Intel command line flags

[cria_ro]

Hello,

Which flags are recommended for the q9xx processors in order to take advantage of all capabilities in fortran?

There was no difference when I used /03 /QxT or /O3 /QxS.

What does /fast mean on 10.x fortran compilers?


Cristian

[TimP]

/QxS specifies generation of code for Penryn family CPUs only. There are a few cases where it is possible to vectorize effectively with /QxS but not /QxT, but I'm not surprised you didn't see a difference. /fastwould set /O3 /Qipo /QxT. /QxT is unlikely to show any difference from /QxP or /QxO, which cover a wider range of CPUs.

The section on optimization in the Windows .chm help file recommends comparison of performance among default (/O2), /O1, /O3, and /fast. Depending on the application, any of those could prove best. In real applications, it may be necessary to set /Qprec-div /Qprec-sqrt /assume:protect_parens to avoid errors; the Penryn family processors are unlikely to lose performance with those options.

[Steven_L_Intel1]

See also our FAQ on Intel processor-specific optimization switches.

[cria_ro]

Hello,

Thank you for your answers. I will test all those options. The FAQ on Intel specific processors switches is quite clear. Those swithces for avoiding the errors, are they specific to intel compilers or do they appear in general at fortran compilers?

Cristian

[Steven_L_Intel1]

All switches are compiler-specific. You may or may not find similar-function switches with other compilers.