On Sun, Oct 7, 2012 at 4:58 PM, Kenneth Zadeck <zad...@naturalbridge.com> wrote: > > On 10/07/2012 09:19 AM, Richard Guenther wrote: >>> >>> >In fact, you could argue that the tree level did it wrong (not that i am >>> >suggesting to change this). But it makes me think what was going on >>> > when >>> >the decision to make TYPE_PRECISION be an INT_CST rather than just a HWI >>> > was >>> >made. For that there is an implication that it could never take more >>> > than >>> >a HWI since no place in the code even checks TREE_INT_CST_HIGH for >>> > these. >> >> Well - on the tree level we now always have two HWIs for all INTEGER_CSTs. >> If >> we can, based on the size of the underlying mode, reduce that to one >> HWI we already >> win something. If we add an explicit length to allow a smaller >> encoding for larger modes >> (tree_base conveniently has an available 'int' for this ...) then we'd >> win in more cases. >> Thus, is CONST_INT really necessarily better than optimized CONST_WIDE_INT >> storage? > > i have to admit, that looking at these data structures gives me a headache. > This all looks like something that Rube Goldberg would have invented had he > done object oriented design (Richard S did not know who Rube Goldberg when > i mentioned this name to him a few years ago since this is an American > thing, but the british had their own equivalent and I assume the germans do > too.). > > i did the first cut of changing the rtl level structure and Richard S threw > up on it and suggested what is there now, which happily (for me) i was able > to get mike to implement. > > mike also did the tree level version of the data structures for me. i will > make sure he used that left over length field. > > The bottom line is that you most likely just save the length, but that is a > big percent of something this small. Both of rtl ints have a mode, so if we > can make that change later, it will be space neutral.
Yes. Btw, as for Richards idea of conditionally placing the length field in rtx_def looks like overkill to me. These days we'd merely want to optimize for 64bit hosts, thus unconditionally adding a 32 bit field to rtx_def looks ok to me (you can wrap that inside a union to allow both descriptive names and eventual different use - see what I've done to tree_base) Richard.
