Compiling files individually lends itself well to parallelization, but forces the compiler to operate on incomplete programs. State-of-the-art points-to analyses guarantee sound solutions only for complete programs, requiring summary functions to describe any missing program parts. Summary functions are rarely available in production compilers, however, where soundness and efficiency are non-negotiable. This paper presents an Andersen-style points-to analysis that efficiently produces sound solutions for incomplete C programs. The analysis accomplishes soundness by tracking memory locations and pointers that are accessible from external modules, and efficiency by performing this tracking implicitly in the constraint graph. We show that implicit pointee tracking makes the constraint solver 15× faster than any combination of five different state-of-the-art techniques using explicit pointee tracking. We also present the Prefer Implicit Pointees (PIP) technique that further reduces the use of explicit pointees. PIP gives an additional speedup of 1.9×, compared to the fastest solver configuration not benefiting from PIP. The precision of the analysis is evaluated in terms of an alias-analysis client, where it reduces the number of MayAlias-responses by 40% compared to LLVM’s BasicAA pass alone. Finally, we show that the analysis is scalable in terms of memory, making it suitable for optimizing compilers in practice.

Demand-based dependence graphs (DDGs), such as the (Regionalized) Value State Dependence Graph ((R)VSDG), are intermediate representations (IRs) well suited for a wide range of program transformations. They explicitly model the flow of data and state, and only implicitly represent a restricted form of control flow. These features make DDGs especially suitable for automatic parallelization and vectorization, but cannot be leveraged by practical compilers without efficient construction and destruction algorithms. Construction algorithms remodel the arbitrarily complex control flow of a procedure to make it amenable to DDG representation, whereas destruction algorithms reestablish control flow for generating efficient object code. Existing literature presents solutions to both problems, but these impose structural constraints on the generatable control flow, and omit qualitative evaluation. The key contribution of this article is to show that there is no intrinsic structural limitation in the control flow directly extractable from RVSDGs. This fundamental result originates from an interpretation of loop repetition and decision predicates as computed continuations, leading to the introduction of the predicate continuation normal form. We provide an algorithm for constructing RVSDGs in predicate continuation form, and propose a novel destruction algorithm for RVSDGs in this form. Our destruction algorithm can generate arbitrarily complex control flow; we show this by proving that the original CFG an RVSDG was derived from can, apart from overspecific detail, be reconstructed perfectly. Additionally, we prove termination and correctness of these algorithms. Furthermore, we empirically evaluate the performance, the representational overhead at compile time, and the reduction in branch instructions compared to existing solutions. In contrast to previous work, our algorithms impose no additional overhead on the control flow of the produced object code. To our knowledge, this is the first scheme that allows the original control flow of a procedure to be recovered from a DDG representation.