[llvm-commits] [polly] r133354 - /polly/trunk/www/documentation/memaccess.html

Sat Jun 18 10:17:16 PDT 2011

Author: raghesh
Date: Sat Jun 18 12:17:16 2011
New Revision: 133354

URL: http://llvm.org/viewvc/llvm-project?rev=133354&view=rev
Log:
www: Adding webpage to track memory access transformation


Added:
    polly/trunk/www/documentation/memaccess.html

Added: polly/trunk/www/documentation/memaccess.html
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/www/documentation/memaccess.html?rev=133354&view=auto
==============================================================================

--- polly/trunk/www/documentation/memaccess.html (added)
+++ polly/trunk/www/documentation/memaccess.html Sat Jun 18 12:17:16 2011
@@ -0,0 +1,143 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
+<html>
+<head>
+  <meta content="text/html; charset=ISO-8859-1"
+ http-equiv="Content-Type">
+  <title>memaccess.html</title>
+</head>
+<body>
+<div style="margin-left: 320px;"><small style="font-weight: bold;"><small><a><big><big><big>Support
+for
+memory access
+transformations in Polly</big></big></big></a></small></small><big><span
+ style="font-weight: bold;"></span></big><br>
+<big><span style="font-weight: bold;"></span></big><br>
+<div style="text-align: left;"><strong></strong>This project adds
+memory access transformations to Polly. In many cases<br>
+changing the memory access pattern yields to better data
+locality or removes<br>
+dependences that would otherwise block
+transformations. They may also<br>
+allow LLVM to use registers to store
+certain values.<br>
+</div>
+<br>
+An examples which uses this feature is given below<br>
+</div>
+<div style="margin-left: 320px;"><br>
+Consider the following loop
+<ul>
+  <ul>
+  </ul>
+</ul>
+<div style="margin-left: 40px;"><small style="font-style: italic;">for
+(i = 0; i < 8; i++)</small><br>
+<small style="font-style: italic;">sum += A[i];</small><br
+ style="font-style: italic;">
+</div>
+<br>
+With support for memory access transformation this loop can be executed<br>
+in parallel. It can be
+transformed to<small style="font-style: italic;"><br>
+<br>
+</small>
+<div style="margin-left: 40px;"><small style="font-style: italic;"><create
+and
+initialize an array 'tmp'
+with size 4></small><br>
+<small style="font-style: italic;">for (i = 0; i < 8; i++) {</small><br>
+<small style="font-style: italic;">tmp[i % 4] += A[i];</small><br>
+<small style="font-style: italic;">}</small><small><span
+ style="font-style: italic;"></span></small><br>
+<small><span style="font-style: italic;">sum = tmp[0] + tmp[1] + tmp[2]
++ tmp[3];</span></small><br>
+</div>
+<br>
+With the help of some optimizer (like
+PluTo) the following code can be <br>
+generated, where the outer loop is
+parallel.
+<p style="padding-left: 30px; font-style: italic;"><small>parfor (ii =
+0; ii < 4; ii++) {<br>
+    tmp[ii] = 0;<br>
+    for (i = ii * 2; i < (ii+1) * 2; i++)<br>
+        tmp[ii] += A[i];</small></p>
+<p style="padding-left: 30px; font-style: italic; font-weight: bold;"><small><span
+ style="font-weight: normal;">}</span><br style="font-weight: normal;">
+<span style="font-weight: normal;">sum = tmp[0] + tmp[1] + tmp[2] +
+tmp[3];</span><br>
+<strong></strong></small></p>
+<p><strong><span style="text-decoration: underline;">TODO<br>
+</span></strong></p>
+<p><strong><span style="text-decoration: underline;"><small>Step 1</small><br>
+</span></strong></p>
+Polly exports its polyhedral description in a JSCoP file. Define how
+memory <small><br>
+</small>layout transformations are going to be expressed in Polly and
+in
+the JSCOP file. <br>
+A simple example is given below.<br>
+<br>
+Consider the following loop.<br>
+<br>
+<div style="margin-left: 40px;"><small><span style="font-style: italic;">for
+(i
+= 0; i < 12; i++)</span><br style="font-style: italic;">
+<span style="font-style: italic;">     A[i] = 0;</span><br
+ style="font-style: italic;">
+</small></div>
+<br>
+In the JSCOP file the memory is represented as follows.<br>
+<br>
+<div style="margin-left: 40px;"><small><span style="font-style: italic;">  
+"accesses":
+[{</span></small><br style="font-style: italic;">
+<small><span style="font-style: italic;">          
+"kind":
+"write",</span></small><br style="font-style: italic;">
+<small><span style="font-style: italic;">          
+"relation":
+"{
+Stmt[i] -> </span><strong
+ style="font-style: italic; font-weight: bold;">A</strong><span
+ style="font-style: italic;"><span style="font-weight: bold;">[i]</span>
+}"</span></small><br style="font-style: italic;">
+<small><span style="font-style: italic;">    }]</span></small><br
+ style="font-style: italic;">
+</div>
+<br>
+Suppose
+we want to perform a transformation such that the following<br>
+code is generated<br>
+<br>
+<div style="margin-left: 40px;"><small><span style="font-style: italic;">for
+(i
+= 0; i < 12; i++)</span><br style="font-style: italic;">
+<span style="font-style: italic;">
+     A[0] = i;</span><br style="font-style: italic;">
+</small></div>
+<br>
+The corresponding JSCOP file represenation would be<br>
+<br>
+<div style="margin-left: 40px;"><small><span style="font-style: italic;">   
+"accesses":
+[{</span><br style="font-style: italic;">
+<span style="font-style: italic;">          
+"kind":
+"read",</span><br style="font-style: italic;">
+<span style="font-style: italic;">          
+"relation":
+"{
+Stmt[i] -> </span><strong
+ style="font-style: italic; font-weight: bold;">A</strong><span
+ style="font-style: italic;"><span style="font-weight: bold;">[0]</span>
+}"</span><br style="font-style: italic;">
+<span style="font-style: italic;">    }]</span><br
+ style="font-style: italic;">
+</small></div>
+<br>
+We need to detect this access function change.<br>
+</div>
+<span id="q_12f99e5de7fd0932_1" class="h4"></span>
+</body>
+</html>



