iso_c_bindings and optimization interaction bug

iso_c_bindings and optimization interaction bug

[Ryan S. Elliott]

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Hello,

I may have discovered a problem 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.

I would greatly appreciate any analysis of this issue.  Is it a bug?  Is my 
code non-compliant in some way? etc.

Thanks,  Ryan

-------------------------------------------------------------------------------

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

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Re: iso_c_bindings and optimization interaction bug

[Ryan S. Elliott]

I've now submitted this as a bug to bugzilla.  It is number 71412

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71412


On Fri, 29 Apr 2016, Ryan S. Elliott wrote:

> Hello,
>
> I may have discovered a problem 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.
>
> I would greatly appreciate any analysis of this issue.  Is it a bug?  Is my 
> code non-compliant in some way? etc.
>
> Thanks,  Ryan
>
> -------------------------------------------------------------------------------
>
> 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
>

-- 
Ryan S. Elliott, Ph.D. and Associate Professor
Aerospace Engineering & Mechanics, University of Minnesota
(612) 624-2376 (626-1558 fax)
http://www.aem.umn.edu/~relliott/
download vCard <http://www.aem.umn.edu/~relliott/relliott.vcf>

KIM Editor (http://openKIM.org)
Associate Editor: Journal of Elasticity (http://springer.com/10659)
MSI Associate Fellow (http://msi.umn.edu)

CMT textbook webpage (http://modelingmaterials.org)
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