Intermediate Code Generation Questions and Answers

41.

The width of a record type is computed during declaration processing by

A.summing the widths of its fields with any alignment padding
B.taking the width of the largest field in the record
C.counting up the number of fields and then multiplying that by four
D.asking the target machine at run time for the value

Answer: A

Correct answer: summing the widths of its fields with any alignment padding

The width is the total the fields occupy, including any padding inserted so that each field begins at an address its type requires. That padding is why a record can be wider than the sum of its fields, and why reordering fields can change the size of a structure without changing its contents.

Discuss in Forum

42.

Field offsets within a record are computed using

A.the alphabetical order of the field names in the record
B.a running total carried along the list of fields
C.the width of the whole record divided by the field count
D.a value supplied by the programmer for each field

Answer: B

Correct answer: a running total carried along the list of fields

Each field is placed at the current total, after which the total is advanced by that field’s width plus any padding. The offset is therefore an inherited attribute passed along the field list, and it is one of the standard illustrations of a syntax-directed definition using inherited attributes.

Discuss in Forum

43.

Intermediate code generation for declarations mainly produces

A.a jump table listing all the declared names in order
B.nothing at all
C.symbol table entries rather than executable instructions
D.one instruction for every variable declared in the program

Answer: C

A declaration reserves storage and records a type, both of which live in the symbol table. Any initialiser attached to it does generate ordinary assignment code. Storage layout decisions are recorded there rather than emitted as instructions.

Discuss in Forum

44.

State whether the following is true or false.
Intermediate code is always machine independent.

A.True only at large scales
B.False only at small scales
C.True
D.False

Answer: D

Some intermediate forms deliberately expose machine properties such as word size or the register set, and the widths used in address arithmetic come from the target. Machine independence is a design goal that is approached rather than absolutely achieved.

Discuss in Forum

45.

A high level intermediate representation, compared with a low level one,

A.retains more of the source structure and less machine detail
B.is always faster to translate into target code
C.cannot be optimised at all before code generation
D.requires that the source language be entirely free of pointers

Answer: A

Correct answer: retains more of the source structure and less machine detail

A high level representation keeps array indexing, structure references and loops as such, which suits optimisations that reason about program structure. Lowering it exposes address arithmetic and machine operations, which suits optimisations closer to the target. Neither is better in general, which is why several are used in sequence.

Discuss in Forum

46.

A compiler that uses several intermediate representations in succession is

A.restricted to a single source language and target machine
B.lowering the program gradually toward the target machine
C.necessarily slower than one using a single representation
D.unable to perform any machine independent optimisation

Answer: B

Correct answer: lowering the program gradually toward the target machine

Each level exposes different detail and permits different optimisations, so a modern compiler moves through several - a structured form, then a linear one, then something close to the machine. Optimisations are placed where the information they need is still visible, which no single representation could achieve.

Discuss in Forum

47.

Bytecode such as that produced for a virtual machine is

A.a form of source code that the programmer has written out directly
B.a representation that cannot be optimised in any way
C.an intermediate representation designed to be portable and executable
D.the target code of a compiler for a specific processor

Answer: C

Correct answer: an intermediate representation designed to be portable and executable

Bytecode occupies both roles: it is an intermediate representation in the compiler’s sense and a program the virtual machine can execute directly. That combination is what allows the same compiled file to run wherever the virtual machine exists, and it can be optimised both before and during execution.

Discuss in Forum

48.

Three address code is usually generated during

A.the scanning phase
B.the code generation phase
C.the linking phase when object modules are combined
D.a syntax directed translation over the parse tree or during the parse

Answer: D

Semantic rules attached to the productions emit the instructions. Whether an explicit tree is built first depends on how many passes the compiler makes. A one pass compiler emits instructions as the productions are reduced.

Discuss in Forum

49.

The place attribute of a nonterminal in expression translation names

A.the temporary or variable holding the value of that subexpression
B.the position of that subexpression within the source program text
C.the machine register that the value will eventually occupy
D.the line number at which the subexpression appears

Answer: A

Each rule emits an instruction computing into a new place and reports that place upward. Register assignment happens much later, in the code generator. The name is all the translation needs to refer to the value again.

Discuss in Forum

50.

Two instructions in the same basic block are guaranteed to

A.refer to different variables from one another in every case
B.execute the same number of times whenever the block is entered
C.compute values that are entirely independent of one another
D.be adjacent in the final target code that is generated

Answer: B

Control enters only at the top and leaves only at the bottom, so either every instruction in the block runs or none does. That guarantee is what makes local optimisation within a block so much simpler than reasoning across the whole procedure.

Discuss in Forum

Intermediate Code Generation Questions and Answers

Topics

Other Subjects

About Us

Intermediate Code Generation Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications