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|Oracle Solaris Studio 12.3: Fortran User's Guide Oracle Solaris Studio 12.3 Information Library|
The next sections suggest a number of ways to use the Fortran compiler efficiently. A complete compiler options reference follows in the next chapter.
Some compiler flags allow the user to tune code generation to a specific set of hardware platform options. The compiler’s -dryrun option can be used to determine the native processor:
<sparc>%f95 -dryrun -xtarget=native ### command line files and options (expanded): ### -dryrun -xarch=sparcvis2 -xcache=64/32/4:1024/64/4 -xchip=ultra3i <x64>%f95 -dryrun -xtarget=native ### command line files and options (expanded): ### -dryrun -xarch=sse2a -xcache=64/64/2:1024/64/16 -xchip=opteron
You can specify options by setting the FFLAGS or OPTIONS variables.
Either FFLAGS or OPTIONS can be used explicitly in the command line. When you are using the implicit compilation rules of make, FFLAGS is used automatically by the make program.
demo% setenv FFLAGS ’-fast -Xlist’
Example: Use FFLAGS explicitly:
demo% f95 $FFLAGS any.f
When using make, if the FFLAGS variable is set as above and the makefile’s compilation rules are implicit, that is, there is no explicit compiler command line, then invoking make will result in a compilation equivalent to:
f95 -fast -Xlist files…
make is a very powerful program development tool that can easily be used with all Sun compilers. See the make(1) man page and the Program Development chapter in the Fortran Programming Guide.
Note - Default implicit rules assumed by make may not recognize files with extensions .f95 and .mod (Module files). See the Fortran Programming Guide for details.
A compilation may need to use a lot of memory. This will depend on the optimization level chosen and the size and complexity of the files being compiled. If the optimizer runs out of memory, it tries to recover by retrying the current procedure at a lower level of optimization and resumes subsequent routines at the original level specified in the -On option on the command line.
A processor running the compiler should have at least 64 megabytes of memory; 256 megabytes are recommended. Enough swap space should also be allocated. 200 megabytes is the minimum; 300 megabytes is recommended.
Compiling a single source file containing many routines could cause the compiler to run out of memory or swap space.
If the compiler runs out of memory, try reducing the level of optimization, or split multiple-routine source files into files with one routine per file, using fsplit(1).
Example: Use the swap command:
demo% swap -s total: 40236k bytes allocated + 7280k reserved = 47516k used, 1058708k available To determine the actual real memory:
demo% /usr/sbin/dmesg | grep mem mem = 655360K (0x28000000) avail mem = 602476544
Use mkfile(1M) and swap(1M) to increase the size of the swap space on a workstation. You must become superuser to do this. mkfile creates a file of a specific size, and swap -a adds the file to the system swap space:
demo# mkfile -v 90m /home/swapfile /home/swapfile 94317840 bytes demo# /usr/sbin/swap -a /home/swapfile
Compiling very large routines (thousands of lines of code in a single procedure) at optimization level -O3 or higher may require additional memory that could degrade compile-time performance. You can control this by limiting the amount of virtual memory available to a single process.
demo$ ulimit -d 16000
Example: Limit virtual memory to 16 Mbytes:
demo% limit datasize 16M
Each of these command lines causes the optimizer to try to recover at 16 Mbytes of data space.
This limit cannot be greater than the system’s total available swap space and, in practice, must be small enough to permit normal use of the system while a large compilation is in progress. Be sure that no compilation consumes more than half the space.
Example: With 32 Mbytes of swap space, use the following commands:
In a sh shell:
demo$ ulimit -d 1600
In a csh shell:
demo% limit datasize 16M
The best setting depends on the degree of optimization requested and the amount of real and virtual memory available.
In 64-bit Solaris environments, the soft limit for the size of an application data segment is 2 Gbytes. If your application needs to allocate more space, use the shell’s limit or ulimit command to remove the limit.
For csh use:
demo% limit datasize unlimited
For sh or ksh, use:
demo$ ulimit -d unlimited
See the Oracle Solaris 64-bit Developer’s Guide for more information.