Re: -funsafe-loop-optimizations

[Robert Dewar <dewar at adacore dot com>]

Paul Schlie wrote:

> I suspect we're not referring to the same thread of context; I made the
> comment in response to: http://gcc.gnu.org/ml/gcc/2005-01/msg00084.html
> which I didn't interpret as referring to the portability of the compiler,
> but rather code compiled by it having potentially different semantics as
> a function of the "target's" type-sizes,

That's not a compiler issue, the author was simply pointing out that code
of the type we are talking about is inherently non-portable. If you have
a loop that is infinite if the size of unsigned is 16 and well behaved if
the size of unsigned is 32, as required by the standard, then you have simply
written non-portable code. This is nothing to do with the compiler. Indeed
if anything the improper "optimization" might have the effect of increasing
portability in practice of this incorrect code. What MK was noting was that
even though this code is non-portable, in practice, it may be portable to
32-bit architectures. That's nothing new, and nothing to do with the code
that gcc generates. C is a language where it is very easy to write non-
portable code if you are not very careful. The compiler cannot somehow
magically correct such programs.