Title: Detecting Type-Based Aliasing Violations in C

Authors: Iain Ireland, Jose Nelson Amaral, Shimin Cui, Raul Silvera
Speaker: Iain Ireland

Abstract:

The goal of an alias analysis is to compute the set of variables that
can access a given memory location. An accurate alias analysis is
critical for many back-end optimizations. Type-based alias analysis is
a straightforward concept: two variables of different types should not
be aliases for the same memory location. The C language specification
details the situations in which aliasing may legally occur. However,
many real-world programs violate the C specification.  As a result,
type-based alias analysis is often disabled, eliminating any benefits
it would have provided in the sections of the program where the type
restrictions are respected.

We present a demand-driven analysis implemented in the IBM XL C
compiler. This new analysis identifies assignments that could
potentially lead to a memory state that violates the C specification.
This analysis is an important step towards a type-based alias analysis
that remains safe even in the presence of violations. The analysis can
also provide a report to the programmer about violations of typing
rules.