On 2015.08.12 at 13:01 +0200, Richard Biener wrote: > On Tue, Aug 11, 2015 at 9:49 PM, Jeff Law <l...@redhat.com> wrote: > > On 08/06/2015 04:25 AM, Mikael Morin wrote: > >> > >> Hello, > >> > >> this avoids an error found with bootstrap-ubsan. > >> Regression tested on x86_64-unknown-linux-gnu. OK for trunk? > >> > >> Mikael > >> > >> > >> noub_sext.CL > >> > >> > >> 2015-08-05 Mikael Morin<mik...@gcc.gnu.org> > >> > >> * hwint.h (sext_hwi): Rewrite without undefined behaviour on > >> negative SRC. > > > > OK. Hopefully most of the time the precision is known at compile-time which > > would allow for optimization of the resulting code back to the > > pair-of-shifts form by combine. > > I think it is not. The code also lacks a comment on why we do this kind > of obfuscation. > > What kind of error does ubsan run into? That is, for which 'prec'?
See: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67042 -- Markus
