On 2013-09-26 18:30:10 +0100, Andrew Haley wrote: > On 09/26/2013 06:02 PM, Vincent Lefevre wrote: > > On 2013-09-26 15:49:05 +0100, Andrew Haley wrote: > >> On 09/26/2013 09:29 AM, Vincent Lefevre wrote: > >>> On 2013-09-25 22:29:58 -0400, James K. Lowden wrote: > >>>> You mean that a naïve rendering of the source code implies an overflow > >>>> where none might exist in the actual emitted object code. And, > >>>> presumably, the converse: that even if the source is written such that > >>>> there logically can't be an overflow, the compiler might render object > >>>> code that does. > >>> > >>> The converse is forbidden. > >> > >> You'll find it hard to justify that by any language in the standard. > > > > What do you mean? > > There is no reason why a compiler should not generate an overflow > where none is written in the program, as long as it doesn't generate > a different result. OK, I wouldn't call that an overflow, then. I thought you meant rewrite the code in an intermediate step, generating an overflow, before knowing the consequences at the target level. The term "overflow" has a connotation of exception / undefined behavior. -- Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <http://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
