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Chez Scheme: update docs for expand/optimize and run-cp0

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Mention that it runs cptypes.
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Matthew Flatt 2021-03-08 09:44:50 -07:00
parent 75ba7ff5bc
commit 5a2b6aab1e
1 changed files with 22 additions and 12 deletions
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racket/src/ChezScheme/csug/system.stex
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@ -1898,7 +1898,9 @@ an expression.
or unannotated value. or unannotated value.
\scheme{expand/optimize} expands the expression in environment \var{env} \scheme{expand/optimize} expands the expression in environment \var{env}
and passes the expression through the source optimizer \scheme{cp0} and passes the expression through the source optimizer \scheme{cp0}
(unless \scheme{cp0} is disabled via \scheme{run-cp0}). and a type-inferring optimizer \scheme{cptypes}
(unless \scheme{cp0} and \scheme{cptypes} are disabled via \scheme{run-cp0},
or unless \scheme{cptypes} is disabled via \scheme{enable-type-recovery}).
It also simplifies \scheme{letrec} and \scheme{letrec*} expressions within It also simplifies \scheme{letrec} and \scheme{letrec*} expressions within
the expression and makes their undefined checks explicit. the expression and makes their undefined checks explicit.
It returns an object representing the expanded, simplified, and optimized form. It returns an object representing the expanded, simplified, and optimized form.
@ -1906,7 +1908,7 @@ If no environment is provided, it defaults to the environment
returned by \scheme{interaction-environment}. returned by \scheme{interaction-environment}.
\scheme{expand/optimize} is primarily useful for understanding what \scheme{expand/optimize} is primarily useful for understanding what
\scheme{cp0} does and does not optimize. \scheme{cp0} plus \scheme{cptypes} does and does not optimize.
Many optimizations are performed later in the compiler, Many optimizations are performed later in the compiler,
so \scheme{expand/optimize} does not give a complete picture of so \scheme{expand/optimize} does not give a complete picture of
optimizations performed. optimizations performed.
@ -2864,9 +2866,10 @@ When the parameter is set to \scheme{#f}, the message is not printed.
\endentryheader \endentryheader
\noindent \noindent
These parameters control the operation of \scheme{cp0}, a source These parameters control the operation of \scheme{cp0} plus \scheme{cptypes}, source
optimization pass that runs after macro expansion and prior optimization passes that run after macro expansion and prior
to most other compiler passes. to most other compiler passes.
\scheme{cp0} performs procedure inlining, in which the code of one \scheme{cp0} performs procedure inlining, in which the code of one
procedure is inlined at points where it is called by other procedures, procedure is inlined at points where it is called by other procedures,
as well as copy propagation, constant folding, useless code as well as copy propagation, constant folding, useless code
@ -2874,6 +2877,13 @@ elimination, and several related optimizations.
The algorithm used by the optimizer is described in detail in the paper The algorithm used by the optimizer is described in detail in the paper
``Fast and effective procedure inlining''~\cite{waddell:sas97}. ``Fast and effective procedure inlining''~\cite{waddell:sas97}.
\scheme{cptypes} performs additional optimizations based on type
information about primitives, such as the fact that \scheme{+} always
returns a number; since it primarily removes unneecssary run-time
checks, \scheme{cptypes} primarly benefits compilation in safe mode.
The \scheme{cptypes} pass can be independently disabled through the
\scheme{enable-type-recovery} parameter.
When \scheme{cp0} is enabled, the programmer can count on the compiler When \scheme{cp0} is enabled, the programmer can count on the compiler
to fold constants, eliminate unnecessary \scheme{let} bindings, and to fold constants, eliminate unnecessary \scheme{let} bindings, and
eliminate unnecessary and inaccessible code. eliminate unnecessary and inaccessible code.
@ -2903,9 +2913,9 @@ if \scheme{e} turns out to be an unassigned variable, and count on
the entire \scheme{case} expression to be folded if \scheme{e} turns the entire \scheme{case} expression to be folded if \scheme{e} turns
out to be a constant. out to be a constant.
It is possible to see what \scheme{cp0} does with an expression It is possible to see what \scheme{cp0} plus \scheme{cptypes} does with an expression
via the procedure \index{\scheme{expand/optimize}}\scheme{expand/optimize}, via the procedure \index{\scheme{expand/optimize}}\scheme{expand/optimize},
which expands its argument and passes the result through \scheme{cp0}, as which expands its argument and passes the result through \scheme{cp0} and \scheme{cptypes}, as
illustrated by the following transcript. illustrated by the following transcript.
\schemedisplay \schemedisplay
@ -2914,9 +2924,9 @@ illustrated by the following transcript.
'(lambda (x) '(lambda (x)
(case x [(a) 1] [(b c) 2] [(d) 3] [else 4]))) (case x [(a) 1] [(b c) 2] [(d) 3] [else 4])))
(lambda (x) (lambda (x)
(if (#2%memv x '(a)) (if (#2%member x '(a))
1 1
(if (#2%memv x '(b c)) 2 (if (#2%memv x '(d)) 3 4)))) (if (#2%member x '(b c)) 2 (if (#2%member x '(d)) 3 4))))
> (expand/optimize > (expand/optimize
'(+ (let ([f (lambda (x) '(+ (let ([f (lambda (x)
(case x [(a) 1] [(b c) 2] [(d) 3] [else 4]))]) (case x [(a) 1] [(b c) 2] [(d) 3] [else 4]))])
@ -2928,7 +2938,7 @@ illustrated by the following transcript.
In the first example, the \scheme{let} expression produced by \scheme{case} In the first example, the \scheme{let} expression produced by \scheme{case}
is eliminated, and in the second, the entire expression is optimized down is eliminated, and in the second, the entire expression is optimized down
to the constant \scheme{17}. to the constant \scheme{17}.
Although not shown by \scheme{expand/optimize}, the \scheme{memv} calls Although not shown by \scheme{expand/optimize}, the \scheme{member} calls
in the output code for the first example will be replaced by calls to the in the output code for the first example will be replaced by calls to the
less expensive \scheme{eq?} by a later pass of the compiler. less expensive \scheme{eq?} by a later pass of the compiler.
Additional examples are given in the description Additional examples are given in the description
@ -2937,9 +2947,9 @@ of \scheme{expand/optimize}.
The value of \scheme{run-cp0} must be a procedure. The value of \scheme{run-cp0} must be a procedure.
Whenever the compiler is invoked on a Scheme form, the value \var{p} Whenever the compiler is invoked on a Scheme form, the value \var{p}
of this parameter is called to determine whether and how of this parameter is called to determine whether and how
\scheme{cp0} is run. \scheme{cp0} and \scheme{cptypes} are run.
\var{p} receives two arguments: \var{cp0}, the entry point into \var{p} receives two arguments: \var{cp0}, the entry point into the
\scheme{cp0}, and \var{x}, the form being compiled. \scheme{cp0} plus \scheme{cptypes} passes, and \var{x}, the form being compiled.
The default value of \scheme{run-cp0} simply invokes \var{cp0} on The default value of \scheme{run-cp0} simply invokes \var{cp0} on
\var{x}, then \var{cp0} again on the result. \var{x}, then \var{cp0} again on the result.
The second run is useful in some cases because the first run The second run is useful in some cases because the first run