> > > > 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? > > The point is to make location info occupy not even whole byte most of time. > Adding a simple stats claims that for tramp3d 30% of time location is > undefined, 15% of time file changes, 39% of time line changes and 44% of time > column changes (on tramp3d). So assuming one byte for each uleb (that is > optimistic, of course) one need 4 bits for the changed flags + less than a > byte > for the data. Situation is similar for combine.c where unknown id 10%, file > change is 0.5% and line change is 30%.
Note that for tramp3d the function sections reduce in size by about 16%, decl section by about 10%. So there is some immediate benefit. Honza