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| author | John McCall <rjmccall@apple.com> | 2011-06-19 09:59:33 +0000 |
|---|---|---|
| committer | John McCall <rjmccall@apple.com> | 2011-06-19 09:59:33 +0000 |
| commit | 3914a306e495358a3334a242de7d1781a62e3ba9 (patch) | |
| tree | 0db865d6538a8f21cfc5871b9f85d1f3d225558f | |
| parent | 98a48cf99d78b7969b0aedaa8b24dea5cee07fff (diff) | |
Improve the intro to the runtime-functions section.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@133386 91177308-0d34-0410-b5e6-96231b3b80d8
| -rw-r--r-- | docs/AutomaticReferenceCounting.html | 31 |
1 files changed, 27 insertions, 4 deletions
diff --git a/docs/AutomaticReferenceCounting.html b/docs/AutomaticReferenceCounting.html index 6b0e1bb9ba..cbc509f44a 100644 --- a/docs/AutomaticReferenceCounting.html +++ b/docs/AutomaticReferenceCounting.html @@ -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> <p>The runtime tracks <tt>__weak</tt> objects which holds non-null -values. It is undefined behavior to modify a <tt>__weak</tt> 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_destroyWeak"><tt>objc_destroyWeak</tt></a> +values. It is undefined behavior to direct modify a <tt>__weak</tt> +object which is being tracked by the runtime except through an +<a href="#runtime.objc_storeWeak"><tt>objc_storeWeak</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> +<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"> <h1><tt>id objc_autorelease(id value);</tt></h1> <p><i>Precondition:</i> <tt>value</tt> is null or a pointer to a |