[llvm-commits] [llvm] r96598 - /llvm/trunk/docs/AdvancedGetElementPtr.html
Dan Gohman
gohman at apple.com
Thu Feb 18 10:40:30 PST 2010
Author: djg
Date: Thu Feb 18 12:40:29 2010
New Revision: 96598
URL: http://llvm.org/viewvc/llvm-project?rev=96598&view=rev
Log:
Clarify that ptrtoint+inttoptr are an alternative to GEP which are
not restricted by the GEP rules.
Modified:
llvm/trunk/docs/AdvancedGetElementPtr.html
Modified: llvm/trunk/docs/AdvancedGetElementPtr.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/AdvancedGetElementPtr.html?rev=96598&r1=96597&r2=96598&view=diff
==============================================================================
--- llvm/trunk/docs/AdvancedGetElementPtr.html (original)
+++ llvm/trunk/docs/AdvancedGetElementPtr.html Thu Feb 18 12:40:29 2010
@@ -200,9 +200,9 @@
to null?</b></a>
</div>
<div class="doc_text">
- <p>You can compute an address that way, but you can't use that pointer to
- actually access the object if you do, unless the object is managed
- outside of LLVM.</p>
+ <p>You can compute an address that way, but if you use GEP to do the add,
+ you can't use that pointer to actually access the object, unless the
+ object is managed outside of LLVM.</p>
<p>The underlying integer computation is sufficiently defined; null has a
defined value -- zero -- and you can add whatever value you want to it.</p>
@@ -211,6 +211,11 @@
object with such a pointer. This includes GlobalVariables, Allocas, and
objects pointed to by noalias pointers.</p>
+ <p>If you really need this functionality, you can do the arithmetic with
+ explicit integer instructions, and use inttoptr to convert the result to
+ an address. Most of GEP's special aliasing rules do not apply to pointers
+ computed from ptrtoint, arithmetic, and inttoptr sequences.</p>
+
</div>
<!-- *********************************************************************** -->
@@ -219,9 +224,12 @@
that value to one address to compute the other address?</b></a>
</div>
<div class="doc_text">
- <p>As with arithmetic on null, You can compute an address that way, but
- you can't use that pointer to actually access the object if you do,
- unless the object is managed outside of LLVM.</p>
+ <p>As with arithmetic on null, You can use GEP to compute an address that
+ way, but you can't use that pointer to actually access the object if you
+ do, unless the object is managed outside of LLVM.</p>
+
+ <p>Also as above, ptrtoint and inttoptr provide an alternative way to do this
+ which do not have this restriction.</p>
</div>
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