On 07/24/2018 11:18 AM, Segher Boessenkool wrote: > This patch allows combine to combine two insns into two. This helps > in many cases, by reducing instruction path length, and also allowing > further combinations to happen. PR85160 is a typical example of code > that it can improve. > > This patch does not allow such combinations if either of the original > instructions was a simple move instruction. In those cases combining > the two instructions increases register pressure without improving the > code. With this move test register pressure does no longer increase > noticably as far as I can tell. > > (At first I also didn't allow either of the resulting insns to be a > move instruction. But that is actually a very good thing to have, as > should have been obvious). > > Tested for many months; tested on about 30 targets. > > I'll commit this later this week if there are no objections. > > > Segher > > > 2018-07-24 Segher Boessenkool <seg...@kernel.crashing.org> > > PR rtl-optimization/85160 > * combine.c (is_just_move): New function. > (try_combine): Allow combining two instructions into two if neither of > the original instructions was a move. I've had several instances where a 2->2 combination would be useful through the years. I didn't save any of those examples though... Good to see the limitation being addressed.
jeff
