect Triples.

15. What are the methods of translating Boolean expressions?

There are two principal methods of representing the value of a Boolean
expression.
a) Encode true and false numerically and to evaluate a Boolean
expression analogous to an arithmetic expression.
b) Flow-of –control. Represent the value of a Boolean expression by a
position reached in a program.

16. What are the two purposes of Boolean expressions?

a) They are used to compute logical expressions.
b) Often they are used as condition expression in statements that alter the
flow of control, such as if-then, if-then-else, or while-do statements.

17. Define quadruple. Give an example?

A quadruple is a record structure with four fields: op, arg1, arg2 and result. The op
field contains an internal code for the operator.
Example: x: =y op z

18. Give the advantages of quadruples?

i) Can perform peephole optimization.
ii) The contents of field’s arg1, arg2 and result are normally
pointers
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iii) The symbol-table entries for the names represented by these

fields.
iv) If So, temporary names must be entered into the symbol table
as they Are created.

19. Define triple. Give an example?

Triple is a record structure with three fields: op, arg1 and arg2. The fields arg1 and
arg2 are either pointes to the symbol-table or pointers into the triple structure. This
method is used to avoid temporary names into the symbol table.

20. Define indirect triples. Give the advantage?

Listing pointers to triples rather than listing the triples themselves are called
indirect triples.
Advantages: it can save some space compared with quadruples, if the same
temporary value is used more than once.

21. Define translation scheme?

A translation scheme is a CFG in which program fragments called semantic action
are embedded within the right sides of productions. A translation scheme is like a
syntax-directed definition, except that the order of evaluation of the semantic rules
is explicitly shown.

22. What are the three address code for a or b and not c?
The three address sequence is
T1:= not c
T2:= b and T1
T3:= a or T2.

23. Write a three address code for the expression a < b or c < d?
100: if a<b goto 103
101: t1:=0
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102: goto 104

103: t1:=1
104: if c<d goto 107
105: t2:=0
106: goto 108
107: t2:=1
108: t3:=t1 or t2

24. What are the parameter transmission mechanisms?

1. Call by value
2. Call by value-result
3. Call by reference
4. Call by name

25. Construct a DAG for the expression I: = I + 10?

:=

I 10

26.What are the various data structure used for implementing the symbol
table?
1. Linear list
2. Binary tree
3. Hash table

27. What is the purpose of DAG?

i) A label for each node. For leaves the label is an identifier
and for interior nodes, an operator symbol
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ii) For each node a list of attached identifiers.

28. Define backpatching?

It constructs the syntax tree for the input, and then walks the tree in depth-first
order. Backpatching can be used to generate code for Boolean expressions and
flow-of-control statements in a single pass is that during one single pass we may
not know the labels that control must go to at the time the jump statements are
generated.

29. What are the three functions of backpatching?

i) Makelist(i) – create a new list.
ii) Merge(p1,p2) – concatenates the lists pointed to by p1 and p2.
iii) Backpatch(p,i) – insert i as the target label for the statements
pointed to by p.

30. Give short note about call-by-name?

Call by name, at every reference to a formal parameter in a procedure body the
name of the corresponding actual parameter is evaluated. Access is then made to
the effective parameter.

31. How parameters are passed to procedures in call-by-value method?

This mechanism transmits values of the parameters of call to the called program.
The transfer is one way only and therefore the only way to returned can be the
value of a function.
Main ( )
{ print (5); }
Int
Void print (int n)
{ printf (“%d”, n); }

32. Define symbol table?

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A compiler uses a symbol-table to keep track of scope and binding information

about names. It is searched every time a name is encountered in the source text
changes to the table occur, if a new name or new information about an existing
name is discovered.

33. What are the semantic rules are defined in the declarations operations?
1) Mktable(previous)
2) Enter(table, name,type,offset)
3) Addwidth(table,width)
4) Enterproc(table,namenewtable)

34. Define short circuit code?

Translate the Boolean expression into three-address code without generating code
for any of the Boolean operators and without having the code necessarily evaluate
the entire expression. This style of evaluation is sometimes is called short-circuit
or jumping code.

35. Give the syntax of case statements?

Switch expression
Begin
Case value: statement
Case value: statement

Case value: statement

Default : statement
End

36. Give the 2 attributes of syntax directed translation into 3-addr code?
i) E.place, the name that will hold the value of E and
ii) E.code , the sequence of 3-addr statements evaluating E.
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37. Write a short note on declarations?

Declarations in a procedure, for each local name, we create a symbol table entry
with information like the type and the relative address of the storage for the name.
The relative address consists of an offset from the base of the static data area or
the field for local data in an activation record. The procedure enter (name, type,
offset) create a symbol table entry.

38. Give the two parts of basic hashing scheme?

1) A hash table consisting of a fixed array of m pointers to table entries.
2) Table entries organized into m separate linked lists, called buckets. Each
record in the symbol table appears on exactly one of these lists.

39. Write the grammar for flow-of-control statements?

The following grammar generates the flow-of-control statements, if-then, if-
then-else, and while-do statements.
S  if E then S1
| If E then S1 else S2
| While E do S1.
40. Write the 3-addr code for the statements a =b*-c + b*-c?
Three address codes are: a=b*-c + b*-c

T1 = -c
T2 = b*T1
T3 = -c
T4 = b*T3
T5 = T2+T4
a:= T5.

PART B:
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1. Explain intermediate language with e.g.

2. What is three address codes. Mention the types. How would you implement
the three address statement with e.g.
3. Explain about declaration with e.g.
4. Describe the case statement.
5. How would you generate the intermediate code for the Boolean expression?
6. What are the various ways of calling the procedure? Explain in detail.
7. Explain how declarations are done in a procedure using syntax directed
translation scheme.
8. How would you generate the intermediate code for the flow of control
statements and control flow expression in the statement. Explain in detail with
e.g.
9. Explain procedure call with e.g.
10.Describe the methods for generating syntax directed definition for control
statements.
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Department of Computer Applications

COURSE MCA, IV SEM,
(2019-20) Even Semester
Compiler Design (RCA:404)
QUESTION BANK

UNIT V – CODE OPTIMIZATION/ GENERATION

1. Define code generations with ex?

It is the final phase in compiler model and it takes as an input an intermediate
representation of the source program and output produces as equivalent target
programs. Then intermediate instructions are each translated into a sequence of
machine instructions that perform the same task.

2. What are the issues in the design of code generator?

 Input to the generator
 Target programs
 Memory management
 Instruction selection
 Register allocation
 Choice of evaluation order
 Approaches to code generation.

3. Give the variety of forms in target program.

 Absolute machine language.
 Relocatable machine language.
 Assembly language.

4. Give the factors of instruction selections.

 Uniformity and completeness of the instruction sets
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 Instruction speed and machine idioms

 Size of the instruction sets.

5. What are the sub problems in register allocation strategies?

 During register allocation, we select the set of variables that will reside in
register at a point in the program.
 During a subsequent register assignment phase, we pick the specific register
that a variable reside in.

6. Give the standard storage allocation strategies.

 Static allocation
 Stack allocation.

7. Define static allocations and stack allocations

Static allocation is defined as lays out for all data objects at compile time.
Names are bound to storage as a program is compiled, so there is no need for a
Run time support package.
Stack allocation is defined as process in which manages the run time as a
Stack. It is based on the idea of a control stack; storage is organized as a stack,
And activation records are pushed and popped as activations begin and end.

8. Write the addressing mode and associated costs in the target machine.

MODE FORM ADDRESS ADDED COST

Absolute M M 1
Register R R 0
Indexed c(R) c+contents(R) 1
Indirect register *R contents(R) 0
Indirect indexed *c(R) contents(c+contents(R)) 1

9. Define basic block and flow graph.

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A basic block is a sequence of consecutive statements in which flow of

Control enters at the beginning and leaves at the end without halt or possibility
Of branching except at the end.
A flow graph is defined as the adding of flow of control information to the
Set of basic blocks making up a program by constructing a directed graph.

10. Write the step to partition a sequence of 3 address statements into basic
blocks.

1. First determine the set of leaders, the first statement of basic blocks.
 The rules we can use are the following.
 The first statement is a leader.
 Any statement that is the target of a conditional or unconditional goto is a
leader.
 Any statement that immediately follows a goto or conditional goto statement
is a leader.
2. For each leader, its basic blocks consists of the leader and all statements
Up to but not including the next leader or the end of the program.

11. Give the important classes of local transformations on basic blocks

 Structure preservation transformations
 Algebraic transformations.

12. Describe algebraic transformations.

It can be used to change the set of expressions computed by a basic blocks into
A algebraically equivalent sets. The useful ones are those that simplify the
Expressions place expensive operations by cheaper ones.
X = X+ 0
X=X*1
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13. What is meant by register descriptors and address descriptors?

A register descriptor keeps track of what is currently in each register. It is
Consulted whenever a new register is needed.

An address descriptor keeps track of the location where ever the current
Value of the name can be found at run time. The location might be a register, a
Stack location, a memory address,

14. What are the actions to perform the code generation algorithms?
 Invoke a function get reg to determine the location L.
 Consult the address descriptor for y to determine y’, the current location of y.
 If the current values of y and/or z have no next uses, are not live on exit from
the block, and are in register, alter the register descriptor.

15. Write the code sequence for the d:=(a-b)+(a-c)+(a-c).

Statement Code generation Register descriptor Address

descriptor
t:=a-b MOV a,R0 R0 contains t t in R0
SUB b,R0
u:=a-c MOV a,R1 R0 contains t t in R0
SUB c,R1 R1 contains u u in R1
v:=t+u ADD R1,R0 R0 contains v u in R1
R1 contains u v in R0
d:=v+u ADD R1,R0 R0 contains d d in R0
MOV R0,d d in R0 and
memory

16. Write the labels on nodes in DAG.

A DAG for a basic block is a directed acyclic graph with the following
Labels on nodes:
 Leaves are labeled by unique identifiers, either variable names or constants.
 Interior nodes are labeled by an operator symbol.
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 Nodes are also optionally given a sequence of identifiers for labels.

17. Give the applications of DAG.

 Automatically detect the common sub expressions
 Determine which identifiers have their values used in the block.
 Determine which statements compute values that could be used outside the
blocks.

18. Define Peephole optimization.

A Statement by statement code generation strategy often produces target
code that contains redundant instructions and suboptimal constructs. “Optimizing” is
misleading because there is no guarantee that the resulting code is optimal. It is a
method for trying to improve the performance of the target program by examining the
short sequence of target instructions and replacing this instructions by shorter or
faster sequence.

19. Write the characteristics of peephole optimization?

 Redundant-instruction elimination
 Flow-of-control optimizations.
 Algebraic simplifications
 Use of machine idioms

20. What are the structure preserving transformations on basic blocks?

 Common sub-expression elimination
 Dead-code elimination
 Renaming of temporary variables
 Interchange of two independent adjacent statement
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21. Define Common sub-expression elimination with ex.

It is defined as the process in which eliminate the statements which has the
Same expressions. Hence this basic block may be transformed into the equivalent
Block.
Ex:
a : =b + c
b :=a - d
c :=b + c
After elimination:
a : =b + c
b :=a - d
c :=a

22. Define Dead-code elimination with ex.

It is defined as the process in which the statement x=y+z appear in a basic
block, where x is a dead that is never subsequently used. Then this statement may
be safely removed without changing the value of basic blocks.

23. Define Renaming of temporary variables with ex.

We have the statement u:=b + c ,where u is a new temporary variable, and
change all uses of this instance of t to u, then the value of the basic block is not
changed.

24. Define reduction in strength with ex.

Reduction in strength replaces expensive operations by equivalent cheaper ones
on the target machines. Certain machine instructions are cheaper than others and can
often be used as special cases of more expensive operators.
Ex:
X^2 is invariably cheaper to implement as x*x than as a call to an
exponentiation routine.
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25. Define use of machine idioms.

The target machine may have harder instructions to implement certain specific
operations efficiently. Detecting situations that permit the use of these instructions
can reduce execution time significantly.

26. Define code optimization and optimizing compiler

The term code-optimization refers to techniques a compiler can employ in an
attempt to produce a better object language program than the most obvious for a
given source program.
Compilers that apply code-improving transformations are called
Optimizing-compilers.

PART B:

1. What are the issues in the design of code generator? Explain in detail.
2. Discuss about the run time storage management.
3. Explain basic blocks and flow graphs.
4. Explain about transformation on a basic block.
5. Write a code generation algorithm. Explain about the descriptor and function
getreg().Give an example.
6. Explain peephole optimization
7. Explain DAG representation of basic blocks.
8. Explain principle sources of code optimization in details.
9. Explain the Source language issues with details.
10. Explain the Storage organization strategies with examples.
11. Explain storage allocation strategy.
12. Explain about Parameter passing.
13. Explain the non local names in runtime storage managements.
14. Explain about activation records and its purpose.
15. Explain about Optimization of basic blocks.
16. Explain the various approaches to compiler development.
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17. Explain simple code generator with suitable example.

18. Discuss about the following:
a) Copy Propagation b) Dead-code Elimination and c) Code motion