[Bug tree-optimization/67328] range test rather than single bit test for code testing enum values

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67328

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2015-08-25
     Ever confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note this is already fold-const.c:optimize_bit_field_compare at work.  With
-DALT (non-working code) we get

;; Function test_pic (null)
;; enabled by -tree-original


{
  if ((BIT_FIELD_REF <*info, 8, 0> & 3) + 254 <= 1)

and

;; Function test_exe (null)
;; enabled by -tree-original


{
  if ((SAVE_EXPR <BIT_FIELD_REF <*info, 8, 0> & 3>) == 0 || (SAVE_EXPR
<BIT_FIELD_REF <*info, 8, 0> & 3>) == 2)

from it.  Without -DALT

;; Function test_pic (null)
;; enabled by -tree-original


{
  if ((SAVE_EXPR <BIT_FIELD_REF <*info, 8, 0> & 3>) == 3 || (SAVE_EXPR
<BIT_FIELD_REF <*info, 8, 0> & 3>) == 1)

;; Function test_exe (null)
;; enabled by -tree-original


{
  if ((BIT_FIELD_REF <*info, 8, 0> & 3) <= 1)


I see more that a single bit test for both cases btw, mostly because we
need to mask the padding.  Not sure what optimal code you expect here.