[Bug rtl-optimization/64081] [5/6/7 Regression] r217827 prevents RTL loop unroll

[dje at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64081

--- Comment #48 from David Edelsohn <dje at gcc dot gnu.org> ---
Based on Comment #45, is this a problem in the Stage 1 compilers?  Note that
Alan and Segher adjusted the doloop patterns in this release cycle.  Does
backporting that patch or bootstrapping with current trunk function better?