From: Stephen Adams Date: Sun, 27 Aug 1995 18:52:39 +0000 (+0000) Subject: Added some information about writing faster code. At the moment it is X-Git-Tag: 20090517-FFI~6009 X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=4d35dc91ebec8a7528200571f0a95f861f65803b;p=mit-scheme.git Added some information about writing faster code. At the moment it is pretty unstructured, but at least this information is finding its way onto paper. --- diff --git a/v7/doc/user-manual/user.texinfo b/v7/doc/user-manual/user.texinfo index ce3528e84..3a300c455 100644 --- a/v7/doc/user-manual/user.texinfo +++ b/v7/doc/user-manual/user.texinfo @@ -2,7 +2,7 @@ @iftex @finalout @end iftex -@comment $Id: user.texinfo,v 1.28 1995/08/21 13:14:14 adams Exp $ +@comment $Id: user.texinfo,v 1.29 1995/08/27 18:52:39 adams Exp $ @comment %**start of header (This is for running Texinfo on a region.) @setfilename user.info @settitle MIT Scheme User's Manual @@ -196,6 +196,7 @@ Compiling Files * Compilation Procedures:: * Declarations:: +* Efficiency Tips:: Declarations @@ -204,6 +205,12 @@ Declarations * Replacement of Operators:: * Reduction of Operators:: +Efficiency Tips + +* Global variables:: +* Flonum arithmetic:: +* Miscellaneous:: + Edwin * Starting Edwin:: @@ -3342,6 +3349,7 @@ available on machines that support native-code compilation. @menu * Compilation Procedures:: * Declarations:: +* Efficiency Tips:: @end menu @node Compilation Procedures, Declarations, Compiling Files, Compiling Files @@ -3488,7 +3496,7 @@ the output file. If this argument is a directory, then the output file has its normal name but is put in that directory instead. @end deffn -@node Declarations, , Compilation Procedures, Compiling Files +@node Declarations, Efficiency Tips, Compilation Procedures, Compiling Files @section Declarations @cindex declarations @@ -3651,9 +3659,11 @@ Finally, remove the @code{((lambda () @dots{}))} to produce @end lisp -Useful tip: to see the effect of integration declarations (and of -macros) on a source file, pretty-print the @file{.bin} file like this -(be prepared for a lot of output). +@subsubheading Useful tip +@cindex integrations, seeing effects of +To see the effect of integration declarations (and of macros) on a +source file, pretty-print the @file{.bin} file like this (be prepared +for a lot of output). @lisp (sf "foo.scm") @@ -3976,6 +3986,149 @@ should not be reduced. @end itemize @end deffn +@node Efficiency Tips, , Declarations, Compiling Files +@section Efficiency Tips + +How you write your programs can have a large impact on how efficiently the +compiled program runs. The most important thing to do, after choosing +suitable data structures, is to put the following declaration near the +beginning of the file. + +@lisp +(declare (usual-integrations)) +@end lisp + +Without this declaration the compiler cannot recognize any of the common +operators and compile them efficiently. + +The @code{usual-integrations} declaration is usually sufficient to get +good quality compiled code. + +If you really need to squeeze more performance out of you code then we +hope that you find the following grab-bag of tips, hints and +explanations useful. + + +@menu +* Global variables:: +* Flonum arithmetic:: +* Miscellaneous:: +@end menu + +@node Global variables, Flonum arithmetic, Efficiency Tips, Efficiency Tips +@subsection Global variables + +@cindex variable caches +@cindex reference traps +Compiled code usually accesses variables in top level first-class +environments via @emph{variable caches}. Each compiled procedure has a +set of variable caches for the global variables that it uses. There are +three kinds of variable cache - read caches for getting the value of a +variable (referencing the variable), write caches for changing the +value, and execute caches for calling the procedure assigned to that +variable. + +Sometimes the variable caches contain special objects, reference traps, +which mean that the operation cannot proceed normally and must either be +completed by the system in order to keep the caches coherent, or must +signal an error. For example, the assignment + +@lisp +(set! newline my-better-newline) +@end lisp + +will cause the system to go to each compiled procedure that calls +@code{newline} and update its execute cache. Obviously you want to +avoid doing this in a loop. Using @code{fluid-let} to temporarily +redefine a procedure has the same inefficiency (but twice!). + +To behave correctly in all situations, each variable reference or +assignment must check for the reference traps. + +Sometimes you can prove that the variable (a) will always be bound, (b) +will always be assigned and (c) there will never be any compiled calls +to that variable. +In these cases the following declarations can speed up and reduce the +size of a program that uses global variables. + + +@deffn {declaration+} ignore-reference-traps variables +This declaration is relatively safe. If the variable is unbound or +unassigned then a variable reference will yield a reference trap object, +instead of signaling an error. The reference trap object may later find +its way into interpreted code and cause some `unrelated' variable to +mysteriously become unbound or unassigned. +@end deffn + +@deffn {declaration+} ignore-assignment-traps variables +This declaration can cause a great deal of trouble. An assignment to a +variable that ignores assignment traps can cause a great deal of +trouble. If there is a compiled procedure call anywhere in the system +to this variable, the execute caches will not be updated, causing an +inconsistency between the value used for the procedure call and the +value seen by reading the variable. This mischief is compounded by the +fact that the assignment can cause other assignments that were compiled +with checks to behave this way too. +@end deffn + +The @var{variables} are specified with expressions from the following +set language. + +@deffn {variable-specification} set name ... +All of the explicitly listed names. +@end deffn + +@deffn {variable-specification} all +@deffnx {variable-specification} none +@deffnx {variable-specification} free +@deffnx {variable-specification} bound +@deffnx {variable-specification} assigned +These expressions name sets of variables. @code{all} is the set of all +variables, @code{none} is the empty set, @code{free} is all of the +variables bound outside the current block, @code{bound} is all of the +variables bound in the current block and @code{assigned} is all of the +variables for which there exists an assignment (@code{set!}). +@end deffn + +@deffn {variable-specification} union set1 set2 +@deffnx {variable-specification} intersection set1 set2 +@deffnx {variable-specification} difference set1 set2 + +For example, to ignore reference traps on all the variables except +@var{x}, @var{y} and any variable that is assigned to + +@example +(declare (ignore-reference-traps + (difference all (union assigned (set x y))))) +@end example + +@end deffn + +@node Flonum arithmetic, Miscellaneous, Global variables, Efficiency Tips +@subsection Flonum arithmetic + + +@node Miscellaneous, , Flonum arithmetic, Efficiency Tips +@subsection Miscellaneous + +@subsubheading @code{in-package} and declarations + +Declarations from outside of an @code{in-package} form do not apply to +the body of the form. This is because the assumptions behind +declarations in the enclosing text might not apply to the body. As the +@code{usual-integrations} declaration is included in this rule, it is a +good idea to repeat the declaration e.g@:. + +@lisp + ... + (in-package some-environment + (declare (usual-integrations)) + ...) + ... +@end lisp + + + @node GNU Emacs Interface, Edwin, Compiling Files, Top @chapter GNU Emacs Interface