Compiler Design

Our compiler is divided into three parts, a front-end, a middle, and a back-end.

Front End

The front-end of the Harlan compiler is comprised of our parser, typechecker, and several passes that are responsible for making the code more uniform and simple.

• parse-harlan verifies the input program, and inserts tags around all scalar expressions (for example, the integer 0 becomes (int 0)). This reduces ambiguity in the typechecker.
• returnify will insert a return around the last expression in each function body, if one does not exist already. This pass must run before typechecking, so that the typechecker can enforce that all returns are returning expressions of the same type.
• typecheck does exactly what it sounds like. Every expression is tagged with its type, assuming that the program is statically well-typed. If not, the typechecker will error.
• expand-primitives rewrites front-end primitives, such as write-pgm (primitives that are too complex to deal with in passes later), or print and assert that are called on complex data-types.
• remove-danger adds safety-checks before vector-refs, to ensure safe memory access.

Middle

• make-kernel-dimensions-explicit
• optimize-fuse-kernels
• lift-complex
• remove-nested-kernels
• optimize-lift-lets
• returnify-kernels
• make-vector-refs-explicit
• annotate-free-vars
• insert-let-regions
• infer-regions
• uglify-vectors
• remove-let-regions
• flatten-lets
• hoist-kernels
• generate-kernel-calls
• compile-module
• convert-types

Back End

Currently, harlan-format-c is the only pass in the back-end of the compiler, and it is responsible for turning s-expressions into a string of C++ with OpenCL.