Re: ANSI alias rules checker in GCC, other optimizing compilers

Silvius Rus wrote:
> I am about to send in a patch to GCC 4.3 that will address some
> shortcomings. The new implementation performs single function
> (intraprocedural) alias and data flow analysis to rule out false
> negatives and to discover more cases which are not caught by the
> current implementation, such as aliases through malloc-ed memory.


Silvius, do you plan to leave meaning of current options intact? As I
quoted, GCC manual says:


"-Wstrict-aliasing
This option is only active when '-fstrict-aliasing' is active. It warns
about code which might break the strict aliasing rules that the
compiler is using for optimization. The warning does not catch all
cases, but does attempt to catch the more common pitfalls. It is
included in '-Wall'.


-Wstrict-aliasing=2
This option is only active when '-fstrict-aliasing' is active. It warns
about code which might break the strict aliasing rules that the
compiler is using for optimization. This warning catches more cases
than '-Wstrict-aliasing', but it will also give a warning for some
ambiguous cases that are safe."




Let us pay attention to these words: "This warning
[-Wstrict-aliasing=2] catches more cases than '-Wstrict-aliasing', but
it will also give a warning for some ambiguous cases that are safe."
But as Ian suggested, both warning levels produce false positives. The
only difference is that =2 also pays attention to "restrict" qualifier.
So, the current options description is a misguiding one?


Yours,
Andrey

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