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To: GCC Patches <gcc-patches@gcc.gnu.org>, Jan Hubicka <hubicka@ucw.cz>
From: =?UTF-8?Q?Martin_Li=c5=a1ka?= <mliska@suse.cz>
Subject: [wwwdocs] changes.html - Fortran changes
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Date: Wed, 25 Jan 2017 14:53:00 -0000
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Hello.

Following patch documents DO loop changes which were done for upcoming GCC 7.1.

Thanks for feedback,
Martin

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Index: htdocs/gcc-7/changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-7/changes.html,v
retrieving revision 1.40
diff --unified -r1.40 changes.html
--- htdocs/gcc-7/changes.html	25 Jan 2017 10:10:56 -0000	1.40
+++ htdocs/gcc-7/changes.html	25 Jan 2017 13:09:28 -0000
@@ -362,6 +362,27 @@
     derived-type variables.
   </li>
 
+  <li>
+    DO loops with step equal to 1 or -1 generate faster code as they do not
+    have a loop preheader.  New warning <code>-Wundefined-do-loop</code>
+    warns when a loop iterates either to <code>HUGE(i)</code> (with step equal
+    to 1), or to <code>-HUGE(i)</code> (with step equal to -1). Apart from
+    that the invalid behaviour can be caught during run-time of a program with
+    <code>-fcheck=do</code>:
+    <blockquote><pre>
+program test
+  implicit none
+  integer(1) :: i
+  do i = -HUGE(i)+10, -HUGE(i)-1, -1
+    print *, i
+  end do
+end program test
+
+At line 8 of file /home/marxin/Programming/gcc/gcc/testsuite/gfortran.dg/do_check_12.f90
+Fortran runtime error: Loop iterates infinitely
+    </pre></blockquote>
+  </li>
+
 </ul>
 
 <!-- <h3 id="go">Go</h3> -->

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