Diff for /gforth/doc/vmgen.texi between versions 1.15 and 1.24

version 1.15, 2002/08/20 16:59:01 version 1.24, 2003/03/02 13:12:33
Line 10  This manual is for Vmgen Line 10  This manual is for Vmgen
 (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, 03 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
Line 27  Software Foundation raise funds for GNU Line 27  Software Foundation raise funds for GNU
 @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
Line 85  Input File Format Line 85  Input File Format
 * Input File Grammar::            * Input File Grammar::          
 * Simple instructions::           * Simple instructions::         
 * Superinstructions::             * Superinstructions::           
   * Store Optimization::          
 * Register Machines::           How to define register VM instructions  * Register Machines::           How to define register VM instructions
   
   Input File Grammar
   
   * Eval escapes::                what follows \E
   
 Simple instructions  Simple instructions
   
 * 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
   
Line 601  Most examples are taken from the example Line 607  Most examples are taken from the example
 * Input File Grammar::            * Input File Grammar::          
 * Simple instructions::           * Simple instructions::         
 * Superinstructions::             * Superinstructions::           
   * Store Optimization::          
 * Register Machines::           How to define register VM instructions  * Register Machines::           How to define register VM instructions
 @end menu  @end menu
   
Line 683  Vmgen understands a few extensions beyon Line 690  Vmgen understands a few extensions beyon
 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}.
   
   @menu
   * Eval escapes::                what follows \E
   @end menu
   
   @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
Line 698  text according to the following grammar; Line 710  text according to the following grammar;
 Forth you need for using Vmgen:  Forth you need for using Vmgen:
   
 @example  @example
 text: stack-decl|type-prefix-decl|stack-prefix-decl  text: stack-decl|type-prefix-decl|stack-prefix-decl|set-flag
   
 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
   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
Line 723  are: Line 736  are:
 @findex single  @findex single
 @findex double  @findex double
 @findex stack-prefix  @findex stack-prefix
   @findex store-optimization
 @example  @example
 stack        ( "name" "pointer" "type" -- )  stack                 ( "name" "pointer" "type" -- )
              ( name execution: -- stack )                        ( name execution: -- stack )
 type-prefix  ( addr u item-size stack "prefix" -- )  type-prefix           ( addr u item-size stack "prefix" -- )
 single       ( -- item-size )  single                ( -- item-size )
 double       ( -- item-size )  double                ( -- item-size )
 stack-prefix ( stack "prefix" -- )  stack-prefix          ( stack "prefix" -- )
   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.
Line 789  Before we can use @code{data-stack} in t Line 805  Before we can use @code{data-stack} in t
 @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
Line 832  first one (just as the intuition suggest Line 847  first one (just as the intuition suggest
 @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
   * Stack growth direction::      is configurable per stack
 @end menu  @end menu
   
 @c --------------------------------------------------------------------  @c --------------------------------------------------------------------
Line 901  a C preprocessor macro. Line 917  a C preprocessor macro.
   
   
 @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 961  macros can be implemented in several way Line 977  macros can be implemented in several way
 @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, 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 1020  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 -------------------------------------------------------------------  @c -------------------------------------------------------------------
 @node Register Machines,  , Superinstructions, Input File Format  @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 -------------------------------------------------------------------
   @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 1091  You have used an instruction-stream pref Line 1203  You have used an instruction-stream pref
 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}.
Line 1101  defining its direct prefix (e.g., @code{ Line 1213  defining its direct prefix (e.g., @code{
 If you are using a preprocessor (e.g., @command{m4}) to generate Vmgen  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  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  lines).  This error indicates that such a line is not in th syntax
 expected by Vmgen (this should not happen).  expected by Vmgen (this should not happen; please report the offending
   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.  Note that Vmgen is sometimes anal retentive about white  A syntax error.  If you do not see right away where the error is, it may
 space, especially about newlines.  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  @cindex @code{too many stacks} error
 @item too many stacks  @item too many stacks
 Vmgen currently supports 4 stacks; if you need more, let us know.  Vmgen currently supports 3 stacks (plus the instruction stream); if you
   need more, let us know.
   
 @cindex @code{unknown prefix} error  @cindex @code{unknown prefix} error
 @item unknown prefix  @item unknown prefix
Line 1118  The stack item does not match any define Line 1236  The stack item does not match any define
 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.
Line 1308  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 1708  a major change, and it's ramifications a Line 1832  a major change, and it's ramifications a
 @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?
Line 1731  please let us know. Line 1855  please let us know.
 @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 1765  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

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