Credible Compilation with Pointers

This paper presents the formal foundations and architectural design of a credible compiler, or a compiler that, in addition to a transformed program, produces a proof that the transformed program correctly implements the original input program. In our design, programs are represented using a standard low-level intermediate form based on controlow graphs. The compiler is structured as a set of components. Each component performs a speci c transformation and produces a proof that the transformation is correct. Typically, the correctness proof will consist of two subproofs: a subproof that the analysis of the input program produced a correct result, and a subproof that establishes a simulation relation between the original and transformed programs. The paper presents two logics, one for each kind of subproof, and shows that the logics are sound. A novel and important feature of our framework is its simultaneous support for both formal reasoning and sophisticated compiler transformations that deal with the program and the target machine at a very low level. In particular, our logics allow the compiler to prove the correctness of lowlevel optimizations such as register allocation and instruction scheduling even in the presence of potentially aliased pointers into the memory of the machine.