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Pekka Manninen


Pekka Manninen, CSC, Performance Engineering, here. Presentation slides. I like the part where the flags have no standard semantics. That’s one of the ways you can tell when it’s your people talking.

De-facto standard flags for enabling typical optimizations

– ’–O[0-4]’, sometimes also ’fast’ § For example gcc –O3 or icc –fast

– The higher the level, the more aggressive optimization § Compilers default to some ”safe” level (typically ’-O2’) § ’-O0’ disables optimizations completely

Typically improves performance but not always

No standardized definition what the flags actually mean


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