version 1.12, 2002/08/16 09:43:49
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version 1.22, 2003/02/25 22:58:49
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Line 57 Software Foundation raise funds for GNU
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Line 57 Software Foundation raise funds for GNU
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* Invoking Vmgen:: |
* Invoking Vmgen:: |
* Example:: |
* Example:: |
* Input File Format:: |
* Input File Format:: |
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* Error messages:: reported by Vmgen |
* Using the generated code:: |
* Using the generated code:: |
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* Hints:: VM archictecture, efficiency |
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* The future:: |
* Changes:: from earlier versions |
* Changes:: from earlier versions |
* Contact:: Bug reporting etc. |
* Contact:: Bug reporting etc. |
* Copying This Manual:: Manual License |
* Copying This Manual:: Manual License |
Line 82 Input File Format
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Line 85 Input File Format
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* Input File Grammar:: |
* Input File Grammar:: |
* Simple instructions:: |
* Simple instructions:: |
* Superinstructions:: |
* Superinstructions:: |
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* Store Optimization:: |
* Register Machines:: How to define register VM instructions |
* Register Machines:: How to define register VM instructions |
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Input File Grammar |
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* Eval escapes:: what follows \E |
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Simple instructions |
Simple instructions |
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* C Code Macros:: Macros recognized by Vmgen |
* C Code Macros:: Macros recognized by Vmgen |
* C Code restrictions:: Vmgen makes assumptions about C code |
* C Code restrictions:: Vmgen makes assumptions about C code |
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* Stack growth direction:: is configurable per stack |
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Using the generated code |
Using the generated code |
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Line 98 Using the generated code
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Line 107 Using the generated code
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* VM disassembler:: for debugging the front end |
* VM disassembler:: for debugging the front end |
* VM profiler:: for finding worthwhile superinstructions |
* VM profiler:: for finding worthwhile superinstructions |
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Hints |
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* Floating point:: and stacks |
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Copying This Manual |
Copying This Manual |
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* GNU Free Documentation License:: License for copying this manual. |
* GNU Free Documentation License:: License for copying this manual. |
Line 151 In this setup, Vmgen can generate most o
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Line 164 In this setup, Vmgen can generate most o
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machine instructions from a simple description of the virtual machine |
machine instructions from a simple description of the virtual machine |
instructions (@pxref{Input File Format}), in particular: |
instructions (@pxref{Input File Format}), in particular: |
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@table @asis |
@table @strong |
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@item VM instruction execution |
@item VM instruction execution |
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Line 172 Useful for optimizing the VM interpreter
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Line 185 Useful for optimizing the VM interpreter
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@end table |
@end table |
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To create parts of the interpretive system that do not deal with VM |
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instructions, you have to use other tools (e.g., @command{bison}) and/or |
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hand-code them. |
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@cindex efficiency features overview |
@cindex efficiency features overview |
@noindent |
@noindent |
Vmgen supports efficient interpreters though various optimizations, in |
Vmgen supports efficient interpreters though various optimizations, in |
Line 209 offered by Vmgen.
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Line 226 offered by Vmgen.
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There are many potential uses of the instruction descriptions that are |
There are many potential uses of the instruction descriptions that are |
not implemented at the moment, but we are open for feature requests, and |
not implemented at the moment, but we are open for feature requests, and |
we will implement new features if someone asks for them; so the feature |
we will consider new features if someone asks for them; so the feature |
list above is not exhaustive. |
list above is not exhaustive. |
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@c ********************************************************************* |
@c ********************************************************************* |
Line 300 interpreter, but some systems also suppo
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Line 317 interpreter, but some systems also suppo
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as an image file, or in a full-blown linkable file format (e.g., JVM). |
as an image file, or in a full-blown linkable file format (e.g., JVM). |
Vmgen currently has no special support for such features, but the |
Vmgen currently has no special support for such features, but the |
information in the instruction descriptions can be helpful, and we are |
information in the instruction descriptions can be helpful, and we are |
open for feature requests and suggestions. |
open to feature requests and suggestions. |
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@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
@node Data handling, Dispatch, Front end and VM interpreter, Concepts |
@node Data handling, Dispatch, Front end and VM interpreter, Concepts |
Line 310 open for feature requests and suggestion
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Line 327 open for feature requests and suggestion
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@cindex register machine |
@cindex register machine |
Most VMs use one or more stacks for passing temporary data between VM |
Most VMs use one or more stacks for passing temporary data between VM |
instructions. Another option is to use a register machine architecture |
instructions. Another option is to use a register machine architecture |
for the virtual machine; however, this option is either slower or |
for the virtual machine; we believe that using a stack architecture is |
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usually both simpler and faster. |
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however, this option is slower or |
significantly more complex to implement than a stack machine architecture. |
significantly more complex to implement than a stack machine architecture. |
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Vmgen has special support and optimizations for stack VMs, making their |
Vmgen has special support and optimizations for stack VMs, making their |
Line 356 After executing one VM instruction, the
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Line 376 After executing one VM instruction, the
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the next VM instruction (Vmgen calls the dispatch routine @samp{NEXT}). |
the next VM instruction (Vmgen calls the dispatch routine @samp{NEXT}). |
Vmgen supports two methods of dispatch: |
Vmgen supports two methods of dispatch: |
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@table @asis |
@table @strong |
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@item switch dispatch |
@item switch dispatch |
@cindex switch dispatch |
@cindex switch dispatch |
Line 379 instruction. Threaded code cannot be im
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Line 399 instruction. Threaded code cannot be im
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be implemented using GNU C's labels-as-values extension (@pxref{Labels |
be implemented using GNU C's labels-as-values extension (@pxref{Labels |
as Values, , Labels as Values, gcc.info, GNU C Manual}). |
as Values, , Labels as Values, gcc.info, GNU C Manual}). |
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@c call threading |
@end table |
@end table |
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Threaded code can be twice as fast as switch dispatch, depending on the |
Threaded code can be twice as fast as switch dispatch, depending on the |
Line 392 interpreter, the benchmark, and the mach
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Line 413 interpreter, the benchmark, and the mach
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The usual way to invoke Vmgen is as follows: |
The usual way to invoke Vmgen is as follows: |
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@example |
@example |
vmgen @var{infile} |
vmgen @var{inputfile} |
@end example |
@end example |
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Here @var{infile} is the VM instruction description file, which usually |
Here @var{inputfile} is the VM instruction description file, which |
ends in @file{.vmg}. The output filenames are made by taking the |
usually ends in @file{.vmg}. The output filenames are made by taking |
basename of @file{infile} (i.e., the output files will be created in the |
the basename of @file{inputfile} (i.e., the output files will be created |
current working directory) and replacing @file{.vmg} with @file{-vm.i}, |
in the current working directory) and replacing @file{.vmg} with |
@file{-disasm.i}, @file{-gen.i}, @file{-labels.i}, @file{-profile.i}, |
@file{-vm.i}, @file{-disasm.i}, @file{-gen.i}, @file{-labels.i}, |
and @file{-peephole.i}. E.g., @command{vmgen hack/foo.vmg} will create |
@file{-profile.i}, and @file{-peephole.i}. E.g., @command{vmgen |
@file{foo-vm.i} etc. |
hack/foo.vmg} will create @file{foo-vm.i}, @file{foo-disasm.i}, |
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@file{foo-gen.i}, @file{foo-labels.i}, @file{foo-profile.i} and |
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@file{foo-peephole.i}. |
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The command-line options supported by Vmgen are |
The command-line options supported by Vmgen are |
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Line 563 sort -k 3 >mini-super.vmg #sort se
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Line 586 sort -k 3 >mini-super.vmg #sort se
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The file @file{peephole-blacklist} contains all instructions that |
The file @file{peephole-blacklist} contains all instructions that |
directly access a stack or stack pointer (for mini: @code{call}, |
directly access a stack or stack pointer (for mini: @code{call}, |
@code{return}); the sort step is necessary to ensure that prefixes |
@code{return}); the sort step is necessary to ensure that prefixes |
preceed larger superinstructions. |
precede larger superinstructions. |
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Now you can create a version of mini with superinstructions by just |
Now you can create a version of mini with superinstructions by just |
saying @samp{make} |
saying @samp{make} |
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@c *************************************************************** |
@c *************************************************************** |
@node Input File Format, Using the generated code, Example, Top |
@node Input File Format, Error messages, Example, Top |
@chapter Input File Format |
@chapter Input File Format |
@cindex input file format |
@cindex input file format |
@cindex format, input file |
@cindex format, input file |
Line 584 Most examples are taken from the example
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Line 607 Most examples are taken from the example
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* Input File Grammar:: |
* Input File Grammar:: |
* Simple instructions:: |
* Simple instructions:: |
* Superinstructions:: |
* Superinstructions:: |
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* Store Optimization:: |
* Register Machines:: How to define register VM instructions |
* Register Machines:: How to define register VM instructions |
@end menu |
@end menu |
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Line 598 The grammar is in EBNF format, with @cod
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Line 622 The grammar is in EBNF format, with @cod
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of @var{c} and @code{[@var{d}]} meaning 0 or 1 repetitions of @var{d}. |
of @var{c} and @code{[@var{d}]} meaning 0 or 1 repetitions of @var{d}. |
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@cindex free-format, not |
@cindex free-format, not |
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@cindex newlines, significance in syntax |
Vmgen input is not free-format, so you have to take care where you put |
Vmgen input is not free-format, so you have to take care where you put |
spaces and especially newlines; it's not as bad as makefiles, though: |
newlines (and, in a few cases, white space). |
any sequence of spaces and tabs is equivalent to a single space. |
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@example |
@example |
description: @{instruction|comment|eval-escape@} |
description: @{instruction|comment|eval-escape|c-escape@} |
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instruction: simple-inst|superinst |
instruction: simple-inst|superinst |
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simple-inst: ident ' (' stack-effect ' )' newline c-code newline newline |
simple-inst: ident '(' stack-effect ')' newline c-code newline newline |
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stack-effect: @{ident@} ' --' @{ident@} |
stack-effect: @{ident@} '--' @{ident@} |
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super-inst: ident ' =' ident @{ident@} |
super-inst: ident '=' ident @{ident@} |
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comment: '\ ' text newline |
comment: '\ ' text newline |
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eval-escape: '\e ' text newline |
eval-escape: '\E ' text newline |
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c-escape: '\C ' text newline |
@end example |
@end example |
@c \+ \- \g \f \c |
@c \+ \- \g \f \c |
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Note that the @code{\}s in this grammar are meant literally, not as |
Note that the @code{\}s in this grammar are meant literally, not as |
C-style encodings for non-printable characters. |
C-style encodings for non-printable characters. |
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The C code in @code{simple-inst} must not contain empty lines (because |
There are two ways to delimit the C code in @code{simple-inst}: |
Vmgen would mistake that as the end of the simple-inst. The text in |
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@code{comment} and @code{eval-escape} must not contain a newline. |
@itemize @bullet |
@code{Ident} must conform to the usual conventions of C identifiers |
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(otherwise the C compiler would choke on the Vmgen output). |
@item |
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If you start it with a @samp{@{} at the start of a line (i.e., not even |
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white space before it), you have to end it with a @samp{@}} at the start |
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of a line (followed by a newline). In this case you may have empty |
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lines within the C code (typically used between variable definitions and |
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statements). |
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@item |
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You do not start it with @samp{@{}. Then the C code ends at the first |
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empty line, so you cannot have empty lines within this code. |
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@end itemize |
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The text in @code{comment}, @code{eval-escape} and @code{c-escape} must |
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not contain a newline. @code{Ident} must conform to the usual |
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conventions of C identifiers (otherwise the C compiler would choke on |
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the Vmgen output), except that idents in @code{stack-effect} may have a |
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stack prefix (for stack prefix syntax, @pxref{Eval escapes}). |
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@cindex C escape |
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@cindex @code{\C} |
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@cindex conditional compilation of Vmgen output |
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The @code{c-escape} passes the text through to each output file (without |
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the @samp{\C}). This is useful mainly for conditional compilation |
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(i.e., you write @samp{\C #if ...} etc.). |
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@cindex sync lines |
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@cindex @code{#line} |
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In addition to the syntax given in the grammer, Vmgen also processes |
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sync lines (lines starting with @samp{#line}), as produced by @samp{m4 |
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-s} (@pxref{Invoking m4, , Invoking m4, m4.info, GNU m4}) and similar |
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tools. This allows associating C compiler error messages with the |
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original source of the C code. |
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Vmgen understands a few extensions beyond the grammar given here, but |
Vmgen understands a few extensions beyond the grammar given here, but |
these extensions are only useful for building Gforth. You can find a |
these extensions are only useful for building Gforth. You can find a |
description of the format used for Gforth in @file{prim}. |
description of the format used for Gforth in @file{prim}. |
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@menu |
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* Eval escapes:: what follows \E |
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@end menu |
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@node Eval escapes, , Input File Grammar, Input File Grammar |
@subsection Eval escapes |
@subsection Eval escapes |
@cindex escape to Forth |
@cindex escape to Forth |
@cindex eval escape |
@cindex eval escape |
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@cindex @code{\E} |
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@c woanders? |
@c woanders? |
The text in @code{eval-escape} is Forth code that is evaluated when |
The text in @code{eval-escape} is Forth code that is evaluated when |
Vmgen reads the line. If you do not know (and do not want to learn) |
Vmgen reads the line. You will normally use this feature to define |
Forth, you can build the text according to the following grammar; these |
stacks and types. |
rules are normally all Forth you need for using Vmgen: |
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If you do not know (and do not want to learn) Forth, you can build the |
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text according to the following grammar; these rules are normally all |
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Forth you need for using Vmgen: |
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@example |
@example |
text: stack-decl|type-prefix-decl|stack-prefix-decl |
text: stack-decl|type-prefix-decl|stack-prefix-decl|set-flag |
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stack-decl: 'stack ' ident ident ident |
stack-decl: 'stack ' ident ident ident |
type-prefix-decl: |
type-prefix-decl: |
's" ' string '" ' ('single'|'double') ident 'type-prefix' ident |
's" ' string '" ' ('single'|'double') ident 'type-prefix' ident |
stack-prefix-decl: ident 'stack-prefix' string |
stack-prefix-decl: ident 'stack-prefix' string |
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set-flag: ('store-optimization'|'include-skipped-insts') ('on'|'off') |
@end example |
@end example |
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Note that the syntax of this code is not checked thoroughly (there are |
Note that the syntax of this code is not checked thoroughly (there are |
many other Forth program fragments that could be written there). |
many other Forth program fragments that could be written in an |
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eval-escape). |
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A stack prefix can contain letters, digits, or @samp{:}, and may start |
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with an @samp{#}; e.g., in Gforth the return stack has the stack prefix |
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@samp{R:}. This restriction is not checked during the stack prefix |
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definition, but it is enforced by the parsing rules for stack items |
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later. |
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If you know Forth, the stack effects of the non-standard words involved |
If you know Forth, the stack effects of the non-standard words involved |
are: |
are: |
Line 661 are:
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Line 736 are:
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@findex single |
@findex single |
@findex double |
@findex double |
@findex stack-prefix |
@findex stack-prefix |
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@findex store-optimization |
@example |
@example |
stack ( "name" "pointer" "type" -- ) |
stack ( "name" "pointer" "type" -- ) |
( name execution: -- stack ) |
( name execution: -- stack ) |
type-prefix ( addr u xt1 xt2 n stack "prefix" -- ) |
type-prefix ( addr u item-size stack "prefix" -- ) |
single ( -- xt1 xt2 n ) |
single ( -- item-size ) |
double ( -- xt1 xt2 n ) |
double ( -- item-size ) |
stack-prefix ( stack "prefix" -- ) |
stack-prefix ( stack "prefix" -- ) |
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store-optimization ( -- addr ) |
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include-skipped-insts ( -- addr ) |
@end example |
@end example |
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An @var{item-size} takes three cells on the stack. |
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@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
@node Simple instructions, Superinstructions, Input File Grammar, Input File Format |
@node Simple instructions, Superinstructions, Input File Grammar, Input File Format |
Line 726 Before we can use @code{data-stack} in t
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Line 805 Before we can use @code{data-stack} in t
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@cindex stack basic type |
@cindex stack basic type |
@cindex basic type of a stack |
@cindex basic type of a stack |
@cindex type of a stack, basic |
@cindex type of a stack, basic |
@cindex stack growth direction |
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This line defines the stack @code{data-stack}, which uses the stack |
This line defines the stack @code{data-stack}, which uses the stack |
pointer @code{sp}, and each item has the basic type @code{Cell}; other |
pointer @code{sp}, and each item has the basic type @code{Cell}; other |
types have to fit into one or two @code{Cell}s (depending on whether the |
types have to fit into one or two @code{Cell}s (depending on whether the |
type is @code{single} or @code{double} wide), and are cast from and to |
type is @code{single} or @code{double} wide), and are cast from and to |
Cells on accessing the @code{data-stack} with type cast macros |
Cells on accessing the @code{data-stack} with type cast macros |
(@pxref{VM engine}). Stacks grow towards lower addresses in |
(@pxref{VM engine}). By default, stacks grow towards lower addresses in |
Vmgen-erated interpreters. |
Vmgen-erated interpreters (@pxref{Stack growth direction}). |
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@cindex stack prefix |
@cindex stack prefix |
@cindex prefix, stack |
@cindex prefix, stack |
Line 769 first one (just as the intuition suggest
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Line 847 first one (just as the intuition suggest
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@menu |
@menu |
* C Code Macros:: Macros recognized by Vmgen |
* C Code Macros:: Macros recognized by Vmgen |
* C Code restrictions:: Vmgen makes assumptions about C code |
* C Code restrictions:: Vmgen makes assumptions about C code |
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* Stack growth direction:: is configurable per stack |
@end menu |
@end menu |
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@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
Line 793 level, this also sets the instruction po
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Line 872 level, this also sets the instruction po
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This ends a basic block (for profiling), even if the instruction |
This ends a basic block (for profiling), even if the instruction |
contains no @code{SET_IP}. |
contains no @code{SET_IP}. |
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@item TAIL; |
@item INST_TAIL; |
@findex TAIL; |
@findex INST_TAIL; |
Vmgen replaces @samp{TAIL;} with code for ending a VM instruction and |
Vmgen replaces @samp{INST_TAIL;} with code for ending a VM instruction and |
dispatching the next VM instruction. Even without a @samp{TAIL;} this |
dispatching the next VM instruction. Even without a @samp{INST_TAIL;} this |
happens automatically when control reaches the end of the C code. If |
happens automatically when control reaches the end of the C code. If |
you want to have this in the middle of the C code, you need to use |
you want to have this in the middle of the C code, you need to use |
@samp{TAIL;}. A typical example is a conditional VM branch: |
@samp{INST_TAIL;}. A typical example is a conditional VM branch: |
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@example |
@example |
if (branch_condition) @{ |
if (branch_condition) @{ |
SET_IP(target); TAIL; |
SET_IP(target); INST_TAIL; |
@} |
@} |
/* implicit tail follows here */ |
/* implicit tail follows here */ |
@end example |
@end example |
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In this example, @samp{TAIL;} is not strictly necessary, because there |
In this example, @samp{INST_TAIL;} is not strictly necessary, because there |
is another one implicitly after the if-statement, but using it improves |
is another one implicitly after the if-statement, but using it improves |
branch prediction accuracy slightly and allows other optimizations. |
branch prediction accuracy slightly and allows other optimizations. |
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Line 822 typical application is in conditional VM
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Line 901 typical application is in conditional VM
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@example |
@example |
if (branch_condition) @{ |
if (branch_condition) @{ |
SET_IP(target); TAIL; /* now this TAIL is necessary */ |
SET_IP(target); INST_TAIL; /* now this INST_TAIL is necessary */ |
@} |
@} |
SUPER_CONTINUE; |
SUPER_CONTINUE; |
@end example |
@end example |
Line 832 SUPER_CONTINUE;
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Line 911 SUPER_CONTINUE;
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Note that Vmgen is not smart about C-level tokenization, comments, |
Note that Vmgen is not smart about C-level tokenization, comments, |
strings, or conditional compilation, so it will interpret even a |
strings, or conditional compilation, so it will interpret even a |
commented-out SUPER_END as ending a basic block (or, e.g., |
commented-out SUPER_END as ending a basic block (or, e.g., |
@samp{RETAIL;} as @samp{TAIL;}). Conversely, Vmgen requires the literal |
@samp{RESET_IP;} as @samp{SET_IP;}). Conversely, Vmgen requires the literal |
presence of these strings; Vmgen will not see them if they are hiding in |
presence of these strings; Vmgen will not see them if they are hiding in |
a C preprocessor macro. |
a C preprocessor macro. |
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@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
@node C Code restrictions, , C Code Macros, Simple instructions |
@node C Code restrictions, Stack growth direction, C Code Macros, Simple instructions |
@subsection C Code restrictions |
@subsection C Code restrictions |
@cindex C code restrictions |
@cindex C code restrictions |
@cindex restrictions on C code |
@cindex restrictions on C code |
Line 879 The Vmgen-erated code loads the stack it
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Line 958 The Vmgen-erated code loads the stack it
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memory into variables before the user-supplied C code, and stores them |
memory into variables before the user-supplied C code, and stores them |
from variables to stack-pointer-indexed memory afterwards. If you do |
from variables to stack-pointer-indexed memory afterwards. If you do |
any writes to the stack through its stack pointer in your C code, it |
any writes to the stack through its stack pointer in your C code, it |
will not affact the variables, and your write may be overwritten by the |
will not affect the variables, and your write may be overwritten by the |
stores after the C code. Similarly, a read from a stack using a stack |
stores after the C code. Similarly, a read from a stack using a stack |
pointer will not reflect computations of stack items in the same VM |
pointer will not reflect computations of stack items in the same VM |
instruction. |
instruction. |
Line 898 macros can be implemented in several way
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Line 977 macros can be implemented in several way
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@samp{IP} points to the next instruction, and @samp{IPTOS} is its |
@samp{IP} points to the next instruction, and @samp{IPTOS} is its |
contents. |
contents. |
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@c -------------------------------------------------------------------- |
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@node Stack growth direction, , C Code restrictions, Simple instructions |
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@subsection Stack growth direction |
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@cindex stack growth direction |
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@cindex @code{stack-access-transform} |
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By default, the stacks grow towards lower addresses. You can change |
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this for a stack by setting the @code{stack-access-transform} field of |
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the stack to an xt @code{( itemnum -- index )} that performs the |
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appropriate index transformation. |
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E.g., if you want to let @code{data-stack} grow towards higher |
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addresses, with the stack pointer always pointing just beyond the |
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top-of-stack, use this right after defining @code{data-stack}: |
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@example |
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\E : sp-access-transform ( itemnum -- index ) negate 1- ; |
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\E ' sp-access-transform ' data-stack >body stack-access-transform ! |
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@end example |
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This means that @code{sp-access-transform} will be used to generate |
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indexes for accessing @code{data-stack}. The definition of |
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@code{sp-access-transform} above transforms n into -n-1, e.g, 1 into -2. |
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This will access the 0th data-stack element (top-of-stack) at sp[-1], |
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the 1st at sp[-2], etc., which is the typical way upward-growing |
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stacks are used. If you need a different transform and do not know |
|
enough Forth to program it, let me know. |
|
|
@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
@node Superinstructions, Register Machines, Simple instructions, Input File Format |
@node Superinstructions, Store Optimization, Simple instructions, Input File Format |
@section Superinstructions |
@section Superinstructions |
@cindex superinstructions, defining |
@cindex superinstructions, defining |
@cindex defining superinstructions |
@cindex defining superinstructions |
Line 957 accesses a stack pointer should not be u
|
Line 1063 accesses a stack pointer should not be u
|
does not check these restrictions, they just result in bugs in your |
does not check these restrictions, they just result in bugs in your |
interpreter. |
interpreter. |
|
|
|
@cindex include-skipped-insts |
|
The Vmgen flag @code{include-skipped-insts} influences superinstruction |
|
code generation. Currently there is no support in the peephole |
|
optimizer for both variations, so leave this flag alone for now. |
|
|
|
@c ------------------------------------------------------------------- |
|
@node Store Optimization, Register Machines, Superinstructions, Input File Format |
|
@section Store Optimization |
|
@cindex store optimization |
|
@cindex optimization, stack stores |
|
@cindex stack stores, optimization |
|
@cindex eliminating stack stores |
|
|
|
This minor optimization (0.6\%--0.8\% reduction in executed instructions |
|
for Gforth) puts additional requirements on the instruction descriptions |
|
and is therefore disabled by default. |
|
|
|
What does it do? Consider an instruction like |
|
|
|
@example |
|
dup ( n -- n n ) |
|
@end example |
|
|
|
For simplicity, also assume that we are not caching the top-of-stack in |
|
a register. Now, the C code for dup first loads @code{n} from the |
|
stack, and then stores it twice to the stack, one time to the address |
|
where it came from; that time is unnecessary, but gcc does not optimize |
|
it away, so vmgen can do it instead (if you turn on the store |
|
optimization). |
|
|
|
Vmgen uses the stack item's name to determine if the stack item contains |
|
the same value as it did at the start. Therefore, if you use the store |
|
optimization, you have to ensure that stack items that have the same |
|
name on input and output also have the same value, and are not changed |
|
in the C code you supply. I.e., the following code could fail if you |
|
turn on the store optimization: |
|
|
|
@example |
|
add1 ( n -- n ) |
|
n++; |
|
@end example |
|
|
|
Instead, you have to use different names, i.e.: |
|
|
|
@example |
|
add1 ( n1 -- n1 ) |
|
n2=n1+1; |
|
@end example |
|
|
|
Similarly, the store optimization assumes that the stack pointer is only |
|
changed by Vmgen-erated code. If your C code changes the stack pointer, |
|
use different names in input and output stack items to avoid a (probably |
|
wrong) store optimization, or turn the store optimization off for this |
|
VM instruction. |
|
|
|
To turn on the store optimization, write |
|
|
|
@example |
|
\E store-optimization on |
|
@end example |
|
|
|
at the start of the file. You can turn this optimization on or off |
|
between any two VM instruction descriptions. For turning it off again, |
|
you can use |
|
|
|
@example |
|
\E store-optimization off |
|
@end example |
|
|
@c ------------------------------------------------------------------- |
@c ------------------------------------------------------------------- |
@node Register Machines, , Superinstructions, Input File Format |
@node Register Machines, , Store Optimization, Input File Format |
@section Register Machines |
@section Register Machines |
@cindex Register VM |
@cindex Register VM |
@cindex Superinstructions for register VMs |
@cindex Superinstructions for register VMs |
Line 1013 VM interpreters. However, if you have i
|
Line 1188 VM interpreters. However, if you have i
|
direction, please let me know (@pxref{Contact}). |
direction, please let me know (@pxref{Contact}). |
|
|
@c ******************************************************************** |
@c ******************************************************************** |
@node Using the generated code, Changes, Input File Format, Top |
@node Error messages, Using the generated code, Input File Format, Top |
|
@chapter Error messages |
|
@cindex error messages |
|
|
|
These error messages are created by Vmgen: |
|
|
|
@table @code |
|
|
|
@cindex @code{# can only be on the input side} error |
|
@item # can only be on the input side |
|
You have used an instruction-stream prefix (usually @samp{#}) after the |
|
@samp{--} (the output side); you can only use it before (the input |
|
side). |
|
|
|
@cindex @code{prefix for this combination must be defined earlier} error |
|
@item the prefix for this superinstruction must be defined earlier |
|
You have defined a superinstruction (e.g. @code{abc = a b c}) without |
|
defining its direct prefix (e.g., @code{ab = a b}), |
|
@xref{Superinstructions}. |
|
|
|
@cindex @code{sync line syntax} error |
|
@item sync line syntax |
|
If you are using a preprocessor (e.g., @command{m4}) to generate Vmgen |
|
input code, you may want to create @code{#line} directives (aka sync |
|
lines). This error indicates that such a line is not in th syntax |
|
expected by Vmgen (this should not happen; please report the offending |
|
line in a bug report). |
|
|
|
@cindex @code{syntax error, wrong char} error |
|
@item syntax error, wrong char |
|
A syntax error. If you do not see right away where the error is, it may |
|
be helpful to check the following: Did you put an empty line in a VM |
|
instruction where the C code is not delimited by braces (then the empty |
|
line ends the VM instruction)? If you used brace-delimited C code, did |
|
you put the delimiting braces (and only those) at the start of the line, |
|
without preceding white space? Did you forget a delimiting brace? |
|
|
|
@cindex @code{too many stacks} error |
|
@item too many stacks |
|
Vmgen currently supports 3 stacks (plus the instruction stream); if you |
|
need more, let us know. |
|
|
|
@cindex @code{unknown prefix} error |
|
@item unknown prefix |
|
The stack item does not match any defined type prefix (after stripping |
|
away any stack prefix). You should either declare the type prefix you |
|
want for that stack item, or use a different type prefix |
|
|
|
@cindex @code{unknown primitive} error |
|
@item unknown primitive |
|
You have used the name of a simple VM instruction in a superinstruction |
|
definition without defining the simple VM instruction first. |
|
|
|
@end table |
|
|
|
In addition, the C compiler can produce errors due to code produced by |
|
Vmgen; e.g., you need to define type cast functions. |
|
|
|
@c ******************************************************************** |
|
@node Using the generated code, Hints, Error messages, Top |
@chapter Using the generated code |
@chapter Using the generated code |
@cindex generated code, usage |
@cindex generated code, usage |
@cindex Using vmgen-erated code |
@cindex Using vmgen-erated code |
|
|
The easiest way to create a working VM interpreter with Vmgen is |
The easiest way to create a working VM interpreter with Vmgen is |
probably to start with @file{vmgen-ex}, and modify it for your purposes. |
probably to start with @file{vmgen-ex}, and modify it for your purposes. |
This chapter is just the reference manual for the macros etc. used by |
This chapter explains what the various wrapper and generated files do. |
the generated code, the other context expected by the generated code, |
It also contains reference-manual style descriptions of the macros, |
and what you can do with the various generated files. |
variables etc. used by the generated code, and you can skip that on |
|
first reading. |
|
|
@menu |
@menu |
* VM engine:: Executing VM code |
* VM engine:: Executing VM code |
Line 1059 In our example the engine function also
|
Line 1294 In our example the engine function also
|
@file{@var{name}-labels.i} (@pxref{VM instruction table}). |
@file{@var{name}-labels.i} (@pxref{VM instruction table}). |
|
|
@cindex tracing VM code |
@cindex tracing VM code |
|
@cindex superinstructions and tracing |
In addition to executing the code, the VM engine can optionally also |
In addition to executing the code, the VM engine can optionally also |
print out a trace of the executed instructions, their arguments and |
print out a trace of the executed instructions, their arguments and |
results. For superinstructions it prints the trace as if only component |
results. For superinstructions it prints the trace as if only component |
Line 1080 The following macros and variables are u
|
Line 1316 The following macros and variables are u
|
@item LABEL(@var{inst_name}) |
@item LABEL(@var{inst_name}) |
This is used just before each VM instruction to provide a jump or |
This is used just before each VM instruction to provide a jump or |
@code{switch} label (the @samp{:} is provided by Vmgen). For switch |
@code{switch} label (the @samp{:} is provided by Vmgen). For switch |
dispatch this should expand to @samp{case @var{label}}; for |
dispatch this should expand to @samp{case @var{label}:}; for |
threaded-code dispatch this should just expand to @samp{@var{label}}. |
threaded-code dispatch this should just expand to @samp{@var{label}:}. |
In either case @var{label} is usually the @var{inst_name} with some |
In either case @var{label} is usually the @var{inst_name} with some |
prefix or suffix to avoid naming conflicts. |
prefix or suffix to avoid naming conflicts. |
|
|
Line 1093 should expand to nothing.
|
Line 1329 should expand to nothing.
|
@findex NAME |
@findex NAME |
@item NAME(@var{inst_name_string}) |
@item NAME(@var{inst_name_string}) |
Called on entering a VM instruction with a string containing the name of |
Called on entering a VM instruction with a string containing the name of |
the VM instruction as parameter. In normal execution this should be a |
the VM instruction as parameter. In normal execution this should be |
noop, but for tracing this usually prints the name, and possibly other |
expand to nothing, but for tracing this usually prints the name, and |
information (several VM registers in our example). |
possibly other information (several VM registers in our example). |
|
|
@findex DEF_CA |
@findex DEF_CA |
@item DEF_CA |
@item DEF_CA |
Line 1114 different ways for best performance on v
|
Line 1350 different ways for best performance on v
|
@samp{NEXT_P0} is invoked right at the start of the VM instruction (but |
@samp{NEXT_P0} is invoked right at the start of the VM instruction (but |
after @samp{DEF_CA}), @samp{NEXT_P1} right after the user-supplied C |
after @samp{DEF_CA}), @samp{NEXT_P1} right after the user-supplied C |
code, and @samp{NEXT_P2} at the end. The actual jump has to be |
code, and @samp{NEXT_P2} at the end. The actual jump has to be |
performed by @samp{NEXT_P2}. |
performed by @samp{NEXT_P2} (if you would do it earlier, important parts |
|
of the VM instruction would not be executed). |
|
|
The simplest variant is if @samp{NEXT_P2} does everything and the other |
The simplest variant is if @samp{NEXT_P2} does everything and the other |
macros do nothing. Then also related macros like @samp{IP}, |
macros do nothing. Then also related macros like @samp{IP}, |
Line 1189 type. For @samp{inst-stream}, the name
|
Line 1426 type. For @samp{inst-stream}, the name
|
plain r-value; typically it is a macro that abstracts away the |
plain r-value; typically it is a macro that abstracts away the |
differences between the various implementations of @code{NEXT_P*}. |
differences between the various implementations of @code{NEXT_P*}. |
|
|
|
@cindex IMM_ARG |
|
@findex IMM_ARG |
|
@item IMM_ARG(access,value) |
|
Define this to expland to ``(access)''. This is just a placeholder for |
|
future extensions. |
|
|
@cindex top of stack caching |
@cindex top of stack caching |
@cindex stack caching |
@cindex stack caching |
@cindex TOS |
@cindex TOS |
Line 1541 it uses variables and functions defined
|
Line 1784 it uses variables and functions defined
|
plus @code{VM_IS_INST} already defined for the VM disassembler |
plus @code{VM_IS_INST} already defined for the VM disassembler |
(@pxref{VM disassembler}). |
(@pxref{VM disassembler}). |
|
|
|
@c ********************************************************** |
|
@node Hints, The future, Using the generated code, Top |
|
@chapter Hints |
|
@cindex hints |
|
|
|
@menu |
|
* Floating point:: and stacks |
|
@end menu |
|
|
|
@c -------------------------------------------------------------------- |
|
@node Floating point, , Hints, Hints |
|
@section Floating point |
|
|
|
How should you deal with floating point values? Should you use the same |
|
stack as for integers/pointers, or a different one? This section |
|
discusses this issue with a view on execution speed. |
|
|
|
The simpler approach is to use a separate floating-point stack. This |
|
allows you to choose FP value size without considering the size of the |
|
integers/pointers, and you avoid a number of performance problems. The |
|
main downside is that this needs an FP stack pointer (and that may not |
|
fit in the register file on the 386 arhitecture, costing some |
|
performance, but comparatively little if you take the other option into |
|
account). If you use a separate FP stack (with stack pointer @code{fp}), |
|
using an fpTOS is helpful on most machines, but some spill the fpTOS |
|
register into memory, and fpTOS should not be used there. |
|
|
|
The other approach is to share one stack (pointed to by, say, @code{sp}) |
|
between integer/pointer and floating-point values. This is ok if you do |
|
not use @code{spTOS}. If you do use @code{spTOS}, the compiler has to |
|
decide whether to put that variable into an integer or a floating point |
|
register, and the other type of operation becomes quite expensive on |
|
most machines (because moving values between integer and FP registers is |
|
quite expensive). If a value of one type has to be synthesized out of |
|
two values of the other type (@code{double} types), things are even more |
|
interesting. |
|
|
|
One way around this problem would be to not use the @code{spTOS} |
|
supported by Vmgen, but to use explicit top-of-stack variables (one for |
|
integers, one for FP values), and having a kind of accumulator+stack |
|
architecture (e.g., Ocaml bytecode uses this approach); however, this is |
|
a major change, and it's ramifications are not completely clear. |
|
|
@c ********************************************************** |
@c ********************************************************** |
@node Changes, Contact, Using the generated code, Top |
@node The future, Changes, Hints, Top |
|
@chapter The future |
|
@cindex future ideas |
|
|
|
We have a number of ideas for future versions of Vmgen. However, there |
|
are so many possible things to do that we would like some feedback from |
|
you. What are you doing with Vmgen, what features are you missing, and |
|
why? |
|
|
|
One idea we are thinking about is to generate just one @file{.c} file |
|
instead of letting you copy and adapt all the wrapper files (you would |
|
still have to define stuff like the type-specific macros, and stack |
|
pointers etc. somewhere). The advantage would be that, if we change the |
|
wrapper files between versions, you would not need to integrate your |
|
changes and our changes to them; Vmgen would also be easier to use for |
|
beginners. The main disadvantage of that is that it would reduce the |
|
flexibility of Vmgen a little (well, those who like flexibility could |
|
still patch the resulting @file{.c} file, like they are now doing for |
|
the wrapper files). In any case, if you are doing things to the wrapper |
|
files that would cause problems in a generated-@file{.c}-file approach, |
|
please let us know. |
|
|
|
@c ********************************************************** |
|
@node Changes, Contact, The future, Top |
@chapter Changes |
@chapter Changes |
@cindex Changes from old versions |
@cindex Changes from old versions |
|
|
|
User-visible changes between 0.5.9-20020822 and 0.5.9-20020901: |
|
|
|
The store optimization is now disabled by default, but can be enabled by |
|
the user (@pxref{Store Optimization}). Documentation for this |
|
optimization is also new. |
|
|
|
User-visible changes between 0.5.9-20010501 and 0.5.9-20020822: |
|
|
|
There is now a manual (in info, HTML, Postscript, or plain text format). |
|
|
|
There is the vmgen-ex2 variant of the vmgen-ex example; the new |
|
variant uses a union type instead of lots of casting. |
|
|
|
Both variants of the example can now be compiled with an ANSI C compiler |
|
(using switch dispatch and losing quite a bit of performance); tested |
|
with @command{lcc}. |
|
|
Users of the gforth-0.5.9-20010501 version of Vmgen need to change |
Users of the gforth-0.5.9-20010501 version of Vmgen need to change |
several things in their source code to use the current version. I |
several things in their source code to use the current version. I |
recommend keeping the gforth-0.5.9-20010501 version until you have |
recommend keeping the gforth-0.5.9-20010501 version until you have |
Line 1558 The required changes are:
|
Line 1883 The required changes are:
|
|
|
@table @code |
@table @code |
|
|
|
@cindex @code{TAIL;}, changes |
|
@item TAIL; |
|
has been renamed into @code{INST_TAIL;} (less chance of an accidental |
|
match). |
|
|
@cindex @code{vm_@var{A}2@var{B}}, changes |
@cindex @code{vm_@var{A}2@var{B}}, changes |
@item vm_@var{A}2@var{B} |
@item vm_@var{A}2@var{B} |
now takes two arguments. |
now takes two arguments. |
Line 1576 Also some new macros have to be defined,
|
Line 1906 Also some new macros have to be defined,
|
@node Contact, Copying This Manual, Changes, Top |
@node Contact, Copying This Manual, Changes, Top |
@chapter Contact |
@chapter Contact |
|
|
|
To report a bug, use |
|
@url{https://savannah.gnu.org/bugs/?func=addbug&group_id=2672}. |
|
|
|
For discussion on Vmgen (e.g., how to use it), use the mailing list |
|
@email{bug-vmgen@@mail.freesoftware.fsf.org} (use |
|
@url{http://mail.gnu.org/mailman/listinfo/help-vmgen} to subscribe). |
|
|
|
You can find vmgen information at |
|
@url{http://www.complang.tuwien.ac.at/anton/vmgen/}. |
|
|
@c *********************************************************** |
@c *********************************************************** |
@node Copying This Manual, Index, Contact, Top |
@node Copying This Manual, Index, Contact, Top |
@appendix Copying This Manual |
@appendix Copying This Manual |