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Update docs to not mention gcse/loadvn and mention memdep and

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new stuff.  PR3924.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70077 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2009-04-25 21:11:37 +00:00
parent c2dbff3ba6
commit 4f4365eb4e
1 changed files with 12 additions and 24 deletions
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docs/AliasAnalysis.html
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@ -36,7 +36,7 @@
<li><a href="#using">Using alias analysis results</a>
<ul>
<li><a href="#loadvn">Using the <tt>-load-vn</tt> Pass</a></li>
<li><a href="#memdep">Using the <tt>MemoryDependenceAnalysis</tt> Pass</a></li>
<li><a href="#ast">Using the <tt>AliasSetTracker</tt> class</a></li>
<li><a href="#direct">Using the <tt>AliasAnalysis</tt> interface directly</a></li>
</ul>
@ -537,16 +537,16 @@ preference, these are...</p>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="loadvn">Using the <tt>-load-vn</tt> Pass</a>
<a name="memdep">Using the <tt>MemoryDependenceAnalysis</tt> Pass</a>
</div>
<div class="doc_text">
<p>The <tt>load-vn</tt> pass uses alias analysis to provide value numbering
information for <tt>load</tt> instructions and pointer values. If your analysis
or transformation can be modeled in a form that uses value numbering
information, you don't have to do anything special to handle load instructions:
just use the <tt>load-vn</tt> pass, which uses alias analysis.</p>
<p>The <tt>memdep</tt> pass uses alias analysis to provide high-level dependence
information about memory-using instructions. This will tell you which store
feeds into a load, for example. It uses caching and other techniques to be
efficient, and is used by Dead Store Elimination, GVN, and memcpy optimizations.
</p>
</div>
@ -710,7 +710,7 @@ aggressive local analysis that "knows" many important facts:</p>
for internal global variables that don't "have their address taken". If a
global does not have its address taken, the pass knows that no pointers alias
the global. This pass also keeps track of functions that it knows never access
memory or never read memory. This allows certain optimizations (e.g. GCSE) to
memory or never read memory. This allows certain optimizations (e.g. GVN) to
eliminate call instructions entirely.
</p>
@ -855,26 +855,14 @@ pointer.</p>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="gcseloadvn">The <tt>-load-vn</tt> &amp; <tt>-gcse</tt> passes</a>
<a name="gvn">The <tt>-gvn</tt>, <tt>-memcpyopt</tt>, and <tt>-dse</tt>
passes</a>
</div>
<div class="doc_text">
<p>The <tt>-load-vn</tt> pass uses alias analysis to "<a href="#loadvn">value
number</a>" loads and pointers values, which is used by the GCSE pass to
eliminate instructions. The <tt>-load-vn</tt> pass relies on alias information
and must-alias information. This combination of passes can make the following
transformations:</p>
<ul>
<li>Redundant load instructions are eliminated.</li>
<li>Load instructions that follow a store to the same location are replaced with
the stored value ("store forwarding").</li>
<li>Pointers values (e.g. formal arguments) that must-alias simpler expressions
(e.g. global variables or the null pointer) are replaced. Note that this
implements transformations like "virtual method resolution", turning indirect
calls into direct calls.</li>
</ul>
<p>These passes use AliasAnalysis information to reason about loads and stores.
</p>
</div>