[Vladimir Eltsov <ve@boojum.hut.fi>] bug with -fcaller-saves

[Dave Love]

This appears to be a (non-critical?) backend problem reported as a g77
bug.  I can reproduce it, but (only) with -O[2].  Any ideas other than
`don't do that, then'? :-)

------- Start of forwarded message -------
Date: Tue, 27 Jan 1998 19:25:19 +0200 (EET)
From: Vladimir Eltsov <ve@boojum.hut.fi>
To: fortran@gnu.org
Subject: bug with -fcaller-saves
Message-ID: <Pine.LNX.3.96.980127190257.1606A-100000@slon.hut.fi>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

Hello!

Following program would hang after printing 6 lines when compiled with 
'g77 -O2 test.f' on x86 architecture, but would work OK when compiled with 
'g77 -O2 -fno-caller-saves test.f' both for gnu and egcs variants of the
compiler.

Details follow:
-------  test.f -------
      program test
      implicit double precision (a-h,o-z)

      t = 0
      tend = 1
      dt = 6d-7
      h = 0.314d-7
      k = 1
      ti = dt

      do while (t.lt.tend)
         do while(t.lt.ti)
            if (t+h.gt.ti) then
               h = ti-t
            end if
            call fun(t,h)
         end do
         print *,k,t,t/5d-7
         k = k+1
         ti = k*dt
      end do

      end

      subroutine fun(t,h)
      implicit double precision (a-h,o-z)

      t = t+h
      h = 0.314d-7

      return
      end
------- correct output -------
 1  6.E-07  1.2
 2  1.2E-06  2.4
 3  1.8E-06  3.6
 4  2.4E-06  4.8
 5  3.E-06  6.
 6  3.6E-06  7.2
 7  4.2E-06  8.4
 8  4.8E-06  9.6
 9  5.4E-06  10.8
 10  6.E-06  12.
 11  6.6E-06  13.2
 12  7.2E-06  14.4
 13  7.8E-06  15.6
 14  8.4E-06  16.8
 15  9.E-06  18.
 16  9.6E-06  19.2
 17  1.02E-05  20.4
 18  1.08E-05  21.6
 19  1.14E-05  22.8
 20  1.2E-05  24.
 21  1.26E-05  25.2
 22  1.32E-05  26.4
.... and a lot more lines ....
------- incorrect behaviour ----------
 1  6.E-07  1.2
 2  1.2E-06  2.4
 3  1.8E-06  3.6
 4  2.4E-06  4.8
 5  3.E-06  6.
 6  3.6E-06  7.2
... hang here ...
-----------------------------------

> uname -a
Linux slon.hut.fi 2.0.32 #1 Wed Nov 19 00:46:45 EST 1997 i686 unknown

> cat /proc/cpuinfo
processor       : 0
cpu             : 686
model           : 3
vendor_id       : GenuineIntel
stepping        : 3
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid           : yes
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 11 mtrr pge mca cmov
mmx
bogomips        : 267.06

> ldd ./a.out
        libm.so.6 => /lib/libm.so.6 (0x40003000)
        libc.so.6 => /lib/libc.so.6 (0x4001c000)
        /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00000000)

> g77 -v
g77 version 0.5.21
 gcc -v -fnull-version -o /tmp/gfa01630 -xf77-cpp-input /tmp/gfa01630.f
-xnone -lf2c -lm
Reading specs from /usr/lib/gcc-lib/i686-unknown-linux/2.7.2.3.f.1/specs
gcc version 2.7.2.3.f.1
 /usr/lib/gcc-lib/i686-unknown-linux/2.7.2.3.f.1/cpp -lang-c -v -undef
-D__GNUC__=2 -D__GNUC_MINOR__=7 -D__ELF__ -D__unix__ -D__i386__
-D__linux__ -D__unix -D__i386 -D__linux -Asystem(unix) -Asystem(posix)
-Acpu(i386) -Amachine(i386) -D_LANGUAGE_FORTRAN -traditional
/tmp/gfa01630.f /tmp/cca01631.i
GNU CPP version 2.7.2.3.f.1 (i386 Linux/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/i686-unknown-linux/include
 /usr/lib/gcc-lib/i686-unknown-linux/2.7.2.3.f.1/include
 /usr/include
End of search list.
 /usr/lib/gcc-lib/i686-unknown-linux/2.7.2.3.f.1/f771 /tmp/cca01631.i
-fset-g77-defaults -m486 -quiet -dumpbase gfa01630.F -version -fversion
-fnull-version -o /tmp/cca01631.s
GNU F77 version 2.7.2.3.f.1 (i386 Linux/ELF) compiled by GNU C version
2.7.2.3.f.1.
GNU Fortran Front End version 0.5.21 compiled: Dec 14 1997 15:23:12
 as -V -Qy -o /tmp/cca016311.o /tmp/cca01631.s
GNU assembler version 2.8.1 (i686-pc-linux-gnu), using BFD version
linux-2.8.1.0.1
 ld -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o /tmp/gfa01630
/usr/lib/crt1.o /usr/lib/crti.o
/usr/lib/gcc-lib/i686-unknown-linux/2.7.2.3.f.1/crtbegin.o
-L/usr/lib/gcc-lib/i686-unknown-linux/2.7.2.3.f.1 /tmp/cca016311.o -lf2c
-lm -lgcc -lc -lgcc
/usr/lib/gcc-lib/i686-unknown-linux/2.7.2.3.f.1/crtend.o /usr/lib/crtn.o
__G77_LIBF77_VERSION__: 0.5.21
@(#)LIBF77 VERSION 19970404
__G77_LIBI77_VERSION__: 0.5.21
@(#) LIBI77 VERSION pjw,dmg-mods 19970816
__G77_LIBU77_VERSION__: 0.5.21
@(#) LIBU77 VERSION 19970609

> gcc -v
Reading specs from /usr/lib/gcc-lib/i686-unknown-linux/2.7.2.3.f.1/specs
gcc version 2.7.2.3.f.1

> /usr/local/bin/g77 -v
Reading specs from
/usr/local/lib/gcc-lib/i686-pc-linux-gnu/egcs-2.90.23/specs
gcc version egcs-2.90.23 980102 (egcs-1.0.1 release)

> /usr/local/bin/gcc -v
Reading specs from
/usr/local/lib/gcc-lib/i686-pc-linux-gnu/egcs-2.90.23/specs
gcc version egcs-2.90.23 980102 (egcs-1.0.1 release)

----------------------------

Sincerely yours,

      Vladimir Eltsov


------- End of forwarded message -------