Re: [PATCH 1/5] add SWAP macro

From: René Scharfe <l.s.r@web.de>
Date: Jan 30, 2017, 16:48 UTC
Message-ID: <9bcae427-d654-a671-4368-030150168102@web.de>
In-Reply-To: <alpine.DEB.2.20.1701301637570.3469@virtualbox>

Am 30.01.2017 um 16:39 schrieb Johannes Schindelin:

Show 12 quoted lines

> Hi René,
>
> On Sat, 28 Jan 2017, René Scharfe wrote:
>
>> Add a macro for exchanging the values of variables.  It allows users to
>> avoid repetition and takes care of the temporary variable for them.  It
>> also makes sure that the storage sizes of its two parameters are the
>> same.  Its memcpy(1) calls are optimized away by current compilers.
>
> How certain are we that "current compilers" optimize that away? And about
> which "current compilers" are we talking? GCC? GCC 6? Clang? Clang 3?
> Clang 3.8.*? Visual C 2005+?

GCC 4.4.7 and clang 3.2 on x86-64 compile the macro to the same object 
code as a manual swap ; see https://godbolt.org/g/F4b9M9.  Both were 
released 2012.  That website doesn't offer Visual C(++), but since you 
added the original macro in e5a94313c0 ("Teach git-apply about '-R'", 
2006) I guess we have that part covered. ;)

René