https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81253
Bug ID: 81253 Summary: Flags -march and -mtune are ignored Product: gcc Version: 6.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: fortran Assignee: unassigned at gcc dot gnu.org Reporter: kidon at posteo dot de Target Milestone: --- I have built GCC 6.3.0 on a Intel Broadwell machine with FreeBSD 11. The binary package of GCC is used on different client machines (each != Broadwell). Trying to compile arbitrary Fortran code with GNU Fortran results in an internal compiler error: $ gfortran6 test.f08 -o test <built-in>: internal compiler error: Illegal instruction It seems that Broadwell-specific instructions are compiled into GNU Fortran even if additional flags to prevend this are set: CFLAGS="-march=x86-64 -mtune=generic" MAKE_ENV+= BOOT_CFLAGS="-march=x86-64 -mtune=generic" CONFIGURE_ENV+= BOOT_CFLAGS="-march=x86-64 -mtune=generic" These flags are ignored after stage 3 of the build process. The same behaviour can be seen when building GCC 4.9/5.4/7.0.