[PATCH] rs6000: Make some BIFs vectorized on P10

Kewen.Lin linkw@linux.ibm.com
Wed Aug 25 04:57:16 GMT 2021


on 2021/8/25 上午5:56, Segher Boessenkool wrote:
> On Fri, Aug 13, 2021 at 11:18:46AM +0800, Kewen.Lin wrote:
>> on 2021/8/12 下午11:51, Segher Boessenkool wrote:
>>> It is a bad idea to initialise things unnecessary: it hinders many
>>> optimisations, but much more importantly, it silences warnings without
>>> fixing the problem.
>>
>> OK, I've made it uninitialized in v2. :-)  I believe the context here is simple
>> and the uninit-ed var detector can easily catch and warn the bad thing in future.
> 
> And those warnings generally are for "MAY BE used uninitialised",
> anyway.  They will warn :-)
> 
> (When the warning says "IS used uninitialised" the compiler should be
> sure about that!)
> 
>> Sorry for chasing dead ends, I don't follow how it can hinder optimizations here,
>> IIUC it would be optimized as a dead store here?
> 
> When the compiler is not sure if something needs initialisation or not
> it cannot remove actually superfluous initialisation.  Such cases are
> always too complicated code, so that should be fixed, not silenced :-)
> 

aha, you meant complicated code, got it.  :)

>> As to the warning, although
>> there is no warning, I'd expect it causes ICE since the init-ed bif name isn't
>> reasonable for generation.  Wouldn't it be better than warning?  Sometimes we
>> don't have a proper value for initialization, I agree it should be better to
>> just leave it be, but IMHO it isn't the case here.  :)
> 
> ICEing is always wrong.  A user should never see an ICE (not counting
> "sorry"s as ICEs here -- not that those are good, but they tell the user
> exactly what is going on).
> 

Yeah, but here I was expecting the ICE happens when GCC developers are testing
the newly added bif supports.  :)


BR,
Kewen


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