[gforth] / gforth / doc / vmgen.texi  

gforth: gforth/doc/vmgen.texi

Diff for /gforth/doc/vmgen.texi between version 1.19 and 1.30

version 1.19, Sun Sep 1 15:15:07 2002 UTC version 1.30, Mon Dec 31 18:56:18 2007 UTC
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 (version @value{VERSION}, @value{UPDATED}),  (version @value{VERSION}, @value{UPDATED}),
 the virtual machine interpreter generator  the virtual machine interpreter generator
   
 Copyright @copyright{} 2002 Free Software Foundation, Inc.  Copyright @copyright{} 2002,2003,2005 Free Software Foundation, Inc.
   
 @quotation  @quotation
 Permission is granted to copy, distribute and/or modify this document  Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.1 or  under the terms of the GNU Free Documentation License, Version 1.2 or
 any later version published by the Free Software Foundation; with no  any later version published by the Free Software Foundation; with no
 Invariant Sections, with the Front-Cover texts being ``A GNU Manual,''  Invariant Sections, with the Front-Cover texts being ``A GNU Manual,''
 and with the Back-Cover Texts as in (a) below.  A copy of the  and with the Back-Cover Texts as in (a) below.  A copy of the
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 @end quotation  @end quotation
 @end copying  @end copying
   
 @dircategory GNU programming tools  @dircategory Software development
 @direntry  @direntry
 * Vmgen: (vmgen).               Interpreter generator  * Vmgen: (vmgen).               Virtual machine interpreter generator
 @end direntry  @end direntry
   
 @titlepage  @titlepage
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 Simple instructions  Simple instructions
   
   * Explicit stack access::       If the C code accesses a stack pointer
 * 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
   * Stack growth direction::      is configurable per stack
   
 Using the generated code  Using the generated code
   
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 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
 set-flag: 'store-optimization' ('on'|'off')  set-flag: ('store-optimization'|'include-skipped-insts') ('on'|'off')
 @end example  @end example
   
 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
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 double             ( -- item-size )  double             ( -- item-size )
 stack-prefix       ( stack "prefix" -- )  stack-prefix       ( stack "prefix" -- )
 store-optimization ( -- addr )  store-optimization ( -- addr )
   include-skipped-insts ( -- addr )
 @end example  @end example
   
 An @var{item-size} takes three cells on the stack.  An @var{item-size} takes three cells on the stack.
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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  
 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}).
   
 @cindex stack prefix  @cindex stack prefix
 @cindex prefix, stack  @cindex prefix, stack
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 @example  @example
 \E inst-stream stack-prefix #  \E inst-stream stack-prefix #
   \E data-stack  stack-prefix S:
 @end example  @end example
   
 This definition defines that the stack prefix @code{#} specifies the  This definition defines that the stack prefix @code{#} specifies the
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 first one (just as the intuition suggests).  first one (just as the intuition suggests).
   
 @menu  @menu
   * Explicit stack access::       If the C code accesses a stack pointer
 * 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
   * Stack growth direction::      is configurable per stack
 @end menu  @end menu
   
 @c --------------------------------------------------------------------  @c --------------------------------------------------------------------
 @node C Code Macros, C Code restrictions, Simple instructions, Simple instructions  @node  Explicit stack access, C Code Macros, Simple instructions, Simple instructions
   @subsection Explicit stack access
   @cindex stack access, explicit
   @cindex Stack pointer access
   @cindex explicit stack access
   
   Not all stack effects can be specified using the stack effect
   specifications above.  For VM instructions that have other stack
   effects, you can specify them explicitly by accessing the stack
   pointer in the C code; however, you have to notify Vmgen of such
   explicit stack accesses, otherwise Vmgens optimizations could conflict
   with your explicit stack accesses.
   
   You notify Vmgen by putting @code{...} with the appropriate stack
   prefix into the stack comment.  Then the VM instruction will first
   take the other stack items specified in the stack effect into C
   variables, then make sure that all other stack items for that stack
   are in memory, and that the stack pointer for the stack points to the
   top-of-stack (by default, unless you change the stack access
   transformation: @pxref{Stack growth direction}).
   
   The general rule is: If you mention a stack pointer in the C code of a
   VM instruction, you should put a @code{...} for that stack in the stack
   effect.
   
   Consider this example:
   
   @example
   return ( #iadjust S:... target afp i1 -- i2 )
   SET_IP(target);
   sp = (Cell *)(((char *)sp)+iadjust);
   fp = afp;
   i2=i1;
   @end example
   
   First the variables @code{target afp i1} are popped off the stack,
   then the stack pointer @code{sp} is set correctly for the new stack
   depth, then the C code changes the stack depth and does other things,
   and finally @code{i2} is pushed on the stack with the new depth.
   
   The position of the @code{...} within the stack effect does not
   matter.  You can use several @code{...}s, for different stacks, and
   also several for the same stack (that has no additional effect).  If
   you use @code{...} without a stack prefix, this specifies all the
   stacks except the instruction stream.
   
   You cannot use @code{...} for the instruction stream, but that is not
   necessary: At the start of the C code, @code{IP} points to the start
   of the next VM instruction (i.e., right beyond the end of the current
   VM instruction), and you can change the instruction pointer with
   @code{SET_IP} (@pxref{VM engine}).
   
   
   @c --------------------------------------------------------------------
   @node C Code Macros, C Code restrictions, Explicit stack access, Simple instructions
 @subsection C Code Macros  @subsection C Code Macros
 @cindex macros recognized by Vmgen  @cindex macros recognized by Vmgen
 @cindex basic block, VM level  @cindex basic block, VM level
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 SUPER_CONTINUE;  SUPER_CONTINUE;
 @end example  @end example
   
   @item VM_JUMP
   @findex VM_JUMP
   @code{VM_JUMP(target)} is equivalent to @code{goto *(target)}, but
   allows Vmgen to do dynamic superinstructions and replication.  You
   still need to say @code{SUPER_END}.  Also, the goto only happens at
   the end (wherever the VM_JUMP is).  Essentially, this just suppresses
   much of the ordinary dispatch mechanism.
   
 @end table  @end table
   
 Note that Vmgen is not smart about C-level tokenization, comments,  Note that Vmgen is not smart about C-level tokenization, comments,
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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
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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.
   
   @c --------------------------------------------------------------------
   @node Stack growth direction,  , C Code restrictions, Simple instructions
   @subsection Stack growth direction
   @cindex stack growth direction
   
   @cindex @code{stack-access-transform}
   By default, the stacks grow towards lower addresses.  You can change
   this for a stack by setting the @code{stack-access-transform} field of
   the stack to an xt @code{( itemnum -- index )} that performs the
   appropriate index transformation.
   
   E.g., if you want to let @code{data-stack} grow towards higher
   addresses, with the stack pointer always pointing just beyond the
   top-of-stack, use this right after defining @code{data-stack}:
   
   @example
   \E : sp-access-transform ( itemnum -- index ) negate 1- ;
   \E ' sp-access-transform ' data-stack >body stack-access-transform !
   @end example
   
   This means that @code{sp-access-transform} will be used to generate
   indexes for accessing @code{data-stack}.  The definition of
   @code{sp-access-transform} above transforms n into -n-1, e.g, 1 into -2.
   This will access the 0th data-stack element (top-of-stack) at sp[-1],
   the 1st at sp[-2], etc., which is the typical way upward-growing
   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, Store Optimization, Simple instructions, Input File Format  @node Superinstructions, Store Optimization, Simple instructions, Input File Format
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 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 -------------------------------------------------------------------  @c -------------------------------------------------------------------
 @node  Store Optimization, Register Machines, Superinstructions, Input File Format  @node  Store Optimization, Register Machines, Superinstructions, Input File Format
 @section Store Optimization  @section Store Optimization
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 Instead, you have to use different names, i.e.:  Instead, you have to use different names, i.e.:
   
 @example  @example
 add1 ( n1 -- n1 )  add1 ( n1 -- n2 )
 n2=n1+1;  n2=n1+1;
 @end example  @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  To turn on the store optimization, write
   
 @example  @example
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 side).  side).
   
 @cindex @code{prefix for this combination must be defined earlier} error  @cindex @code{prefix for this combination must be defined earlier} error
 @item the prefix for this combination must be defined earlier  @item the prefix for this superinstruction must be defined earlier
 You have defined a superinstruction (e.g. @code{abc = a b c}) without  You have defined a superinstruction (e.g. @code{abc = a b c}) without
 defining its direct prefix (e.g., @code{ab = a b}),  defining its direct prefix (e.g., @code{ab = a b}),
 @xref{Superinstructions}.  @xref{Superinstructions}.
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 line in a bug report).  line in a bug report).
   
 @cindex @code{syntax error, wrong char} error  @cindex @code{syntax error, wrong char} error
 @cindex syntax error, wrong char  @item syntax error, wrong char
 A syntax error.  If you do not see right away where the error is, it may  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  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  instruction where the C code is not delimited by braces (then the empty
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 away any stack prefix).  You should either declare the type prefix you  away any stack prefix).  You should either declare the type prefix you
 want for that stack item, or use a different type prefix  want for that stack item, or use a different type prefix
   
 @item @code{unknown primitive} error  @cindex @code{unknown primitive} error
 @item unknown primitive  @item unknown primitive
 You have used the name of a simple VM instruction in a superinstruction  You have used the name of a simple VM instruction in a superinstruction
 definition without defining the simple VM instruction first.  definition without defining the simple VM instruction first.
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 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
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 @item SUPER_CONTINUE  @item SUPER_CONTINUE
 This is just a hint to Vmgen and does nothing at the C level.  This is just a hint to Vmgen and does nothing at the C level.
   
   @findex MAYBE_UNUSED
   @item MAYBE_UNUSED
   This should be defined as @code{__attribute__((unused))} for gcc-2.7 and
   higher.  It suppresses the warnings about unused variables in the code
   for superinstructions.  You need to define this only if you are using
   superinstructions.
   
 @findex VM_DEBUG  @findex VM_DEBUG
 @item VM_DEBUG  @item VM_DEBUG
 If this is defined, the tracing code will be compiled in (slower  If this is defined, the tracing code will be compiled in (slower
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 The code for peephole optimization is in @file{vmgen-ex/peephole.c}.  The code for peephole optimization is in @file{vmgen-ex/peephole.c}.
 You can use this file almost verbatim.  Vmgen generates  You can use this file almost verbatim.  Vmgen generates
 @file{@var{file}-peephole.i} which contains data for the peephoile  @file{@var{file}-peephole.i} which contains data for the peephole
 optimizer.  optimizer.
   
 @findex init_peeptable  @findex init_peeptable
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 @chapter The future  @chapter The future
 @cindex future ideas  @cindex future ideas
   
 We have a number of ideas for future versions of Gforth.  However, there  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  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  you.  What are you doing with Vmgen, what features are you missing, and
 why?  why?
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 * GNU Free Documentation License::  License for copying this manual.  * GNU Free Documentation License::  License for copying this manual.
 @end menu  @end menu
   
   @node GNU Free Documentation License,  , Copying This Manual, Copying This Manual
   @appendixsec GNU Free Documentation License
 @include fdl.texi  @include fdl.texi
   
   

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