Reverse interpretation+mutation analysis = automatic retargeting

There are three popular methods for constructing highly retargetable compilers: (1) the compiler emits abstract machine code which is interpreted at run-time, (2) the compiler emits C code which is subsequently compiled to machine code by the native C compiler, or (3) the compiler's code-generator is generated by a back-end generator from a formal machine description produced by the compiler writer. These methods incur high costs at run-time, compile-time, or compiler-construction time, respectively. In this paper we will describe a novel method which promises to significantly reduce the effort required to retarget a compiler to a new architecture, while at the same time producing fast and effective compilers. The basic idea is to use the native C compiler at compiler construction time to discover architectural features of the new architecture. From this information a formal machine description is produced. Given this machine description, a native code-generator can be generated by a back-end generator such as BEG or burg. A prototype Automatic Architecture Discovery Unit has been implemented. The current version is general enough to produce machine descriptions for the integer instruction sets of common RISC and CISC architectures such as the Sun SPARC, Digital Alpha, MIPS, DEC VAX, and Intel x86. The tool is completely automatic and requires minimal input from the user: principally, the user needs to provide the internet address of the target machine and the command-lines by which the C compiler, assembler, and linker are invoked.