Re: [PATCH 13/13] rs6000, remove vector set and vector init built-ins.

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi Carl,

on 2024/5/23 08:29, Carl Love wrote:
> Kewen:
> 
> On 5/13/24 22:44, Kewen.Lin wrote:
>>> perform the same operation as setting a specific element in the vector in
>>> C code.  For example:
>>>
>>>   src_v4si = __builtin_vec_set_v4si (src_v4si, int_val, index);
>>>   src_v4si[index] = int_val;
>>>
>>> The built-in actually generates more instructions than the inline C code
>>> with no optimization but is identical with -O3 optimizations.
>>>
>>> All of the above built-ins that are removed do not have test cases and
>>> are not documented.
>>>
>>> Built-ins   __builtin_vec_set_v1ti __builtin_vec_set_v2di,
>>> __builtin_vec_set_v2df are not removed as they are used in function
>>> resolve_vec_insert() in file rs6000-c.cc.
>> I think we can replace these calls with the equivalent gimple codes
>> (early expanding it) and then we can get rid of these instances.
> 
> Hmm, going to need a little coaching here.  I am not sure how to do this.  Looks like I get to lean some  something new.
> 

We have functions rs6000_gimple_fold.*_builtin to fold the builtins,
it's folding (expanding) the bif with equivalent gimple codes, what
we want here is similar, you can refer to some implementation there.
For the expected gimple code, you can refer to what's generated with
normal C code.  Feel free to let me know when you meet some issues
when you are trying, even you prefer me to follow up this.

BR,
Kewen