Update

Posted: October 3rd, 2011 | Author: Mars | Filed under: Uncategorized | Comments Off

Three months since the last update – it was a busy summer!

The garbage collector / multithreaded allocator project is stalled at about 80% complete. It took a global change to calling conventions, which inevitably turned up a lot of odd corners and difficult debugging problems.

On another branch, I’ve built a new non-LLVM-based X64 code generator. This is not to imply anything negative about LLVM, which is a fine piece of software engineering, but it is an extremely large, complex library, dwarfing the rest of the Radian compiler by an order of magnitude, and to justify that footprint it must offer correspondingly extreme benefits. Yet I suspect that much of LLVM’s value is in its array of sophisticated solutions to problems that Radian doesn’t have. As part of the parallelization architecture, I’ve pushed a lot of the analysis work which typically happens in the backend up into the frontend semantics engine, and what reaches the code generator is a long stream of tiny functions which contain no loops, branches, aliasing, or other complications. Loop analysis is finished, register allocation is almost trivial due to the low level of register pressure, and there is basically no type information left. What optimization opportunities I do see tend to be specific to Radian semantics, and I doubt whether LLVM is equipped to do much about them.

I’ll benchmark the two code generators against each other, then, and see whether this Radian-specific EmitX64 module can hold its own against LLVM. If so, I’ll be able to radically simplify the Radian compiler build process and reduce its memory and disk footprint; if not, I’ll learn exactly what it is that makes LLVM worth all that weight.