Date: Wed, 31 Jan 2001 12:04:33 -0600 From: Vikram S. Adve To: Chris Lattner Subject: another thought I have a budding idea about making LLVM a little more ambitious: a customizable runtime system that can be used to implement language-specific virtual machines for many different languages. E.g., a C vm, a C++ vm, a Java vm, a Lisp vm, .. The idea would be that LLVM would provide a standard set of runtime features (some low-level like standard assembly instructions with code generation and static and runtime optimization; some higher-level like type-safety and perhaps a garbage collection library). Each language vm would select the runtime features needed for that language, extending or customizing them as needed. Most of the machine-dependent code-generation and optimization features as well as low-level machine-independent optimizations (like PRE) could be provided by LLVM and should be sufficient for any language, simplifying the language compiler. (This would also help interoperability between languages.) Also, some or most of the higher-level machine-independent features like type-safety and access safety should be reusable by different languages, with minor extensions. The language compiler could then focus on language-specific analyses and optimizations. The risk is that this sounds like a universal IR -- something that the compiler community has tried and failed to develop for decades, and is universally skeptical about. No matter what we say, we won't be able to convince anyone that we have a universal IR that will work. We need to think about whether LLVM is different or if has something novel that might convince people. E.g., the idea of providing a package of separable features that different languages select from. Also, using SSA with or without type-safety as the intermediate representation. One interesting starting point would be to discuss how a JVM would be implemented on top of LLVM a bit more. That might give us clues on how to structure LLVM to support one or more language VMs. --Vikram