[Bug jit/66594] jitted code should use -mtune=native

["schuchart at icl dot utk.edu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66594

Joseph <schuchart at icl dot utk.edu> changed:

           What    |Removed                     |Added
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                 CC|                            |schuchart at icl dot utk.edu

--- Comment #10 from Joseph <schuchart at icl dot utk.edu> ---
The lack of target-specific optimizations is biting us quite a bit and manually
specifying an architecture is not really an option, unless we duplicate the
detection mechanism of GCC, which is not ideal. I am not familiar with the GCC
code base and from the discussion below it's not clear what would be needed to
advance this. If someone could provide some hints on what is missing and
how/where it could be implemented we could probably take a stab at it. 

Would it be sufficient to add a macro to the header of the targets (as
suggested here https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66594#c6) that
provide host_detect_local_cpu and ignore the ones that do not provide it? Or
would it be better to hard-code calls for the architectures that provide them,
like in the referenced patch but with architecture-specific pre-processor
guards? We mostly care about i386 and arm/aarch64 but covering all available
bases would be necessary, I guess.