OK, thank you very much. I interpreted it wrongly.
And I agree with Ross's suggestion like "This option has no
effect unless -fstrict-aliasing is active".
One more question is why we won't make it "sufficient condition"?
I think many newbies like me would not know about "strict-aliasing".
But when we turn on -O2 options, the behavior after apply
strict-aliasing may produce incorrect code.
So if there is not any warnings, the incorrect behavior after applying
strict-aliasing would lead to a misconception that GCC is buggy?
Also, it would cost some time to debug and find the truth about
"strict-aliasing".
//I think I have learned a great lesson that I should always use -Wall
options first to avoid implicitly turned on optimizations without
warnings
Best,
Jim
On Fri, Feb 13, 2009 at 6:53 PM, 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?
>
> Paolo
>
