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1 Date: Wed, 31 Jan 2001 12:04:33 -0600
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2 From: Vikram S. Adve <vadve@cs.uiuc.edu>
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3 To: Chris Lattner <lattner@cs.uiuc.edu>
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4 Subject: another thought
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5
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6 I have a budding idea about making LLVM a little more ambitious: a
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7 customizable runtime system that can be used to implement language-specific
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8 virtual machines for many different languages. E.g., a C vm, a C++ vm, a
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9 Java vm, a Lisp vm, ..
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10
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11 The idea would be that LLVM would provide a standard set of runtime features
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12 (some low-level like standard assembly instructions with code generation and
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13 static and runtime optimization; some higher-level like type-safety and
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14 perhaps a garbage collection library). Each language vm would select the
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15 runtime features needed for that language, extending or customizing them as
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16 needed. Most of the machine-dependent code-generation and optimization
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17 features as well as low-level machine-independent optimizations (like PRE)
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18 could be provided by LLVM and should be sufficient for any language,
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19 simplifying the language compiler. (This would also help interoperability
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20 between languages.) Also, some or most of the higher-level
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21 machine-independent features like type-safety and access safety should be
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22 reusable by different languages, with minor extensions. The language
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23 compiler could then focus on language-specific analyses and optimizations.
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24
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25 The risk is that this sounds like a universal IR -- something that the
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26 compiler community has tried and failed to develop for decades, and is
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27 universally skeptical about. No matter what we say, we won't be able to
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28 convince anyone that we have a universal IR that will work. We need to
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29 think about whether LLVM is different or if has something novel that might
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30 convince people. E.g., the idea of providing a package of separable
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31 features that different languages select from. Also, using SSA with or
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32 without type-safety as the intermediate representation.
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33
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34 One interesting starting point would be to discuss how a JVM would be
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35 implemented on top of LLVM a bit more. That might give us clues on how to
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36 structure LLVM to support one or more language VMs.
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37
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38 --Vikram
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