File:  [gforth] / gforth / README.vmgen
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Fri May 4 07:41:01 2001 UTC (20 years, 5 months ago) by anton
Branches: MAIN
CVS tags: HEAD
interpreted s" now ALLOCATEs the string

    1: Vmgen generates much of the code for efficient virtual machine (VM)
    2: interpreters from simple descriptions of the VM instructions.  It
    3: generates code for executing VM instructions (with optional tracing),
    4: for generating VM code, for disassembling VM code, and for profiling
    5: VM instruction sequences.  A VM instruction description looks like
    6: this:
    8: add  ( i1 i2 -- i )
    9: i = i1+i2;
   11: Vmgen supports several techniques for writing efficient interpreters:
   12: virtual machine interpreters, threaded code, combining VM instructions
   13: into superinstructions, keeping the top-of-stack in a register,
   14: scheduling the dispatch of the next VM instruction, and a couple of
   15: minor optimizations.  Interpreters created with vmgen usually are
   16: faster than competing interpreters and are typically only a factor of
   17: 2-10 slower than the code generateed by native-code compilers.
   19: Vmgen has special support for stack-based VMs (but it can also be
   20: used to advantage when implementing a register-based VM).
   22: The main shortcoming in the current release is the lack of a user
   23: manual; however, there is a paper describing vmgen's operation (at
   24:, and there is a simple,
   25: working and somewhat commented example of using vmgen (in directory
   26: vmgen-ex).
   28: The current release requires GCC both for building and for compiling
   29: the resulting interpreters (threaded code cannot be implemented in
   30: ANSI C).
   32: If you have bugs to report, suggestions to make, questions, or any
   33: other feedback, mail me (
   35: You can find vmgen at
   37: Vmgen is currently distributed with Gforth (because it needs Gforth to
   38: run, and Gforth needs it to build), and is installed together with
   39: Gforth (read INSTALL for instructions).  
   41: Note that future versions of vmgen will probably require small changes
   42: in programs written for the present version (e.g., requiring a few
   43: additional macro definitions).

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