Re: Why does lower-subreg mark copied pseudos as "decomposable"?

[Richard Sandiford <rdsandiford at googlemail dot com>]

Richard Sandiford <rdsandiford@googlemail.com> writes:
>> In fact, the only examples of a pseudo-pseudo copy that won't be 
>> eliminated by fwprop et al would be to do with loops and conditionals, 
>> and I don't understand why they should be special.
>
> Not just those, because loads, stores, calls, volatiles, etc.,
> can't be moved freely.  E.g. code like:
>
>     uint64_t foo (uint64_t *x, uint64_t z)
>     {
>       uint64_t y = *x;
>       *x = z;
>       return y;
>     }
>
> benefits too, because y must be a pseudo.

Er, please ignore this bit :-)  There obviously doesn't need to be
a pseudo copy here.  The later stuff still applies though.

Richard