Re: Simplify and speedup df notes creation

[Paolo Bonzini <bonzini at gnu dot org>]

On 06/11/2010 04:43 PM, Jan Hubicka wrote:
> df-notes is trying to reust old notes by collecting them to linklist and then
> re-insert the originals if they did not change. This seems just useless
> excercise since creation of new note is cheap in theory (we maintain freelist),
> but it is somewhat slow because we do 3 function calls.
>
> This patch removes the linklists and brings add_reg_note inline.

Makes sense, and especially it allows to inline the INSN_LIST/EXPR_LIST 
choice in most of the callees; this might be a small improvement but 
it's obviously there.  The switch statement in alloc_reg_note should be 
well-predicted but not unfortunately the common case is the default and 
requires to go through 2-3 jumps.

Is it really required to inline alloc_EXPR_LIST?  Can you measure the 
.text size with it inlined and without?

> Doing so hits
> the problems with our twisty include files.  It can not go to rtl.h since it
> would be compiled into gen files (and also gen_rtx_EXPR_LIST is not defined
> there yet). I ended up putting it into emit-rtl.h where it seem to belong most
> from other choices that introduces need to include emit-rtl into few extra
> files. In lists.c we need also function.h since note allocation needs crtl.
> I am open to alternatives here and I will mind updating dependencies if the
> patch is accepted.

What about moving all of lists.c to emit-rtl.c?  A lot of it is also 
duplicate for EXPR_LIST and INSN_LIST, the free lists could be reduced 
to one with more simplification using gen_rtx_fmt_ee.  It's all stuff 
for other patches though.

The df bits are fine except that you have two of these:

-  return old;
+  return;

Paolo