On Mon, Aug 20, 2012 at 5:00 PM, Bin.Cheng <amker.ch...@gmail.com> wrote: > Hi, > Currently I am working on improving hoist pass by calculating register > pressure and using the info to guide hoist process. It works well and > I will send a patch once I finish it. > > In this work I reused codes in loop-invariant and called > ira_set_pseudo_classes function to calculate register pressure. The > problem is that ira_set_pseudo_classes sets pseudo_classes_defined_p > to TRUE, which causes function find_costs_and_classes scans > instructions only once to find the best reg class to use for each > allocno. > > In my understanding, these part of codes is introduced for calculating > reg pressure in schedulor and loop-invariant. What I do not understand > is why we make IRA behave differently when register pressure is > calculated before IRA pass? > > In the work of hoist, I found bigger regression in code size causes by > the changed behavior of IRA. > > My questions are: > 1. could somebody give some explanation on this. > 2. Is it possible to calculate register pressure by reusing existing > code while do not change behavior of IRA? > I realized it is designed in this way to ensure register pressure are calculated and modeled in same way for loop-invariant/schedulor and ira. But hoist is an early rtl pass and patterns/pseudo are changed a lot from hoist to ira pass, it's better to not use classes for pseudo registers. The data I collected from CSiBE support this point.
So how about I reset pseudo_classes_define_p after calculating register pressure in hoist pass? Any one give some comments? Thanks. -- Best Regards.
