Code bloat due to silly IRA cost model?

[Segher Boessenkool]

On Fri, Dec 13, 2019 at 12:45:47PM +0000, Richard Sandiford wrote:
> combine's to blame for the fact that we have two pseudo registers rather
> than one.  See the comments about the avr-elf results in:
> 
>    https://gcc.gnu.org/ml/gcc-patches/2019-11/msg02150.html
> 
> for more details.

It's not combine's fault if register allocation does a bad job.  And we
should *not* generate worse code in combine just because it exposes a
problem in RA (with 2-2 and make_more_copies we generate better code on
average, on all targets I tested, 50 or so).

If having two pseudos here is not an advantage, then RA should optimise
one away.  It does usually, why not here?


Segher