On Fri, Nov 8, 2013 at 4:41 PM, Jakub Jelinek wrote: > On Fri, Nov 08, 2013 at 04:32:09PM +0100, Steven Bosscher wrote: >> On Fri, Nov 8, 2013 at 4:18 PM, Joern Rennecke wrote: >> > On 8 November 2013 14:45, Steven Bosscher wrote: >> >> This is IMHO not OK without at least an explanation of why the >> >> comparison of two const_ints is not folded. Better yet would be to fix >> >> that underlying problem. We should not present such non-sense to the >> >> RTL parts of the middle end. >> > >> > Which part would be responsible to folding the comparison at -O1 ? >> > FWIW, as I just commented in the PR, one of the operands is an ssa_name >> > with a known value. >> >> This usually is taken care of by one of the many propagation passes >> (CCP, VRP, forwprop, DOM, even FRE/PRE). The only cases I've >> previously encountered, where a known value ends up not being >> propagated, is when the propagation is somehow overlooked and the >> known value is only replaced at out-of-ssa time, i.e. TER. >> >> The only way to find out where the propagation should have happened, >> is by looking at the gimple dumps. > > Well, most of the passes you've mentioned can be disabled with -fno-tree-* > but still we shouldn't ICE on it, so the expander can't assume that > it will never see something like that, only doesn't have to try too hard > to optimize that unlikely case. Of course, it is nice to know why it hasn't > been optimized in the particular case.
Even with the gimple opts disabled, a const-const comparison would normally be folded by the RTL expanders. Ciao! Steven
