Re: About strict-aliasing warning

[Ross Smith <r-smith at ihug dot co dot nz>]

Paolo Bonzini wrote:
> > "-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.
> > It is equivalent to -Wstrict-aliasing=3 "
> >
> > and -O2 would active -fstrict-aliasing by default, which should also
> > active this options.
>
> No, the text above means that "-fstrict-aliasing" is a *necessary*
> condition to get aliasing warnings, not a sufficient condition.
>
> Do you have suggestions for how to clarify the text?

Pergaps the first sentence should read something like "This option is 
only respected when -fstrict-aliasing is active", or "This option has no 
effect unless -fstrict-aliasing is active". I follow what the existing 
wording was intended to mean, but I can also see how it could easily be 
interpreted to mean that -fstrict-aliasing automatically implies 
-Wstrict-aliasing.

-- Ross Smith