Add tentative support for KNL AVX512

Also what might work on Skylake, but these cpuids are hard to comfirm

m4/ax_cc_maxopt.m4

@@ -128,6 +128,8 @@ if test "$ac_test_CFLAGS" != "set"; then
 		    *3?6[[cf]]?:*:*:*|*4?6[[56]]?:*:*:*|*4?6[[ef]]?:*:*:*) icc_flags="-xCORE-AVX2 -xCORE-AVX-I -xAVX -SSE4.2 -xS -xT -xB -xK" ;;
 		    *000?f[[346]]?:*:*:*|?f[[346]]?:*:*:*|f[[346]]?:*:*:*) icc_flags="-xSSE3 -xP -xO -xN -xW -xK" ;;
 		    *00??f??:*:*:*|??f??:*:*:*|?f??:*:*:*|f??:*:*:*) icc_flags="-xSSE2 -xN -xW -xK" ;;
+		    *5?6E?:*:*:*) icc_flags="-xCORE-AVX512" ;;
+		    *5?67?:*:*:*) icc_flags="-xMIC-AVX512" ;;
                   esac ;;
               esac ;;
           esac

[Matthieu Schaller]

Should we follow the pattern of the other CPUs and use

icc_flags="xCORE-AVX512 -xCORE-AVX2 -xCORE-AVX-I -xAVX -SSE4.2 -xS -xT -xB -xK ?

[Peter W. Draper]

Most of these options are documented as initiated by the higher support flag, except -xS and following which are not documented, so I think we keep it simple until we know otherwise.

[Matthieu Schaller]

[cosma-b] ~ > icc -xS
icc: command line remark #10279: option '-xS' is deprecated and will be removed in a future release. See '-help deprecated'
icc: command line error: no files specified; for help type "icc -help"

According to the help deprecated help pages, it used to be the flag for SSE4.1.

[cosma-b] ~ > icc -help deprecated

Deprecated Options
--------------
[...]
-xK                      use -mia32
-xT                      use -xSSSE3
-xS                      use -xSSE4.1
[...]

Agree with you, let's drop this.

Should we suggest your fix to GNU ?