CODEWITHSUNDEEP
gccvectorizationpragmaiccauto-vectorization
JackWM
JackWM

Reputation: 10535

GCC Vectorization Pragma

Using intel compiler, a loop can still be vectorized if users confirm no dependencies using #pragma ivdep.

I found one in GCC #pragma GCC ivdep, but got an error as below:

warning: ignoring #pragma GCC ivdep [-Wunknown-pragmas] #pragma GCC ivdep

Upvotes: 2

Views: 7026

Answers (1)

zam
zam

Reputation: 1684

"#pragma ivdep" is fully supported starting from GCC4.9.

Which GCC version do you use? #pragma ivdep was not officially supported in GCC at least before 2013.

I'm not sure about official support in other GCC4.x sub-versions between 2013 and 2014, although I've seen there were some partial patches for ivdep support before version 4.9.

In ICC (which you also mentioned among question tags) #pragma ivdep is supported long ago ( at least last 5 years).

For other compilers: Microsoft supports "#pragma loop ivdep" starting from MSVS 2013. Cray and some other "old school" compilers may support it starting from 1990s, but I'm not sure.

Finally, if you look for cross-platform and standard-ized solution, take a look at OpenMP4.x #pragma omp simd. While it's different sematic and also only supported by GCC4.9 + ICC/IFORT, it could be more beneficial in future, because (as opposed to ivdep) - pragma omp simd is true standard, so all compiler vendors will more or less have to support it in future and will have to support the same syntax for it.

Upvotes: 5

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