I am a little hesitant about whether to let -march implicitly set -mtune, because this is equivalent to making -march become another -mcpu with higher priority, and we cannot avoid discussing the priority of -march and -mtune again, and no matter what the priority is, it will introduce more complicated rules, so I prefer not to implicitly set -mtune.
And the option -march=unset was discussed at the RISC-V LLVM sync up meeting, and at that time, the participants, including me, did not realize that ARM already had this option. Although I think -march=unset is ugly, but this does solve the current problem and does not change the semantics or priority order of the current overall options, so this is a valid option we may consider. So we have few options here: 1. Accept -march=<cpu-name>. not changing -mtune 2. Accept -march=<cpu-name>. also implied -mtune 3. Accept -march=unset and -mtune=unset to let -mcpu be able to override both options. Here is example when we want to override arch with a cpu name by different options: 1. riscv64-linux-gcc -march=rv64gc -march=foo-cpu 2. riscv64-linux-gcc -march=rv64gc -march=foo-cpu 3. riscv64-linux-gcc -march=rv64gc -march=unset -mcpu=foo-cpu And when we also want to override mtune: 1. riscv64-linux-gcc -march=rv64gc -march=foo-cpu -mtune=foo-cpu 2. riscv64-linux-gcc -march=rv64gc -march=foo-cpu 3. riscv64-linux-gcc -march=rv64gc -march=unset -mtune=unset -mcpu=foo-cpu Preference to me: - Prefer option 1. - Less prefer option 3. (acceptable but I don't like) - Strongly dislike option 2.
