Oct 3, 2024 · Data flow analysis is a technique used in compiler design to analyze how data flows through a program. It involves tracking the values of variables and expressions as they are computed and used throughout the program, with the goal of identifying opportunities for optimization and identifying potential errors.

Dataflow analysis is usually performed on the program's control-flow graph (CFG); the goal is to associate with each program component (each node of the CFG) information that is guaranteed to hold at that point on all executions. Below are examples illustrating two dataflow-analysis problems: constant propagation and live-variable analysis.

Exercise 1: What would the lattice for simple Sign Analysis look like? Extension of simple Sign Analysis to track when x<0, x<=0, x=0, x>=0, x>0, x!=0, or unknown ( ̄\_( ツ)_/ ̄). Q: Why do we care about all these cases? Exercise 2: What would the lattice for precise Sign Analysis look like?

What is Data Flow Analysis? • Data flow analysis: –Flow-sensitive: sensitive to the control flow in a function –intraprocedural analysis; only on pseudo variables (no aliases) • Examples of optimizations: –Constant propagation –Common subexpression elimination –Dead code elimination CS243: Intro to Data Flow 5 M. Lam Examples of ...

Data Flow Analysis Schema • Build a flow graph (nodes = basic blocks, edges = control flow) • Set up a set of equations between in[b] and out[b] for all basic blocks b

Data flow analysis • Derives informaon about the dynamic behavior of a program by only examining the stac code • Intraprocedural analysis • Flow-sensi=ve: sensi=ve to the control flow in a func=on • Examples – Live variable analysis – Constant propagaon – Common subexpression eliminaon – Dead code detecon 1 a := 0

Dening the Analysis (2) Transfer function: VB entry ( s ) = ( VB exit ( s ) n kill ( s )) [ gen ( S ) Backward analysis: Returns expressions that are very busy expressions at entry of statement Function gen ( s ) All expressions e that appear in s Function kill ( s ) If s assigns to x , all expressions in which x occurs Otherwise: Empty set

Apr 17, 2016 · Data-Flow Analysis is a standard way to formulate intra-procedural program analysis. rst build a control ow graph (CFG). Nodes of a CFG are Basic Blocks. Edges indicate which blocks can follow which other blocks. A Basic Block is a sequence of instructions such that: There are no jumps/branches in the sequence except as the last instruction.

For example, suppose data-flow analysis involves determining the value of variables at points. then both a and b will have the value v after the statement. This relationship between the data-flow values before and after the assignment statement is known as a transfer function. Or it may flow backwards up the execution paths.

The aim of the Available Expressions Analysis is to determine For each program point, which expressions must have already been computed, and not later modified, on all paths to the pro-gram point. Example: point of interest ⇓ [x:= a+b ]1;[y:=a*b]2;while [y> a+b ]3 do ([a:=a+1]4;[x:= a+b ]5) The analysis enables a transformation into