Mentioned here: http://gcc.gnu.org/ml/gcc-help/2007-08/msg00200.html
And I tested it to make sure it was still not supported: [andrew-pinskis-computer:~] apinski% ~/local-gcc/bin/gcc -march=native t.c -O2 -o - -S t.c:1: error: bad value (native) for -march= switch t.c:1: error: bad value (native) for -mtune= switch [andrew-pinskis-computer:~] apinski% uname -a Darwin andrew-pinskis-computer.local 8.10.1 Darwin Kernel Version 8.10.1: Wed May 23 16:33:00 PDT 2007; root:xnu-792.22.5~1/RELEASE_I386 i386 i386 -- Summary: -march=native is not supported under x86 darwin Product: gcc Version: 4.3.0 Status: UNCONFIRMED Severity: enhancement Priority: P3 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org GCC build triplet: i386-apple-darwin8.10 GCC host triplet: i386-apple-darwin8.10 GCC target triplet: i386-apple-darwin8.10 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33115