Basic blocks and flow graphs in Compiler Design - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a basic block in compiler design?

A basic block is a sequence of consecutive statements or instructions in a program with only one entry point (the first instruction) and one exit point (the last instruction), where control enters at the beginning and leaves at the end without any possibility of branching except at the end.

beginner

What is the purpose of a flow graph in compiler design?

A flow graph represents the control flow of a program. It shows how basic blocks are connected through branches and jumps, helping the compiler analyze and optimize the program's execution paths.

intermediate

How does a basic block simplify program analysis?

Since a basic block has no branches inside it, the compiler can treat it as a single unit of execution, making it easier to analyze and optimize without worrying about control flow inside the block.

beginner

What are the nodes and edges in a flow graph?

Nodes in a flow graph represent basic blocks, and edges represent possible control flow paths between these blocks, such as jumps or branches.

intermediate

Why are flow graphs important for compiler optimizations?

Flow graphs help the compiler understand all possible paths the program can take, allowing it to perform optimizations like dead code elimination, loop optimization, and better register allocation.

What defines the start of a basic block?

A An instruction inside a loop

B Any instruction following a jump

C An instruction that is a target of a jump or branch

D The last instruction in a program

A basic block starts at an instruction that can be jumped to, such as the target of a branch or jump.

In a flow graph, what do edges represent?

A Control flow paths between basic blocks

B Memory locations

C Variables used in the program

D Function calls

Edges in a flow graph represent possible control flow paths from one basic block to another.

Which of the following is NOT true about a basic block?

A It contains no branches except at the end

B It has only one entry point

C Control flows sequentially inside it

D It can have multiple exit points

A basic block has only one exit point; multiple exits would break the definition.

Why do compilers use flow graphs?

A To analyze control flow and optimize code

B To represent data types

C To store variable values

D To generate user interfaces

Flow graphs help compilers analyze control flow and perform optimizations.

Which of these is a typical use of basic blocks in compiler design?

A Parsing source code

B Control flow analysis

C Memory management

D User input handling

Basic blocks are used to analyze and represent control flow in programs.

Explain what a basic block is and why it is useful in compiler design.

Think about how instructions flow without interruption inside a basic block.

Describe the role of a flow graph and how it relates to basic blocks.

Consider how the program's execution paths are mapped.