2011/5/26 Jan Hubicka <hubi...@ucw.cz>: >> On Thu, May 26, 2011 at 12:45 PM, Jan Hubicka <hubi...@ucw.cz> wrote: >> >> >> >> This looks all very hackish with no immediate benefit mostly because >> >> of the use of lto_output_string. I think what you should do instead >> >> is split up lto_output_string_with_length into the piece that streams >> >> the string itself to the string-stream and returns an index into it >> >> and the piece streaming the index to the specified stream. Then you >> >> can simply bitpack that index and the two int line / column fields. >> > >> > Hmm, I plan to optimize string streaming (since we always stream one uleb >> > to >> > set it is non-NULL that can be easilly handled by assigining NULL string >> > index >> > 0). How precisely you however suggest to bitpack line/column and string >> > offset >> > together? >> >> Similar to how you suggested, stream bits for a changed flag but >> instead of finishing the bitpack simply stream HOST_BITS_PER_INT >> bits for line (if changed), colunn (if changed) and file string index (if >> changed and the index is 'int'). >> >> I mostly want to avoid the split between the changed bits and the >> data output, esp. breaking the bitpack. > > Well, that won't get me for < 1 byte overhead when location is unchanged or > unknown (that is true for about half of cases in my stats).
Why not? it would be 3 bits. > Additionally > HOST_BITS_PER_INT is host sensitive and wasteful compared to ulebs here as the > line numbers, file indexes and columns are all usually small numbers, so they > ought to fit in 16, 8 and 8 bits most of time. So we would end up in need of > inventing something like uleb in bitpack? Well, we could do that by default for > 8 bit values we pack. I think the location CSE using only 3 bits for unchanged locations should save the most, not so much the use of ulebs for line/column. (you could also encode the number of needed bytes for a changed line/column and then only that many number of bytes). Richard. > Honza >
