[clang] [llvm] [X86] support reserve r8~r15 on X86_64 (PR #180242)

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zhouguangyuan0718 wrote:

> severe compile time regression for stage1-O0-g: @nikic
> 
> https://llvm-compile-time-tracker.com/compare.php?from=1b633d6d6d75c172ecd9b9a4e250842468edb137&to=e71f327b46059fe232b205414a3e8c1fc537c80f&stat=instructions:u

Seems the CPU feature detection is too heavy in the common path, maybe moving it to the place after checking options will solve it.  I will have a try.

https://github.com/llvm/llvm-project/pull/180242