113 lines
5.3 KiB
HTML
113 lines
5.3 KiB
HTML
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<!DOCTYPE html>
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<html>
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>Compiling CPS (Guile Reference Manual)</title>
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<meta name="description" content="Compiling CPS (Guile Reference Manual)">
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<meta name="keywords" content="Compiling CPS (Guile Reference Manual)">
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<meta name="distribution" content="global">
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<meta name="Generator" content=".texi2any-real">
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<meta name="viewport" content="width=device-width,initial-scale=1">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Continuation_002dPassing-Style.html" rel="up" title="Continuation-Passing Style">
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<link href="CPS-Soup.html" rel="prev" title="CPS Soup">
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<style type="text/css">
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</style>
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsubsection-level-extent" id="Compiling-CPS">
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<div class="nav-panel">
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<p>
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Previous: <a href="CPS-Soup.html" accesskey="p" rel="prev">CPS Soup</a>, Up: <a href="Continuation_002dPassing-Style.html" accesskey="u" rel="up">Continuation-Passing Style</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsubsection" id="Compiling-CPS-1"><span>9.4.4.5 Compiling CPS<a class="copiable-link" href="#Compiling-CPS-1"> ¶</a></span></h4>
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<p>Compiling CPS in Guile has three phases: conversion, optimization, and
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code generation.
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</p>
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<p>CPS conversion is the process of taking a higher-level language and
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compiling it to CPS. Source languages can do this directly, or they can
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convert to Tree-IL (which is probably easier) and let Tree-IL convert to
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CPS later. Going through Tree-IL has the advantage of running Tree-IL
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optimization passes, like partial evaluation. Also, the compiler from
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Tree-IL to CPS handles assignment conversion, in which assigned local
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variables (in Tree-IL, locals that are <code class="code"><lexical-set></code>) are
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converted to being boxed values on the heap. See <a class="xref" href="Variables-and-the-VM.html">Variables and the VM</a>.
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</p>
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<p>After CPS conversion, Guile runs some optimization passes over the CPS.
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Most optimization in Guile is done on the CPS language. The one major
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exception is partial evaluation, which for historic reasons is done on
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Tree-IL.
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</p>
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<p>The major optimization performed on CPS is contification, in which
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functions that are always called with the same continuation are
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incorporated directly into a function’s body. This opens up space for
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more optimizations, and turns procedure calls into <code class="code">goto</code>. It can
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also make loops out of recursive function nests. Guile also does dead
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code elimination, common subexpression elimination, loop peeling and
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invariant code motion, and range and type inference.
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</p>
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<p>The rest of the optimization passes are really cleanups and
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canonicalizations. CPS spans the gap between high-level languages and
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low-level bytecodes, which allows much of the compilation process to be
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expressed as source-to-source transformations. Such is the case for
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closure conversion, in which references to variables that are free in a
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function are converted to closure references, and in which functions are
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converted to closures. There are a few more passes to ensure that the
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only primcalls left in the term are those that have a corresponding
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instruction in the virtual machine, and that their continuations expect
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the right number of values.
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</p>
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<p>Finally, the backend of the CPS compiler emits bytecode for each
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function, one by one. To do so, it determines the set of live variables
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at all points in the function. Using this liveness information, it
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allocates stack slots to each variable, such that a variable can live in
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one slot for the duration of its lifetime, without shuffling. (Of
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course, variables with disjoint lifetimes can share a slot.) Finally
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the backend emits code, typically just one VM instruction, for each
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continuation in the function.
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</p>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Previous: <a href="CPS-Soup.html">CPS Soup</a>, Up: <a href="Continuation_002dPassing-Style.html">Continuation-Passing Style</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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