According to the "Snapdragon_LLVM_ARM_37_Compiler_User_Guide", the compiler flags to be set to get best performance are simply:
-Ofast -mcpu=krait or -mcpu=cortex-a57
However if i build with just such flags, i get the warning:
clangSnapdragon_LLVM_for_Android_37++.exe: warning: Vectorization flags ignored because armv7/armv8 and neon not set [-Wvectorizer-no-neon]
If i set -mfpu=neon of course the warning goes away, but what is the best parameter for -mfpu for Krait and Snapdragon 810 cores?
Incidentally, corrently i get about 10% better performance both on krait as well as cortex-a57 by using GCC 4.9 instead of LLVM for Snapdragon.