On Tue, 24 May 2016, Robert Suchanek wrote: > The following changes the default behaviour of shift splitting > for MIPS16 e.g. the shifts will be split only when used with > undocumented -mno-debugd option that is now switched on by default. > > This appears to enable better optimization in certain cases, and hence, > giving slightly better performance.
Thank you for your contribution, however I have some issues with your proposal. First of all since TARGET_DEBUG_D_MODE is used across several places I think this really should be split into two separate pieces, independently reviewed. Then we have two parts: 1. The change to the expander is probably all but obviously correct as it complements a similar one applied to the corresponding splitters eons ago (back in 2001), although I wonder why we need to have both the splitters and instructions split manually in the expander in the first place. Can you please investigatie it? 2. The other change is far from obvious since it flips the splitting default, which has been there since forever (or the addition of MIPS16 support back in 1998). So I think it needs a justification more elaborate than just "certain cases", and perhaps a proper command-line option defined rather than using an obscure debugging hook. It may also make sense to set the default dynamically from the CPU tuning selected -- if the "certain cases" change from CPU to CPU, that is. Can you please look into it? Maciej
