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| 1 : | anton | 1.1 | Vmgen generates much of the code for efficient virtual machine (VM) |
| 2 : | anton | 1.2 | interpreters from simple descriptions of the VM instructions. It |
| 3 : | anton | 1.1 | 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: | ||
| 7 : | |||
| 8 : | add ( i1 i2 -- i ) | ||
| 9 : | i = i1+i2; | ||
| 10 : | |||
| 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. | ||
| 18 : | |||
| 19 : | Vmgen has special support for stack-based VMs (but it can also be | ||
| 20 : | used to advantage when implementing a register-based VM). | ||
| 21 : | |||
| 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 : | http://www.complang.tuwien.ac.at/anton/vmgen/), and there is a simple, | ||
| 25 : | anton | 1.3 | working and somewhat commented example of using vmgen. |
| 26 : | |||
| 27 : | There are two versions of the example: in directory vmgen-ex you find | ||
| 28 : | a version using many casts; in directory vmgen-ex2 you find a version | ||
| 29 : | using unions instead of casts. | ||
| 30 : | anton | 1.2 | |
| 31 : | The current release requires GCC both for building and for compiling | ||
| 32 : | the resulting interpreters (threaded code cannot be implemented in | ||
| 33 : | ANSI C). | ||
| 34 : | anton | 1.1 | |
| 35 : | If you have bugs to report, suggestions to make, questions, or any | ||
| 36 : | other feedback, mail me (anton@mips.complang.tuwien.ac.at). | ||
| 37 : | |||
| 38 : | You can find vmgen at http://www.complang.tuwien.ac.at/anton/vmgen/. | ||
| 39 : | |||
| 40 : | Vmgen is currently distributed with Gforth (because it needs Gforth to | ||
| 41 : | run, and Gforth needs it to build), and is installed together with | ||
| 42 : | Gforth (read INSTALL for instructions). | ||
| 43 : | |||
| 44 : | Note that future versions of vmgen will probably require small changes | ||
| 45 : | in programs written for the present version (e.g., requiring a few | ||
| 46 : | additional macro definitions). |
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