https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107424
--- Comment #15 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Tobias Burnus <bur...@gcc.gnu.org>: https://gcc.gnu.org/g:85da0b40538fb0d17d89de1e7905984668e3dfef commit r14-2634-g85da0b40538fb0d17d89de1e7905984668e3dfef Author: Tobias Burnus <tob...@codesourcery.com> Date: Wed Jul 19 10:18:49 2023 +0200 OpenMP/Fortran: Non-rectangular loops with constant steps other than 1 or -1 [PR107424] Before this commit, gfortran produced with OpenMP for 'do i = 1,10,2' the code for (count.0 = 0; count.0 < 5; count.0 = count.0 + 1) i = count.0 * 2 + 1; While such an inner loop can be collapsed, a non-rectangular could not. With this commit and for all constant loop steps, a simple loop such as 'for (i = 1; i <= 10; i = i + 2)' is created. (Before only for the constant steps of 1 and -1.) The constant step permits to know the direction (increasing/decreasing) that is required for the loop condition. The new code is only valid if one assumes no overflow of the loop variable. However, the Fortran standard can be read that this must be ensured by the user. Namely, the Fortran standard requires (F2023, 10.1.5.2.4): "The execution of any numeric operation whose result is not defined by the arithmetic used by the processor is prohibited." And, for DO loops, F2023's "11.1.7.4.3 The execution cycle" has the following: The number of loop iterations handled by an iteration count, which would permit code like 'do i = huge(i)-5, huge(i),4'. However, in step (3), this count is not only decremented by one but also: "... The DO variable, if any, is incremented by the value of the incrementation parameter m3." And for the example above, 'i' would be 'huge(i)+3' in the last execution cycle, which exceeds the largest model number and should render the example as invalid. PR fortran/107424 gcc/fortran/ChangeLog: * trans-openmp.cc (gfc_nonrect_loop_expr): Accept all constant loop steps. (gfc_trans_omp_do): Likewise; use sign to determine loop direction. libgomp/ChangeLog: * libgomp.texi (Impl. Status 5.0): Add link to new PR110735. * testsuite/libgomp.fortran/non-rectangular-loop-1.f90: Enable commented tests. * testsuite/libgomp.fortran/non-rectangular-loop-1a.f90: Remove test file; tests are in non-rectangular-loop-1.f90. * testsuite/libgomp.fortran/non-rectangular-loop-5.f90: Change testcase to use a non-constant step to retain the 'sorry' test. * testsuite/libgomp.fortran/non-rectangular-loop-6.f90: New test. gcc/testsuite/ChangeLog: * gfortran.dg/gomp/linear-2.f90: Update dump to remove the additional count variable.
