From 01557ce1b165fada60195125dedd4f366be585ed Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sun, 14 Dec 2008 21:08:48 +0000
Subject: 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
---
 docs/AliasAnalysis.html | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

(limited to 'docs')

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 @@ and returns MustAlias, MayAlias, or NoAlias as appropriate.
 </div>
 
 <div class="doc_text">
-
-<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 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 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>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 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>
 
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