On Thu, Oct 13, 2016 at 5:22 PM, Jeff Law <l...@redhat.com> wrote: > On 10/12/2016 02:48 AM, Richard Biener wrote: >> >> On Tue, Oct 11, 2016 at 11:34 PM, Marc Glisse <marc.gli...@inria.fr> >> wrote: >>> >>> On Tue, 11 Oct 2016, Bin Cheng wrote: >>> >>>> We missed folding (convert)(X op const) -> (convert)X op (convert)const >>>> for unsigned narrowing because of reason reported at >>>> https://gcc.gnu.org/ml/gcc/2016-07/msg00126.html >>>> This patch fixes the issue by adding new match&simplify pattern, it also >>>> adds a test case. This is the prerequisite patch for next patch adding >>>> new >>>> vectorization pattern. >>> >>> >>> >>> Some technical comments below. I am sure Jeff and/or Richi will have more >>> to >>> say on the approach. I am a bit surprised to see it as adding a new >>> transformation, instead of moving an old one. >> >> >> The "old one" would be c-family/c-common.c:shorten_binary_op. It's >> generally >> prefered to move stuff, preserving semantics. > > Right. Kai and I hadn't looked much at shorten_binary_op (focusing more on > shorten_compare). But the same principles apply to both. > > Namely that the existing routines should be twiddled to handle warnings > only, but not modify the underlying IL. IL modifications (canonicalization > and optimization) should be moved into the match.pd framework.
fortunately shorten_binary_op itself does not emit any warnings! > When Kai left Red Hat, that work stalled. I've got bits and pieces of that > work lying around, but I don't think they'd help Bin's work right now. > >> >> There is also already a bunch of similar match.pd patterns here: > > [ ... ] > Right. Those were a first start at handling some of the desired narrowing, > focused primarily on BZs that required narrowing to resolve. Like Kai's > work, I have some generalizations and improvements in a half-completed state > here, but haven't had time to work on them. > > > Jeff
