Bug#844036: gfortran-6: spits out false warning about COMPLEX(4) to REAL(4) conversion when using a complex parameter
Package: gfortran-6
Version: 6.2.0-10
Severity: normal
Hello,
I think I found a bug in gfortran.
Please consider the following simple program:
$ cat cpxparam.f
program main
complex iu
parameter (iu=(0,1))
complex val1,val2
write (*,*) 'iu = ',iu
val1 = (+2.0,+3.0)
val2 = (+4.0,-1.0)
c the following should write (2 + j3)/(j*(4 - j) = (14 - j*5)/17
c that is to say about (0.8235294 , -0.2941176)
write (*,*) val1/(iu*val2)
end
If I try to compile this with the following command line:
$ gfortran -pedantic -Wall -fimplicit-none -o cpxparam cpxparam.f
cpxparam.f:4:20:
parameter (iu=(0,1))
1
Warning: Non-zero imaginary part discarded in conversion from ‘COMPLEX(4)’ to ‘REAL(4)’ at (1) [-Wconversion]
I get the above-quoted scary warning about an unintended conversion of
iu to real type!!!
But this conversion seems to never take place (luckily):
$ ./cpxparam
iu = ( 0.00000000 , 1.00000000 )
( 0.823529422 ,-0.294117659 )
As you can see, the output is the expected one.
At first I thought a recent gfortran could maybe have some issues
in dealing with the old Fortran77-style syntax.
So, let's try with some more modern style:
$ cat cpxparam_modern.f
program main
complex,parameter :: iu=(0,1)
complex :: val1,val2
write (*,*) 'iu = ',iu
val1 = (+2.0,+3.0)
val2 = (+4.0,-1.0)
c the following should write (2 + j3)/(j*(4 - j) = (14 - j*5)/17
c that is to say about (0.8235294 , -0.2941176)
write (*,*) val1/(iu*val2)
end
Same story:
$ gfortran -pedantic -Wall -fimplicit-none -o cpxparam_modern cpxparam_modern.f
cpxparam_modern.f:3:30:
complex,parameter :: iu=(0,1)
1
Warning: Non-zero imaginary part discarded in conversion from ‘COMPLEX(4)’ to ‘REAL(4)’ at (1) [-Wconversion]
$ ./cpxparam_modern
iu = ( 0.00000000 , 1.00000000 )
( 0.823529422 ,-0.294117659 )
The scary warning is still produced and the executable output is still
correct, despite the compile-time warning.
Curiously, changing the last expression to be evaluated into a
different, but mathematically equivalent one makes the warning go
away:
$ cat cpxparam2.f
program main
complex iu
parameter (iu=(0,1))
complex val1,val2
write (*,*) 'iu = ',iu
val1 = (+2.0,+3.0)
val2 = (+4.0,-1.0)
c the following should write (2 + j3)/(j*(4 - j) = (14 - j*5)/17
c that is to say about (0.8235294 , -0.2941176)
write (*,*) -iu*val1/val2
end
$ gfortran -pedantic -Wall -fimplicit-none -o cpxparam2 cpxparam2.f
$ ./cpxparam2
iu = ( 0.00000000 , 1.00000000 )
( 0.823529422 ,-0.294117659 )
No warning and correct output from the compiled program.
Please investigate this bug and/or forward my bug report upstream,
as appropriate.
Thanks for your time!
Bye.
P.S.: the above-quoted simple programs are probably trivial enough to
not be copyrighted; in case this turns out to be false, I hereby
release them under the terms of the Expat license
<http://www.jclark.com/xml/copying.txt>
-- System Information:
Debian Release: stretch/sid
APT prefers testing
APT policy: (800, 'testing'), (500, 'unstable')
Architecture: amd64 (x86_64)
Kernel: Linux 4.7.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages gfortran-6 depends on:
ii gcc-6 6.2.0-10
ii gcc-6-base 6.2.0-10
ii libc6 2.24-5
ii libc6-dev 2.24-5
ii libgfortran-6-dev 6.2.0-10
ii libgmp10 2:6.1.1+dfsg-1
ii libisl15 0.17.1-1
ii libmpc3 1.0.3-1
ii libmpfr4 3.1.5-1
ii zlib1g 1:1.2.8.dfsg-2+b3
gfortran-6 recommends no packages.
Versions of packages gfortran-6 suggests:
pn gfortran-6-doc <none>
pn gfortran-6-multilib <none>
pn libcoarrays-dev <none>
pn libgfortran3-dbg <none>
-- no debconf information
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