3 research outputs found
Semantical Equivalence of the Control Flow Graph and the Program Dependence Graph
The program dependence graph (PDG) represents data and control dependence
between statements in a program. This paper presents an operational semantics
of program dependence graphs. Since PDGs exclude artificial order of statements
that resides in sequential programs, executions of PDGs are not unique.
However, we identified a class of PDGs that have unique final states of
executions, called deterministic PDGs. We prove that the operational semantics
of control flow graphs is equivalent to that of deterministic PDGs. The class
of deterministic PDGs properly include PDGs obtained from well-structured
programs. Thus, our operational semantics of PDGs is more general than that of
PDGs for well-structured programs, which are already established in literature.Comment: 30 page
Towards a complete transformational toolkit for compilers
PIM is an equational logic designed to function as a ``transformational toolkit'' for compilers and other programming tools that analyze and manipulate imperative languages.It has been applied to such problems as program slicing, symbolic evaluation, conditional constant propagation, and dependence analysis.PIM consists of the untyped lambda calculus extended with an algebraic data type that characterizes the behavior of lazy stores and generalized conditionals.A graph form of PIM terms is by design closely related to several intermediate representations commonly used in optimizing compilers. In this paper, we show that PIM's core algebraic component, PIM, possesses a complete equational axiomatization (under the assumption of certain reasonable restrictions on term formation). This has the practical consequence of guaranteeing that every semantics-preserving transformation on a program representable in PIM can be derived by application of PIM rules. We systematically derive the complete PIM logic as the culmination of a sequence of increasingly powerful equational systems starting from a straightforward ``interpreter'' for closed PIM terms. This work is an intermediate step in a larger program to develop a set of well-founded tools for manipulation of imperative programs by compilers and other systems that perform program analysis