[Bug tree-optimization/83784] Missed optimization with bitfield

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83784

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-01-11
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  I guess it would need "load merging" as opposed to store merging,
basically what the bswap pass does but for bitfields.  I've always said those
two passes need to be merged somehow ;)

Anyway, bswap analysis is byte-granular currently and its lattice data
structure
would have to be beefed up quite considerably (also making operations on it
more costly).

bitfield lowering would have fixes this bug as well I guess (lowering
accesses to use the bitfield representative).

There are a few related bugs.