UNIT - 5 B Understanding DAG in Code Generation

What does DAG stand for in the context of basic blocks?

• Directed Acyclic Graph

• Dynamic Allocation Graph

• Directed Access Graph

• Dynamic Acyclic Graph

What is the primary purpose of using a DAG to represent basic blocks in a compiler?

• To optimize the execution speed of basic blocks

• To visualize control flow between basic blocks

• To represent the flow of operations and their dependencies

• To allocate memory for variables

How does the DAG help in code generation from basic blocks?

• By eliminating redundant code and optimizing the sequence of instructions

• By representing only the syntax of the code

• By reducing the number of variables used in the program

• By generating machine code from the source code directly

What is heuristic reordering in the context of DAG-based code generation?

• Changing the order of variables in the program

• Rearranging instructions based on frequency or dependencies to improve performance

• Sorting the DAG nodes alphabetically

• Removing instructions from the DAG

What does labeling refer to in the context of code generation and DAGs?

• Assigning temporary labels to variables

• Naming the nodes in the DAG to represent operations and operands

• Labeling memory locations for each instruction

• Annotating DAG nodes with their execution cost

In code generation, what does 'next-use information' represent?

• The next point in the program where a variable is updated

• The next time a variable will be used, helping in register allocation

• The next instruction to be generated in the DAG

• The next block of memory to be allocated

Which of the following best describes the purpose of peephole optimization?

• To eliminate unused variables from the code

• To optimize small sequences of instructions at the assembly or machine level

• To reorder the instructions in a DAG

• To replace large loops with simpler alternatives

In a DAG, what do the edges represent?

• The flow of control between different basic blocks

• Dependencies between operations or instructions

• The storage location of variables

• The sequence of function calls

Why is DAG representation useful for eliminating redundant computations in a compiler?

• It eliminates all branches from the program

• It helps in identifying common subexpressions and reusing computed values

• It removes all loops from the code

• It generates machine code directly

What is a common heuristic used in reordering instructions in a DAG to improve performance?

• Moving instructions with fewer operands to the front

• Reordering based on frequency of use or dependency chains

• Randomly reordering instructions

• Sorting instructions based on variable names