Re: [RFA/dwarf] Optimize partial DIE reading for uninteresting DIEs

[Daniel Jacobowitz <drow@false.org>]

On Thu, Feb 26, 2004 at 09:58:32PM -0500, Jim Blandy wrote:
> 
> Daniel Jacobowitz <drow@false.org> writes:
> > You're mistaken about the expense.  In particular read_unsigned_leb128
> > is much slower than skip_uleb128 because of the computations to build
> > the result; IIRC variable shifts are expensive.  Yes, this was measured
> > with an optimized build and a non-intrusive profiler.  There's also the
> > different memory access patterns.
> 
> No kidding.  I'm amazed.  Okay.
> 
> > Most of the speedup comes from not reading in the attribute values,
> > though.
> 
> If what you say above is so, then two distinct versions of the
> attribute traversal are clearly called for.
> 
> It would be interesting to compare profiling results between two GDB's
> that differ only in whether they use your attribute skipper or the
> attribute value reader.

For this patch, the changes were pretty small.  For the larger change,
with just partial symbol table reading, read_unsigned_leb128 dropped
way down and skip_leb128 didn't climb equally far up.

Let me reproduce those results, though.  Something seems suspicious.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer