Add encoding for VSTR.

[oota-llvm.git] / docs / AliasAnalysis.html

diff --git a/docs/AliasAnalysis.html b/docs/AliasAnalysis.html
index d1f911e32dc53349b43246c76d003df8097d6d9d..a1726aa0c7780dff8d08c8ef2f5c046b9bf8ffb8 100644 (file)
--- a/docs/AliasAnalysis.html
+++ b/docs/AliasAnalysis.html
@@ -117,6 +117,11 @@ as the actual <tt>call</tt> or <tt>invoke</tt> instructions that performs the
 call.  The <tt>AliasAnalysis</tt> interface also exposes some helper methods
 which allow you to get mod/ref information for arbitrary instructions.</p>
 
+<p>All <tt>AliasAnalysis</tt> interfaces require that in queries involving
+multiple values, values which are not
+<a href="LangRef.html#constants">constants</a> are all defined within the
+same function.</p>
+
 </div>
 
 <!-- ======================================================================= -->
@@ -181,9 +186,13 @@ that the accesses alias.</p>
 </div>
   
 <div class="doc_text">
-The <tt>alias</tt> method is the primary interface used to determine whether or
-not two memory objects alias each other.  It takes two memory objects as input
-and returns MustAlias, MayAlias, or NoAlias as appropriate.
+<p>The <tt>alias</tt> method is the primary interface used to determine whether
+or not two memory objects alias each other.  It takes two memory objects as
+input and returns MustAlias, MayAlias, or NoAlias as appropriate.</p>
+
+<p>Like all <tt>AliasAnalysis</tt> interfaces, the <tt>alias</tt> method requires
+that either the two pointer values be defined within the same function, or at
+least one of the values is a <a href="LangRef.html#constants">constant</a>.</p>
 </div>
 
 <!-- _______________________________________________________________________ -->
@@ -192,12 +201,18 @@ and returns MustAlias, MayAlias, or NoAlias as appropriate.
 </div>
 
 <div class="doc_text">
-<p>The NoAlias response is used when the two pointers refer to distinct objects,
-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 NoAlias response may be used when there is never an immediate dependence
+between any memory reference <i>based</i> on one pointer and any memory
+reference <i>based</i> the other. The most obvious example is when the two
+pointers point to non-overlapping memory ranges. Another is when the two
+pointers are only ever used for reading memory. Another is when the memory is
+freed and reallocated between accesses through one pointer and accesses through
+the other -- in this case, there is a dependence, but it's mediated by the free
+and reallocation.</p>
+
+<p>As an exception to this is with the
+<a href="LangRef.html#noalias"><tt>noalias</tt></a> keyword; the "irrelevant"
+dependencies are ignored.</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
@@ -223,10 +238,10 @@ a location, ModRef is returned.</p>
 
 <p>The <tt>AliasAnalysis</tt> class also provides a <tt>getModRefInfo</tt>
 method for testing dependencies between function calls.  This method takes two
-call sites (CS1 &amp; CS2), returns NoModRef if the two calls refer to disjoint
-memory locations, Ref if CS1 reads memory written by CS2, Mod if CS1 writes to
-memory read or written by CS2, or ModRef if CS1 might read or write memory
-accessed by CS2.  Note that this relation is not commutative.</p>
+call sites (CS1 &amp; CS2), returns NoModRef if neither call writes to memory
+read or written by the other, Ref if CS1 reads memory written by CS2, Mod if CS1
+writes to memory read or written by CS2, or ModRef if CS1 might read or write
+memory written to by CS2.  Note that this relation is not commutative.</p>
 
 </div>