I have been facing some issues trying to convert a code previously compiled with compaq visual fortran 6.6 to gfortran.
Here is a specific problem I have met with gfortran :
There is a variable called "et" which takes the value 3E+10. Then the program calls a subroutine. "et" doesn't appear in the subroutine, but after coming back to the main program it has now the value 0.
When compliling with compaq visual fortran I didn't have this problem.
The code I am working on is a huge scientific program, so I put below only a small part of it :
c
c calculate load/unload modulus
c
500 t=(s1-s3)/2.
aa=1.00
if(iconeps.ne.1)bb=1.00
if(smean.lt.ap1) smean=ap1
if(xn.gt.0.000001) aa=(smean/atmp)**xn
if(iconeps.eq.1)go to 220
if(xm.gt.0.000001) bb=(smean/atmp)**xm
220 if(t.ge.0.99*sm1) go to 600
et=xku*aa*atmp+tt*tm1
if(iconeps.ne.1)bt=xkb*atmp*bb
go to 900
600 et=(xkl*aa*atmp+tt*tm1)*(1.0-rf*sr)**2
if(iconeps.ne.1)bt=xkb*atmp*bb
900 continue
btmax=17.0*et
btmin=0.33*et
if(iconeps.ne.1)then
tbt=(alf1+alf3*dtt)*dtt*(1.+vide)*tm2
btf=bt+tbt
bt=btf
endif
if(bt.lt.btmin) bt=btmin
if(bt.gt.btmax) bt=btmax
if(iconeps.eq.1)go to 1100
1000 continue
1050 if(mt.eq.mtyp4c)goto 1100
s=0.0
t=0.0
call shap4n(s,t,f,pfs,pft) ! Modification by NHV
call thick4n(s,t,xe,ye,thick)
call bmat4n(xe,ye,f,pfs,pft,b,detj,thick)
c calculate incremental strains
do 1300 i=1,4
temp=0.0
do 1200 j=1,8
1200 temp=temp+b(i,j)*disp(j)
1300 depi(i)=temp
epsv=0.0
do 1400 i=1,2
1400 epsv=epsv+depi(i)
epsv=epsv+depi(4)
ev=vide-(1.+vide)*epsv
if(ev.lt.0.0)ev=vide*.01
1100 continue
call perm(permws,xkw,coef,rw,tvisc,ev,vide,tt,pp)
: "et" keeps the good value until just before calling the subroutine "perm". Just after this subroutine it takes the value zero.
"et" isn't in any common block
This piece of code is part of a subroutine called by several different subroutines. What is even more strange is that when it is called in other parts of the code I doesn't have this problem ("et" keeps its value)
So if someone has ever met this kind of problem or have any idea about it I will be very gratefull
Perhaps you have a memory access error, such as an array bounds violation, or a mismatch between actual and dummy arguments. Are the interfaces of the subroutines explicit, such as being "used" from a module? Also try turning on compiler debugging options ... obviously subscript checking, but others might catch something. An extensive set for gfortran 4.5 or 4.6 is:
-O2 -fimplicit-none -Wall -Wline-truncation -Wcharacter-truncation -Wsurprising -Waliasing -Wimplicit-interface -Wunused-parameter -fwhole-file -fcheck=all -std=f2008 -pedantic -fbacktrace
Subscript checking is included in fcheck=all