UNIT IV RUN-TIME ENVIRONMENT AND CODE GENERATION

SET A

I.Fill in the Blanks (5 x 1 = 5 Marks)

1. The stack is used for ______ allocation in most run-time environments.

Answer: Stack
2. Heap management is used to handle ______ allocated memory during
program execution.
Answer: Dynamically
3. Access to non-local data is facilitated by maintaining ______ in the stack.
Answer: Activation records
4. The ______ generator translates intermediate code into target machine
code.
Answer: Code
5. One of the major issues in code generation is the optimization of ______
usage.
Answer: Register

II.Multiple Choice Questions (5 x 1 = 5 Marks)

1. Which storage organization is commonly used for recursive function

calls?
a) Heap
b) Stack
c) Static Allocation
d) Global Data Segment
Answer: b) Stack
2. What is the purpose of an activation record in the stack?
a) To store global variables
b) To manage function calls and returns
c) To allocate heap memory
d) To optimize code generation
Answer: b) To manage function calls and returns
3. What does the heap manage in a program’s runtime environment?
a) Memory for global variables
b) Memory for dynamic allocation
c) Memory for local variables
 d) Memory for the program counter
Answer: b) Memory for dynamic allocation
4. A simple code generator's primary goal is to:
a) Minimize memory usage
b) Generate correct and efficient machine code
c) Create a syntax tree
d) Optimize high-level language constructs
Answer: b) Generate correct and efficient machine code
5. Non-local data is accessed in the stack using:
a) Static allocation
b) Control links
c) Dynamic allocation
d) Hash tables
Answer: b) Control links

III.Match the Following (5 x 1 = 5 Marks)

Column A Column B
1. Stack Allocation a) Function call management
2. Heap Management b) Dynamic memory allocation
3. Activation Record c) Maintains function parameters
4. Code Generator d) Translates intermediate code
5. Non-local Data Access e) Control links and displays

Answer:
1 - a, 2 - b, 3 - c, 4 - d, 5 - e

IV. True or False Statements (5 x 1 = 5 Marks)

1. The stack is used to store global variables during program execution.

Answer: False
2. Heap memory is managed using dynamic allocation techniques.
Answer: True
3. Non-local data in nested function calls can be accessed using control
links.
Answer: True
4. A code generator must always optimize for execution speed over
memory usage.
Answer: False
 5. Issues in code generation include register allocation and instruction
selection.
Answer: True

V. Scenario-Based Questions (5 x 1 = 5 Marks)

1. A program has a recursive function. How does the runtime environment

manage memory for the recursive calls?
Answer: The runtime environment uses stack allocation to create
separate activation records for each recursive call, ensuring proper
management of local variables and return addresses.
2. A variable is dynamically allocated memory during execution. Where is
this memory stored?
Answer: This memory is stored in the heap, and it is managed using
dynamic memory allocation techniques like malloc or new.
3. A compiler generates machine code that uses only two registers but
spills other variables into memory. What issue does this highlight in
code generation?
Answer: This highlights the issue of register allocation and the need to
minimize memory spills to improve performance.
4. A nested function requires access to a variable from an outer function.
How is this handled?
Answer: The variable is accessed through control links or displays,
which allow traversal of the stack to locate the variable in the outer
function's activation record.
5. During code generation, the compiler encounters multiple ways to
translate a single intermediate instruction. How should it choose?
Answer: The compiler should choose the translation that optimizes for
performance, such as minimizing execution time or reducing memory
usage, depending on the target system's constraints.
 SET B
I. Fill in the Blanks:

1. The ____________ is a region of memory that is used for dynamically

allocated data that persists until explicitly freed.
Answer: Heap
2. In a compiler, ____________ is used to generate machine code by
converting intermediate representations into target-specific
instructions.
Answer: Code Generation
3. The ____________ refers to the memory area used for storing local
variables, function calls, and return addresses during program
execution.
Answer: Stack
4. Accessing non-local data on the stack in a function is handled by
____________ through the use of a stack frame.
Answer: Stack Pointer
5. A major challenge in heap management is ____________, which occurs
when there is unused space between allocated blocks, leading to
inefficient memory use.
Answer: Fragmentation

II.Multiple Choice Questions:

1. What is the primary function of the stack in memory allocation?

a) To store dynamically allocated objects
b) To store local variables and function call information
c) To manage memory for non-local data
d) To store the program’s machine code
Answer: b) To store local variables and function call information
2. Which of the following is a major issue in heap memory management?
a) Memory leakage
b) Stack overflow
c) Fragmentation
d) Code generation
Answer: c) Fragmentation
 3. In the context of code generation, what does the design of a simple code
generator focus on?
a) Optimizing the program execution time
b) Converting high-level language to intermediate code
c) Translating intermediate code into machine code
d) Managing memory allocation
Answer: c) Translating intermediate code into machine code
4. Which of the following is NOT a valid part of a stack frame?
a) Return address
b) Local variables
c) Global variables
d) Function arguments
Answer: c) Global variables
5. Stack allocation space is primarily used for:
a) Allocating memory for global data
b) Storing function arguments and return values
c) Managing heap fragmentation
d) Managing the system's memory cache
Answer: b) Storing function arguments and return values

III.Match the Following:

Column A Column B
a) Involves managing memory used for non-local
1. Heap Management
variables
2. Stack Allocation
b) Involves managing dynamically allocated memory
Space
3. Access to Non-local
c) Space used for local variables and function calls
Data
4. Code Generator d) Converts intermediate code into machine code
e) Results in inefficient use of memory due to gaps
5. Fragmentation
between allocated blocks

Answer:

1. Heap Management → b) Involves managing dynamically allocated

memory
2. Stack Allocation Space → c) Space used for local variables and function
calls
 3. Access to Non-local Data → a) Involves managing memory used for non-
local variables
4. Code Generator → d) Converts intermediate code into machine code
5. Fragmentation → e) Results in inefficient use of memory due to gaps
between allocated blocks

IV.True or False:

1. The stack is used for managing dynamically allocated memory.

Answer: False
2. Heap fragmentation occurs when memory is allocated and deallocated
in a way that leaves small, unused memory blocks scattered throughout.
Answer: True
3. Code generation is the final phase of a compiler, converting
intermediate code into the machine-specific instructions.
Answer: True
4. Access to non-local data is handled by the heap during program
execution.
Answer: False
5. Stack allocation space is automatically cleaned up when a function
finishes execution, releasing the local variables and return address.
Answer: True

V.One Mark Descriptive Questions:

1. What is the role of a simple code generator in the compilation

process?
Answer: A simple code generator is responsible for translating
intermediate code into machine code or assembly instructions that can
be executed by the computer. It is the final step in the translation
process, where the program’s logic is converted into target-specific
instructions.
2. What is fragmentation in heap memory management, and how
does it affect program performance?
Answer: Fragmentation in heap memory management occurs when
memory is allocated and deallocated in such a way that free memory is
broken into small, non-contiguous blocks. This results in inefficient use
of memory and can lead to allocation failures when the program
requires a large block of memory.
3. Describe the process of accessing non-local data on the stack.
Answer: Non-local data on the stack is accessed by using stack frames.
A stack frame holds the local variables and other information for a
function call. To access non-local data, the compiler uses a mechanism
like the stack pointer to reference the correct memory location, even
when the data is not within the current function’s local scope.
4. What are stack allocation and its significance in memory
management?
Answer: Stack allocation refers to the region of memory that is used for
storing local variables, function arguments, and return addresses. It is
efficient because memory is allocated and deallocated in a last-in, first-
out (LIFO) order, which helps ensure that memory is reclaimed
automatically when functions finish executing.
5. How does the design of a simple code generator contribute to the
overall efficiency of a compiler?
Answer: The design of a simple code generator focuses on translating
intermediate representations into machine code, ensuring that the
generated code is efficient and suitable for the target architecture. This
phase is critical for producing executable code that performs optimally
and correctly on the target machine.

SET C
I. Fill in the Blanks:

1. The ____________ is used for storing local variables and function call
information, and it follows the Last-In-First-Out (LIFO) method of
memory management.
Answer: Stack
2. In a code generator, ____________ is responsible for translating
intermediate code into machine-specific instructions that can be
executed on a target machine.
Answer: Code Generation
3. The process of ____________ in memory management refers to breaking
down large contiguous blocks of memory into smaller chunks for
dynamic allocation.
Answer: Heap Allocation
4. ____________ is a technique used to allocate memory dynamically at
runtime, typically for objects that need to persist throughout the
program's execution.
Answer: Heap Management
5. ____________ occurs when there is unused memory in between allocated
blocks of memory, making it difficult to use the remaining space
efficiently.
Answer: Fragmentation

II. Multiple Choice Questions:

1. What is the purpose of stack memory in a program's execution?

a) To store global variables
b) To store local variables and function call information
c) To store dynamically allocated objects
d) To store program instructions
Answer: b) To store local variables and function call information
2. Which of the following is a disadvantage of heap memory management?
a) It is automatically cleaned up
b) It causes memory fragmentation
c) It is faster than stack memory
d) It uses a simple allocation scheme
Answer: b) It causes memory fragmentation
3. The primary responsibility of a code generator in a compiler is to:
a) Perform lexical analysis
 b) Convert source code into machine code
c) Optimize the intermediate code
d) Parse the syntax of the program
Answer: b) Convert source code into machine code
4. Which of the following is a common issue faced in heap memory
management?
a) Stack overflow
b) Memory fragmentation
c) Register overflow
d) Undefined variable usage
Answer: b) Memory fragmentation
5. Stack allocation space is used to store:
a) Data that persists across function calls
b) Global variables and constants
c) Local variables, function arguments, and return addresses
d) Large data structures like arrays and lists
Answer: c) Local variables, function arguments, and return addresses

III. Match the Following:

Column A Column B
1. Stack Memory a) Memory used for dynamic allocation and deallocation
b) Memory management used for local variables and function
2. Heap Memory
calls
3. Code c) Translates intermediate code into machine-specific
Generator instructions
4. d) Occurs when memory is allocated and deallocated
Fragmentation inefficiently
e) Contains information about a single function call, such as
5. Stack Frame
return address and local variables

Answer:

1. Stack Memory → b) Memory management used for local variables and

function calls
2. Heap Memory → a) Memory used for dynamic allocation and
deallocation
3. Code Generator → c) Translates intermediate code into machine-specific
instructions
 4. Fragmentation → d) Occurs when memory is allocated and deallocated
inefficiently
5. Stack Frame → e) Contains information about a single function call, such
as return address and local variables

IV.True or False:

1. Code generation is responsible for optimizing the program's source

code.
Answer: False
2. The stack automatically manages the memory of local variables and
function calls, and the memory is reclaimed when a function returns.
Answer: True
3. Fragmentation in heap memory makes memory allocation more
efficient as it reduces the number of smaller memory blocks.
Answer: False
4. Heap management is used for storing local variables and function call
information.
Answer: False
5. Stack frames are used to store the information for each function call,
such as local variables and return addresses.
Answer: True

V.One Mark Descriptive Questions:

1. What is the role of a code generator in the compilation process?

Answer: A code generator translates intermediate code, generated by
the compiler's front-end, into machine-specific code or assembly
language instructions. It is the final step in the compilation process,
converting the high-level representation into code that can be executed
by a computer.
2. What is memory fragmentation in heap management, and how
does it affect the performance of a program?
Answer: Fragmentation occurs when memory is allocated and
deallocated in such a way that free memory is broken into small, non-
contiguous blocks, making it difficult to allocate large blocks of memory.
This inefficiency can lead to performance degradation as the system
struggles to find sufficient space for new allocations.
3. Explain how stack allocation space is used during function calls.
Answer: When a function is called, a new stack frame is created to hold
 the function's local variables, arguments, and the return address. The
stack memory is automatically managed, and when the function returns,
the stack frame is popped, freeing up the memory for reuse.
4. Why is heap memory management important in dynamic memory
allocation?
Answer: Heap memory management is crucial for allocating memory
dynamically at runtime, especially for data structures that need to
persist beyond the scope of function calls. Proper heap management
ensures that memory is efficiently used and avoids memory leaks or
fragmentation.
5. Describe what a stack frame contains during a function call.
Answer: A stack frame contains the function's local variables,
parameters, return address (the location to return to after the function
completes), and other data needed to execute the function. It allows the
program to maintain proper control flow and manage local data during
function execution.

SET D
I.Fill in the Blanks:

1. The process of allocating and deallocating memory dynamically at

runtime is known as ____________.
Answer: Heap Management
2. ____________ is used for function calls and stores local variables,
parameters, and the return address of functions.
Answer: Stack Memory
3. A ____________ is a structure that stores information about a single
function call, including its local variables and return address.
Answer: Stack Frame
4. The code generator's main job is to translate ____________ code into
machine-level instructions that can be executed on a specific machine
architecture.
Answer: Intermediate
5. One of the main problems with ____________ in heap memory is the
inability to use small free blocks of memory efficiently, leading to
wasted space.
Answer: Fragmentation

II. Multiple Choice Questions:

1. Which of the following statements is true about stack memory?

a) Stack memory is used for dynamic memory allocation.
b) Stack memory is organized in a first-in-first-out (FIFO) order.
c) Stack memory is used to store local variables, function parameters,
and return addresses.
d) Stack memory is not automatically cleaned up when a function ends.
Answer: c) Stack memory is used to store local variables, function
parameters, and return addresses.
2. What is the primary concern in heap memory management?
a) Stack overflow
b) Fragmentation
c) Access speed
d) Function call management
Answer: b) Fragmentation
3. In the context of code generation, what is the intermediate code
primarily used for?
a) To define syntax and semantic rules
 b) To optimize machine-level code
c) To facilitate translation into target machine code
d) To handle memory allocation
Answer: c) To facilitate translation into target machine code
4. Which of the following is a function of a stack frame?
a) Manage dynamic memory allocation during runtime
b) Store function return values
c) Store local variables and the return address for function calls
d) Store global variables
Answer: c) Store local variables and the return address for function
calls
5. When does memory fragmentation primarily occur in heap
management?
a) During function calls
b) During dynamic memory allocation and deallocation
c) During code optimization
d) When accessing local variables
Answer: b) During dynamic memory allocation and deallocation

III. Match the Following:

Column A Column B
1. Stack Frame a) Dynamic memory allocation and deallocation
2. Heap Memory b) Stores information about a function call
3. Code Generator c) Converts intermediate code to machine code
4. Fragmentation d) Wasted memory space due to inefficient allocation
5. Stack Allocation e) Used to store local variables and function data

Answer:

1. Stack Frame → b) Stores information about a function call

2. Heap Memory → a) Dynamic memory allocation and deallocation
3. Code Generator → c) Converts intermediate code to machine code
4. Fragmentation → d) Wasted memory space due to inefficient allocation
5. Stack Allocation → e) Used to store local variables and function data

IV. True or False:

 1. A stack frame contains the function's local variables and return address.
Answer: True
2. Heap memory is managed by the system and automatically reclaimed
once it is no longer used.
Answer: False
3. Code generation involves translating high-level source code directly into
machine code without intermediate steps.
Answer: False
4. Fragmentation in heap memory results from allocating and deallocating
memory in such a way that free space becomes scattered.
Answer: True
5. The stack is used to store data structures such as arrays and linked lists.
Answer: False

V. One Mark Descriptive Questions:

1. Explain the concept of a stack frame in function calls.

Answer: A stack frame is a block of memory allocated on the stack for a
single function call. It contains the function’s local variables, the
function’s arguments, and the return address, which tells the program
where to continue after the function completes. Stack frames are
created and destroyed as functions are called and return, ensuring that
each function call has its own isolated memory space.
2. Why is heap memory management important in large programs?
Answer: Heap memory management allows for dynamic memory
allocation, which is essential for managing large data structures or
objects whose size is not known at compile-time. It provides flexibility
to allocate and free memory as needed at runtime. However, it requires
careful management to prevent fragmentation, memory leaks, and other
issues.
3. What is fragmentation in heap memory, and how can it affect a
program’s performance?
Answer: Fragmentation in heap memory occurs when free memory
blocks become scattered and are not contiguous. This makes it difficult
for the memory allocator to find large enough blocks of memory for new
allocations, resulting in inefficient memory use and potentially leading
to allocation failures. It can slow down performance and increase the
risk of memory allocation errors.
4. How does the code generation phase of a compiler contribute to
the final output?
Answer: During the code generation phase, the compiler translates the
intermediate code (usually an abstract representation of the program)
into target-specific machine code or assembly code. This machine code
is what the computer will execute, and it must be optimized for
performance, correct operation, and efficiency on the target
architecture.
5. What are the advantages and disadvantages of stack memory
allocation?
Answer: The advantage of stack memory allocation is that it is fast and
automatic. Memory is allocated and deallocated as functions are called
and return. The disadvantage is that stack memory is limited in size, and
large allocations (such as for large data structures) cannot be stored on
the stack. Additionally, stack memory is only valid during the function
call and cannot persist beyond that.

SET E
I.Fill in the Blanks:

1. The process of managing memory in a way that reduces unused space

between allocated blocks is known as ____________.
Answer: Compaction
2. A ____________ is a data structure used to manage memory in the heap,
keeping track of allocated and free blocks of memory.
Answer: Memory Manager
3. The stack is an efficient structure for function calls because it uses a
____________ allocation and deallocation scheme.
Answer: LIFO (Last-In-First-Out)
4. In code generation, ____________ is used to convert intermediate code into
machine-specific assembly or machine code.
Answer: Backend
5. ____________ in memory allocation occurs when the system is unable to
find a large enough contiguous block of memory due to scattered small
free blocks.
Answer: Fragmentation

II.Multiple Choice Questions:

1. What is the key characteristic of stack memory?

a) It is used for dynamic memory allocation.
b) It follows a first-in-first-out (FIFO) allocation scheme.
c) It is automatically managed, allocating and deallocating memory
when functions are called and return.
d) It is used to store large data structures like arrays.
Answer: c) It is automatically managed, allocating and deallocating
memory when functions are called and return.
2. Which of the following is true about heap memory?
a) Heap memory is automatically reclaimed by the system.
b) Heap memory can be used to store data that needs to persist between
function calls.
c) Heap memory is always faster to allocate than stack memory.
d) Heap memory is managed by the operating system only, not the
program.
Answer: b) Heap memory can be used to store data that needs to
persist between function calls.
 3. The primary purpose of a code generator in a compiler is to:
a) Parse the syntax of the source code.
b) Convert high-level language into intermediate code.
c) Translate intermediate code into machine-specific code.
d) Perform lexical analysis.
Answer: c) Translate intermediate code into machine-specific code.
4. Which of the following is a disadvantage of using the stack for memory
allocation?
a) Stack memory is very slow.
b) It is limited in size and cannot store large data structures.
c) Stack memory is not automatically cleaned up.
d) It causes fragmentation in memory.
Answer: b) It is limited in size and cannot store large data structures.
5. Which of the following strategies can help reduce fragmentation in heap
memory?
a) Using a garbage collector
b) Using the stack for all memory allocations
c) Decreasing the size of allocated memory blocks
d) Using a more complex algorithm for memory allocation
Answer: a) Using a garbage collector

III. Match the Following:

Column A Column B
a) Managed by the operating system and persists across
1. Code Generator
function calls
2. Stack
b) Wasted memory space due to fragmented allocations
Allocation
c) Converts intermediate code into machine-specific
3. Fragmentation
instructions
4. Heap Memory d) Uses LIFO scheme to allocate and deallocate memory
e) Reduces fragmentation by reorganizing free memory
5. Compaction
blocks

Answer:

1. Code Generator → c) Converts intermediate code into machine-specific

instructions
 2. Stack Allocation → d) Uses LIFO scheme to allocate and deallocate
memory
3. Fragmentation → b) Wasted memory space due to fragmented
allocations
4. Heap Memory → a) Managed by the operating system and persists
across function calls
5. Compaction → e) Reduces fragmentation by reorganizing free memory
blocks

IV.True or False:

1. The code generator is responsible for parsing the syntax of the source
code.
Answer: False
2. Stack memory is used to store global variables that persist across
function calls.
Answer: False
3. Fragmentation in heap memory occurs when free memory blocks are
scattered in non-contiguous locations.
Answer: True
4. Compaction is a technique used to reduce fragmentation by
reorganizing memory blocks.
Answer: True
5. Heap memory can store data that is created and used only within a
single function's scope.
Answer: False

V.One Mark Descriptive Questions:

1. What is heap memory, and why is it necessary in a program?

Answer: Heap memory is a region of memory used for dynamic
memory allocation, which allows for the storage of data whose size is
not known at compile time or data that needs to persist beyond the
scope of a function call. It is necessary for managing large data
structures, objects, and arrays during runtime.
2. What are the advantages of using stack memory for function calls?
Answer: Stack memory is fast and automatically managed, making it
efficient for storing local variables, function parameters, and return
addresses. It operates on a LIFO (Last-In-First-Out) principle, ensuring
 that memory is reclaimed automatically when functions return,
reducing the risk of memory leaks.
3. How does fragmentation in heap memory affect the performance of
a program?
Answer: Fragmentation in heap memory occurs when memory is
allocated and deallocated in a way that leaves small, non-contiguous
blocks of free space, making it difficult to allocate large blocks of
memory. This inefficiency can lead to performance issues, including
allocation failures, increased runtime for memory management, and
inefficient memory usage.
4. Explain how compaction can help reduce fragmentation in heap
memory.
Answer: Compaction is the process of rearranging memory blocks in
the heap to make larger contiguous blocks of free memory. This helps
reduce fragmentation by eliminating the gaps between allocated
memory blocks, allowing the system to allocate large blocks of memory
more efficiently.
5. What is the role of the code generator in a compiler, and why is it
important?
Answer: The code generator in a compiler translates intermediate code
into machine-specific code, which is the final output that can be
executed by a computer. It is important because it ensures that the
program’s logic is converted into an executable format that is optimized
for the target architecture, enabling efficient execution.