cvs commit: src/sys/kern vfs_vnops.c
bde at optusnet.com.au
Fri May 18 14:11:32 UTC 2007
On Fri, 18 May 2007, Dmitry Marakasov wrote:
> * Bruce Evans (bde at optusnet.com.au) wrote:
>>> peter 2007-05-17 15:31:14 UTC
>>> FreeBSD src repository
>>> Modified files:
>>> sys/kern vfs_vnops.c
>>> Eliminate a micro-optimization that hasn't had any effect for 15+ years.
>>> Revision Changes Path
>>> 1.249 +0 -5 src/sys/kern/vfs_vnops.c
>> Since it was only implemented 11.5 years ago (in rev.1.18), it certainly
>> had no effect 15+ years ago, but it probably had an effect later than 11.5
>> years ago.
> I think it refers more to gcc capability to compile var/CONST expression
> where CONST is 2^n into bit shift instruction instead of division. Which
> is more important, has this capability been confirmed?
gcc did this 15+ years ago, except probably for 64-bit types (IIRC,
gcc didn't support 64-bit types on 32-bit machines 15+ years ago).
The micro-optimization was for a 64-bit type. gcc apparently started
optimizing the 64 on 32--bit case some time in the last 11.5 years.
I only checked that the gcc in -current did this. I didn't do the
binary search to find exactly when gcc started doing this.
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