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Improve the intro to the runtime-functions section. 

llvm-svn: 133386
This commit is contained in:
John McCall 2011-06-19 09:59:33 +00:00
parent 092701c326
commit fb414bc66d
1 changed files with 27 additions and 4 deletions
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31
clang/docs/AutomaticReferenceCounting.html
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@ -1502,12 +1502,35 @@ an object, except that <tt>__weak</tt> objects must always be
appropriately aligned for an object of type <tt>id</tt>.</p> appropriately aligned for an object of type <tt>id</tt>.</p>
<p>The runtime tracks <tt>__weak</tt> objects which holds non-null <p>The runtime tracks <tt>__weak</tt> objects which holds non-null
values. It is undefined behavior to modify a <tt>__weak</tt> object values. It is undefined behavior to direct modify a <tt>__weak</tt>
which is being tracked by the runtime except through an object which is being tracked by the runtime except through an
<a href="#runtime.objc_storeWeak"><tt>objc_storeWeak</tt></a> or <a href="#runtime.objc_storeWeak"><tt>objc_storeWeak</tt></a>,
<a href="#runtime.objc_destroyWeak"><tt>objc_destroyWeak</tt></a> <a href="#runtime.objc_destroyWeak"><tt>objc_destroyWeak</tt></a>,
or <a href="#runtime.objc_moveWeak"><tt>objc_moveWeak</tt></a>
call.</p> call.</p>
<p>The runtime must provide a number of new entrypoints which the
compiler may emit, which are described in the remainder of this
section.</p>
<div class="rationale"><p>Rationale: Several of these functions are
semantically equivalent to a message send; we emit calls to C
functions instead because:</p>
<ul>
<li>the machine code to do so is significantly smaller,</li>
<li>it is much easier to recognize the C functions in the ARC optimizer, and</li>
<li>a sufficient sophisticated runtime may be able to avoid the
message send in common cases.</li>
</ul>
<p>Several other of these functions are <q>fused</q> operations which
can be described entirely in terms of other operations. We use the
fused operations primarily as a code-size optimization, although in
some cases there is also a real potential for avoiding redundant
operations in the runtime.</p>
</div>
<div id="runtime.objc_autorelease"> <div id="runtime.objc_autorelease">
<h1><tt>id objc_autorelease(id value);</tt></h1> <h1><tt>id objc_autorelease(id value);</tt></h1>
<p><i>Precondition:</i> <tt>value</tt> is null or a pointer to a <p><i>Precondition:</i> <tt>value</tt> is null or a pointer to a