> Hello, > > There is code in stmt.c since the initial checkin, that tries to > balance a switch tree according to some ascii heuristics. I see a > couple of problems with this code: > > 1. It doesn't seem to help much. With the attached patch to remove the > code, I see no compile time changes to e.g. compile GCC itself. > > 2. It isn't clear what the heuristic is based on (no reference to any > testing done, or a reference to a book or paper). > > 3. The heuristic is applied for case values in the range <-1,127> > (inclusive) even if the type of the switch expression isn't char or > int but e.g. an enum. This results in funny application of this > heuristic in GCC itself to e.g. some cases of enum rtx_code and enum > tree_code.
Note that it would make a lot of sense to teach this heuristics predict.c and properly identify chars. Also it is possble to get an historgrams from profile feedback into switch expansion. I always wanted to do that once switch expansion code is cleaned up and moved to gimple level... Honza > > > The attached patch removes the heuristic. > > Bootstrapped and tested on powerpc-unknown-linux-gnu. OK for trunk? > > Ciao! > Steven
