Re: Optimization of conditional access to globals: thread-unsafe?

[skaller <skaller at users dot sourceforge dot net>]

On Sun, 2007-10-28 at 18:34 -0700, David Miller wrote:

> More importantly, you cannot break things on people out of mere
> convenience.

If you want a case of this .. its the ill-considered strict aliasing
rules in C. WG14 seems to think C had a strong enough type system
to make this rule, but it does not. So gcc provides a switch
to turn it off.

This is actually a bit annoying, because the granularity is not
so sweet: I'd be happy with floating point aliasing to be strict,
but not integers and *definitely* not pointers.

C is too brain dead for strict aliasing: it could break many
memory management codes which, for example, alias memory
with pointer to void* for alignment purposes, or intptr_t 
for bit fiddling. Or code like this which I write:

	struct X { int x; } x;
	struct Y { int y[1]; } y;
	Y *py  = (Y*)(void*)&x;
	X *px = (X*)(void*)&y;

[My Felix compiler does this cast systematically and deliberately]

-- 
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net