From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 4067 invoked by alias); 11 Jul 2013 22:30:13 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 3935 invoked by uid 55); 11 Jul 2013 22:30:09 -0000 From: "harper at msor dot vuw.ac.nz" To: gcc-bugs@gcc.gnu.org Subject: [Bug fortran/57871] gfortran -freal-4-real-16 gives wrong result for selected_real_kind(1) Date: Thu, 11 Jul 2013 22:30:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: fortran X-Bugzilla-Version: 4.8.1 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: harper at msor dot vuw.ac.nz X-Bugzilla-Status: REOPENED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-SW-Source: 2013-07/txt/msg00656.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57871 --- Comment #5 from harper at msor dot vuw.ac.nz --- I have now found two more oddities of type promotion but I don't claim that these are gfortran bugs, only that the mmanual might need amending. Oddity 1. Although -freal-4-real-8 does what the manual implies with the program below (making the real kinds 8,10,16 on an x86_64 system), -fdefault-real-8 keeps the available kinds at 4,8,10,16 but merely changes the defaults. I suggest that the following sentence be added to the manual sewction on -fdefault-real-8 at the end: If "REAL(KIND=4)" is a real type available with no -f options, then it remains available with -fdefault-real-8 though not with -freal-4-real-8. Oddity 2. If one uses -fdefault-double-8 in a system where default real was 4 bytes wide then one must also use -fdefault-real-8. The manual entries for -fdefault-double-8 and -fdefault-real-8 are both silent on what happens if -fdefault-double-8 is given but -fdefault-real-8 is not. I won't suggest an amendment here because I don't know what happens in a system whose default real with no -f options was 8 bytes wide. Evidence: cayley[~/Jfh] % cat gfkinds.f90 implicit none real xdefault real(4 ) x4 real(8 ) x8 real(10) x10 real(16) x16 print *,kind(xdefault),kind(x4),kind(x8),kind(x10),kind(x16) end cayley[~/Jfh] % gf -freal-4-real-8 gfkinds.f90 cayley[~/Jfh] % ./a.out 8 8 8 10 16 cayley[~/Jfh] % gf -fdefault-real-8 gfkinds.f90 cayley[~/Jfh] % ./a.out 8 4 8 10 16 cayley[~/Jfh] % gf -fdefault-double-8 gfkinds.f90 :0:0: fatal error: Use of -fdefault-double-8 requires -fdefault-real-8 compilation terminated. cayley[~/Jfh] % alias gf /local/scratch/gf/bin/gfortran cayley[~/Jfh] % gf -v Using built-in specs. COLLECT_GCC=/local/scratch/gf/bin/gfortran COLLECT_LTO_WRAPPER=/local/scratch/gf/libexec/gcc/x86_64-unknown-linux-gnu/4.8.1/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: /local/scratch/gcc-4.8-20130530/configure --prefix=/local/scratch/gf --enable-languages=c,fortran --disable-libada --with-local-prefix=/local/scratch --with-gmp=/local/scratch Thread model: posix gcc version 4.8.1 20130530 (prerelease) (GCC) cayley[~/Jfh] % On Wed, 10 Jul 2013, sgk at troutmask dot apl.washington.edu wrote: > Date: Wed, 10 Jul 2013 20:02:43 +0000 > From: sgk at troutmask dot apl.washington.edu > To: john.harper@vuw.ac.nz > Subject: [Bug fortran/57871] gfortran -freal-4-real-16 gives wrong result for > selected_real_kind(1) > Resent-Date: Wed, 10 Jul 2013 20:02:59 +0000 > Resent-From: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57871 > > --- Comment #3 from Steve Kargl --- > On Wed, Jul 10, 2013 at 05:42:03PM +0000, kargl at gcc dot gnu.org wrote: >> implicit none >> integer,parameter:: p1 = selected_real_kind(1) >> >> This initialization expression is requesting the type with >> smallest precision that exceeds 1. With -freal-4-real-16, >> that type is double precision (ie kind=8). The problem >> lies in gfc_simplify_selected_real_kind. It has no knowledge >> of the -freal-*-real-* options. The loop (lines 5447-5457) > > (remove loop code) > >> searchs the ordered set [24, 53, 53, 113] (on FreeBSD-i386) or >> [24, 53, 64, 113] (on FreeBSD-amd64). In either case, the >> initialization expression returns REAL(4). However, with >> -freal-4-real-16, one might expect the ordered set to be >> searched is [113, 53, 64, 113] as REAL(4) has been promoted >> to REAL(16). > > The results of running John's code are odder than what one > might expect. > > The normal results: > > % gfc4x -o foo foo.f90 && ./foo > kind(1.0_p1) 4 precision(1.0_p1) 6 > kind(1.0_dp) 8 precision(1.0_dp) 15 > > One might expect the first line to be 8 and 15, respectively. > > % gfc4x -o foo foo.f90 -freal-4-real-16 && ./foo > kind(1.0_p1) 16 precision(1.0_p1) 33 > kind(1.0_dp) 8 precision(1.0_dp) 15 > > Here the default real kind is promoted to REAL(8), but literal > constants declared with a kind type suffix are not promoted. > The first line is the correct output, although one might > anticipate 8 and 15. But, what may be surprising is that the > double precision kind has been bumped to quad precision. > > troutmask:sgk[207] gfc4x -o foo foo.f90 -fdefault-real-8 && ./foo > kind(1.0_p1) 4 precision(1.0_p1) 6 > kind(1.0_dp) 16 precision(1.0_dp) 33 > > I've always hated these type options as a lzy programmer's > crutch who refuses to properly port an algorithm from > one precision to another. > > -- > You are receiving this mail because: > You reported the bug. > > > -- John Harper, School of Mathematics Statistics and Operations Research Victoria University, PO Box 600, Wellington 6140, New Zealand e-mail john.harper@vuw.ac.nz phone (+64)(4)463 5276 fax (+64)(4)463 5045