C/C++

Several C/C++ compilers are available on ewok. These include GNU, Portland Group, Pathscale and Intel. The compilers are accessed by loading the appropriate module file. Each compiler has a corresponding mvapich module. The mvapich modules take care of loading the correct compiler. So, if you wanted to unload the PGI compiler and load the Pathscale compiler, the best way would be to unload mvapich-pgi and load mvapich-pathscale. You may then use a module swap if you want to change between different versions of a compiler.

NOTE: Descriptions of compiler options have been taken from their respective man pages

Available Compilers

Portland Group (PGI) C/C++

Commands

  • pgcc: C compiler, ANSI (89) and K&R C
  • pgCC: C++ compiler, ANSI C++ with cfront features

pgcc does not currently support the ANSI 99 standard for C. For complex numbers, use pgCC.

Debugging Options

The following options control the amount of debugging information generated by the compiler. They can adversely affect optimization.

Option Description
-g Generates symbolic debug information. Turns off optimization.
-Mbounds Adds array bound checking.

Optimization Options

For most cases, the usual levels of optimization are appropriate (-O0, -O1, -O2 [default], -O3). Here are a few exceptions.

Option Description
-fast Chooses generally optimal flags for the target platform.
Use pgcc -fast -help to see the equivalent switches.
Note this sets the optimization level to a minimum of 2; see -O.
-fastsse Chooses generally optimal flags for a processor that supports the streaming SIMD extensions (SSE) (Pentium 3/4, AthlonXP/MP, Opteron) and SSE2 (Pentium 4, Opteron) instructions. Use pgcc -fastsse -help to see the equivalent switches.
-tp k8-64 Targets optimization to the 64-bit Opteron processor.
-Mflushz Sets SSE to flush-to-zero mode.
-pg
-ql
-Mprof		 Instrument program for profiling.
These flags imply different types of profiling.
Please check the pgcc or pgCC man page for more information.
-Minfo Generates an optimization report to standard error.
This has several suboptions, so check the man page.
-mp Enables the compiler to generate multithreaded code based on the OpenMP directives.

PGI Documentation

See man pgcc or man pgCC for a full list of compiler options. PDF and HTML documentation is also available online from PGI at http://www.pgroup.com/resources/docs.htm.

Pathscale C/C++

Commands

  • pathcc: C compiler
  • pathCC: C++ compiler

Debugging Options

The following options control the amount of debugging information generated by the compiler. They can adversely affect optimization.

Option Description
-g Generates symbolic debug information. Turns off optimization.

Optimization Options

For most cases, the usual levels of optimization are appropriate (-O0, -O1, -O2 [default], -O3). Here are a few exceptions.

Option Description
-Ofast Use optimizations to maximize performance. These optimizations are typically safe, but floating-point accuracy may be affected. -Ofast is equivalent to -O3 -ipa -OPT:Ofast -fno-math-errno -ffast-math.
-pg
-profile

Generate extra code to provide information to the pathprof tool. Both options turn on application-level profiling, but only -profile turns on library-level profiling. See the eko man page for more information.
-openmp Enables the compiler to generate multithreaded code based on the OpenMP directives.

Pathscale Documentation

See man pathcc, man pathCC, or man eko for a full list of compiler options. Additional documentation is also available online from Pathscale at http://pathscale.com/ws/node/70.

Intel C/C++

Commands

  • icc: C/C++ compiler. icc compiles .c and .i files as C and only links C++ libraries if the compile line contains C++ source files.
  • icpc: C++ compiler. icpc compiles .c and .i files as C++ and always links C++ libraries.

Debugging Options

The following options control the amount of debugging information generated by the compiler. They can adversely affect optimization.

Option Description
-g Generates symbolic debug information. Turns off optimization.
-debug Enables debugging information and controls output of debug information. See man icc for a list of options for the <keyword>

Optimization Options

For most cases, the usual levels of optimization are appropriate (-O0, -O1, -O2 [default], -O3). Here are a few exceptions.

Option Description
-fast Maximize speed across the program. -fast is equivalent to -O3 -ipo -static.
-p
-qp

Compile and link for profiling with gprof
-openmp Enables the compiler to generate multithreaded code based on the OpenMP directives.

Intel Documentation

See man icc for a full list of compiler options. Additional documentation is also available online from Intel at http://www.intel.com/support/performancetools/c/linux/.

GNU C/C++

Commands

  • gcc: C compiler
  • g++: C++ compiler

Debugging Options

The following options control the amount of debugging information generated by the compiler. They can adversely affect optimization.

Option Description
-g Generates symbolic debug information. Turns off optimization.

Optimization Options

For most cases, the usual levels of optimization are appropriate (-O0, -O1, -O2 [default], -O3). Here are a few exceptions.

Option Description
-p

Compile and link for profiling with prof. If you use separate compile and link steps, this option must be given both when compiling and when linking.
-pg

Compile and link for profiling with gprof. If you use separate compile and link steps, this option must be given both when compiling and when linking.

GNU Documentation

See man gcc for a full list of compiler options. Additional documentation is also available online from Intel (online and as a downloadable .pdf, .ps, or .tar file) at http://gcc.gnu.org/onlinedocs/.