Diff for /gforth/doc/vmgen.texi between versions 1.17 and 1.21

version 1.17, 2002/08/22 20:07:33 version 1.21, 2003/02/23 21:17:00
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  Input File Grammar
Line 605  Most examples are taken from the example Line 606  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 707  text according to the following grammar; Line 709  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' ('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 732  are: Line 735  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 )
 @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 972  contents. Line 977  contents.
   
   
 @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 1030  does not check these restrictions, they Line 1035  does not check these restrictions, they
 interpreter.  interpreter.
   
 @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
   
   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 1100  You have used an instruction-stream pref Line 1163  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 1723  a major change, and it's ramifications a Line 1786  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 1746  please let us know. Line 1809  please let us know.
 @chapter Changes  @chapter Changes
 @cindex Changes from old versions  @cindex Changes from old versions
   
 Use-visible changes between 0.5.9-20010501 and 0.5.9-20020822:  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 now a manual (in info, HTML, Postscript, or plain text format).
   

Removed from v.1.17  
changed lines
  Added in v.1.21


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