| Date: Wed, 31 Jan 2001 12:04:33 -0600 | |
| From: Vikram S. Adve <vadve@cs.uiuc.edu> | |
| To: Chris Lattner <lattner@cs.uiuc.edu> | |
| 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 | |