------- Comment #5 from rguenther at suse dot de 2009-04-25 14:12 ------- Subject: Re: gcc-4.4 -Wstrict-aliasing and -Wstrict-aliasing=3 behaves like -Wstrict-aliasing=2 in gcc-4.3
On Sat, 25 Apr 2009, Richard Guenther wrote: > On Sat, 25 Apr 2009, edwintorok at gmail dot com wrote: > > > > > > > ------- Comment #2 from edwintorok at gmail dot com 2009-04-25 13:49 > > ------- > > (In reply to comment #1) > > > Casting through a union (2) > > > > > > describes an invalid way of doing type-punning. > > > > There is also a citation from C99 on that page: > > "An object shall have its stored value accessed only by an lvalue expression > > that has one of the following types: > > > > * a type compatible with the effective type of the object, > > * a qualified version of a type compatible with the effective type of > > the > > object, > > * a type that is the signed or unsigned type corresponding to the > > effective > > type of the object, > > * a type that is the signed or unsigned type corresponding to a > > qualified > > version of the effective type of the object, > > * an aggregate or union type that includes one of the aforementioned > > types > > among its members (including, recursively, a member of a subaggregate or > > contained union), or > > * a character type." > > > > I'm casting to a union that has both types as members, why doesn't that fit > > under the 5th case in the above quote? > > Because it is certainly backwards. Or rather, this refers to a compatible type to the type that was used to store the value, so it doesn't apply to type-punning. Richard. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39895
