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[Bug tree-optimization/55559] [4.6/4.7/4.8 Regression] Marshalling double through union with inlines, incorrect behavior with -O2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55559

--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> 2012-12-04 09:02:00 UTC ---
On Mon, 3 Dec 2012, mpreda at gmail dot com wrote:

> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55559
> 
> --- Comment #7 from Mihai Preda <mpreda at gmail dot com> 2012-12-03 22:13:03 UTC ---
> Thanks, I didn't realize that (unsigned)-1.0 is undefined.
> 
> For the behavior I was expecting it's enough to use an intermediary cast
> through int, e.g. (unsigned)(int)-1.0.

Yes, that makes it implementation-defined (and all implementations
I know of do what you expect, modulo-two reduction).

> It may be nice to generate a consistent (-O0/-O1) result for (unsigned)-1.0
> though, even if not required by the standard.

That's unfortunately generally impossible.


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