Compiler Design Unit wise Important Questions as per JNTU Syllabus

Static vs Dynamic Anomaly Detection

Static analysis is analysis done on source code without actually execution it

Example: Source code syntax error detection is the static analysis result

Dynamic analysis is done on the fly, as the program is being executed and is based on intermediate values that result from the programs execution

Example: A division by zero warning is the dynamic result

If a problem, such as a data flow anomaly, can be detected by static analysis methods, then it does not belong in testing, but it belongs in the language processor

There is actually a lot more static analysis for data flow analysis and for data flow anomalies going on in current language processors

Example: Language processors which force variable declarations can detect (-u) and (ku) anomalies

But still there are many things for which current notions of static analysis are inadequate

Why static analysis is not enough? There are many things for which current notions of static analysis are inadequate. They are:

Dead Variables: Although it is often possible to prove that a variable is dead or alive at a given point in the program, the general problem is unsolvable

Arrays:

Arrays are problematic. The array is defined or killed as a single object, but reference is to specific locations within the array

Usually array pointers are dynamically calculate, so there is no way to do a static analysis to validate the pointer value

In many languages, dynamically allocated arrays contain garbage unless explicitly initialized and therefore, -u anomalies are possible

Records and pointers:

The array problem and the difficulty with pointers is a special case of multi part data structures

We have the same problem with records and the pointers to them

Also, in many applications we create files and their names dynamically and there is no way to determine, without execution, whether such objects are in the proper state on a given path or for that matter, whether they exist at all

Dynamic Subroutines and Function Names in a Call:

Subroutine or function name is a dynamic variable in a call

What is passed or a combination of subroutine names and data objects, is constructed on a specific path

There is no way, without execution the path, to determine whether the call is correct or not

False Anomalies:

Anomalies are specific to paths

Even a "clear bug" such as 'ku' may not be a bug if the path along which the anomaly exist is unachievable

Such "anomalies" are false anomalies

Unfortunately, the problem of determining whether a path is or is not achievable, is unsolvable

Recoverable Anomalies and Alternate State Graphs:

Constituting an anomaly depends on context, application, and semantics

How does the compiler know which model I have in mind? It can't, because the definition of "anomaly" is not fundamental

The language processor must have a built-in-anomaly definition with which you may or many not (with good reason) agree

Concurrency, Interrupts System Issues:

Soon as we get away from the simple single task uniprocessor environment and start thinking in terms of systems, most anomaly issues become vastly more complicate

How often the data objects are defined or created at an interrupt level, then they can be processed by a lower-priority routine? Interrupt can make the "correct" anomalous and the "anomalies" correct

Much of integration and system testing is aimed at detecting data flow anomalies that cannot be detected in the context of a single routine.