Re: [PATCH] A jump threading opportunity for condition branch

[Jeff Law]

On 5/30/19 12:44 AM, Richard Biener wrote:
> On May 29, 2019 10:21:46 PM GMT+02:00, Jeff Law <l...@redhat.com> wrote:
>> On 5/24/19 6:45 AM, Richard Biener wrote:
>> [ Aggressive snipping ]
>>
>>> As said in my first review I'd just check whether for the
>>> edge we want to thread through the definition comes from a CMP.
>>> Suppose you have
>>>
>>>  # val_1 = PHI <a_2, b_3, c_4>
>>>  if (val_1 != 0)
>>>
>>> and only one edge has a b_3 = d_5 != 0 condition it's still
>>> worth tail-duplicating the if block.
>> Agreed.  The cost of tail duplicating here is so small we should be
>> doing it highly aggressively.  About the only case where we might not
>> want to would be if we're optimizing for size rather than speed.  That
>> case isn't clearly a win either way.
> 
> Even there the PHI likely causes edge copies to be inserted. So I wouldn't 
> care for the moment. The proper check would be ! Optimize_edge_for_size_p 
> (e). 
Agreed, with capitalization fixed :-)
jeff