Re: [PATCHv14 08/17] x86/mm: Reduce untagged_addr() overhead until the first LAM user

[Peter Zijlstra]

On Wed, Jan 11, 2023 at 03:37:27PM +0300, Kirill A. Shutemov wrote:

>  #define __untagged_addr(untag_mask, addr)	({			\
>  	u64 __addr = (__force u64)(addr);				\
> -	s64 sign = (s64)__addr >> 63;					\
> -	__addr &= untag_mask | sign;					\
> +	if (static_branch_likely(&tagged_addr_key)) {			\
> +		s64 sign = (s64)__addr >> 63;				\
> +		__addr &= untag_mask | sign;				\
> +	}								\
>  	(__force __typeof__(addr))__addr;				\
>  })
>  
> #define untagged_addr(addr) __untagged_addr(current_untag_mask(), addr)

Is the compiler clever enough to put the memop inside the branch?