On Mon, 26 Jan 2015, Jakub Jelinek wrote: > On Mon, Jan 26, 2015 at 04:18:32PM +0100, Richard Biener wrote: > > > > Ok for trunk? Or should I delay this to GCC 6? > > > > > > Does this work even without the other patch? > > > > Yes, I've actually developed 2/2 first. The other patch only ever > > emits more warnings... > > Then it probably should be ok. I'm really afraid of emitting more warnings > with such high false positive rate now. > > > > What do you think about Ilya's patch to set TREE_NO_WARNING in the > > > unrolled > > > iterations where we had to keep the exit check? > > > > I don't like it too much - it papers over the real issue and prevents > > valid warnings from being emitted. Maybe we can set TREE_NO_WARNING on > > the last iteration (that is the only one we usually end up warning > > on - like after this patch). There are also many dups - regressions > > in 4.8 I belive where we warn for the last iteration in an unrolled loop. > > Do we check only the last iteration? Won't we warn about other iterations > too? -Warray-bounds have plenty of warnings in dead jump threaded code that > the compiler can't prove is dead etc.
Sure - but for unrolling int a[2]; for (int i = 0; i < 5; i++) a[i] = i; I'd like to see warnings and we only warn if we unroll this because the value-range of i includes indexes that are valid. > IMHO the warning should be done in VRP1 only. Yeah, I agree - but I remember that people wanted the extra stuff from VRP2 (just quickly checked that gcc.dg/Warray-bounds* doesn't regress with disabling VRP2). So - do we want to disable array bound warnings for VRP2? I'd be happy to approve of that and it will most certainly fix all of the recent (4.8+) regressions related to loop peeling. Thanks, Richard.
