On Tue, Mar 20, 2007 at 09:37:38AM -0400, Doug Gregor wrote: > Even if we only use subcodes for the less often used codes, I think we > still take the performance hit. The problem is that it's very messy to
I'm sure smaller hit than when going to 9 bit tree code, and on i386/x86_64 maybe even than 16 bit tree code (if I remember well, 8-bit and 32-bit accesses are usually faster than 16-bit ones). > deal with a two-level code structure inside, e.g., the C++ front end. > I did a little experiment with a very rarely used tree code > (TYPEOF_TYPE), and the results weren't promising: > > http://gcc.gnu.org/ml/gcc/2007-03/msg00493.html If you use what has been suggested, i.e.: #define LANG_TREE_CODE(NODE) (TREE_CODE (NODE) == LANG_CODE ? ((tree_with_subcode *)(NODE))->subcode : TREE_CODE (NODE)) then it shouldn't be so big. Everywhere where you don't need >= 256 codes you'd just keep using TREE_CODE, only if e.g. some switch contains >= 256 FE specific subcodes you'd use LANG_TREE_CODE instead of TREE_CODE. GCC would warn you if you forget to use LANG_TREE_CODE even when it is needed, at least in switches, you'd get warning: case label value exceeds maximum value for type Jakub
