[PATCH] D118527: [X86] Promote default mtune from generic to sandybridge

Fri Jan 28 23:32:58 PST 2022

pengfei added a comment.

In D118527#3281488 <https://reviews.llvm.org/D118527#3281488>, @craig.topper wrote:

> I believe the design here was supposed to be that "generic" would be updated in X86.td on an ongoing basis to be more modern. So that if users pass -mtune=generic it would evolve over time.
>
> This matches gcc behavior
>
>   ‘generic’
>   Produce code optimized for the most common IA32/AMD64/EM64T processors. If you know the CPU on which your code will run, then you should use the corresponding -mtune or -march option instead of -mtune=generic. But, if you do not know exactly what CPU users of your application will have, then you should use this option.
>   
>   As new processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the processors that are most common at the time that version of GCC is released.
>   
>   There is no -march=generic option because -march indicates the instruction set the compiler can use, and there is no generic instruction set applicable to all processors. In contrast, -mtune indicates the processor (or, in this case, collection of processors) for which the code is optimized.

Thanks for the information, I'll try the other way, thanks Craig!

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https://reviews.llvm.org/D118527