Mysterious decision in combine

[Richard Henderson]

On 03/16/2016 11:35 PM, Dominik Vogt wrote:
> How does combine get this idea (it's the only match in the
> function)?
> 
>   Trying 7 -> 12:
>   Successfully matched this instruction:
>   (set (reg/i:DI 2 %r2)
>       (and:DI (subreg:DI (reg:SI 64) 0)
>           (const_int 4294901775 [0xffff000f])))
>   allowing combination of insns 7 and 12

>From the recorded nonzero_bits.

> (Eventually the two "and"s with constant values
> are not merged into a single "and" with a single constant.)

That's a concern...


r~