memcpy embedded in gcc?

memcpy embedded in gcc?

[Long Li]

Hi,

I am using a gcc 3.0.4 MIPS crosscompiler on Redhat. I
found something interesting: when I use specifly -O1
for compilation, and I can use memcpy function even I
did not tell the compiler where I declard it or define
it. However, when I specify -O0, then the compiler
tells me undefined reference to this memcpy function.
So my questions are:

1. Is memcpy a built-in function for gcc? But why not
for optimization level 0?

2. Besides memcpy, is there any other functions built
in too?


Thanks a lot!


Long


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Re: memcpy embedded in gcc?

[Daniel Jacobowitz]

On Thu, Feb 13, 2003 at 12:07:57PM -0800, Long Li wrote:
> Hi,
> 
> I am using a gcc 3.0.4 MIPS crosscompiler on Redhat. I
> found something interesting: when I use specifly -O1
> for compilation, and I can use memcpy function even I
> did not tell the compiler where I declard it or define
> it. However, when I specify -O0, then the compiler
> tells me undefined reference to this memcpy function.
> So my questions are:
> 
> 1. Is memcpy a built-in function for gcc? But why not
> for optimization level 0?

Because using it is an optimization.

> 2. Besides memcpy, is there any other functions built
> in too?

Lots.  The list varies depending on the GCC version; see the manual.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer