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forbid rtti and exceptions

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120450 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2010-11-30 19:20:40 +00:00
parent 0e1bcdf4f7
commit 558f5d2a39
1 changed files with 23 additions and 0 deletions
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docs/CodingStandards.html
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@ -29,6 +29,7 @@
<li><a href="#ci_warningerrors">Treat Compiler Warnings Like
Errors</a></li>
<li><a href="#ci_portable_code">Write Portable Code</a></li>
<li><a href="#ci_rtti_exceptions">Do not use RTTI or Exceptions</a></li>
<li><a href="#ci_class_struct">Use of <tt>class</tt>/<tt>struct</tt> Keywords</a></li>
</ol></li>
</ol></li>
@ -404,6 +405,28 @@ libSystem.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="ci_rtti_exceptions">Do not use RTTI or Exceptions</a>
</div>
<div class="doc_text">
<p>LLVM does not use RTTI (e.g. dynamic_cast&lt;&gt;) or exceptions, in an
effort to reduce code and executable size. These two language features violate
the general C++ principle of "you only pay for what you use", causing executable
bloat even if exceptions are never used in a code base, or if RTTI is never used
for a class. Because of this, we turn them off globally in the code.
</p>
<p>
That said, LLVM does make extensive use of a hand-rolled form of RTTI that use
templates like <a href="ProgrammersManual.html#isa">isa&lt;&gt;, cast&lt;&gt;,
and dyn_cast&lt;&gt;</a>. This form of RTTI is opt-in and can be added to any
class. It is also substantially more efficient than dynamic_cast&lt;&gt;.
</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>