version 1.16, 2002/08/21 09:36:01
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version 1.22, 2003/02/25 22:58:49
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Line 85 Input File Format
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Line 85 Input File Format
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* Input File Grammar:: |
* Input File Grammar:: |
* Simple instructions:: |
* Simple instructions:: |
* Superinstructions:: |
* Superinstructions:: |
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* Store Optimization:: |
* Register Machines:: How to define register VM instructions |
* Register Machines:: How to define register VM instructions |
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Input File Grammar |
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* Eval escapes:: what follows \E |
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Simple instructions |
Simple instructions |
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* 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 |
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* Stack growth direction:: is configurable per stack |
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Using the generated code |
Using the generated code |
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Line 601 Most examples are taken from the example
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Line 607 Most examples are taken from the example
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* Input File Grammar:: |
* Input File Grammar:: |
* Simple instructions:: |
* Simple instructions:: |
* Superinstructions:: |
* Superinstructions:: |
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* Store Optimization:: |
* Register Machines:: How to define register VM instructions |
* Register Machines:: How to define register VM instructions |
@end menu |
@end menu |
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Line 683 Vmgen understands a few extensions beyon
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Line 690 Vmgen understands a few extensions beyon
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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}. |
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@menu |
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* Eval escapes:: what follows \E |
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@end menu |
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@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;
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Line 710 text according to the following grammar;
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Forth you need for using Vmgen: |
Forth you need for using Vmgen: |
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@example |
@example |
text: stack-decl|type-prefix-decl|stack-prefix-decl |
text: stack-decl|type-prefix-decl|stack-prefix-decl|set-flag |
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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 |
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set-flag: ('store-optimization'|'include-skipped-insts') ('on'|'off') |
@end example |
@end example |
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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:
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Line 736 are:
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@findex single |
@findex single |
@findex double |
@findex double |
@findex stack-prefix |
@findex stack-prefix |
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@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" -- ) |
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store-optimization ( -- addr ) |
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include-skipped-insts ( -- addr ) |
@end example |
@end example |
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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
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Line 805 Before we can use @code{data-stack} in t
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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 |
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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}). |
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@cindex stack prefix |
@cindex stack prefix |
@cindex prefix, stack |
@cindex prefix, stack |
Line 832 first one (just as the intuition suggest
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Line 847 first one (just as the intuition suggest
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@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 |
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* Stack growth direction:: is configurable per stack |
@end menu |
@end menu |
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@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
Line 901 a C preprocessor macro.
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Line 917 a C preprocessor macro.
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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 |
Line 961 macros can be implemented in several way
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Line 977 macros can be implemented in several way
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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. |
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@c -------------------------------------------------------------------- |
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@node Stack growth direction, , C Code restrictions, Simple instructions |
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@subsection Stack growth direction |
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@cindex stack growth direction |
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@cindex @code{stack-access-transform} |
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By default, the stacks grow towards lower addresses. You can change |
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this for a stack by setting the @code{stack-access-transform} field of |
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the stack to an xt @code{( itemnum -- index )} that performs the |
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appropriate index transformation. |
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E.g., if you want to let @code{data-stack} grow towards higher |
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addresses, with the stack pointer always pointing just beyond the |
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top-of-stack, use this right after defining @code{data-stack}: |
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@example |
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\E : sp-access-transform ( itemnum -- index ) negate 1- ; |
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\E ' sp-access-transform ' data-stack >body stack-access-transform ! |
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@end example |
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This means that @code{sp-access-transform} will be used to generate |
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indexes for accessing @code{data-stack}. The definition of |
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@code{sp-access-transform} above transforms n into -n-1, e.g, 1 into -2. |
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This will access the 0th data-stack element (top-of-stack) at sp[-1], |
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the 1st at sp[-2], etc., which is the typical way upward-growing |
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stacks are used. If you need a different transform and do not know |
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enough Forth to program it, let me know. |
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@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
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Line 1063 accesses a stack pointer should not be u
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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. |
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@cindex include-skipped-insts |
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The Vmgen flag @code{include-skipped-insts} influences superinstruction |
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code generation. Currently there is no support in the peephole |
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optimizer for both variations, so leave this flag alone for now. |
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@c ------------------------------------------------------------------- |
@c ------------------------------------------------------------------- |
@node Register Machines, , Superinstructions, Input File Format |
@node Store Optimization, Register Machines, Superinstructions, Input File Format |
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@section Store Optimization |
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@cindex store optimization |
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@cindex optimization, stack stores |
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@cindex stack stores, optimization |
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@cindex eliminating stack stores |
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This minor optimization (0.6\%--0.8\% reduction in executed instructions |
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for Gforth) puts additional requirements on the instruction descriptions |
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and is therefore disabled by default. |
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What does it do? Consider an instruction like |
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@example |
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dup ( n -- n n ) |
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@end example |
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For simplicity, also assume that we are not caching the top-of-stack in |
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a register. Now, the C code for dup first loads @code{n} from the |
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stack, and then stores it twice to the stack, one time to the address |
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where it came from; that time is unnecessary, but gcc does not optimize |
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it away, so vmgen can do it instead (if you turn on the store |
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optimization). |
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Vmgen uses the stack item's name to determine if the stack item contains |
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the same value as it did at the start. Therefore, if you use the store |
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optimization, you have to ensure that stack items that have the same |
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name on input and output also have the same value, and are not changed |
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in the C code you supply. I.e., the following code could fail if you |
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turn on the store optimization: |
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@example |
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add1 ( n -- n ) |
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n++; |
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@end example |
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Instead, you have to use different names, i.e.: |
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@example |
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add1 ( n1 -- n1 ) |
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n2=n1+1; |
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@end example |
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Similarly, the store optimization assumes that the stack pointer is only |
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changed by Vmgen-erated code. If your C code changes the stack pointer, |
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use different names in input and output stack items to avoid a (probably |
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wrong) store optimization, or turn the store optimization off for this |
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VM instruction. |
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To turn on the store optimization, write |
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@example |
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\E store-optimization on |
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@end example |
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at the start of the file. You can turn this optimization on or off |
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between any two VM instruction descriptions. For turning it off again, |
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you can use |
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@example |
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\E store-optimization off |
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@end example |
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@c ------------------------------------------------------------------- |
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@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
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Line 1203 You have used an instruction-stream pref
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side). |
side). |
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@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 1105 expected by Vmgen (this should not happe
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Line 1217 expected by Vmgen (this should not happe
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line in a bug report). |
line in a bug report). |
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@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 |
Line 1124 The stack item does not match any define
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Line 1236 The stack item does not match any define
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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 |
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@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 1314 type. For @samp{inst-stream}, the name
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Line 1426 type. For @samp{inst-stream}, the name
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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*}. |
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@cindex IMM_ARG |
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@findex IMM_ARG |
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@item IMM_ARG(access,value) |
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Define this to expland to ``(access)''. This is just a placeholder for |
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future extensions. |
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@cindex top of stack caching |
@cindex top of stack caching |
@cindex stack caching |
@cindex stack caching |
@cindex TOS |
@cindex TOS |
Line 1714 a major change, and it's ramifications a
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Line 1832 a major change, and it's ramifications a
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@chapter The future |
@chapter The future |
@cindex future ideas |
@cindex future ideas |
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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 1737 please let us know.
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Line 1855 please let us know.
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@chapter Changes |
@chapter Changes |
@cindex Changes from old versions |
@cindex Changes from old versions |
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User-visible changes between 0.5.9-20020822 and 0.5.9-20020901: |
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The store optimization is now disabled by default, but can be enabled by |
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the user (@pxref{Store Optimization}). Documentation for this |
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optimization is also new. |
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User-visible changes between 0.5.9-20010501 and 0.5.9-20020822: |
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There is now a manual (in info, HTML, Postscript, or plain text format). |
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There is the vmgen-ex2 variant of the vmgen-ex example; the new |
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variant uses a union type instead of lots of casting. |
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Both variants of the example can now be compiled with an ANSI C compiler |
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(using switch dispatch and losing quite a bit of performance); tested |
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with @command{lcc}. |
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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 1771 Also some new macros have to be defined,
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Line 1906 Also some new macros have to be defined,
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@node Contact, Copying This Manual, Changes, Top |
@node Contact, Copying This Manual, Changes, Top |
@chapter Contact |
@chapter Contact |
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To report a bug, use |
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@url{https://savannah.gnu.org/bugs/?func=addbug&group_id=2672}. |
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For discussion on Vmgen (e.g., how to use it), use the mailing list |
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@email{bug-vmgen@@mail.freesoftware.fsf.org} (use |
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@url{http://mail.gnu.org/mailman/listinfo/help-vmgen} to subscribe). |
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You can find vmgen information at |
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@url{http://www.complang.tuwien.ac.at/anton/vmgen/}. |
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@c *********************************************************** |
@c *********************************************************** |
@node Copying This Manual, Index, Contact, Top |
@node Copying This Manual, Index, Contact, Top |
@appendix Copying This Manual |
@appendix Copying This Manual |