[gmx-developers] CFLAGS for ppc, etc. with CMake

[Szilárd Páll]

Hi,

> -Kieee. Does someone know whether this is required for GROMACS? One can also
> gain with GCC by adding -ffast-math. Is this safe?

When testing/debugging the strange performance hit we experienced a
while ago with gcc 4.3.3/4 - which turned out to be a problem with
expf - I also tried the -ffast-math flag and as far as I remember I
got no relevant performance improvement (tested on x86_64). With some
gcc versions it even seemed to produce a small performance hit,
overall showing -1-2% "improvement".

Take these metrics with a grain of salt though as my benchmarking was
focused on a 10-20% performance hit on PME. Moreover it was done ~1.5
months ago so It might be worth to test again.

--
Szilárd