Failure of "long x(cp) char * cp; { return *((long *) cp); }" is a bug?

[Guy Harris]

> Isn't this really a compiler bug?  Doesn't the cast in the
> 		return *((long *) cp);
> give the compiler all the evidence it needs that it should, *on its own*,
> produce code that's the equivalent of the function call?

A piece of software has a "bug" if it's supposed to do something and it
doesn't; for instance, if it's supposed to generate correct code and it
generates incorrect code instead.  The C compiler isn't *supposed* to do
unaligned copying in circumstances like this, so it can hardly be a "bug" if
it doesn't.

> Does the latest version of X3J11 have anything to say on the matter?

The August 11, 1985 draft says:

	C.3.3.2 Address and indirection operators

	...

	Semantics

	...

	     If an invalid value has been assigned to the pointer, the
	behavior of the unary * operator is undefined.  Such invalid
	values include ... *an address inappropriately aligned for the
	type of the object pointed to*...

I *very* sincerely doubt this has been changed in any later drafts.  Such
dereferences are uncommon occurrences, and a programmer can damn well write
their own code to do the unaligned copy.

So a C compiler which doesn't generate unaligned copies is perfectly within
its rights to do so, and has no bug.
-- 
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy at sun.com (or guy at sun.arpa)