Hello.
Following patch documents DO loop changes which were done for upcoming GCC 7.1.
Thanks for feedback,
Martin
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>
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