Nicolas Pitre wrote:
> On Thu, 9 Oct 2008, Brandon Casey wrote:
>
>> "Possible" benefits:
>>
>> 1) more concise, so it improves readability in most cases
>> 2) gives compiler more flexibility when optimizing
>
> Beware beware. At some point this wasn't a gain at all with some gcc
> versions as it was stupid enough to construct a temporary object on the
> stack corresponding to "{ 0, }" and afterward do the assignment by
> *copying* this object to a different stack slot corresponding to the
> actual variable instead of constructing the initial value in place.
>
> Also note that, on the other hand, gcc is smart enough to optimize a
> memset() using a constant size and value already by doing appropriate
> code replacement inline. I've also seen cases where gcc did the
> opposite and replaced an explicit assignment like your patch does with
> an actual call to memset() when optimizing for size.
I'd call that flexibility.
> So when claiming flexibility for the compiler to better optimize things,
> please make sure this is really what is happening through assembly dump
> inspection.
I didn't claim the compiler _would_ do a better job at optimizing if
memset wasn't used (though my expectation is that it would do no worse,
and I don't have assembly dumps to back that up). I suggested it could
give the compiler more flexibility. In some strange way you seem to
agree with me and have given 3 examples of ways that compilers may
optimize static initialization. :)
Anyway, this is a nothing patch. There is no functional change.
If readability is not improved, it is not worth applying. Of course, I
don't plan on scanning through and converting all of the existing assignments
which use { 0, } to use memset. I find a single step declaration/initialization
simpler. Not sure why that seems to be the case in the git source for simple
variables but not structures.
-brandon
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