[Bug tree-optimization/59924] [4.9 Regression] uninit memory hog

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59924

--- Comment #4 from Richard Henderson <rth at gcc dot gnu.org> ---
Created attachment 32033
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32033&action=edit
proposed patch

Properly handling default definitions wasn't enough, so
also add a pointer set to avoid processing ssa names twice.