2008-06-11 10:19:49 +04:00
|
|
|
<html>
|
|
|
|
|
<head>
|
2008-11-23 11:16:56 +03:00
|
|
|
<title>"Clang" CFE Internals Manual</title>
|
2008-06-11 10:19:49 +04:00
|
|
|
<link type="text/css" rel="stylesheet" href="../menu.css" />
|
|
|
|
|
<link type="text/css" rel="stylesheet" href="../content.css" />
|
2008-11-23 01:16:45 +03:00
|
|
|
<style type="text/css">
|
|
|
|
|
td {
|
|
|
|
|
vertical-align: top;
|
|
|
|
|
}
|
|
|
|
|
</style>
|
2008-06-11 10:19:49 +04:00
|
|
|
</head>
|
|
|
|
|
<body>
|
|
|
|
|
|
|
|
|
|
<!--#include virtual="../menu.html.incl"-->
|
|
|
|
|
|
|
|
|
|
<div id="content">
|
2007-07-31 09:42:17 +04:00
|
|
|
|
2008-11-23 11:16:56 +03:00
|
|
|
<h1>"Clang" CFE Internals Manual</h1>
|
2007-07-31 09:42:17 +04:00
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li><a href="#intro">Introduction</a></li>
|
|
|
|
|
<li><a href="#libsystem">LLVM System and Support Libraries</a></li>
|
2008-11-23 11:16:56 +03:00
|
|
|
<li><a href="#libbasic">The Clang 'Basic' Library</a>
|
2007-07-31 09:42:17 +04:00
|
|
|
<ul>
|
2008-11-23 00:41:31 +03:00
|
|
|
<li><a href="#Diagnostics">The Diagnostics Subsystem</a></li>
|
2007-07-31 09:42:17 +04:00
|
|
|
<li><a href="#SourceLocation">The SourceLocation and SourceManager
|
|
|
|
|
classes</a></li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
<li><a href="#liblex">The Lexer and Preprocessor Library</a>
|
|
|
|
|
<ul>
|
|
|
|
|
<li><a href="#Token">The Token class</a></li>
|
|
|
|
|
<li><a href="#Lexer">The Lexer class</a></li>
|
2008-03-09 05:27:26 +03:00
|
|
|
<li><a href="#TokenLexer">The TokenLexer class</a></li>
|
2007-07-31 09:42:17 +04:00
|
|
|
<li><a href="#MultipleIncludeOpt">The MultipleIncludeOpt class</a></li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
<li><a href="#libparse">The Parser Library</a>
|
|
|
|
|
<ul>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
<li><a href="#libast">The AST Library</a>
|
|
|
|
|
<ul>
|
|
|
|
|
<li><a href="#Type">The Type class and its subclasses</a></li>
|
|
|
|
|
<li><a href="#QualType">The QualType class</a></li>
|
2008-11-17 17:58:09 +03:00
|
|
|
<li><a href="#DeclarationName">Declaration names</a></li>
|
2007-10-11 03:01:43 +04:00
|
|
|
<li><a href="#CFG">The CFG class</a></li>
|
2008-11-17 00:48:07 +03:00
|
|
|
<li><a href="#Constants">Constant Folding in the Clang AST</a></li>
|
2007-07-31 09:42:17 +04:00
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h2 id="intro">Introduction</h2>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>This document describes some of the more important APIs and internal design
|
2008-11-23 11:16:56 +03:00
|
|
|
decisions made in the Clang C front-end. The purpose of this document is to
|
2007-07-31 09:42:17 +04:00
|
|
|
both capture some of this high level information and also describe some of the
|
|
|
|
|
design decisions behind it. This is meant for people interested in hacking on
|
2008-11-23 11:16:56 +03:00
|
|
|
Clang, not for end-users. The description below is categorized by
|
2007-07-31 09:42:17 +04:00
|
|
|
libraries, and does not describe any of the clients of the libraries.</p>
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h2 id="libsystem">LLVM System and Support Libraries</h2>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
2008-11-23 11:16:56 +03:00
|
|
|
<p>The LLVM libsystem library provides the basic Clang system abstraction layer,
|
2007-07-31 09:42:17 +04:00
|
|
|
which is used for file system access. The LLVM libsupport library provides many
|
|
|
|
|
underlying libraries and <a
|
|
|
|
|
href="http://llvm.org/docs/ProgrammersManual.html">data-structures</a>,
|
|
|
|
|
including command line option
|
|
|
|
|
processing and various containers.</p>
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2008-11-23 11:16:56 +03:00
|
|
|
<h2 id="libbasic">The Clang 'Basic' Library</h2>
|
2007-07-31 09:42:17 +04:00
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>This library certainly needs a better name. The 'basic' library contains a
|
|
|
|
|
number of low-level utilities for tracking and manipulating source buffers,
|
|
|
|
|
locations within the source buffers, diagnostics, tokens, target abstraction,
|
|
|
|
|
and information about the subset of the language being compiled for.</p>
|
|
|
|
|
|
|
|
|
|
<p>Part of this infrastructure is specific to C (such as the TargetInfo class),
|
|
|
|
|
other parts could be reused for other non-C-based languages (SourceLocation,
|
|
|
|
|
SourceManager, Diagnostics, FileManager). When and if there is future demand
|
|
|
|
|
we can figure out if it makes sense to introduce a new library, move the general
|
|
|
|
|
classes somewhere else, or introduce some other solution.</p>
|
|
|
|
|
|
|
|
|
|
<p>We describe the roles of these classes in order of their dependencies.</p>
|
|
|
|
|
|
2008-11-23 00:41:31 +03:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="Diagnostics">The Diagnostics Subsystem</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The Clang Diagnostics subsystem is an important part of how the compiler
|
|
|
|
|
communicates with the human. Diagnostics are the warnings and errors produced
|
|
|
|
|
when the code is incorrect or dubious. In Clang, each diagnostic produced has
|
|
|
|
|
(at the minimum) a unique ID, a <a href="#SourceLocation">SourceLocation</a> to
|
|
|
|
|
"put the caret", an English translation associated with it, and a severity (e.g.
|
|
|
|
|
<tt>WARNING</tt> or <tt>ERROR</tt>). They can also optionally include a number
|
|
|
|
|
of arguments to the dianostic (which fill in "%0"'s in the string) as well as a
|
|
|
|
|
number of source ranges that related to the diagnostic.</p>
|
|
|
|
|
|
2008-11-23 11:16:56 +03:00
|
|
|
<p>In this section, we'll be giving examples produced by the Clang command line
|
2008-11-23 00:41:31 +03:00
|
|
|
driver, but diagnostics can be <a href="#DiagnosticClient">rendered in many
|
|
|
|
|
different ways</a> depending on how the DiagnosticClient interface is
|
|
|
|
|
implemented. A representative example of a diagonstic is:</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
t.c:38:15: error: invalid operands to binary expression ('int *' and '_Complex float')
|
|
|
|
|
<font color="darkgreen">P = (P-42) + Gamma*4;</font>
|
|
|
|
|
<font color="blue">~~~~~~ ^ ~~~~~~~</font>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>In this example, you can see the English translation, the severity (error),
|
|
|
|
|
you can see the source location (the caret ("^") and file/line/column info),
|
|
|
|
|
the source ranges "~~~~", arguments to the diagnostic ("int*" and "_Complex
|
|
|
|
|
float"). You'll have to believe me that there is a unique ID backing the
|
|
|
|
|
diagnostic :).</p>
|
|
|
|
|
|
|
|
|
|
<p>Getting all of this to happen has several steps and involves many moving
|
|
|
|
|
pieces, this section describes them and talks about best practices when adding
|
|
|
|
|
a new diagnostic.</p>
|
|
|
|
|
|
|
|
|
|
<!-- ============================ -->
|
|
|
|
|
<h4>The DiagnosticKinds.def file</h4>
|
|
|
|
|
<!-- ============================ -->
|
|
|
|
|
|
|
|
|
|
<p>Diagnostics are created by adding an entry to the <tt><a
|
|
|
|
|
href="http://llvm.org/svn/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticKinds.def"
|
|
|
|
|
>DiagnosticKinds.def</a></tt> file. This file encodes the unique ID of the
|
|
|
|
|
diagnostic (as an enum, the first argument), the severity of the diagnostic
|
|
|
|
|
(second argument) and the English translation + format string.</p>
|
|
|
|
|
|
|
|
|
|
<p>There is little sanity with the naming of the unique ID's right now. Some
|
|
|
|
|
start with err_, warn_, ext_ to encode the severity into the name. Since the
|
|
|
|
|
enum is referenced in the C++ code that produces the diagnostic, it is somewhat
|
|
|
|
|
useful for it to be reasonably short.</p>
|
|
|
|
|
|
|
|
|
|
<p>The severity of the diagnostic comes from the set {<tt>NOTE</tt>,
|
|
|
|
|
<tt>WARNING</tt>, <tt>EXTENSION</tt>, <tt>EXTWARN</tt>, <tt>ERROR</tt>}. The
|
|
|
|
|
<tt>ERROR</tt> severity is used for diagnostics indicating the program is never
|
|
|
|
|
acceptable under any circumstances. When an error is emitted, the AST for the
|
|
|
|
|
input code may not be fully built. The <tt>EXTENSION</tt> and <tt>EXTWARN</tt>
|
|
|
|
|
severities are used for extensions to the language that Clang accepts. This
|
|
|
|
|
means that Clang fully understands and can represent them in the AST, but we
|
|
|
|
|
produce diagnostics to tell the user their code is non-portable. The difference
|
|
|
|
|
is that the former are ignored by default, and the later warn by default. The
|
|
|
|
|
<tt>WARNING</tt> severity is used for constructs that are valid in the currently
|
|
|
|
|
selected source language but that are dubious in some way. The <tt>NOTE</tt>
|
|
|
|
|
level is used to staple more information onto a previous diagnostics.</p>
|
|
|
|
|
|
|
|
|
|
<p>These <em>severities</em> are mapped into a smaller set (the
|
|
|
|
|
Diagnostic::Level enum, {<tt>Ignored</tt>, <tt>Note</tt>, <tt>Warning</tt>,
|
|
|
|
|
<tt>Error</tt> }) of output <em>levels</em> by the diagnostics subsystem based
|
|
|
|
|
on various configuration options. For example, if the user specifies
|
|
|
|
|
<tt>-pedantic</tt>, <tt>EXTENSION</tt> maps to <tt>Warning</tt>, if they specify
|
|
|
|
|
<tt>-pedantic-errors</tt>, it turns into <tt>Error</tt>. Clang also internally
|
|
|
|
|
supports a fully fine grained mapping mechanism that allows you to map any
|
|
|
|
|
diagnostic that doesn't have <tt>ERRROR</tt> severity to any output level that
|
|
|
|
|
you want. This is used to implement options like <tt>-Wunused_macros</tt>,
|
|
|
|
|
<tt>-Wundef</tt> etc.</p>
|
|
|
|
|
|
|
|
|
|
<!-- ================= -->
|
|
|
|
|
<h4>The Format String</h4>
|
|
|
|
|
<!-- ================= -->
|
|
|
|
|
|
|
|
|
|
<p>The format string for the diagnostic is very simple, but it has some power.
|
|
|
|
|
It takes the form of a string in English with markers that indicate where and
|
|
|
|
|
how arguments to the diagnostic are inserted and formatted. For example, here
|
|
|
|
|
are some simple format strings:</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
"binary integer literals are an extension"
|
|
|
|
|
"format string contains '\\0' within the string body"
|
|
|
|
|
"more '<b>%%</b>' conversions than data arguments"
|
2008-11-23 23:27:13 +03:00
|
|
|
"invalid operands to binary expression (<b>%0</b> and <b>%1</b>)"
|
2008-11-23 00:41:31 +03:00
|
|
|
"overloaded '<b>%0</b>' must be a <b>%select{unary|binary|unary or binary}2</b> operator"
|
|
|
|
|
" (has <b>%1</b> parameter<b>%s1</b>)"
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>These examples show some important points of format strings. You can use any
|
|
|
|
|
plain ASCII character in the diagnostic string except "%" without a problem,
|
|
|
|
|
but these are C strings, so you have to use and be aware of all the C escape
|
|
|
|
|
sequences (as in the second example). If you want to produce a "%" in the
|
|
|
|
|
output, use the "%%" escape sequence, like the third diagnostic. Finally,
|
2008-11-23 11:16:56 +03:00
|
|
|
Clang uses the "%...[digit]" sequences to specify where and how arguments to
|
2008-11-23 00:41:31 +03:00
|
|
|
the diagnostic are formatted.</p>
|
|
|
|
|
|
|
|
|
|
<p>Arguments to the diagnostic are numbered according to how they are specified
|
|
|
|
|
by the C++ code that <a href="#producingdiag">produces them</a>, and are
|
|
|
|
|
referenced by <tt>%0</tt> .. <tt>%9</tt>. If you have more than 10 arguments
|
2008-11-23 11:16:56 +03:00
|
|
|
to your diagnostic, you are doing something wrong :). Unlike printf, there
|
2008-11-23 00:41:31 +03:00
|
|
|
is no requirement that arguments to the diagnostic end up in the output in
|
|
|
|
|
the same order as they are specified, you could have a format string with
|
|
|
|
|
<tt>"%1 %0"</tt> that swaps them, for example. The text in between the
|
|
|
|
|
percent and digit are formatting instructions. If there are no instructions,
|
|
|
|
|
the argument is just turned into a string and substituted in.</p>
|
|
|
|
|
|
|
|
|
|
<p>Here are some "best practices" for writing the English format string:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li>Keep the string short. It should ideally fit in the 80 column limit of the
|
|
|
|
|
<tt>DiagnosticKinds.def</tt> file. This avoids the diagnostic wrapping when
|
|
|
|
|
printed, and forces you to think about the important point you are conveying
|
|
|
|
|
with the diagnostic.</li>
|
|
|
|
|
<li>Take advantage of location information. The user will be able to see the
|
|
|
|
|
line and location of the caret, so you don't need to tell them that the
|
|
|
|
|
problem is with the 4th argument to the function: just point to it.</li>
|
|
|
|
|
<li>Do not capitalize the diagnostic string, and do not end it with a
|
|
|
|
|
period.</li>
|
|
|
|
|
<li>If you need to quote something in the diagnostic string, use single
|
|
|
|
|
quotes.</li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
<p>Diagnostics should never take random English strings as arguments: you
|
|
|
|
|
shouldn't use <tt>"you have a problem with %0"</tt> and pass in things like
|
|
|
|
|
<tt>"your argument"</tt> or <tt>"your return value"</tt> as arguments. Doing
|
|
|
|
|
this prevents <a href="translation">translating</a> the Clang diagnostics to
|
|
|
|
|
other languages (because they'll get random English words in their otherwise
|
|
|
|
|
localized diagnostic). The exceptions to this are C/C++ language keywords
|
|
|
|
|
(e.g. auto, const, mutable, etc) and C/C++ operators (<tt>/=</tt>). Note
|
|
|
|
|
that things like "pointer" and "reference" are not keywords. On the other
|
|
|
|
|
hand, you <em>can</em> include anything that comes from the user's source code,
|
2008-11-23 11:16:56 +03:00
|
|
|
including variable names, types, labels, etc. The 'select' format can be
|
|
|
|
|
used to achieve this sort of thing in a localizable way, see below.</p>
|
2008-11-23 00:41:31 +03:00
|
|
|
|
|
|
|
|
<!-- ==================================== -->
|
|
|
|
|
<h4>Formatting a Diagnostic Argument</a></h4>
|
|
|
|
|
<!-- ==================================== -->
|
|
|
|
|
|
|
|
|
|
<p>Arguments to diagnostics are fully typed internally, and come from a couple
|
|
|
|
|
different classes: integers, types, names, and random strings. Depending on
|
|
|
|
|
the class of the argument, it can be optionally formatted in different ways.
|
|
|
|
|
This gives the DiagnosticClient information about what the argument means
|
|
|
|
|
without requiring it to use a specific presentation (consider this MVC for
|
|
|
|
|
Clang :).</p>
|
|
|
|
|
|
|
|
|
|
<p>Here are the different diagnostic argument formats currently supported by
|
|
|
|
|
Clang:</p>
|
|
|
|
|
|
|
|
|
|
<table>
|
|
|
|
|
<tr><td colspan="2"><b>"s" format</b></td></tr>
|
|
|
|
|
<tr><td>Example:</td><td><tt>"requires %1 parameter%s1"</tt></td></tr>
|
2008-11-23 11:16:56 +03:00
|
|
|
<tr><td>Class:</td><td>Integers</td></tr>
|
2008-11-23 00:41:31 +03:00
|
|
|
<tr><td>Description:</td><td>This is a simple formatter for integers that is
|
|
|
|
|
useful when producing English diagnostics. When the integer is 1, it prints
|
|
|
|
|
as nothing. When the integer is not 1, it prints as "s". This allows some
|
2008-11-23 03:28:33 +03:00
|
|
|
simple grammatical forms to be to be handled correctly, and eliminates the
|
|
|
|
|
need to use gross things like <tt>"requires %1 parameter(s)"</tt>.</td></tr>
|
2008-11-23 00:41:31 +03:00
|
|
|
|
|
|
|
|
<tr><td colspan="2"><b>"select" format</b></td></tr>
|
|
|
|
|
<tr><td>Example:</td><td><tt>"must be a %select{unary|binary|unary or binary}2
|
|
|
|
|
operator"</tt></td></tr>
|
2008-11-23 11:16:56 +03:00
|
|
|
<tr><td>Class:</td><td>Integers</td></tr>
|
2008-11-23 02:50:47 +03:00
|
|
|
<tr><td>Description:</td><td>This format specifier is used to merge multiple
|
|
|
|
|
related diagnostics together into one common one, without requiring the
|
2008-11-23 11:16:56 +03:00
|
|
|
difference to be specified as an English string argument. Instead of
|
2008-11-23 02:50:47 +03:00
|
|
|
specifying the string, the diagnostic gets an integer argument and the
|
|
|
|
|
format string selects the numbered option. In this case, the "%2" value
|
|
|
|
|
must be an integer in the range [0..2]. If it is 0, it prints 'unary', if
|
|
|
|
|
it is 1 it prints 'binary' if it is 2, it prints 'unary or binary'. This
|
|
|
|
|
allows other language translations to substitute reasonable words (or entire
|
|
|
|
|
phrases) based on the semantics of the diagnostic instead of having to do
|
|
|
|
|
things textually.</td></tr>
|
2008-11-23 00:41:31 +03:00
|
|
|
|
|
|
|
|
<tr><td colspan="2"><b>"plural" format</b></td></tr>
|
2008-11-23 01:16:45 +03:00
|
|
|
<tr><td>Example:</td><td><tt>"you have %1 %plural{1:mouse|:mice}1 connected to
|
|
|
|
|
your computer"</tt></td></tr>
|
2008-11-23 11:16:56 +03:00
|
|
|
<tr><td>Class:</td><td>Integers</td></tr>
|
2008-11-23 01:16:45 +03:00
|
|
|
<tr><td>Description:</td><td><p>This is a formatter for complex plural forms.
|
|
|
|
|
It is designed to handle even the requirements of languages with very
|
|
|
|
|
complex plural forms, as many Baltic languages have. The argument consists
|
|
|
|
|
of a series of expression/form pairs, separated by ':', where the first form
|
|
|
|
|
whose expression evaluates to true is the result of the modifier.</p>
|
|
|
|
|
<p>An expression can be empty, in which case it is always true. See the
|
|
|
|
|
example at the top. Otherwise, it is a series of one or more numeric
|
|
|
|
|
conditions, separated by ','. If any condition matches, the expression
|
|
|
|
|
matches. Each numeric condition can take one of three forms.</p>
|
|
|
|
|
<ul>
|
|
|
|
|
<li>number: A simple decimal number matches if the argument is the same
|
2008-11-23 03:28:33 +03:00
|
|
|
as the number. Example: <tt>"%plural{1:mouse|:mice}4"</tt></li>
|
2008-11-23 01:16:45 +03:00
|
|
|
<li>range: A range in square brackets matches if the argument is within
|
2008-11-23 11:16:56 +03:00
|
|
|
the range. Then range is inclusive on both ends. Example:
|
2008-11-23 03:28:33 +03:00
|
|
|
<tt>"%plural{0:none|1:one|[2,5]:some|:many}2"</tt></li>
|
|
|
|
|
<li>modulo: A modulo operator is followed by a number, and
|
|
|
|
|
equals sign and either a number or a range. The tests are the
|
|
|
|
|
same as for plain
|
2008-11-23 01:16:45 +03:00
|
|
|
numbers and ranges, but the argument is taken modulo the number first.
|
2008-11-23 03:28:33 +03:00
|
|
|
Example: <tt>"%plural{%100=0:even hundred|%100=[1,50]:lower half|:everything
|
|
|
|
|
else}1"</tt></li>
|
2008-11-23 01:16:45 +03:00
|
|
|
</ul>
|
|
|
|
|
<p>The parser is very unforgiving. A syntax error, even whitespace, will
|
|
|
|
|
abort, as will a failure to match the argument against any
|
|
|
|
|
expression.</p></td></tr>
|
2008-11-23 00:41:31 +03:00
|
|
|
|
|
|
|
|
</table>
|
|
|
|
|
|
2008-11-23 02:50:47 +03:00
|
|
|
<p>It is really easy to add format specifiers to the Clang diagnostics system,
|
2008-11-23 11:16:56 +03:00
|
|
|
but they should be discussed before they are added. If you are creating a lot
|
|
|
|
|
of repetitive diagnostics and/or have an idea for a useful formatter, please
|
|
|
|
|
bring it up on the cfe-dev mailing list.</p>
|
2008-11-23 02:50:47 +03:00
|
|
|
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- ===================================================== -->
|
|
|
|
|
<h4><a name="#producingdiag">Producing the Diagnostic</a></h4>
|
|
|
|
|
<!-- ===================================================== -->
|
|
|
|
|
|
2008-11-23 03:28:33 +03:00
|
|
|
<p>Now that you've created the diagnostic in the DiagnosticKinds.def file, you
|
2008-11-23 11:16:56 +03:00
|
|
|
need to write the code that detects the condition in question and emits the
|
|
|
|
|
new diagnostic. Various components of Clang (e.g. the preprocessor, Sema,
|
2008-11-23 03:28:33 +03:00
|
|
|
etc) provide a helper function named "Diag". It creates a diagnostic and
|
|
|
|
|
accepts the arguments, ranges, and other information that goes along with
|
|
|
|
|
it.</p>
|
2008-11-23 00:41:31 +03:00
|
|
|
|
2008-11-23 11:16:56 +03:00
|
|
|
<p>For example, the binary expression error comes from code like this:</p>
|
2008-11-23 03:28:33 +03:00
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
if (various things that are bad)
|
|
|
|
|
Diag(Loc, diag::err_typecheck_invalid_operands)
|
|
|
|
|
<< lex->getType() << rex->getType()
|
|
|
|
|
<< lex->getSourceRange() << rex->getSourceRange();
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>This shows that use of the Diag method: they take a location (a <a
|
|
|
|
|
href="#SourceLocation">SourceLocation</a> object) and a diagnostic enum value
|
|
|
|
|
(which matches the name from DiagnosticKinds.def). If the diagnostic takes
|
|
|
|
|
arguments, they are specified with the << operator: the first argument
|
|
|
|
|
becomes %0, the second becomes %1, etc. The diagnostic interface allows you to
|
2008-11-23 03:42:53 +03:00
|
|
|
specify arguments of many different types, including <tt>int</tt> and
|
|
|
|
|
<tt>unsigned</tt> for integer arguments, <tt>const char*</tt> and
|
|
|
|
|
<tt>std::string</tt> for string arguments, <tt>DeclarationName</tt> and
|
|
|
|
|
<tt>const IdentifierInfo*</tt> for names, <tt>QualType</tt> for types, etc.
|
|
|
|
|
SourceRanges are also specified with the << operator, but do not have a
|
|
|
|
|
specific ordering requirement.</p>
|
2008-11-23 03:28:33 +03:00
|
|
|
|
|
|
|
|
<p>As you can see, adding and producing a diagnostic is pretty straightforward.
|
|
|
|
|
The hard part is deciding exactly what you need to say to help the user, picking
|
|
|
|
|
a suitable wording, and providing the information needed to format it correctly.
|
2008-11-23 03:42:53 +03:00
|
|
|
The good news is that the call site that issues a diagnostic should be
|
|
|
|
|
completely independent of how the diagnostic is formatted and in what language
|
|
|
|
|
it is rendered.
|
2008-11-23 03:28:33 +03:00
|
|
|
</p>
|
2008-11-23 00:41:31 +03:00
|
|
|
|
|
|
|
|
<!-- ============================================================= -->
|
|
|
|
|
<h4><a name="DiagnosticClient">The DiagnosticClient Interface</a></h4>
|
|
|
|
|
<!-- ============================================================= -->
|
|
|
|
|
|
2008-11-23 03:28:33 +03:00
|
|
|
<p>Once code generates a diagnostic with all of the arguments and the rest of
|
|
|
|
|
the relevant information, Clang needs to know what to do with it. As previously
|
|
|
|
|
mentioned, the diagnostic machinery goes through some filtering to map a
|
|
|
|
|
severity onto a diagnostic level, then (assuming the diagnostic is not mapped to
|
|
|
|
|
"<tt>Ignore</tt>") it invokes an object that implements the DiagnosticClient
|
|
|
|
|
interface with the information.</p>
|
|
|
|
|
|
|
|
|
|
<p>It is possible to implement this interface in many different ways. For
|
|
|
|
|
example, the normal Clang DiagnosticClient (named 'TextDiagnosticPrinter') turns
|
|
|
|
|
the arguments into strings (according to the various formatting rules), prints
|
|
|
|
|
out the file/line/column information and the string, then prints out the line of
|
|
|
|
|
code, the source ranges, and the caret. However, this behavior isn't required.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>Another implementation of the DiagnosticClient interface is the
|
2008-11-23 11:16:56 +03:00
|
|
|
'TextDiagnosticBuffer' class, which is used when Clang is in -verify mode.
|
2008-11-23 03:42:53 +03:00
|
|
|
Instead of formatting and printing out the diagnostics, this implementation just
|
|
|
|
|
captures and remembers the diagnostics as they fly by. Then -verify compares
|
2008-11-23 11:16:56 +03:00
|
|
|
the list of produced diagnostics to the list of expected ones. If they disagree,
|
2008-11-23 03:42:53 +03:00
|
|
|
it prints out its own output.
|
2008-11-23 03:28:33 +03:00
|
|
|
</p>
|
|
|
|
|
|
2008-11-23 03:42:53 +03:00
|
|
|
<p>There are many other possible implementations of this interface, and this is
|
|
|
|
|
why we prefer diagnostics to pass down rich structured information in arguments.
|
|
|
|
|
For example, an HTML output might want declaration names be linkified to where
|
|
|
|
|
they come from in the source. Another example is that a GUI might let you click
|
|
|
|
|
on typedefs to expand them. This application would want to pass significantly
|
|
|
|
|
more information about types through to the GUI than a simple flat string. The
|
|
|
|
|
interface allows this to happen.</p>
|
2008-11-23 00:41:31 +03:00
|
|
|
|
|
|
|
|
<!-- ====================================================== -->
|
|
|
|
|
<h4><a name="translation">Adding Translations to Clang</a></h4>
|
|
|
|
|
<!-- ====================================================== -->
|
|
|
|
|
|
2008-11-23 03:28:33 +03:00
|
|
|
<p>Not possible yet! Diagnostic strings should be written in UTF-8, the client
|
2008-11-23 03:42:53 +03:00
|
|
|
can translate to the relevant code page if needed. Each translation completely
|
|
|
|
|
replaces the format string for the diagnostic.</p>
|
2008-11-23 00:41:31 +03:00
|
|
|
|
|
|
|
|
|
2007-07-31 09:42:17 +04:00
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="SourceLocation">The SourceLocation and SourceManager classes</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>Strangely enough, the SourceLocation class represents a location within the
|
|
|
|
|
source code of the program. Important design points include:</p>
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>sizeof(SourceLocation) must be extremely small, as these are embedded into
|
|
|
|
|
many AST nodes and are passed around often. Currently it is 32 bits.</li>
|
|
|
|
|
<li>SourceLocation must be a simple value object that can be efficiently
|
|
|
|
|
copied.</li>
|
|
|
|
|
<li>We should be able to represent a source location for any byte of any input
|
|
|
|
|
file. This includes in the middle of tokens, in whitespace, in trigraphs,
|
|
|
|
|
etc.</li>
|
|
|
|
|
<li>A SourceLocation must encode the current #include stack that was active when
|
|
|
|
|
the location was processed. For example, if the location corresponds to a
|
|
|
|
|
token, it should contain the set of #includes active when the token was
|
|
|
|
|
lexed. This allows us to print the #include stack for a diagnostic.</li>
|
|
|
|
|
<li>SourceLocation must be able to describe macro expansions, capturing both
|
|
|
|
|
the ultimate instantiation point and the source of the original character
|
|
|
|
|
data.</li>
|
|
|
|
|
</ol>
|
|
|
|
|
|
|
|
|
|
<p>In practice, the SourceLocation works together with the SourceManager class
|
|
|
|
|
to encode two pieces of information about a location: it's physical location
|
|
|
|
|
and it's virtual location. For most tokens, these will be the same. However,
|
|
|
|
|
for a macro expansion (or tokens that came from a _Pragma directive) these will
|
|
|
|
|
describe the location of the characters corresponding to the token and the
|
|
|
|
|
location where the token was used (i.e. the macro instantiation point or the
|
|
|
|
|
location of the _Pragma itself).</p>
|
|
|
|
|
|
2008-11-23 11:32:53 +03:00
|
|
|
<p>For efficiency, we only track one level of macro instantiations: if a token was
|
2007-07-31 09:42:17 +04:00
|
|
|
produced by multiple instantiations, we only track the source and ultimate
|
|
|
|
|
destination. Though we could track the intermediate instantiation points, this
|
|
|
|
|
would require extra bookkeeping and no known client would benefit substantially
|
|
|
|
|
from this.</p>
|
|
|
|
|
|
2008-11-23 11:16:56 +03:00
|
|
|
<p>The Clang front-end inherently depends on the location of a token being
|
2007-07-31 09:42:17 +04:00
|
|
|
tracked correctly. If it is ever incorrect, the front-end may get confused and
|
|
|
|
|
die. The reason for this is that the notion of the 'spelling' of a Token in
|
2008-11-23 11:16:56 +03:00
|
|
|
Clang depends on being able to find the original input characters for the token.
|
2007-07-31 09:42:17 +04:00
|
|
|
This concept maps directly to the "physical" location for the token.</p>
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h2 id="liblex">The Lexer and Preprocessor Library</h2>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The Lexer library contains several tightly-connected classes that are involved
|
|
|
|
|
with the nasty process of lexing and preprocessing C source code. The main
|
|
|
|
|
interface to this library for outside clients is the large <a
|
|
|
|
|
href="#Preprocessor">Preprocessor</a> class.
|
|
|
|
|
It contains the various pieces of state that are required to coherently read
|
|
|
|
|
tokens out of a translation unit.</p>
|
|
|
|
|
|
|
|
|
|
<p>The core interface to the Preprocessor object (once it is set up) is the
|
|
|
|
|
Preprocessor::Lex method, which returns the next <a href="#Token">Token</a> from
|
|
|
|
|
the preprocessor stream. There are two types of token providers that the
|
|
|
|
|
preprocessor is capable of reading from: a buffer lexer (provided by the <a
|
|
|
|
|
href="#Lexer">Lexer</a> class) and a buffered token stream (provided by the <a
|
2008-03-09 05:27:26 +03:00
|
|
|
href="#TokenLexer">TokenLexer</a> class).
|
2007-07-31 09:42:17 +04:00
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="Token">The Token class</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The Token class is used to represent a single lexed token. Tokens are
|
|
|
|
|
intended to be used by the lexer/preprocess and parser libraries, but are not
|
|
|
|
|
intended to live beyond them (for example, they should not live in the ASTs).<p>
|
|
|
|
|
|
|
|
|
|
<p>Tokens most often live on the stack (or some other location that is efficient
|
|
|
|
|
to access) as the parser is running, but occasionally do get buffered up. For
|
|
|
|
|
example, macro definitions are stored as a series of tokens, and the C++
|
2008-11-23 11:32:53 +03:00
|
|
|
front-end periodically needs to buffer tokens up for tentative parsing and
|
2007-07-31 09:42:17 +04:00
|
|
|
various pieces of look-ahead. As such, the size of a Token matter. On a 32-bit
|
|
|
|
|
system, sizeof(Token) is currently 16 bytes.</p>
|
|
|
|
|
|
|
|
|
|
<p>Tokens contain the following information:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li><b>A SourceLocation</b> - This indicates the location of the start of the
|
|
|
|
|
token.</li>
|
|
|
|
|
|
|
|
|
|
<li><b>A length</b> - This stores the length of the token as stored in the
|
|
|
|
|
SourceBuffer. For tokens that include them, this length includes trigraphs and
|
|
|
|
|
escaped newlines which are ignored by later phases of the compiler. By pointing
|
|
|
|
|
into the original source buffer, it is always possible to get the original
|
|
|
|
|
spelling of a token completely accurately.</li>
|
|
|
|
|
|
|
|
|
|
<li><b>IdentifierInfo</b> - If a token takes the form of an identifier, and if
|
|
|
|
|
identifier lookup was enabled when the token was lexed (e.g. the lexer was not
|
|
|
|
|
reading in 'raw' mode) this contains a pointer to the unique hash value for the
|
|
|
|
|
identifier. Because the lookup happens before keyword identification, this
|
|
|
|
|
field is set even for language keywords like 'for'.</li>
|
|
|
|
|
|
|
|
|
|
<li><b>TokenKind</b> - This indicates the kind of token as classified by the
|
|
|
|
|
lexer. This includes things like <tt>tok::starequal</tt> (for the "*="
|
|
|
|
|
operator), <tt>tok::ampamp</tt> for the "&&" token, and keyword values
|
|
|
|
|
(e.g. <tt>tok::kw_for</tt>) for identifiers that correspond to keywords. Note
|
|
|
|
|
that some tokens can be spelled multiple ways. For example, C++ supports
|
|
|
|
|
"operator keywords", where things like "and" are treated exactly like the
|
|
|
|
|
"&&" operator. In these cases, the kind value is set to
|
|
|
|
|
<tt>tok::ampamp</tt>, which is good for the parser, which doesn't have to
|
|
|
|
|
consider both forms. For something that cares about which form is used (e.g.
|
|
|
|
|
the preprocessor 'stringize' operator) the spelling indicates the original
|
|
|
|
|
form.</li>
|
|
|
|
|
|
|
|
|
|
<li><b>Flags</b> - There are currently four flags tracked by the
|
|
|
|
|
lexer/preprocessor system on a per-token basis:
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li><b>StartOfLine</b> - This was the first token that occurred on its input
|
|
|
|
|
source line.</li>
|
|
|
|
|
<li><b>LeadingSpace</b> - There was a space character either immediately
|
|
|
|
|
before the token or transitively before the token as it was expanded
|
|
|
|
|
through a macro. The definition of this flag is very closely defined by
|
|
|
|
|
the stringizing requirements of the preprocessor.</li>
|
|
|
|
|
<li><b>DisableExpand</b> - This flag is used internally to the preprocessor to
|
|
|
|
|
represent identifier tokens which have macro expansion disabled. This
|
|
|
|
|
prevents them from being considered as candidates for macro expansion ever
|
|
|
|
|
in the future.</li>
|
|
|
|
|
<li><b>NeedsCleaning</b> - This flag is set if the original spelling for the
|
|
|
|
|
token includes a trigraph or escaped newline. Since this is uncommon,
|
|
|
|
|
many pieces of code can fast-path on tokens that did not need cleaning.
|
|
|
|
|
</p>
|
|
|
|
|
</ol>
|
|
|
|
|
</li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
<p>One interesting (and somewhat unusual) aspect of tokens is that they don't
|
|
|
|
|
contain any semantic information about the lexed value. For example, if the
|
|
|
|
|
token was a pp-number token, we do not represent the value of the number that
|
|
|
|
|
was lexed (this is left for later pieces of code to decide). Additionally, the
|
|
|
|
|
lexer library has no notion of typedef names vs variable names: both are
|
|
|
|
|
returned as identifiers, and the parser is left to decide whether a specific
|
|
|
|
|
identifier is a typedef or a variable (tracking this requires scope information
|
|
|
|
|
among other things).</p>
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="Lexer">The Lexer class</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The Lexer class provides the mechanics of lexing tokens out of a source
|
|
|
|
|
buffer and deciding what they mean. The Lexer is complicated by the fact that
|
|
|
|
|
it operates on raw buffers that have not had spelling eliminated (this is a
|
|
|
|
|
necessity to get decent performance), but this is countered with careful coding
|
|
|
|
|
as well as standard performance techniques (for example, the comment handling
|
|
|
|
|
code is vectorized on X86 and PowerPC hosts).</p>
|
|
|
|
|
|
|
|
|
|
<p>The lexer has a couple of interesting modal features:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li>The lexer can operate in 'raw' mode. This mode has several features that
|
|
|
|
|
make it possible to quickly lex the file (e.g. it stops identifier lookup,
|
|
|
|
|
doesn't specially handle preprocessor tokens, handles EOF differently, etc).
|
|
|
|
|
This mode is used for lexing within an "<tt>#if 0</tt>" block, for
|
|
|
|
|
example.</li>
|
|
|
|
|
<li>The lexer can capture and return comments as tokens. This is required to
|
|
|
|
|
support the -C preprocessor mode, which passes comments through, and is
|
|
|
|
|
used by the diagnostic checker to identifier expect-error annotations.</li>
|
|
|
|
|
<li>The lexer can be in ParsingFilename mode, which happens when preprocessing
|
2007-09-16 23:25:23 +04:00
|
|
|
after reading a #include directive. This mode changes the parsing of '<'
|
2007-07-31 09:42:17 +04:00
|
|
|
to return an "angled string" instead of a bunch of tokens for each thing
|
|
|
|
|
within the filename.</li>
|
|
|
|
|
<li>When parsing a preprocessor directive (after "<tt>#</tt>") the
|
|
|
|
|
ParsingPreprocessorDirective mode is entered. This changes the parser to
|
|
|
|
|
return EOM at a newline.</li>
|
|
|
|
|
<li>The Lexer uses a LangOptions object to know whether trigraphs are enabled,
|
|
|
|
|
whether C++ or ObjC keywords are recognized, etc.</li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
<p>In addition to these modes, the lexer keeps track of a couple of other
|
|
|
|
|
features that are local to a lexed buffer, which change as the buffer is
|
|
|
|
|
lexed:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li>The Lexer uses BufferPtr to keep track of the current character being
|
|
|
|
|
lexed.</li>
|
|
|
|
|
<li>The Lexer uses IsAtStartOfLine to keep track of whether the next lexed token
|
|
|
|
|
will start with its "start of line" bit set.</li>
|
|
|
|
|
<li>The Lexer keeps track of the current #if directives that are active (which
|
|
|
|
|
can be nested).</li>
|
|
|
|
|
<li>The Lexer keeps track of an <a href="#MultipleIncludeOpt">
|
|
|
|
|
MultipleIncludeOpt</a> object, which is used to
|
|
|
|
|
detect whether the buffer uses the standard "<tt>#ifndef XX</tt> /
|
|
|
|
|
<tt>#define XX</tt>" idiom to prevent multiple inclusion. If a buffer does,
|
|
|
|
|
subsequent includes can be ignored if the XX macro is defined.</li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2008-03-09 05:27:26 +03:00
|
|
|
<h3 id="TokenLexer">The TokenLexer class</h3>
|
2007-07-31 09:42:17 +04:00
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
2008-03-09 05:27:26 +03:00
|
|
|
<p>The TokenLexer class is a token provider that returns tokens from a list
|
2007-07-31 09:42:17 +04:00
|
|
|
of tokens that came from somewhere else. It typically used for two things: 1)
|
|
|
|
|
returning tokens from a macro definition as it is being expanded 2) returning
|
|
|
|
|
tokens from an arbitrary buffer of tokens. The later use is used by _Pragma and
|
|
|
|
|
will most likely be used to handle unbounded look-ahead for the C++ parser.</p>
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="MultipleIncludeOpt">The MultipleIncludeOpt class</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The MultipleIncludeOpt class implements a really simple little state machine
|
|
|
|
|
that is used to detect the standard "<tt>#ifndef XX</tt> / <tt>#define XX</tt>"
|
|
|
|
|
idiom that people typically use to prevent multiple inclusion of headers. If a
|
|
|
|
|
buffer uses this idiom and is subsequently #include'd, the preprocessor can
|
|
|
|
|
simply check to see whether the guarding condition is defined or not. If so,
|
|
|
|
|
the preprocessor can completely ignore the include of the header.</p>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h2 id="libparse">The Parser Library</h2>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h2 id="libast">The AST Library</h2>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="Type">The Type class and its subclasses</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The Type class (and its subclasses) are an important part of the AST. Types
|
|
|
|
|
are accessed through the ASTContext class, which implicitly creates and uniques
|
|
|
|
|
them as they are needed. Types have a couple of non-obvious features: 1) they
|
|
|
|
|
do not capture type qualifiers like const or volatile (See
|
|
|
|
|
<a href="#QualType">QualType</a>), and 2) they implicitly capture typedef
|
2007-07-31 10:37:39 +04:00
|
|
|
information. Once created, types are immutable (unlike decls).</p>
|
2007-07-31 09:42:17 +04:00
|
|
|
|
|
|
|
|
<p>Typedefs in C make semantic analysis a bit more complex than it would
|
|
|
|
|
be without them. The issue is that we want to capture typedef information
|
|
|
|
|
and represent it in the AST perfectly, but the semantics of operations need to
|
|
|
|
|
"see through" typedefs. For example, consider this code:</p>
|
|
|
|
|
|
|
|
|
|
<code>
|
|
|
|
|
void func() {<br>
|
2007-10-06 05:56:01 +04:00
|
|
|
typedef int foo;<br>
|
|
|
|
|
foo X, *Y;<br>
|
|
|
|
|
typedef foo* bar;<br>
|
|
|
|
|
bar Z;<br>
|
|
|
|
|
*X; <i>// error</i><br>
|
|
|
|
|
**Y; <i>// error</i><br>
|
|
|
|
|
**Z; <i>// error</i><br>
|
2007-07-31 09:42:17 +04:00
|
|
|
}<br>
|
|
|
|
|
</code>
|
|
|
|
|
|
|
|
|
|
<p>The code above is illegal, and thus we expect there to be diagnostics emitted
|
|
|
|
|
on the annotated lines. In this example, we expect to get:</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2007-07-31 10:37:39 +04:00
|
|
|
<b>test.c:6:1: error: indirection requires pointer operand ('foo' invalid)</b>
|
2007-07-31 09:42:17 +04:00
|
|
|
*X; // error
|
|
|
|
|
<font color="blue">^~</font>
|
2007-07-31 10:37:39 +04:00
|
|
|
<b>test.c:7:1: error: indirection requires pointer operand ('foo' invalid)</b>
|
2007-07-31 09:42:17 +04:00
|
|
|
**Y; // error
|
|
|
|
|
<font color="blue">^~~</font>
|
2007-07-31 10:37:39 +04:00
|
|
|
<b>test.c:8:1: error: indirection requires pointer operand ('foo' invalid)</b>
|
|
|
|
|
**Z; // error
|
|
|
|
|
<font color="blue">^~~</font>
|
2007-07-31 09:42:17 +04:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>While this example is somewhat silly, it illustrates the point: we want to
|
|
|
|
|
retain typedef information where possible, so that we can emit errors about
|
|
|
|
|
"<tt>std::string</tt>" instead of "<tt>std::basic_string<char, std:...</tt>".
|
|
|
|
|
Doing this requires properly keeping typedef information (for example, the type
|
|
|
|
|
of "X" is "foo", not "int"), and requires properly propagating it through the
|
2007-07-31 10:37:39 +04:00
|
|
|
various operators (for example, the type of *Y is "foo", not "int"). In order
|
|
|
|
|
to retain this information, the type of these expressions is an instance of the
|
|
|
|
|
TypedefType class, which indicates that the type of these expressions is a
|
|
|
|
|
typedef for foo.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>Representing types like this is great for diagnostics, because the
|
|
|
|
|
user-specified type is always immediately available. There are two problems
|
|
|
|
|
with this: first, various semantic checks need to make judgements about the
|
2007-07-31 22:54:50 +04:00
|
|
|
<em>actual structure</em> of a type, ignoring typdefs. Second, we need an
|
|
|
|
|
efficient way to query whether two types are structurally identical to each
|
|
|
|
|
other, ignoring typedefs. The solution to both of these problems is the idea of
|
2007-07-31 10:37:39 +04:00
|
|
|
canonical types.</p>
|
|
|
|
|
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- =============== -->
|
2007-07-31 10:37:39 +04:00
|
|
|
<h4>Canonical Types</h4>
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- =============== -->
|
2007-07-31 10:37:39 +04:00
|
|
|
|
|
|
|
|
<p>Every instance of the Type class contains a canonical type pointer. For
|
|
|
|
|
simple types with no typedefs involved (e.g. "<tt>int</tt>", "<tt>int*</tt>",
|
|
|
|
|
"<tt>int**</tt>"), the type just points to itself. For types that have a
|
|
|
|
|
typedef somewhere in their structure (e.g. "<tt>foo</tt>", "<tt>foo*</tt>",
|
|
|
|
|
"<tt>foo**</tt>", "<tt>bar</tt>"), the canonical type pointer points to their
|
|
|
|
|
structurally equivalent type without any typedefs (e.g. "<tt>int</tt>",
|
|
|
|
|
"<tt>int*</tt>", "<tt>int**</tt>", and "<tt>int*</tt>" respectively).</p>
|
|
|
|
|
|
|
|
|
|
<p>This design provides a constant time operation (dereferencing the canonical
|
|
|
|
|
type pointer) that gives us access to the structure of types. For example,
|
|
|
|
|
we can trivially tell that "bar" and "foo*" are the same type by dereferencing
|
|
|
|
|
their canonical type pointers and doing a pointer comparison (they both point
|
|
|
|
|
to the single "<tt>int*</tt>" type).</p>
|
|
|
|
|
|
|
|
|
|
<p>Canonical types and typedef types bring up some complexities that must be
|
|
|
|
|
carefully managed. Specifically, the "isa/cast/dyncast" operators generally
|
|
|
|
|
shouldn't be used in code that is inspecting the AST. For example, when type
|
|
|
|
|
checking the indirection operator (unary '*' on a pointer), the type checker
|
|
|
|
|
must verify that the operand has a pointer type. It would not be correct to
|
|
|
|
|
check that with "<tt>isa<PointerType>(SubExpr->getType())</tt>",
|
|
|
|
|
because this predicate would fail if the subexpression had a typedef type.</p>
|
|
|
|
|
|
|
|
|
|
<p>The solution to this problem are a set of helper methods on Type, used to
|
|
|
|
|
check their properties. In this case, it would be correct to use
|
|
|
|
|
"<tt>SubExpr->getType()->isPointerType()</tt>" to do the check. This
|
|
|
|
|
predicate will return true if the <em>canonical type is a pointer</em>, which is
|
|
|
|
|
true any time the type is structurally a pointer type. The only hard part here
|
|
|
|
|
is remembering not to use the <tt>isa/cast/dyncast</tt> operations.</p>
|
|
|
|
|
|
|
|
|
|
<p>The second problem we face is how to get access to the pointer type once we
|
|
|
|
|
know it exists. To continue the example, the result type of the indirection
|
|
|
|
|
operator is the pointee type of the subexpression. In order to determine the
|
|
|
|
|
type, we need to get the instance of PointerType that best captures the typedef
|
|
|
|
|
information in the program. If the type of the expression is literally a
|
|
|
|
|
PointerType, we can return that, otherwise we have to dig through the
|
|
|
|
|
typedefs to find the pointer type. For example, if the subexpression had type
|
|
|
|
|
"<tt>foo*</tt>", we could return that type as the result. If the subexpression
|
|
|
|
|
had type "<tt>bar</tt>", we want to return "<tt>foo*</tt>" (note that we do
|
|
|
|
|
<em>not</em> want "<tt>int*</tt>"). In order to provide all of this, Type has
|
2007-07-31 20:50:51 +04:00
|
|
|
a getAsPointerType() method that checks whether the type is structurally a
|
2007-07-31 10:37:39 +04:00
|
|
|
PointerType and, if so, returns the best one. If not, it returns a null
|
|
|
|
|
pointer.</p>
|
|
|
|
|
|
|
|
|
|
<p>This structure is somewhat mystical, but after meditating on it, it will
|
|
|
|
|
make sense to you :).</p>
|
2007-07-31 09:42:17 +04:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="QualType">The QualType class</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The QualType class is designed as a trivial value class that is small,
|
|
|
|
|
passed by-value and is efficient to query. The idea of QualType is that it
|
|
|
|
|
stores the type qualifiers (const, volatile, restrict) separately from the types
|
|
|
|
|
themselves: QualType is conceptually a pair of "Type*" and bits for the type
|
|
|
|
|
qualifiers.</p>
|
|
|
|
|
|
|
|
|
|
<p>By storing the type qualifiers as bits in the conceptual pair, it is
|
|
|
|
|
extremely efficient to get the set of qualifiers on a QualType (just return the
|
|
|
|
|
field of the pair), add a type qualifier (which is a trivial constant-time
|
|
|
|
|
operation that sets a bit), and remove one or more type qualifiers (just return
|
|
|
|
|
a QualType with the bitfield set to empty).</p>
|
|
|
|
|
|
|
|
|
|
<p>Further, because the bits are stored outside of the type itself, we do not
|
|
|
|
|
need to create duplicates of types with different sets of qualifiers (i.e. there
|
|
|
|
|
is only a single heap allocated "int" type: "const int" and "volatile const int"
|
|
|
|
|
both point to the same heap allocated "int" type). This reduces the heap size
|
|
|
|
|
used to represent bits and also means we do not have to consider qualifiers when
|
|
|
|
|
uniquing types (<a href="#Type">Type</a> does not even contain qualifiers).</p>
|
|
|
|
|
|
|
|
|
|
<p>In practice, on hosts where it is safe, the 3 type qualifiers are stored in
|
|
|
|
|
the low bit of the pointer to the Type object. This means that QualType is
|
|
|
|
|
exactly the same size as a pointer, and this works fine on any system where
|
|
|
|
|
malloc'd objects are at least 8 byte aligned.</p>
|
2007-10-11 03:01:43 +04:00
|
|
|
|
2008-11-17 17:58:09 +03:00
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="DeclarationName">Declaration names</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The <tt>DeclarationName</tt> class represents the name of a
|
|
|
|
|
declaration in Clang. Declarations in the C family of languages can
|
2008-11-23 11:32:53 +03:00
|
|
|
take several different forms. Most declarations are named by
|
2008-11-17 17:58:09 +03:00
|
|
|
simple identifiers, e.g., "<code>f</code>" and "<code>x</code>" in
|
|
|
|
|
the function declaration <code>f(int x)</code>. In C++, declaration
|
|
|
|
|
names can also name class constructors ("<code>Class</code>"
|
|
|
|
|
in <code>struct Class { Class(); }</code>), class destructors
|
|
|
|
|
("<code>~Class</code>"), overloaded operator names ("operator+"),
|
|
|
|
|
and conversion functions ("<code>operator void const *</code>"). In
|
|
|
|
|
Objective-C, declaration names can refer to the names of Objective-C
|
|
|
|
|
methods, which involve the method name and the parameters,
|
2008-11-23 11:32:53 +03:00
|
|
|
collectively called a <i>selector</i>, e.g.,
|
2008-11-17 17:58:09 +03:00
|
|
|
"<code>setWidth:height:</code>". Since all of these kinds of
|
2008-11-23 11:32:53 +03:00
|
|
|
entities - variables, functions, Objective-C methods, C++
|
|
|
|
|
constructors, destructors, and operators - are represented as
|
2008-11-17 17:58:09 +03:00
|
|
|
subclasses of Clang's common <code>NamedDecl</code>
|
|
|
|
|
class, <code>DeclarationName</code> is designed to efficiently
|
|
|
|
|
represent any kind of name.</p>
|
|
|
|
|
|
|
|
|
|
<p>Given
|
|
|
|
|
a <code>DeclarationName</code> <code>N</code>, <code>N.getNameKind()</code>
|
2008-11-17 23:34:05 +03:00
|
|
|
will produce a value that describes what kind of name <code>N</code>
|
Extend DeclarationName to support C++ overloaded operators, e.g.,
operator+, directly, using the same mechanism as all other special
names.
Removed the "special" identifiers for the overloaded operators from
the identifier table and IdentifierInfo data structure. IdentifierInfo
is back to representing only real identifiers.
Added a new Action, ActOnOperatorFunctionIdExpr, that builds an
expression from an parsed operator-function-id (e.g., "operator
+"). ActOnIdentifierExpr used to do this job, but
operator-function-ids are no longer represented by IdentifierInfo's.
Extended Declarator to store overloaded operator names.
Sema::GetNameForDeclarator now knows how to turn the operator
name into a DeclarationName for the overloaded operator.
Except for (perhaps) consolidating the functionality of
ActOnIdentifier, ActOnOperatorFunctionIdExpr, and
ActOnConversionFunctionExpr into a common routine that builds an
appropriate DeclRefExpr by looking up a DeclarationName, all of the
work on normalizing declaration names should be complete with this
commit.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59526 91177308-0d34-0410-b5e6-96231b3b80d8
2008-11-18 17:39:36 +03:00
|
|
|
stores. There are 8 options (all of the names are inside
|
2008-11-17 17:58:09 +03:00
|
|
|
the <code>DeclarationName</code> class)</p>
|
|
|
|
|
<dl>
|
|
|
|
|
<dt>Identifier</dt>
|
|
|
|
|
<dd>The name is a simple
|
|
|
|
|
identifier. Use <code>N.getAsIdentifierInfo()</code> to retrieve the
|
|
|
|
|
corresponding <code>IdentifierInfo*</code> pointing to the actual
|
|
|
|
|
identifier. Note that C++ overloaded operators (e.g.,
|
|
|
|
|
"<code>operator+</code>") are represented as special kinds of
|
|
|
|
|
identifiers. Use <code>IdentifierInfo</code>'s <code>getOverloadedOperatorID</code>
|
|
|
|
|
function to determine whether an identifier is an overloaded
|
|
|
|
|
operator name.</dd>
|
|
|
|
|
|
|
|
|
|
<dt>ObjCZeroArgSelector, ObjCOneArgSelector,
|
|
|
|
|
ObjCMultiArgSelector</dt>
|
|
|
|
|
<dd>The name is an Objective-C selector, which can be retrieved as a
|
|
|
|
|
<code>Selector</code> instance
|
|
|
|
|
via <code>N.getObjCSelector()</code>. The three possible name
|
|
|
|
|
kinds for Objective-C reflect an optimization within
|
|
|
|
|
the <code>DeclarationName</code> class: both zero- and
|
|
|
|
|
one-argument selectors are stored as a
|
|
|
|
|
masked <code>IdentifierInfo</code> pointer, and therefore require
|
|
|
|
|
very little space, since zero- and one-argument selectors are far
|
|
|
|
|
more common than multi-argument selectors (which use a different
|
|
|
|
|
structure).</dd>
|
|
|
|
|
|
|
|
|
|
<dt>CXXConstructorName</dt>
|
|
|
|
|
<dd>The name is a C++ constructor
|
|
|
|
|
name. Use <code>N.getCXXNameType()</code> to retrieve
|
|
|
|
|
the <a href="#QualType">type</a> that this constructor is meant to
|
|
|
|
|
construct. The type is always the canonical type, since all
|
|
|
|
|
constructors for a given type have the same name.</dd>
|
|
|
|
|
|
|
|
|
|
<dt>CXXDestructorName</dt>
|
|
|
|
|
<dd>The name is a C++ destructor
|
|
|
|
|
name. Use <code>N.getCXXNameType()</code> to retrieve
|
|
|
|
|
the <a href="#QualType">type</a> whose destructor is being
|
|
|
|
|
named. This type is always a canonical type.</dd>
|
|
|
|
|
|
|
|
|
|
<dt>CXXConversionFunctionName</dt>
|
|
|
|
|
<dd>The name is a C++ conversion function. Conversion functions are
|
|
|
|
|
named according to the type they convert to, e.g., "<code>operator void
|
|
|
|
|
const *</code>". Use <code>N.getCXXNameType()</code> to retrieve
|
|
|
|
|
the type that this conversion function converts to. This type is
|
|
|
|
|
always a canonical type.</dd>
|
Extend DeclarationName to support C++ overloaded operators, e.g.,
operator+, directly, using the same mechanism as all other special
names.
Removed the "special" identifiers for the overloaded operators from
the identifier table and IdentifierInfo data structure. IdentifierInfo
is back to representing only real identifiers.
Added a new Action, ActOnOperatorFunctionIdExpr, that builds an
expression from an parsed operator-function-id (e.g., "operator
+"). ActOnIdentifierExpr used to do this job, but
operator-function-ids are no longer represented by IdentifierInfo's.
Extended Declarator to store overloaded operator names.
Sema::GetNameForDeclarator now knows how to turn the operator
name into a DeclarationName for the overloaded operator.
Except for (perhaps) consolidating the functionality of
ActOnIdentifier, ActOnOperatorFunctionIdExpr, and
ActOnConversionFunctionExpr into a common routine that builds an
appropriate DeclRefExpr by looking up a DeclarationName, all of the
work on normalizing declaration names should be complete with this
commit.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59526 91177308-0d34-0410-b5e6-96231b3b80d8
2008-11-18 17:39:36 +03:00
|
|
|
|
|
|
|
|
<dt>CXXOperatorName</dt>
|
|
|
|
|
<dd>The name is a C++ overloaded operator name. Overloaded operators
|
|
|
|
|
are named according to their spelling, e.g.,
|
|
|
|
|
"<code>operator+</code>" or "<code>operator new
|
|
|
|
|
[]</code>". Use <code>N.getCXXOverloadedOperator()</code> to
|
|
|
|
|
retrieve the overloaded operator (a value of
|
|
|
|
|
type <code>OverloadedOperatorKind</code>).</dd>
|
2008-11-17 17:58:09 +03:00
|
|
|
</dl>
|
|
|
|
|
|
|
|
|
|
<p><code>DeclarationName</code>s are cheap to create, copy, and
|
|
|
|
|
compare. They require only a single pointer's worth of storage in
|
Extend DeclarationName to support C++ overloaded operators, e.g.,
operator+, directly, using the same mechanism as all other special
names.
Removed the "special" identifiers for the overloaded operators from
the identifier table and IdentifierInfo data structure. IdentifierInfo
is back to representing only real identifiers.
Added a new Action, ActOnOperatorFunctionIdExpr, that builds an
expression from an parsed operator-function-id (e.g., "operator
+"). ActOnIdentifierExpr used to do this job, but
operator-function-ids are no longer represented by IdentifierInfo's.
Extended Declarator to store overloaded operator names.
Sema::GetNameForDeclarator now knows how to turn the operator
name into a DeclarationName for the overloaded operator.
Except for (perhaps) consolidating the functionality of
ActOnIdentifier, ActOnOperatorFunctionIdExpr, and
ActOnConversionFunctionExpr into a common routine that builds an
appropriate DeclRefExpr by looking up a DeclarationName, all of the
work on normalizing declaration names should be complete with this
commit.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59526 91177308-0d34-0410-b5e6-96231b3b80d8
2008-11-18 17:39:36 +03:00
|
|
|
the common cases (identifiers, zero-
|
2008-11-17 17:58:09 +03:00
|
|
|
and one-argument Objective-C selectors) and use dense, uniqued
|
|
|
|
|
storage for the other kinds of
|
|
|
|
|
names. Two <code>DeclarationName</code>s can be compared for
|
|
|
|
|
equality (<code>==</code>, <code>!=</code>) using a simple bitwise
|
|
|
|
|
comparison, can be ordered
|
|
|
|
|
with <code><</code>, <code>></code>, <code><=</code>,
|
|
|
|
|
and <code>>=</code> (which provide a lexicographical ordering for
|
|
|
|
|
normal identifiers but an unspecified ordering for other kinds of
|
|
|
|
|
names), and can be placed into LLVM <code>DenseMap</code>s
|
|
|
|
|
and <code>DenseSet</code>s.</p>
|
|
|
|
|
|
|
|
|
|
<p><code>DeclarationName</code> instances can be created in different
|
|
|
|
|
ways depending on what kind of name the instance will store. Normal
|
Extend DeclarationName to support C++ overloaded operators, e.g.,
operator+, directly, using the same mechanism as all other special
names.
Removed the "special" identifiers for the overloaded operators from
the identifier table and IdentifierInfo data structure. IdentifierInfo
is back to representing only real identifiers.
Added a new Action, ActOnOperatorFunctionIdExpr, that builds an
expression from an parsed operator-function-id (e.g., "operator
+"). ActOnIdentifierExpr used to do this job, but
operator-function-ids are no longer represented by IdentifierInfo's.
Extended Declarator to store overloaded operator names.
Sema::GetNameForDeclarator now knows how to turn the operator
name into a DeclarationName for the overloaded operator.
Except for (perhaps) consolidating the functionality of
ActOnIdentifier, ActOnOperatorFunctionIdExpr, and
ActOnConversionFunctionExpr into a common routine that builds an
appropriate DeclRefExpr by looking up a DeclarationName, all of the
work on normalizing declaration names should be complete with this
commit.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59526 91177308-0d34-0410-b5e6-96231b3b80d8
2008-11-18 17:39:36 +03:00
|
|
|
identifiers (<code>IdentifierInfo</code> pointers) and Objective-C selectors
|
2008-11-17 17:58:09 +03:00
|
|
|
(<code>Selector</code>) can be implicitly converted
|
|
|
|
|
to <code>DeclarationName</code>s. Names for C++ constructors,
|
Extend DeclarationName to support C++ overloaded operators, e.g.,
operator+, directly, using the same mechanism as all other special
names.
Removed the "special" identifiers for the overloaded operators from
the identifier table and IdentifierInfo data structure. IdentifierInfo
is back to representing only real identifiers.
Added a new Action, ActOnOperatorFunctionIdExpr, that builds an
expression from an parsed operator-function-id (e.g., "operator
+"). ActOnIdentifierExpr used to do this job, but
operator-function-ids are no longer represented by IdentifierInfo's.
Extended Declarator to store overloaded operator names.
Sema::GetNameForDeclarator now knows how to turn the operator
name into a DeclarationName for the overloaded operator.
Except for (perhaps) consolidating the functionality of
ActOnIdentifier, ActOnOperatorFunctionIdExpr, and
ActOnConversionFunctionExpr into a common routine that builds an
appropriate DeclRefExpr by looking up a DeclarationName, all of the
work on normalizing declaration names should be complete with this
commit.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59526 91177308-0d34-0410-b5e6-96231b3b80d8
2008-11-18 17:39:36 +03:00
|
|
|
destructors, conversion functions, and overloaded operators can be retrieved from
|
2008-11-17 17:58:09 +03:00
|
|
|
the <code>DeclarationNameTable</code>, an instance of which is
|
|
|
|
|
available as <code>ASTContext::DeclarationNames</code>. The member
|
|
|
|
|
functions <code>getCXXConstructorName</code>, <code>getCXXDestructorName</code>,
|
Extend DeclarationName to support C++ overloaded operators, e.g.,
operator+, directly, using the same mechanism as all other special
names.
Removed the "special" identifiers for the overloaded operators from
the identifier table and IdentifierInfo data structure. IdentifierInfo
is back to representing only real identifiers.
Added a new Action, ActOnOperatorFunctionIdExpr, that builds an
expression from an parsed operator-function-id (e.g., "operator
+"). ActOnIdentifierExpr used to do this job, but
operator-function-ids are no longer represented by IdentifierInfo's.
Extended Declarator to store overloaded operator names.
Sema::GetNameForDeclarator now knows how to turn the operator
name into a DeclarationName for the overloaded operator.
Except for (perhaps) consolidating the functionality of
ActOnIdentifier, ActOnOperatorFunctionIdExpr, and
ActOnConversionFunctionExpr into a common routine that builds an
appropriate DeclRefExpr by looking up a DeclarationName, all of the
work on normalizing declaration names should be complete with this
commit.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59526 91177308-0d34-0410-b5e6-96231b3b80d8
2008-11-18 17:39:36 +03:00
|
|
|
<code>getCXXConversionFunctionName</code>, and <code>getCXXOperatorName</code>, respectively,
|
|
|
|
|
return <code>DeclarationName</code> instances for the four kinds of
|
2008-11-17 17:58:09 +03:00
|
|
|
C++ special function names.</p>
|
|
|
|
|
|
2007-10-11 03:01:43 +04:00
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="CFG">The <tt>CFG</tt> class</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>The <tt>CFG</tt> class is designed to represent a source-level
|
|
|
|
|
control-flow graph for a single statement (<tt>Stmt*</tt>). Typically
|
|
|
|
|
instances of <tt>CFG</tt> are constructed for function bodies (usually
|
|
|
|
|
an instance of <tt>CompoundStmt</tt>), but can also be instantiated to
|
|
|
|
|
represent the control-flow of any class that subclasses <tt>Stmt</tt>,
|
|
|
|
|
which includes simple expressions. Control-flow graphs are especially
|
|
|
|
|
useful for performing
|
|
|
|
|
<a href="http://en.wikipedia.org/wiki/Data_flow_analysis#Sensitivities">flow-
|
|
|
|
|
or path-sensitive</a> program analyses on a given function.</p>
|
|
|
|
|
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- ============ -->
|
2007-10-11 03:01:43 +04:00
|
|
|
<h4>Basic Blocks</h4>
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- ============ -->
|
2007-10-11 03:01:43 +04:00
|
|
|
|
|
|
|
|
<p>Concretely, an instance of <tt>CFG</tt> is a collection of basic
|
|
|
|
|
blocks. Each basic block is an instance of <tt>CFGBlock</tt>, which
|
|
|
|
|
simply contains an ordered sequence of <tt>Stmt*</tt> (each referring
|
|
|
|
|
to statements in the AST). The ordering of statements within a block
|
|
|
|
|
indicates unconditional flow of control from one statement to the
|
|
|
|
|
next. <a href="#ConditionalControlFlow">Conditional control-flow</a>
|
|
|
|
|
is represented using edges between basic blocks. The statements
|
|
|
|
|
within a given <tt>CFGBlock</tt> can be traversed using
|
|
|
|
|
the <tt>CFGBlock::*iterator</tt> interface.</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
2007-10-19 02:50:52 +04:00
|
|
|
A <tt>CFG</tt> object owns the instances of <tt>CFGBlock</tt> within
|
2007-10-11 03:01:43 +04:00
|
|
|
the control-flow graph it represents. Each <tt>CFGBlock</tt> within a
|
|
|
|
|
CFG is also uniquely numbered (accessible
|
|
|
|
|
via <tt>CFGBlock::getBlockID()</tt>). Currently the number is
|
|
|
|
|
based on the ordering the blocks were created, but no assumptions
|
|
|
|
|
should be made on how <tt>CFGBlock</tt>s are numbered other than their
|
|
|
|
|
numbers are unique and that they are numbered from 0..N-1 (where N is
|
|
|
|
|
the number of basic blocks in the CFG).</p>
|
|
|
|
|
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- ===================== -->
|
2007-10-11 03:01:43 +04:00
|
|
|
<h4>Entry and Exit Blocks</h4>
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- ===================== -->
|
2007-10-11 03:01:43 +04:00
|
|
|
|
|
|
|
|
Each instance of <tt>CFG</tt> contains two special blocks:
|
|
|
|
|
an <i>entry</i> block (accessible via <tt>CFG::getEntry()</tt>), which
|
|
|
|
|
has no incoming edges, and an <i>exit</i> block (accessible
|
|
|
|
|
via <tt>CFG::getExit()</tt>), which has no outgoing edges. Neither
|
|
|
|
|
block contains any statements, and they serve the role of providing a
|
|
|
|
|
clear entrance and exit for a body of code such as a function body.
|
|
|
|
|
The presence of these empty blocks greatly simplifies the
|
|
|
|
|
implementation of many analyses built on top of CFGs.
|
|
|
|
|
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- ===================================================== -->
|
2007-10-11 03:01:43 +04:00
|
|
|
<h4 id ="ConditionalControlFlow">Conditional Control-Flow</h4>
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- ===================================================== -->
|
2007-10-11 03:01:43 +04:00
|
|
|
|
|
|
|
|
<p>Conditional control-flow (such as those induced by if-statements
|
|
|
|
|
and loops) is represented as edges between <tt>CFGBlock</tt>s.
|
|
|
|
|
Because different C language constructs can induce control-flow,
|
|
|
|
|
each <tt>CFGBlock</tt> also records an extra <tt>Stmt*</tt> that
|
|
|
|
|
represents the <i>terminator</i> of the block. A terminator is simply
|
|
|
|
|
the statement that caused the control-flow, and is used to identify
|
|
|
|
|
the nature of the conditional control-flow between blocks. For
|
|
|
|
|
example, in the case of an if-statement, the terminator refers to
|
|
|
|
|
the <tt>IfStmt</tt> object in the AST that represented the given
|
|
|
|
|
branch.</p>
|
|
|
|
|
|
|
|
|
|
<p>To illustrate, consider the following code example:</p>
|
|
|
|
|
|
|
|
|
|
<code>
|
|
|
|
|
int foo(int x) {<br>
|
|
|
|
|
x = x + 1;<br>
|
|
|
|
|
<br>
|
|
|
|
|
if (x > 2) x++;<br>
|
|
|
|
|
else {<br>
|
|
|
|
|
x += 2;<br>
|
|
|
|
|
x *= 2;<br>
|
|
|
|
|
}<br>
|
|
|
|
|
<br>
|
|
|
|
|
return x;<br>
|
|
|
|
|
}
|
|
|
|
|
</code>
|
|
|
|
|
|
|
|
|
|
<p>After invoking the parser+semantic analyzer on this code fragment,
|
|
|
|
|
the AST of the body of <tt>foo</tt> is referenced by a
|
|
|
|
|
single <tt>Stmt*</tt>. We can then construct an instance
|
|
|
|
|
of <tt>CFG</tt> representing the control-flow graph of this function
|
|
|
|
|
body by single call to a static class method:</p>
|
|
|
|
|
|
|
|
|
|
<code>
|
|
|
|
|
Stmt* FooBody = ...<br>
|
|
|
|
|
CFG* FooCFG = <b>CFG::buildCFG</b>(FooBody);
|
|
|
|
|
</code>
|
|
|
|
|
|
|
|
|
|
<p>It is the responsibility of the caller of <tt>CFG::buildCFG</tt>
|
|
|
|
|
to <tt>delete</tt> the returned <tt>CFG*</tt> when the CFG is no
|
|
|
|
|
longer needed.</p>
|
|
|
|
|
|
|
|
|
|
<p>Along with providing an interface to iterate over
|
|
|
|
|
its <tt>CFGBlock</tt>s, the <tt>CFG</tt> class also provides methods
|
|
|
|
|
that are useful for debugging and visualizing CFGs. For example, the
|
|
|
|
|
method
|
|
|
|
|
<tt>CFG::dump()</tt> dumps a pretty-printed version of the CFG to
|
|
|
|
|
standard error. This is especially useful when one is using a
|
|
|
|
|
debugger such as gdb. For example, here is the output
|
|
|
|
|
of <tt>FooCFG->dump()</tt>:</p>
|
|
|
|
|
|
|
|
|
|
<code>
|
|
|
|
|
[ B5 (ENTRY) ]<br>
|
|
|
|
|
Predecessors (0):<br>
|
|
|
|
|
Successors (1): B4<br>
|
|
|
|
|
<br>
|
|
|
|
|
[ B4 ]<br>
|
|
|
|
|
1: x = x + 1<br>
|
|
|
|
|
2: (x > 2)<br>
|
|
|
|
|
<b>T: if [B4.2]</b><br>
|
|
|
|
|
Predecessors (1): B5<br>
|
|
|
|
|
Successors (2): B3 B2<br>
|
|
|
|
|
<br>
|
|
|
|
|
[ B3 ]<br>
|
|
|
|
|
1: x++<br>
|
|
|
|
|
Predecessors (1): B4<br>
|
|
|
|
|
Successors (1): B1<br>
|
|
|
|
|
<br>
|
|
|
|
|
[ B2 ]<br>
|
|
|
|
|
1: x += 2<br>
|
|
|
|
|
2: x *= 2<br>
|
|
|
|
|
Predecessors (1): B4<br>
|
|
|
|
|
Successors (1): B1<br>
|
|
|
|
|
<br>
|
|
|
|
|
[ B1 ]<br>
|
|
|
|
|
1: return x;<br>
|
|
|
|
|
Predecessors (2): B2 B3<br>
|
|
|
|
|
Successors (1): B0<br>
|
|
|
|
|
<br>
|
|
|
|
|
[ B0 (EXIT) ]<br>
|
|
|
|
|
Predecessors (1): B1<br>
|
|
|
|
|
Successors (0):
|
|
|
|
|
</code>
|
|
|
|
|
|
|
|
|
|
<p>For each block, the pretty-printed output displays for each block
|
|
|
|
|
the number of <i>predecessor</i> blocks (blocks that have outgoing
|
|
|
|
|
control-flow to the given block) and <i>successor</i> blocks (blocks
|
|
|
|
|
that have control-flow that have incoming control-flow from the given
|
|
|
|
|
block). We can also clearly see the special entry and exit blocks at
|
|
|
|
|
the beginning and end of the pretty-printed output. For the entry
|
|
|
|
|
block (block B5), the number of predecessor blocks is 0, while for the
|
|
|
|
|
exit block (block B0) the number of successor blocks is 0.</p>
|
|
|
|
|
|
|
|
|
|
<p>The most interesting block here is B4, whose outgoing control-flow
|
|
|
|
|
represents the branching caused by the sole if-statement
|
|
|
|
|
in <tt>foo</tt>. Of particular interest is the second statement in
|
|
|
|
|
the block, <b><tt>(x > 2)</tt></b>, and the terminator, printed
|
|
|
|
|
as <b><tt>if [B4.2]</tt></b>. The second statement represents the
|
|
|
|
|
evaluation of the condition of the if-statement, which occurs before
|
|
|
|
|
the actual branching of control-flow. Within the <tt>CFGBlock</tt>
|
|
|
|
|
for B4, the <tt>Stmt*</tt> for the second statement refers to the
|
|
|
|
|
actual expression in the AST for <b><tt>(x > 2)</tt></b>. Thus
|
|
|
|
|
pointers to subclasses of <tt>Expr</tt> can appear in the list of
|
|
|
|
|
statements in a block, and not just subclasses of <tt>Stmt</tt> that
|
|
|
|
|
refer to proper C statements.</p>
|
|
|
|
|
|
|
|
|
|
<p>The terminator of block B4 is a pointer to the <tt>IfStmt</tt>
|
|
|
|
|
object in the AST. The pretty-printer outputs <b><tt>if
|
|
|
|
|
[B4.2]</tt></b> because the condition expression of the if-statement
|
|
|
|
|
has an actual place in the basic block, and thus the terminator is
|
|
|
|
|
essentially
|
|
|
|
|
<i>referring</i> to the expression that is the second statement of
|
|
|
|
|
block B4 (i.e., B4.2). In this manner, conditions for control-flow
|
|
|
|
|
(which also includes conditions for loops and switch statements) are
|
|
|
|
|
hoisted into the actual basic block.</p>
|
|
|
|
|
|
2008-11-23 00:41:31 +03:00
|
|
|
<!-- ===================== -->
|
|
|
|
|
<!-- <h4>Implicit Control-Flow</h4> -->
|
|
|
|
|
<!-- ===================== -->
|
2007-10-11 03:01:43 +04:00
|
|
|
|
|
|
|
|
<!--
|
|
|
|
|
<p>A key design principle of the <tt>CFG</tt> class was to not require
|
|
|
|
|
any transformations to the AST in order to represent control-flow.
|
|
|
|
|
Thus the <tt>CFG</tt> does not perform any "lowering" of the
|
|
|
|
|
statements in an AST: loops are not transformed into guarded gotos,
|
|
|
|
|
short-circuit operations are not converted to a set of if-statements,
|
|
|
|
|
and so on.</p>
|
|
|
|
|
-->
|
2008-06-11 10:19:49 +04:00
|
|
|
|
2008-11-17 00:48:07 +03:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
<h3 id="Constants">Constant Folding in the Clang AST</h3>
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
|
|
|
|
<p>There are several places where constants and constant folding matter a lot to
|
|
|
|
|
the Clang front-end. First, in general, we prefer the AST to retain the source
|
|
|
|
|
code as close to how the user wrote it as possible. This means that if they
|
|
|
|
|
wrote "5+4", we want to keep the addition and two constants in the AST, we don't
|
|
|
|
|
want to fold to "9". This means that constant folding in various ways turns
|
|
|
|
|
into a tree walk that needs to handle the various cases.</p>
|
|
|
|
|
|
|
|
|
|
<p>However, there are places in both C and C++ that require constants to be
|
|
|
|
|
folded. For example, the C standard defines what an "integer constant
|
|
|
|
|
expression" (i-c-e) is with very precise and specific requirements. The
|
|
|
|
|
language then requires i-c-e's in a lot of places (for example, the size of a
|
|
|
|
|
bitfield, the value for a case statement, etc). For these, we have to be able
|
|
|
|
|
to constant fold the constants, to do semantic checks (e.g. verify bitfield size
|
|
|
|
|
is non-negative and that case statements aren't duplicated). We aim for Clang
|
|
|
|
|
to be very pedantic about this, diagnosing cases when the code does not use an
|
|
|
|
|
i-c-e where one is required, but accepting the code unless running with
|
|
|
|
|
<tt>-pedantic-errors</tt>.</p>
|
|
|
|
|
|
|
|
|
|
<p>Things get a little bit more tricky when it comes to compatibility with
|
|
|
|
|
real-world source code. Specifically, GCC has historically accepted a huge
|
|
|
|
|
superset of expressions as i-c-e's, and a lot of real world code depends on this
|
|
|
|
|
unfortuate accident of history (including, e.g., the glibc system headers). GCC
|
|
|
|
|
accepts anything its "fold" optimizer is capable of reducing to an integer
|
|
|
|
|
constant, which means that the definition of what it accepts changes as its
|
|
|
|
|
optimizer does. One example is that GCC accepts things like "case X-X:" even
|
|
|
|
|
when X is a variable, because it can fold this to 0.</p>
|
|
|
|
|
|
|
|
|
|
<p>Another issue are how constants interact with the extensions we support, such
|
|
|
|
|
as __builtin_constant_p, __builtin_inf, __extension__ and many others. C99
|
|
|
|
|
obviously does not specify the semantics of any of these extensions, and the
|
|
|
|
|
definition of i-c-e does not include them. However, these extensions are often
|
|
|
|
|
used in real code, and we have to have a way to reason about them.</p>
|
|
|
|
|
|
|
|
|
|
<p>Finally, this is not just a problem for semantic analysis. The code
|
|
|
|
|
generator and other clients have to be able to fold constants (e.g. to
|
|
|
|
|
initialize global variables) and has to handle a superset of what C99 allows.
|
|
|
|
|
Further, these clients can benefit from extended information. For example, we
|
|
|
|
|
know that "foo()||1" always evaluates to true, but we can't replace the
|
|
|
|
|
expression with true because it has side effects.</p>
|
|
|
|
|
|
|
|
|
|
<!-- ======================= -->
|
|
|
|
|
<h4>Implementation Approach</h4>
|
|
|
|
|
<!-- ======================= -->
|
|
|
|
|
|
|
|
|
|
<p>After trying several different approaches, we've finally converged on a
|
|
|
|
|
design (Note, at the time of this writing, not all of this has been implemented,
|
|
|
|
|
consider this a design goal!). Our basic approach is to define a single
|
|
|
|
|
recursive method evaluation method (<tt>Expr::Evaluate</tt>), which is
|
|
|
|
|
implemented in <tt>AST/ExprConstant.cpp</tt>. Given an expression with 'scalar'
|
|
|
|
|
type (integer, fp, complex, or pointer) this method returns the following
|
|
|
|
|
information:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li>Whether the expression is an integer constant expression, a general
|
|
|
|
|
constant that was folded but has no side effects, a general constant that
|
|
|
|
|
was folded but that does have side effects, or an uncomputable/unfoldable
|
|
|
|
|
value.
|
|
|
|
|
</li>
|
|
|
|
|
<li>If the expression was computable in any way, this method returns the APValue
|
|
|
|
|
for the result of the expression.</li>
|
|
|
|
|
<li>If the expression is not evaluatable at all, this method returns
|
|
|
|
|
information on one of the problems with the expression. This includes a
|
|
|
|
|
SourceLocation for where the problem is, and a diagnostic ID that explains
|
|
|
|
|
the problem. The diagnostic should be have ERROR type.</li>
|
|
|
|
|
<li>If the expression is not an integer constant expression, this method returns
|
|
|
|
|
information on one of the problems with the expression. This includes a
|
|
|
|
|
SourceLocation for where the problem is, and a diagnostic ID that explains
|
|
|
|
|
the problem. The diagnostic should be have EXTENSION type.</li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
<p>This information gives various clients the flexibility that they want, and we
|
|
|
|
|
will eventually have some helper methods for various extensions. For example,
|
|
|
|
|
Sema should have a <tt>Sema::VerifyIntegerConstantExpression</tt> method, which
|
|
|
|
|
calls Evaluate on the expression. If the expression is not foldable, the error
|
|
|
|
|
is emitted, and it would return true. If the expression is not an i-c-e, the
|
|
|
|
|
EXTENSION diagnostic is emitted. Finally it would return false to indicate that
|
|
|
|
|
the AST is ok.</p>
|
|
|
|
|
|
|
|
|
|
<p>Other clients can use the information in other ways, for example, codegen can
|
|
|
|
|
just use expressions that are foldable in any way.</p>
|
|
|
|
|
|
|
|
|
|
<!-- ========== -->
|
|
|
|
|
<h4>Extensions</h4>
|
|
|
|
|
<!-- ========== -->
|
|
|
|
|
|
2008-11-23 11:16:56 +03:00
|
|
|
<p>This section describes how some of the various extensions Clang supports
|
2008-11-17 00:48:07 +03:00
|
|
|
interacts with constant evaluation:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li><b><tt>__extension__</tt></b>: The expression form of this extension causes
|
|
|
|
|
any evaluatable subexpression to be accepted as an integer constant
|
|
|
|
|
expression.</li>
|
|
|
|
|
<li><b><tt>__builtin_constant_p</tt></b>: This returns true (as a integer
|
|
|
|
|
constant expression) if the operand is any evaluatable constant.</li>
|
|
|
|
|
<li><b><tt>__builtin_choose_expr</tt></b>: The condition is required to be an
|
|
|
|
|
integer constant expression, but we accept any constant as an "extension of
|
|
|
|
|
an extension". This only evaluates one operand depending on which way the
|
|
|
|
|
condition evaluates.</li>
|
|
|
|
|
<li><b><tt>__builtin_classify_type</tt></b>: This always returns an integer
|
|
|
|
|
constant expression.</li>
|
|
|
|
|
<li><b><tt>__builtin_inf,nan,..</tt></b>: These are treated just like a
|
|
|
|
|
floating-point literal.</li>
|
|
|
|
|
<li><b><tt>__builtin_abs,copysign,..</tt></b>: These are constant folded as
|
|
|
|
|
general constant expressions.</li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2008-06-11 10:19:49 +04:00
|
|
|
</div>
|
|
|
|
|
</body>
|
2008-11-17 17:58:09 +03:00
|
|
|
</html>
|
