I'm experimentally rebuilding rawhide with the not-yet-released GCC 15 to see if anything breaks, and to help write the porting guide.  See https://fedoraproject.org/wiki/User:Dmalcolm/gcc-15

My test build with GCC 15 failed on x86_64:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed/build/8476130/

whereas my test build with GCC 14 succeeded:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed.checker/build/8477832/

Looking at the failure logs
https://download.copr.fedorainfracloud.org/results/dmalcolm/gcc-15-smoketest-3.failed/fedora-rawhide-x86_64/08476130-blis/builder-live.log.gz

I see:

gcc -O2 -O3 -mavx512f -mavx512pf -mfpmath=sse -march=knl -O2 -fexceptions -g -grecord-gcc-switches -pipe -Wall -Wno-complain-wrong-lang -Werror=format-security -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -march=x86-64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -mtls-dialect=gnu2 -O3 -funsafe-math-optimizations -g -Wall -Wno-unused-function -Wfatal-errors -fPIC -std=c99 -D_POSIX_C_SOURCE=200112L -fopenmp -Iinclude/x86_64 -I./frame/3/ -I./frame/1m/ -I./frame/1f/ -I./frame/1/ -I./frame/include -I./frame/compat/cblas/src/ -DBLIS_VERSION_STRING=\"0.9.0\" -DBLIS_IS_BUILDING_LIBRARY -fvisibility=hidden -c kernels/knl/1m/bli_dpackm_knl_asm_24x8.c -o obj/x86_64/kernels/knl/1m/bli_dpackm_knl_asm_24x8.o
cc1: error: unrecognized command-line option ‘-mavx512pf’
make: *** [Makefile:652: obj/x86_64/kernels/knl/1m/bli_dpackm_knl_asm_24x8.o] Error 1

Looking at https://gcc.gnu.org/gcc-15/changes.html I see:
"Support for Xeon Phi CPUs (a.k.a. Knight Landing and Knight Mill) were removed in GCC 15. GCC will no longer accept -march=knl, -march=knm, -mavx5124fmaps, -mavx5124vnniw, -mavx512er, -mavx512pf, -mprefetchwt1, -mtune=knl, and -mtune=knm compiler switches."

I'm not sure what you need to do at this point, but I'm recording the failure here to help keep track of it.

Reproducible: Always