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This discussion is done as of May 9, 2017.

As of now using -march=znver1 doesn't seem like the best choice: — The preceding unsigned comment was added by Lilithium (talkcontribs) 10:40, April 13, 2017‎

I will look into it. Thank you. --Maffblaster (talk) 19:08, 13 April 2017 (UTC)
After collaborating with another Gentoo developer (Tobias Klausmann (klausman)), it looks like haswell was causing him segfaults. I changed it to the previously supported -march value. --Maffblaster (talk) 23:58, 9 May 2017 (UTC)
According to this forum discussion -march= should be either haswell, broadwell or skylake.
Using -march=bdver4 is not a good option as pointed out in this Phoronix article, simply because Bulldozer's instruction set extension FMA4/XOP is no longer available on the Zen architecture.
Code built for bdver1 through bdver4 might or might not work on Zen, depending on the actual instructions included during compilation. This is automatic and no one can say for sure what the compiler descides to use and not to use.
My recommendation is to use a lower subset of instructions to build GCC 6 (I used -march=skylake without issues, Ryzen 7 1800X) and then use -march=znver1 with GCC 6 set as the system GCC version (I removed GCC 5.4 completely). The caveat is that some packages need the ~amd64 ACCEPT_KEYWORDS flag set, because not all stable amd64 ebuilds include a GCC6 patch (yet).
Anyway, I just put that information into Safe CFLAGS, which now shows contradictory information to this article. One should be changed to equalize the information and remove the contradiction.
Luttztfz (talk) 23:05, 15 May 2017 (UTC)
Luttztfz , Thanks for putting this discussion point together. I have been discussion with other Gentoo developers, but haven't received back much information from them (yet). I have been using -march=native on my system with GCC and have experienced no issues whatsoever. I would actually be okay with transcluding the information from the Safe CFLAGS article to this article. I'll check into that. Thanks again for your efforts! Feel free to edit more around the wiki; my workload is high right now and it's hard for me to keep up. :) --Maffblaster (talk) 00:37, 16 May 2017 (UTC)
Might also be worth adding a note that Ryzen users really should be using at least gcc 6.3? Or maybe if using -march=bdver{1..4} users should then add further switches that disable FMA4/XOP. Is this possible? --Zucca (talk) 09:27, 16 May 2017 (UTC)
Yes, -mno-fma4 and -mno-xop will disable the use of these specific instruction set extensions. According to GCC x86 options one more difference between -march=bdver4 and -march=znver1 is the LWP extension. Thus -mno-lwp may also be a good idea.
I hope that these -mno- options will cancel the standard options of -march=.
The result would be: -march=bdver4 -mno-fma4 -mno-xop -mno-lwp for Zen on GCC 5.4. As I currently use GCC 6, I cannot test this right away, but I plan to do so in a couple of days. Luttztfz (talk) 20:17, 16 May 2017 (UTC)
I also found this PDF that states (on PDF page 12) that Zen lacks not only the FMA4 and XOP, but also the TBM instruction extension. In the Wikipedia article XOP instruction set (section History, last paragraph) it states exactly the same, that Zen lacks Piledrivers FMA4, TBM, XOP and LWP.
I changed the recommended CFLAGS in Safe CFLAGS and this article accordingly. Luttztfz (talk) 17:15, 17 May 2017 (UTC)
Naib ,

Yup, this can be shown via GCC echo | gcc -### -E - -march=native | grep -i lwp Using built-in specs.

COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/7.1.0/gcc Target: x86_64-pc-linux-gnu Configured with: /var/tmp/portage/sys-devel/gcc-7.1.0-r1/work/gcc-7.1.0/configure --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/7.1.0 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/7.1.0/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.1.0 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.1.0/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.1.0/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/7.1.0/include/g++-v7 --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/7.1.0/python --enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt --disable-werror --with-system-zlib --enable-nls --without-included-gettext --enable-checking=release --with-bugurl= --with-pkgversion='Gentoo 7.1.0-r1 p1.1' --disable-esp --enable-libstdcxx-time --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-multilib --with-multilib-list=m32,m64 --disable-altivec --disable-fixed-point --enable-targets=all --disable-libgcj --enable-libgomp --disable-libmudflap --disable-libssp --disable-libcilkrts --disable-libmpx --enable-vtable-verify --enable-libvtv --enable-lto --without-isl --enable-libsanitizer --disable-default-pie --enable-default-ssp Thread model: posix gcc version 7.1.0 (Gentoo 7.1.0-r1 p1.1) COLLECT_GCC_OPTIONS='-E' '-march=native'

/usr/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/cc1 -E -quiet - "-march=znver1" -mmmx -mno-3dnow -msse -msse2 -msse3 -mssse3 -msse4a -mcx16 -msahf -mmovbe -maes -msha -mpclmul -mpopcnt -mabm -mno-lwp -mfma -mno-fma4 -mno-xop -mbmi -mno-sgx -mbmi2 -mno-tbm -mavx -mavx2 -msse4.2 -msse4.1 -mlzcnt -mno-rtm -mno-hle -mrdrnd -mf16c -mfsgsbase -mrdseed -mprfchw -madx -mfxsr -mxsave -mxsaveopt -mno-avx512f -mno-avx512er -mno-avx512cd -mno-avx512pf -mno-prefetchwt1 -mclflushopt -mxsavec -mxsaves -mno-avx512dq -mno-avx512bw -mno-avx512vl -mno-avx512ifma -mno-avx512vbmi -mno-avx5124fmaps -mno-avx5124vnniw -mno-clwb -mmwaitx -mclzero -mno-pku -mno-rdpid --param "l1-cache-size=32" --param "l1-cache-line-size=64" --param "l2-cache-size=512" "-mtune=znver1"


LIBRARY_PATH=/usr/lib/gcc/x86_64-pc-linux-gnu/7.1.0/:/usr/lib/gcc/x86_64-pc-linux-gnu/7.1.0/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-pc-linux-gnu/7.1.0/../../../../x86_64-pc-linux-gnu/lib/:/usr/lib/gcc/x86_64-pc-linux-gnu/7.1.0/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-E' '-march=native'

--Naib (talk) 18:29, 17 May 2017 (UTC)