On Fri, Nov 18, 2011 at 11:27 PM, Ralf Corsepius <rc040203@xxxxxxxxxx> wrote:
> [1] -Wstrict-aliasing is one of these cases.
> The spots such warnings point to, often are broken, but not always,
> because GCC has difficulties in identifying these.
This use to be more true, but there are multiple levels of -Wstrict-aliasing and
I would be _highly_ surprised if the default gave a false alarm. I think you
can reliably say that if you get a warning at the default level then you do
have a language standards conformance problem, and that it actually changes
the generated code... but maybe you don't actually crash on any
particular system.
I don't think 'the code is objectively wrong in a meaningful way' is a
false alarm.
I've seen code that miscompiled and crashed due to violating the aliasing rules
but only threw a warning at higher levels. It's arguably too
conservative already.
>If GCC is sure something is wrong, it is supposed to raise errors.
This isn't true. E.g. you can write code which reads and uses
uninitialized memory
where the compiler is _absolutely sure_ of it. You still just get a warning. The
compiler would be compatible with the spec if it replaced this program with
system("rm -rf /"), but you only get a warning.
I quote the manual: "Errors report problems that make it impossible to
compile your program."
(Though I agree with your view wrt the unfortunateness of
style-warnings ("omg you used a
^ without fifty parentheses") being hard to separate from ones where
the compiler knows
that your code is broken.)
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