--- gforth/doc/vmgen.texi 2003/02/23 21:17:00 1.21 +++ gforth/doc/vmgen.texi 2003/03/01 22:39:16 1.23 @@ -10,7 +10,7 @@ This manual is for Vmgen (version @value{VERSION}, @value{UPDATED}), the virtual machine interpreter generator -Copyright @copyright{} 2002 Free Software Foundation, Inc. +Copyright @copyright{} 2002, 03 Free Software Foundation, Inc. @quotation Permission is granted to copy, distribute and/or modify this document @@ -27,7 +27,7 @@ Software Foundation raise funds for GNU @end quotation @end copying -@dircategory GNU programming tools +@dircategory Software development @direntry * Vmgen: (vmgen). Interpreter generator @end direntry @@ -96,6 +96,7 @@ Simple instructions * C Code Macros:: Macros recognized by Vmgen * C Code restrictions:: Vmgen makes assumptions about C code +* Stack growth direction:: is configurable per stack Using the generated code @@ -715,7 +716,7 @@ stack-decl: 'stack ' ident ident ident type-prefix-decl: 's" ' string '" ' ('single'|'double') ident 'type-prefix' ident stack-prefix-decl: ident 'stack-prefix' string -set-flag: 'store-optimization' ('on'|'off') +set-flag: ('store-optimization'|'include-skipped-insts') ('on'|'off') @end example Note that the syntax of this code is not checked thoroughly (there are @@ -737,13 +738,14 @@ are: @findex stack-prefix @findex store-optimization @example -stack ( "name" "pointer" "type" -- ) - ( name execution: -- stack ) -type-prefix ( addr u item-size stack "prefix" -- ) -single ( -- item-size ) -double ( -- item-size ) -stack-prefix ( stack "prefix" -- ) -store-optimization ( -- addr ) +stack ( "name" "pointer" "type" -- ) + ( name execution: -- stack ) +type-prefix ( addr u item-size stack "prefix" -- ) +single ( -- item-size ) +double ( -- item-size ) +stack-prefix ( stack "prefix" -- ) +store-optimization ( -- addr ) +include-skipped-insts ( -- addr ) @end example An @var{item-size} takes three cells on the stack. @@ -803,14 +805,13 @@ Before we can use @code{data-stack} in t @cindex stack basic type @cindex basic type of a stack @cindex type of a stack, basic -@cindex stack growth direction 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 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 Cells on accessing the @code{data-stack} with type cast macros -(@pxref{VM engine}). Stacks grow towards lower addresses in -Vmgen-erated interpreters. +(@pxref{VM engine}). By default, stacks grow towards lower addresses in +Vmgen-erated interpreters (@pxref{Stack growth direction}). @cindex stack prefix @cindex prefix, stack @@ -846,6 +847,7 @@ first one (just as the intuition suggest @menu * C Code Macros:: Macros recognized by Vmgen * C Code restrictions:: Vmgen makes assumptions about C code +* Stack growth direction:: is configurable per stack @end menu @c -------------------------------------------------------------------- @@ -915,7 +917,7 @@ a C preprocessor macro. @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 @cindex C code restrictions @cindex restrictions on C code @@ -975,6 +977,33 @@ macros can be implemented in several way @samp{IP} points to the next instruction, and @samp{IPTOS} is its 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 -------------------------------------------------------------------- @node Superinstructions, Store Optimization, Simple instructions, Input File Format @@ -1034,6 +1063,11 @@ accesses a stack pointer should not be u does not check these restrictions, they just result in bugs in your 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 @@ -1078,6 +1112,12 @@ 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 @@ -1177,7 +1217,7 @@ expected by Vmgen (this should not happe line in a bug report). @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 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 @@ -1196,7 +1236,7 @@ The stack item does not match any define away any stack prefix). You should either declare the type prefix you want for that stack item, or use a different type prefix -@item @code{unknown primitive} error +@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. @@ -1386,6 +1426,12 @@ type. For @samp{inst-stream}, the name plain r-value; typically it is a macro that abstracts away the 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 stack caching @cindex TOS