[lkml]   [2007]   [Jun]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] trivial: the memset operation on a automatic array variable should be optimized out by data initialization
On Mon, Jun 18, 2007 at 10:07:21AM -0700, Jeremy Fitzhardinge wrote:
> Denis Cheng wrote:
> > From: Denis Cheng <>
> >
> > 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



"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

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-06-19 15:29    [W:0.079 / U:1.196 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site