[Bug tree-optimization/79460] gcc fails to optimise out a trivial additive loop for seemingly arbitrary numbers of iterations

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79460

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot 
gnu.org

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
In this case it is complete unrolling that can estimate the non-vector code to
constant fold but not the vectorized code.  OTOH it's quite excessive work done
by the unroller when doing this for large N...

And yes, SCEV final value replacement doesn't know how to handle float
reductions
(we have a different PR for that).

Let's track the unroll cost model issue here (I believe I have partial patches
for that somewhere, so mine).