[dpdk-dev] [PATCH v2] mk: gcc -march support for intel processors code names

[Thomas Monjalon]

2016-09-28 10:54, Liu, Yong:
> Tested-by: Yong Liu <yong.liu at intel.com>
>             FangFang Wei <fangfangx.wei at intel.com>
[...]
>    Description: Build test on different distributions
>    Command / instruction:
>      Verify build pass on listed distributions.
> 
>      OS                   GCC            Kernel
>      Ubuntu 16.04         5.4.0          4.4.0-36-generic
>      Fedora23             5.3.1          4.2.3-300
>      Fedora24             6.1.1          4.6.4-301
>      Ubuntu 12.04         4.6.3          3.8.0-29
>      Ubuntu 12.04 i686    4.6.3          3.8.0-29
>      Ubuntu 14.04         4.8.4          3.16.0-30
>      Ubuntu 14.04 i686    4.8.4          3.16.0-30
>      Fedora18             4.7.2          3.6.10-4
>      Fedora18 i686        4.7.2          3.6.10-4
>      Fedora20             4.8.2          3.15.6-200
>      Fedora20 i686        4.8.3          3.11.0
>      Suse11SP2            4.5.1          3.0.13-0.2
>      Suse12SP3            4.7.2          3.7.10-1.1
>      RHEL7.0              4.8.2          3.10.0-123
>      RHEL7.2              4.8.5          3.10.0-327
>      CentOS7.0            4.8.5          3.10.0-327
>      FreeBSD10.0          4.8.4          10.0-RELEASE
>      FreeBSD10.3          4.8.5          10.3-RELEASE

I do not understand this test.
This patch is dropping a lot of optimizations with compilers older than 4.9 !

Why not recommend GCC 4.9 and keep the graceful degradation for older versions,
at least for one more year, even if it is not optimal for newer architectures?