https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86837
Bug ID: 86837
Summary: Optimization breaks an unformatted read with implicit
loop on Mac OS X
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: tmp147 at neuf dot fr
Target Milestone: ---
Created attachment 44497
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44497&action=edit
minimal standalone program showing the problem
The attached code compiles and runs fine with -O0, but gives an inappropriate
warning and crashes at least with -O1 and -O2. In close variants, I've also had
no message when compiling, no error at runtime, but no read either.
OS : Mac OS X High Sierra 10.13.6
Version: gfortran 8.2.0 installed by an up-to-date brew
same problem with gcc@5, gcc@6, gcc@7
The results are ok at least on some linux, tested on
- CentOS 6.5 / gcc 4.4.7 20120313 (Red Hat 4.4.7-4)
- Mageia 4 / gcc 4.8.2
- Mageia 6 / gcc 5.4 (or 5.5, not at work anymore...)
#### Run ok
gfortran -O0 -Wall -Wextra -fcheck=all read_loop.f90 -o read_loop &&
./read_loop
1.
11. 12.
21. 22. 23. 24.
Full array two_d:
1. 11. 21.
-9. 12. 22.
-9. -9. 23.
-9. -9. 24.
#### Run ko (only changed -O0 to -O1)
gfortran -O1 -Wall -Wextra -fcheck=all read_loop.f90 -o read_loop &&
./read_loop
read_loop.f90:40:0:
read(10) ((two_d(i,j), i=1,nvalues(j)), j=1,3)
Warning: 'j' may be used uninitialized in this function [-Wmaybe-uninitialized]
At line 40 of file read_loop.f90
Fortran runtime error: Index '0' of dimension 1 of array 'nvalues' below lower
bound of 1
Error termination. Backtrace:
#0 0x1006e61ac
#1 0x1006e6e45
#2 0x1006e71ea
#3 0x1006debfe
#4 0x1006dec1d
