Optimizations dependent on availability of OpenMP threads

I have a working environment where $OMP_NUM_THREADS=1 is enforced (login node), but the system has many more available threads. It seems that when -O2 and -O3 optimizations are included in my compile command, the optimizations hard code instructions assuming OpenMP thread availability based on the host system, or at least the optimizations prevent the graceful handling of $OMP_NUM_THREADS. On execution, I get a segfault on entering __kmp_enter_single().

home$ ifort diagonalize.f90 -g -debug -assume buffered_io -ipo -fpic -openmp -O2 -I$MKLROOT/include/intel64/lp64 -I$MKLROOT/include $MKLROOT/lib/intel64/libmkl_blas95_lp64.a $MKLROOT/lib/intel64/libmkl_lapack95_lp64.a -Wl,--start-group $MKLROOT/lib/intel64/libmkl_intel_lp64.a $MKLROOT/lib/intel64/libmkl_core.a $MKLROOT/lib/intel64/libmkl_intel_thread.a -Wl,--end-group -lpthread -lm -o diagonalize

	ipo: remark #11000: performing multi-file optimizations

	ipo: remark #11006: generating object file /tmp/ipo_ifortuRFRzr.o

	home$ diagonalize

	forrtl: severe (174): SIGSEGV, segmentation fault occurred

	Image              PC                Routine            Line        Source             

	libiomp5.so        00002B52D2AFB71A  Unknown               Unknown  Unknown

	libiomp5.so        00002B52D2ADEE16  Unknown               Unknown  Unknown

	diagonalize_16     0000000000411514  Unknown               Unknown  Unknown

	libiomp5.so        00002B52D2B20FE3  Unknown               Unknown  Unknown

	home$ idbc diagonalize

	Intel(R) Debugger for applications running on Intel(R) 64, Version 13.0, Build [79.936.23]

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

	object file name: diagonalize

	Reading symbols from /home/me/diagonalize...done.

	(idb) run

	Starting program: /home/me/diagonalize

	[New Thread 26293 (LWP 26293)]

	Program received signal SIGSEGV

	__kmp_enter_single () in /opt/apps/intel/13/composer_xe_2013.2.146/compiler/lib/intel64/libiomp5.so

	(idb) where

	#0  0x00002b92e998671a in __kmp_enter_single () in /opt/apps/intel/13/composer_xe_2013.2.146/compiler/lib/intel64/libiomp5.so

	#1  0x00002b92e9969e16 in __kmpc_single () in /opt/apps/intel/13/composer_xe_2013.2.146/compiler/lib/intel64/libiomp5.so

	#2  0x0000000000411514 in diagonalize () at /home/me/diagonalize.f90:403

	#3  0x000000000040f6ed in diagonalize () at /home/me/diagonalize.f90:333

	#4  0x000000000040dfec in main () in /home/me/diagonalize

	#5  0x00000038cc81ecdd in __libc_start_main () in /lib64/libc-2.12.so

	(idb) set $cmdset='dbx'

	(idb) file diagonalize.f90

	(idb) list 403,406

	    403       !$omp workshare

	    404         ! zero result array

	    405         resArray(ptr(2):ptr(2)+dim_matrix-1) = 0_dbl_real

	    406       !$omp end workshare

	

If I only use -O1 level optimizations, the program runs fine. However, this is a HPC environment and for real data sets I will need at least -O2 functioning.

Also, the segfault is usually present and rarely absent from this executable. I'm fairly certain it's due to varying load on the host system and thus, thread availability.

As a side note, the source works fine with gfortran and the GOMP library with -O2 and -O3 (main point is that there's nothing odd with this code).

Any suggestions?

Thanks,
Jonathan