Clarify the meaning of the NoAlias response. The plan is to refer to this from
a future version of LangRef.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61010 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/AliasAnalysis.html b/docs/AliasAnalysis.html
index 1c4ca99..1569fb8 100644
--- a/docs/AliasAnalysis.html
+++ b/docs/AliasAnalysis.html
@@ -191,16 +191,20 @@
</div>
<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>
-<p>An Alias Analysis implementation can return one of three responses:
-MustAlias, MayAlias, and NoAlias. The No and May alias results are obvious: if
-the two pointers can never equal each other, return NoAlias, if they might,
-return MayAlias.</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
+location, return MayAlias.</p>
-<p>The MustAlias response is trickier though. In LLVM, the Must Alias response
-may only be returned if the two memory objects are guaranteed to always start at
-exactly the same location. If two memory objects overlap, but do not start at
-the same location, return MayAlias.</p>
+<p>The MustAlias response may only be returned if the two memory objects are
+guaranteed to always start at exactly the same location. A MustAlias response
+implies that the pointers compare equal.</p>
</div>