From mboxrd@z Thu Jan  1 00:00:00 1970
From: Toon Moene <toon@moene.indiv.nluug.nl>
To: egcs@cygnus.com
Subject: ss-199805171100UTC oddity with statement functions (Fortran)
Date: Mon, 18 May 1998 08:51:00 -0000
Message-id: <9805181439.AA06196@moene.indiv.nluug.nl>
X-SW-Source: 1998-05/msg00633.html

Consider the following Fortran code:

      program stmfun
      integer n
      values(i,j) = val((i-1)*n+j)
      end

where `values' is a statement function (Fortran's idea of a macro,  
but then at the compiler, not the preprocessor, level) that's not  
used, accessing an array `val' that's not defined.

Now watch this:

% g77 -v -O2 stmfun.f
g77 version 0.5.22-19980315
 gcc -v -O2 -xf77 stmfun.f -xnone -lf2c -lm
Reading specs from  
/usr/local/lib/gcc-lib/m68k-next-nextstep3/2.7.2.3.f.2/specs
gcc version 2.7.2.3.f.2
 /usr/local/lib/gcc-lib/m68k-next-nextstep3/2.7.2.3.f.2/f771  
stmfun.f -fset-g77-defaults -quiet -dumpbase stmfun.f -O2 -version  
-fversion -o /usr/tmp/cc006183.s
GNU F77 version 2.7.2.3.f.2 (68k, MIT syntax) compiled by GNU C  
version 2.7.2.3.f.2.
GNU Fortran Front End version 0.5.22-19980315 compiled: Mar 15 1998  
19:35:34
 as -o /usr/tmp/cc0061831.o /usr/tmp/cc006183.s
 ld -lcrt0.o  
-L/usr/local/lib/gcc-lib/m68k-next-nextstep3/2.7.2.3.f.2  
-L/usr/local/lib /usr/tmp/cc0061831.o -lf2c -lm -lgcc -lsys_s -lgcc

% /usr/snp/bin/g77 -v -O2 stmfun.f
Reading specs from  
/usr/snp/lib/gcc-lib/m68k-next-nextstep3/egcs-2.91.29/specs
gcc version egcs-2.91.29 19980517 (gcc2 ss-980502 experimental)
 /usr/snp/lib/gcc-lib/m68k-next-nextstep3/egcs-2.91.29/f771  
stmfun.f -fset-g77-defaults -quiet -dumpbase stmfun.f -O2 -version  
-fversion -o /usr/tmp/cc006188.s
GNU F77 version egcs-2.91.29 19980517 (gcc2 ss-980502 experimental)  
(m68k-next-nextstep3) compiled by GNU C version egcs-2.91.29  
19980517 (gcc2 ss-980502 experimental).
GNU Fortran Front End version 0.5.22-release
 as -o /usr/tmp/cc0061881.o /usr/tmp/cc006188.s
 /usr/snp/lib/gcc-lib/m68k-next-nextstep3/egcs-2.91.29/collect2  
-lcrt0.o -L/usr/snp/lib/gcc-lib/m68k-next-nextstep3/egcs-2.91.29  
-L/usr/snp/m68k-next-nextstep3/lib -L/usr/snp/lib  
/usr/tmp/cc0061881.o -lf2c -lm -lgcc -lsys_s -lgcc
/bin/ld: Undefined symbols:
_val_
collect2: ld returned 1 exit status

Anyone with a bright idea ?

Note that this is not contrary to the Standard - I have seen this  
with Digital's Fortran compiler too, and as far as I understand the  
Fortran 90 Handbook (as close to the Standard as I can get) there is  
nothing to prevent the compiler to generate code for `values' (and  
hence trying to access `val') even if it's not used.

Note 2: For complete understanding of this example one should know  
that in Fortran an identifier, followed by something between  
parentheses, *that isn't declared as an array* is an implicitly  
declared function call :-) :-)

Cheers,
Toon.