Re: Faster compilation speed

[Nathan Sidwell <nathan at codesourcery dot com>]

Neil Booth wrote:

> Just my opinion, Mike, but I think a lot of current slowness is due to
> redo-ing too many things, and not taking advantage of ordering or whatever
> technique so that conclusions deduced from internal representations are
> made in a logical, efficent way.  (e.g. I think we try to constant fold
> things that we've already tried to constant fold and failed, repeatedly,
> and we don't do the constant folding we do do in an optimal way.  I could
> be wrong, though; I've not looked in detail).  I cannot explain this
Yup, redoing things seems to happen a lot in the c++ front end.
The type conversion machinery seems to work a lot like
	if (complicated fn to try conversion 1)
	  complicated fn to do conversion 1
	else if (complicated fn to try conversion 2)
	  complicated fn to do conversion 2
	...
unifying static_cast, (cast), const_cast, implicit_conversion, overload
arg resolution might be a win.

I think you might be right about fold-const. That's recursive itself,
so we should only need to call that when we really need to flatten
a const, rather than after every new operation.

As you'll have noticed I'm tweaking the coverage machinery to
try and find hotspots and deadspots. My immediate plan for this
is to
a) fix .da files so they don't grow indefinitly large - nearly done
b) add some kind of __builtin_unexpected (), to mark expected
dead code
c) write some perl scripts to munge the gcov output

I hope some of that is useful to others.

nathan

-- 
Dr Nathan Sidwell   ::   http://www.codesourcery.com   ::   CodeSourcery LLC
         'But that's a lie.' - 'Yes it is. What's your point?'
nathan@codesourcery.com : http://www.cs.bris.ac.uk/~nathan/ : nathan@acm.org