NORM2 Intrinsic Performance

NORM2 Intrinsic Performance


I'm just wondering if there is a good reason why calling SQRT( DOT_PRODUCT( V,V ) ) seems to perform better than NORM2(V). I'm trying to improve performance for a large program written in Fortran and I thought an easy first step would be to switch the first call to the second, but more testing proved otherwise. I compiled a test program with /O3 and /fp:source. I will admit when I use /fp:fast NORM2 is faster. Unfortunately, our legacy program requires /fp:source. I've attached the really rough source file for the program I used to test the performance. Is my test program flawed? This really is more of a curiosity than anything else. Thanks.

Downloadapplication/octet-stream Console1_0.f901.53 KB
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Your program doesn't use the result of either call, so the compiler optimized both away. Your program doesn't show what you think it does.

Steve - Intel Developer Support

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