[aarch64-port-dev ] RFC: Change stack bang sequence

[Aleksey Shipilev]

On 07/04/2017 05:50 PM, Andrew Haley wrote:
> This patch changes
> 
>   0x0000007fa8f748d4: mov	x9, #0xffffffffffffc000    	// #-16384
>   0x0000007fa8f748d8: movk	x9, #0xfffe, lsl #16
>   0x0000007fa8f748dc: str	xzr, [sp,x9]
> 
> to
> 
>   0x0000007f88bae8d4: sub	x9, sp, #0x14, lsl #12
>   0x0000007f88bae8d8: str	xzr, [x9]
> 
> There's no measurable speed difference on a system I have tested, so
> do we care?  I suppose we do, given that it makes the code slightly
> smaller.  Opinions welcome.

Yes, we do care about code quality cleanups, even if they are not measurable on
a limited amount of workloads we have. This change looks okay to me.

-Aleksey