Compile times are very long with this flag, however depending on the application there may be appreciable performance improvements when combined with the -O* flags. This flag must be used to compile and when linking. (GNU only) Link-time optimization, a step that examines function calls between files when the program is linked. The GNU documentation notes that this option results in a disregard of 'strict standards compliance. Recommended for codes that loops involving intensive floating point calculations.Īllows for higher performance with floating point calculations at the risk of a slight loss of precision. More aggressive than -O2 with longer compile times. Using these flags does not result in any incompatibility between CPU architectures. The basic optimization flags are summarized below. The GNU Compiler Collection has their optimization flags described in an online document. Manuals are available for all of the compilers after their modules are loaded: man g++ List available versions of the LLVM compilers. The LLVM compilers commands are summarized here: Command

List available versions of the GNU compilers. The following table summarizes some relevant commands on the SCC for the GNU compilers: Command If the numeric output is incorrect or lacks the desired accuracy less-aggressive compile options should be tried. As with all compilers, programs compiled with optimization should have their output double-checked for accuracy. As the LLVM C and C++ compilers deliberately share the majority of their optimization flags with their GNU equivalents the information here applies to both sets of compilers. The GNU family of compilers produce highly optimized code for Intel and AMD CPUs.

Intel c compiler flag list -c++