[Bug tree-optimization/126969] If x is racecar (known to be 0 or all-ones), bitreverse (x) -> x

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126969

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I'm not sure this is common enough to bother.
That said, if you want to bother, the way to deal with this is check if range
of the argument is a union of singleton ranges (i.e. [a,a][b,b][c,c][d,d]) and
for each of the arguments the operation (I think BITREVERSE, BSWAP and rotates
by constant amount come to my mind as candidates) for all the values result in
identity.