[Patch, wwwdocs] Update 4.4 release notes for Fortran & OpenMP

[Sebastian Pop]

On Mon, Sep 15, 2008 at 5:21 PM, Gerald Pfeifer <gerald@pfeifer.com> wrote:
> Added bonus points for adding notes/examples or pointers to those which
> we have in our texi (online) documentation now, I believe?

For more bonus points ;-), here is a longer version.  Okay to commit?

Sebastian

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        the new array size and the original switch branches does not exceed
        the parameter <code>--param switch-conversion-max-branch-ratio</code>
        (default is eight).  </li>
+
+     <li><p>The <a href="http://gcc.gnu.org/wiki/Graphite">Graphite</a>
+       branch has been merged.  This merge has brought in a new
+       framework for loop optimizations based on a polyhedral
+       intermediate representation.  These optimizations apply to all
+       the languages supported by GCC.  The following new code
+       transformations are available in GCC 4.4:</p>
+
+       <ul>
+ 	<li><code>-floop-interchange</code>
+ 	    Perform loop interchange transformations on loops.  Interchanging two
+ 	    nested loops switches the inner and outer loops.  For example, given a
+ 	    loop like:
+ 	    <pre class="smallexample">
+           DO J = 1, M
+             DO I = 1, N
+               A(J, I) = A(J, I) * C
+             ENDDO
+           ENDDO
+ 	    </pre>
+ 	    <p>loop interchange will transform the loop as if the user had written:
+ 	      <pre class="smallexample">
+           DO I = 1, N
+             DO J = 1, M
+               A(J, I) = A(J, I) * C
+             ENDDO
+           ENDDO
+ 	      </pre>
+ 	    <p>which can be beneficial when <code>N</code> is larger than the caches,
+ 	      because in Fortran, the elements of an array are stored in memory
+ 	      contiguously by column, and the original loop iterates over rows,
+ 	      potentially creating at each access a cache miss.</p>
+ 	</li>
+ 	<li><code>-floop-strip-mine</code>
+ 	  Perform loop strip mining transformations on loops.  Strip mining
+ 	  splits a loop into two nested loops.  The outer loop has strides
+ 	  equal to the strip size and the inner loop has strides of the
+ 	  original loop within a strip.  For example, given a loop like:
+ 	  <pre class="smallexample">
+           DO I = 1, N
+             A(I) = A(I) + C
+           ENDDO
+ 	  </pre>
+ 	  <p>loop strip mining will transform the loop as if the user had
written:</p>
+ 	    <pre class="smallexample">
+           DO II = 1, N, 4
+             DO I = II, min (II + 4, N)
+               A(I) = A(I) + C
+             ENDDO
+           ENDDO
+ 	    </pre>
+ 	</li>
+ 	<li><code>-floop-block</code>
+ 	  Perform loop blocking transformations on loops.  Blocking strip mines
+ 	  each loop in the loop nest such that the memory accesses of the
+ 	  element loops fit inside caches.  For example, given a loop like:
+ 	  <pre class="smallexample">
+           DO I = 1, N
+             DO J = 1, M
+               A(J, I) = B(I) + C(J)
+             ENDDO
+           ENDDO
+ 	  </pre>
+ 	  <p>loop blocking will transform the loop as if the user had written:</p>
+ 	    <pre class="smallexample">
+           DO II = 1, N, 64
+             DO JJ = 1, M, 64
+               DO I = II, min (II + 64, N)
+                 DO J = JJ, min (JJ + 64, M)
+                   A(J, I) = B(I) + C(J)
+                 ENDDO
+               ENDDO
+             ENDDO
+           ENDDO
+ 	    </pre>
+ 	  <p>which can be beneficial when <code>M</code> is larger than the caches,
+ 	    because the innermost loop will iterate over a smaller amount of data
+ 	    that can be kept in the caches.</p>
+ 	</li>
+       </ul>
+     </li>
    </ul>

  <h2>New Languages and Language specific improvements</h2>