Diff for /gforth/doc/vmgen.texi between versions 1.28 and 1.29

version 1.28, 2005/01/26 21:24:15 version 1.29, 2005/10/02 11:30:34
Line 94  Input File Grammar Line 94  Input File Grammar
   
 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  * Stack growth direction::      is configurable per stack
Line 829  name.  Stack prefixes are defined like t Line 830  name.  Stack prefixes are defined like t
   
 @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
Line 845  If there are multiple instruction stream Line 847  If there are multiple instruction stream
 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  * 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

Removed from v.1.28  
changed lines
  Added in v.1.29


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