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- <title>A Few Coding Standards</title>
+ <title>LLVM Coding Standards</title>
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<div class="doc_title">
- A Few Coding Standards
+ LLVM Coding Standards
</div>
<ol>
<div class="doc_code">
<pre>
//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
-//
+//
// The LLVM Compiler Infrastructure
//
-// This file was developed by <whoever started the file> and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
//===----------------------------------------------------------------------===//
//
// This file contains the declaration of the Instruction class, which is the
</pre>
</div>
-<p>A few things to note about this particular format: The 'developed by' line
-should be the name of the person or organization who initially contributed the
-file. The "<tt>-*- C++
+<p>A few things to note about this particular format: The "<tt>-*- C++
-*-</tt>" string on the first line is there to tell Emacs that the source file
is a C++ file, not a C file (Emacs assumes .h files are C files by default).
Note that this tag is not necessary in .cpp files. The name of the file is also
file. This is important when printing out code and flipping though lots of
pages.</p>
-<p>The next section in the file is a concise note that defines the license that
-the file is released under. This makes it perfectly clear what terms the source
-code can be distributed under.</p>
+<p>The next section in the file is a concise note that defines the license
+that the file is released under. This makes it perfectly clear what terms the
+source code can be distributed under and should not be modified in any way.</p>
<p>The main body of the description does not have to be very long in most cases.
Here it's only two lines. If an algorithm is being implemented or something
<li>System <tt>#includes</tt></li>
</ol>
-<p>... and each catagory should be sorted by name.</p>
+<p>... and each category should be sorted by name.</p>
<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
which implement an interface defined by a .h file. This <tt>#include</tt>
like to print out code and look at your code in an xterm without resizing
it.</p>
+<p>The longer answer is that there must be some limit to the width of the code
+in order to reasonably allow developers to have multiple files side-by-side in
+windows on a modest display. If you are going to pick a width limit, it is
+somewhat arbitrary but you might as well pick something standard. Going with
+90 columns (for example) instead of 80 columns wouldn't add any significant
+value and would be detrimental to printing out code. Also many other projects
+have standardized on 80 columns, so some people have already configured their
+editors for it (vs something else, like 90 columns).</p>
+
+<p>This is one of many contentious issues in coding standards, but is not up
+for debate.</p>
+
</div>
<!-- _______________________________________________________________________ -->
put more pressure on the VM system on low-memory machines.</li>
</ol>
-<div align="center">
+<p>Note that using the other stream headers (<tt><sstream></tt> for
+example) is allowed normally, it is just <tt><iostream></tt> that is
+causing problems.</p>
+
<table>
<tbody>
<tr>
<td align="left"><pre>void print(std::ostream &Out);
// ...
print(std::cerr);</pre></td>
- <td align="left"><pre>void print(llvm::OStream Out);<sup>1</sup>
-// ...
-print(llvm::cerr);</pre>
+ <td align="left"><tt>void print(llvm::OStream Out);<sup><a href="#sn_1">1</a></sup><br>
+// ...<br>
+print(llvm::cerr);</tt>
+ </td>
+ </tr>
+ </tbody>
+</table>
-</td> </tbody> </table>
-</div>
+<p><b>Notes:</b></p>
-<div class="doc_text">
-<p><sup>1</sup><tt>llvm::OStream</tt> is a light-weight class so it should never
-be passed by reference. This is important because in some configurations,
-<tt>DOUT</tt> is an rvalue.</p>
+<div class="doc_notes">
+<ol>
+<li><a name="sn_1"><tt>llvm::OStream</tt></a> is a light-weight class so it
+ should never be passed by reference. This is important because in some
+ configurations, <tt>DOUT</tt> is an rvalue.</li>
+</ol>
</div>
</div>
<p>You get the idea...</p>
+<p>Please be aware when adding assert statements that not all compilers are aware of
+the semantics of the assert. In some places, asserts are used to indicate a piece of
+code that should not be reached. These are typically of the form:</p>
+
+<div class="doc_code">
+<pre>
+assert(0 && "Some helpful error message");
+</pre>
+</div>
+
+<p>When used in a function that returns a value, they should be followed with a return
+statement and a comment indicating that this line is never reached. This will prevent
+a compiler which is unable to deduce that the assert statement never returns from
+generating a warning.</p>
+
+<div class="doc_code">
+<pre>
+assert(0 && "Some helpful error message");
+// Not reached
+return 0;
+</pre>
+</div>
+
</div>
<!-- _______________________________________________________________________ -->
"<tt>using namespace std;</tt>".</p>
<p> In header files, adding a '<tt>using namespace XXX</tt>' directive pollutes
-the namespace of any source file that includes the header. This is clearly a
-bad thing.</p>
+the namespace of any source file that <tt>#include</tt>s the header. This is
+clearly a bad thing.</p>
<p>In implementation files (e.g. .cpp files), the rule is more of a stylistic
rule, but is still important. Basically, using explicit namespace prefixes
<p>If a class is defined in a header file and has a v-table (either it has
virtual methods or it derives from classes with virtual methods), it must
always have at least one out-of-line virtual method in the class. Without
-this, the compiler will copy the vtable and RTTI into every .o file that
-#includes the header, bloating .o file sizes and increasing link times.
-</p>
+this, the compiler will copy the vtable and RTTI into every <tt>.o</tt> file
+that <tt>#include</tt>s the header, bloating <tt>.o</tt> file sizes and
+increasing link times.</p>
</div>
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
projects / oota-llvm.git / blobdiff