PointsTo Analysis

from Chakaravarthy [3]: Given a program and two variables p and q, the goal of points­to analysis is to check if p can point to q in some execution of the program. This well­ studied problem plays a crucial role in compiler optimization. The problem is known to be un­ decidable when dynamic memory is allowed. But the result is known only when variables are al­ lowed to be structures. We extend the result to show that, the problem remains undecidable, even when only scalar variables are allowed. Our sec­ ond result deals with a version of points­to anal­ ysis called flow­insensitive analysis, where one ig­ nores the control flow of the program and assumes that the statements can be executed in any or­ der. The problem is known to be NP­Hard, even when dynamic memory is not allowed and vari­ ables are scalar. We show that when the variables are further restricted to have well­defined data types, the problem is in P. The corresponding flow­ sensitive version, even with further restrictions, is known to be PSPACE­Complete. Thus, our result gives some theoretical evidence that flow­ insensitive analysis is easier than flow­sensitive analysis. Moreover, while most variations of the points­to analysis are known to be computation­ ally hard, our result gives a rare instance of a non­ trivial points­to problem solvable in polynomial time. Ramalingam [27]: Aliasing is undecidable Landi [17]: PSPACE­complete even with no procedures or memory allocations Landi and Ryder [18]