> From: Segher Boessenkool <seg...@kernel.crashing.org> > Date: Fri, 17 Jul 2020 02:05:19 +0200
> On Tue, Jul 14, 2020 at 04:33:42PM -0500, Segher Boessenkool wrote: > > > If combine only did lower-cost combinations (perhaps with > > > Richard Sandifords lower-size-when-tied suggestion), I guess > > > this wouldn't happen. 0:-) > > > > And we would regress (a LOT). > > Like this. C0 is an unmodified compiler. C1 is with the single_set > modification to is_just_move I committed a minute ago (84c5396d4bdb). > C2 is with this patch: Thanks for doing the numbers. Most targets are of course keyed on the cheaper=same_cost behaviour of combine.c. Just try fixing any obvious general cost-related bug! I mentioned running the test-suites for each of x86_64-linux, aarch64-linux and ppc64le-linux (your numbers confirm my observation) but didn't mention that I *did* inspect one case, IIRC the first regression for x86_64, but decided to break off less than half-way down the rabbit-hole with no obvious target-cost tweak. I'm considering updating my suggested patch with something implementing "INSN_COST(log_link) = 1", but don't hold your breath. brgds, H-P
