Optimization flags for Intel c++ compiler

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Is there any set of recommanded flags to choose in order to get the most optimized code with the Intel c++ compiler?

for example I use /O3 /Arch:AVX /Oy /Ot /Qopt_matmul /fp:fast=2

However activating /Qparallel dramatically slows down the opencv functions!! What flags do you guys use to produce opencv release versions??