Re: new sign/zero extension elimination pass

[Tom de Vries <tom@codesourcery.com>]

Eric,

Paolo Bonzini wrote:
> On Mon, Nov 8, 2010 at 22:21, Tom de Vries <tom@codesourcery.com> wrote:
>> I just looked into using DF_INSN_USES, and I'm not sure that using that is a
>> good idea. There is a difference between using note_uses and DF_INSN_USES.
>>
>> If there is an insn
>> ...
>> (set
>>  (reg:SI 1)
>>  (plus:SI (reg:SI 2)
>>           (reg:SI 3)))
>> ...
>>
>> the note_uses helper function will be visited with the plus expression,
>> something that is used in the pass (see note_use in ee.c).
> 
> This is an interesting point, thanks.
> 
>> Furthermore, I would like to know whether there is a problem with checking in
>> the pass into trunk in its current form. My understanding of the discussion up
>> until now is that the consensus is that the pass is useful, but not fully efficient.
>> I agree with the fact that it's possible to improve it, but I also think that
>> the runtime is negligible (it's an O(n) pass currently) and the benefit of
>> improving the pass will not be worth the effort. I will try to confirm this with
>> a profiling run on spec2000. If the profiling run confirms that the runtime is
>> negligible, is the pass (in principle) ok for trunk?
> 
> I am not an RTL reviewer, so my opinion doesn't weigh too much.
> 
> Paolo

I profiled the pass on spec2000:

                    -mabi=32     -mabi=64
ee-pass (usr time):     0.70         1.16
total   (usr time):   919.30       879.26
ee-pass        (%):     0.08         0.13

The pass takes 0.13% or less of the total usr runtime. Is it necessary to
improve the runtime of this pass?

Thanks,
- Tom