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That means GCC cannot compile Linux; it already optimises
some accesses to scalars to smaller accesses when it knows
it is allowed to.  Not often though, since it hardly ever
helps in the cost model it employs.

Please give an example code snippet + gcc version + arch
to back this up.

	unsigned char f(unsigned long *p)
	{
	        return *p & 1;
	}

This doesn't really matter since we only care about the LSB.

It is exactly what I claimed, and what you asked proof of.

Do you have an example where gcc reads it non-atmoically and
we care about all parts?

Like I explained in the original mail; no, I suspect such
a testcase will be really hard to construct, esp. as a small
testcase.  I have no reason to believe it is impossible to
do so though -- maybe someone else can write trickier code
than I can, in which case, please do so.


Segher