Global Data Flow Analysis in Compiler Design
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To efficiently optimize the code, the compiler gathers all of the program’s information and distributes it to each block of the flow graph. Data-flow graph analysis is the term for this procedure.
It is the analysis of data flow in a control flow graph, that is, the analysis that defines details about data description and usage in a program. It is possible to optimize with the aid of this study. In general, it’s a tool for estimating values using data flow analysis. The data flow property reflects data that can be used to improve efficiency.
Dataflow Analysis is a term that refers to a collection of techniques for obtaining information on the flow of data along program execution paths.
Finding out if two textually identical expressions evaluate to the same value in every conceivable execution path of the program is one way to enforce global common subexpression elimination.
Consider another scenario: if the outcome of an assignment isn’t included in any subsequent execution direction, the assignment can be considered dead code. Dataflow analysis will address these and several other essential questions.
Global Optimization: Global optimization is used on a wide scale, such as a process or function body, while local optimization is used on a smaller scale.
The representation of a program in terms of global optimization is in the form of a program flow graph.
The program flow graph is a diagram in which each node represents a simple block and the edges reflect the flow of control from one block to the next.
There are two types of analysis performed for global optimizations Global Data Flow Analysis in Compiler Design
- Control Flow Analysis
- Dataflow Analysis
Control Flow Analysis: Global Data Flow Analysis in Compiler Design
The control flow analysis specifies the arrangement of graph nodes (basic blocks), the existence of loops, the nesting of loops, and the nodes visited before the execution of a particular node. With the aid of this analytical data, optimization can be carried out.
As a result, in the case of control flow analysis, the flow of control is analyzed by carefully analyzing the program flow graph.
Dataflow Analysis: Global Data Flow Analysis in Compiler Design
Dataflow Analysis is the process of analyzing the flow of data.
Details about the definition and use of data in the software can be collected using Dataflow Analysis. This type of analysis can be used to achieve optimization.
In a nutshell, Dataflow Analysis is a method for calculating values in relation to dataflow properties.
Certain optimizations are only possible if the entire software is tested. It’s impossible to do by just looking at a part of the curriculum.
- One problem with this form of optimization is user-defined chaining.
- We try to figure out which meaning of a variable is applicable in a statement using the variable’s value.
A compiler can perform some optimizations based on the local data. Take the following code as an example:
x = a + b;
x = 6 * 3
The first assignment of x in this code is meaningless. In the program, the value machine for x is never used.
The expression 6*3 will be computed at compile time, simplifying the second assignment statement to x = 18; some optimizations require more global data. Take the following code as an example:
a = 1;
b = 2;
c = 3;
if (….) x = a + 5;
else x = b + 4;
c = x + 1;
The initial assignment at line 3 is unnecessary in this code, and the x +1 expression can be simplified to 7.
However, how a compiler can discover these facts by looking at only one or two consecutive statements is less apparent. A more comprehensive review is needed so that the compiler is aware of the following information at each stage of the program:
- The variables will always have the same value?
- Until being redefined, the variables will be used?
This form of property is discovered using data flow analysis. The control flow graph of the software can be used to perform the data flow analysis (CFG).
A program’s control flow graph is used to decide which parts of the program a particular value assigned to a variable can propagate to.
Basic Terminologies – Global Data Flow Analysis in Compiler Design
- Definition Point: a point in a program containing some definition.
- Reference Point: a point in a program containing a reference to a data item.
- Evaluation Point: a point in a program containing an evaluation of an expression.
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