-march=native option not supported on powerpc

[lee218llnl]

It looks like mfem's build system automatically sets -march=native for the GNU compilers. However, this is an x86-specific option and give an error on PowerPC systems:

'''[lee218@ray23:Crandom]$ uname -a
Linux ray23 3.10.0-514.2.2.2chaos.ch6.ppc64le #1 SMP Wed Jan 11 16:59:26 PST 2017 ppc64le ppc64le ppc64le GNU/Linux
[lee218@ray23:blueos_3_ppc64le_ib]$ gcc -march=native -Q --help=target
gcc: error: unrecognized command line option '-march=native'
'''

Here are a few relevant links:

https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html
https://gcc.gnu.org/onlinedocs/gcc/RS_002f6000-and-PowerPC-Options.html#RS_002f6000-and-PowerPC-Options

Can the build system be updated such that -march=native is only set when building for x86?

[v-dobrev]

I believe on PowerPC you can use -mcpu=native -mtune=native instead. The options in that makefile (miniapps/performance/makefile) are meant to be just an illustration for the specific case of GCC compiler and Intel processor.

[lee218llnl]

The problem that I see is that this option is not just an illustration, it is actually set and will be thrown at g++ by default. That said, no one will be able to just download mfem and build it on PowerPC without tripping on this error and having to modify the makefile. My suggestion here is to not set this option for all g++ invocations, either removing it entirely or only setting it when run on x86.

[tzanio]

@lee218llnl, please see and comment on PR #219.

[lee218llnl]

#219 looks good to me, thanks!

[tzanio]

Resolved by cbb74a9.