This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Aliasing brokenness (Was: Re: [patch RFC] SH: Use FRAME_GROWS_DOWNWARD)


Andreas Schwab wrote:
Gabriel Dos Reis <gdr@integrable-solutions.net> writes:


Is the conclusion that a presence of "potentially unused" union that
contains two structures with the same prefix destroys non-aliasing
assumptions?


IMHO the third example in 6.5.2.3 gives a strong hint at that.  AFAIU the
second fragment becomes valid as soon as declaration of the union is moved
before function f.

Exactly.


I think it's hard to read 6.5.2.3 to say anything other than that the mere visibilty implies that sturctures contained in the union with common initial sequences may alias. I don't particularly like that rule, but I think that's what it says.

--
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
(916) 791-8304


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]