OpenGL core profile incredible slowdown on OS X

Question

I added a new GL renderer to my engine, which uses the core profile. While it runs fine on Windows and/or nvidia cards, it is like 10 times slower on OS X (

Answer 1

Finally, I was able to reproduce the slowdown. This is just crazy... It is clearly caused by glBindAttribLocation being called on the "my_Position" attribute. Now I did some testing:

• 1 is default (as returned by glGetAttribLocation)
• if I set it to zero, theres no problem
• if I set it to 1, the rendering becomes slow
• if I set it to any larger number, it is slow again

Obviously I relink the program (check code). It is not a problem in the implementation, I tested it with "normal" values too.

Test program:

https://www.dropbox.com/s/dgg48g1fwgyc5h0/SLOWDOWN_REPRO.zip

How to repro:

• open with XCode
• open common/glext.h (don't be disturbed by the name)
• modify the GLDECLUSAGE_POSITION constant from 0 to 1
• compile and run => slow
• changing back to zero => good