Help with PR97872

[Richard Biener]

On Tue, 1 Dec 2020, Prathamesh Kulkarni wrote:

> Hi,
> For the test mentioned in PR, I was trying to see if we could do
> specialized expansion for vcond in target when operands are -1 and 0.
> arm_expand_vcond gets the following operands:
> (reg:V8QI 113 [ _2 ])
> (reg:V8QI 117)
> (reg:V8QI 118)
> (lt (reg/v:V8QI 115 [ a ])
>     (reg/v:V8QI 116 [ b ]))
> (reg/v:V8QI 115 [ a ])
> (reg/v:V8QI 116 [ b ])
> 
> where r117 and r118 are set to vector constants -1 and 0 respectively.
> However, I am not sure if there's a way to check if the register is
> constant during expansion time (since we don't have df analysis yet) ?
> 
> Alternatively, should we add a target hook that returns true if the
> result of vector comparison is set to all-ones or all-zeros, and then
> use this hook in gimple ISEL to effectively turn VEC_COND_EXPR into nop ?

Would everything match-up for a .VEC_CMP IFN producing a non-mask
vector type?  ISEL could special case the a ? -1 : 0 case this way.

> Thanks,
> Prathamesh
> 

-- 
Richard Biener <rguenther@suse.de>
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