Suggestions for OS X install wiki

[coatless]

@Bob_Carpenter

coatless:

it’s noisy in the default state because it does not include the CXXFLAGS recommended on the Installing RStan on Mac or Linux wiki page.

What is the default?

Both -O3 (in CXXFLAGS) and -mtune=native (in CXX) are necessary for optimal compiled code. The former is what’s going to unfold everything as we expect and the latter’s going to allow loop vectorization, etc.

The default flags for macOS are:

-fPIC  -Wall -g -O2

rstan from Installing RStan on Mac or Linux wiki page recommends:

CXXFLAGS=-O3 -mtune=native -march=native -Wno-unused-variable -Wno-unused-function  -Wno-macro-redefined

“Noise” is generated due to the lack of -Wno-unused-variable -Wno-unused-function -Wno-macro-redefined in the default flags. There is also less optimization -O2 vs. -O3.