<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>
<div class="doc_text">
<p>The NoAlias response is used when the two pointers refer to distinct objects,
-even regardless of whether the pointers compare equal. For example, freed
-pointers don't alias any pointers that were allocated afterwards. As a
-degenerate case, pointers returned by malloc(0) have no bytes for an object,
-and are considered NoAlias even when malloc returns the same pointer. The same
-rule applies to NULL pointers.</p>
+regardless of whether the pointers compare equal. For example, freed pointers
+don't alias any pointers that were allocated afterwards. As a degenerate case,
+pointers returned by malloc(0) have no bytes for an object, and are considered
+NoAlias even when malloc returns the same pointer. The same rule applies to
+NULL pointers.</p>
<p>The MayAlias response is used whenever the two pointers might refer to the
same object. If the two memory objects overlap, but do not start at the same
<!-- ======================================================================= -->
<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>
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>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
- <a name="gcseloadvn">The <tt>-load-vn</tt> & <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>
projects / oota-llvm.git / blobdiff