Re: [PATCH] trivial: the memset operation on a automatic arrayvariable should be optimized out by data initialization

[Adrian Bunk]

On Mon, Jun 18, 2007 at 10:07:21AM -0700, Jeremy Fitzhardinge wrote:
> Denis Cheng wrote:
> > From: Denis Cheng <crquan@xxxxxxxxx>
> >
> > the explicit memset call could be optimized out by data initialization,
> > thus all the fill working can be done by the compiler implicitly.
> 
> How does the generated code change?  Does gcc do something stupid like
> statically allocate a prototype structure full of zeros, and then memcpy
> it in?  Or does it generate a series of explicit assignments for each
> member?  Or does it generate a memset anyway?
> 
> Seems to me that this gives gcc the opportunity to be more stupid, and
> the only right answer is what we're doing anyway.

I checked with gcc 4.2, and gcc is quite clever:

If an array is big, gcc uses memset.
If an array is small, gcc does it directly in assembler.

>     J

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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