https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71412
Bug ID: 71412
Summary: iso_c_bindings and optimization interaction bug
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: relliott at umn dot edu
Target Milestone: ---
Created attachment 38644
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38644&action=edit
minimal skeleton code that illustrates the bug
A problem exists in the way gfortran optimizes functions/subroutines when c
interoperability (and specifically the c_loc() intrinsic) are used.
The attached code illustrates the issue. A variable is allocated and a pointer
is to the allocated memory is sent to C and stored in global memory. Next the
memory is initialized in the same routine that it was allocated. Finally, in a
different routine the memory pointer is retrieved from c and the value stored
in memory is printed. With optimization -O3 the initialization is optimized
out. With optimization -O0 the initialization occurs and the code runs
correctly.
The typical output and sequence of steps to run the code is given below.
vagrant@vagrant-ubuntu-trusty-64:/vagrant$ cd skeleton/
vagrant@vagrant-ubuntu-trusty-64:/vagrant/skeleton$ make
gfortran -m32 -O3 -g -Wall -pedantic -c skeleton-f.F90
gcc -m32 -O3 -g -Wall -ansi -pedantic -c skeleton-c.c
gfortran -m32 -O3 -g -Wall skeleton*.o -o skeleton
vagrant@vagrant-ubuntu-trusty-64:/vagrant/skeleton$ ./skeleton
-- in storePtr: pointer address --> 0x95caba0 <-- value --> -144534256
-- just a print statement --> nothing
-- in getPtr: pointer address --> 0x95caba0 <-- value --> -144534256
-- value of 'val2' variable --> -144534256
vagrant@vagrant-ubuntu-trusty-64:/vagrant/skeleton$ make clean
rm -f skeleton skeleton*.o *.mod
vagrant@vagrant-ubuntu-trusty-64:/vagrant/skeleton$ make OPT=-O0
gfortran -m32 -O0 -g -Wall -pedantic -c skeleton-f.F90
gcc -m32 -O0 -g -Wall -ansi -pedantic -c skeleton-c.c
gfortran -m32 -O0 -g -Wall skeleton*.o -o skeleton
vagrant@vagrant-ubuntu-trusty-64:/vagrant/skeleton$ ./skeleton
-- in storePtr: pointer address --> 0x8d09ba0 <-- value --> -143915760
-- just a print statement --> nothing
-- in getPtr: pointer address --> 0x8d09ba0 <-- value --> 21
-- value of 'val2' variable --> 21
