[Bug tree-optimization/56049] [7 Regression] Simplification to constants not done

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56049

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
   Target Milestone|7.0                         |8.0

--- Comment #20 from Richard Biener <rguenth at gcc dot gnu.org> ---
Agreed.  I've briefly looked into LIM and it's not easy to teach it this.  LIM
uses its own "value numbering" and dependence analysis (ugh, well - it's
supposed
to be "cheaper" ...).  The VN used for store-motion (store and load memory
location have to be detected as equal) is using operand_equal/hash_tree which
is too simplistic here.

There is the general issue of LIM dependence analysis that it doesn't handle
dependence distance <= 0 for read-write and > 0 for write-read dependences
more optimistically.