[Bug other/63155] [4.9/5 Regression] memory hog

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63155

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I wonder why we need to explicitely represent abnormal PHIs in the dispatcher.
All incoming edges are abnormal and all SSA names have to be coalesced anyway.
Thus we could instead have

  <bb 5>:
/* Not: # _2(ab) = PHI <_17(D)(ab)(2), _1(ab)(6), _1(ab)(7), _3(ab)(11),
_3(ab)(12), _4(ab)(15), _4(ab)(16), _5(ab)(20), _5(ab)(21), _5(ab)(22)> */
  ABNORMAL_DISPATCHER (0);
  _2(ab) = D.12345;

or simply rewrite all must-coalesce vars out-of-SSA?  (or not into SSA
in the first place)

The question is whether accesses to them should be loads/stores (I think so)
and if that will cause other similar issues.

We'd have to factor abnormal edges into a block to a separate forwarder
of course, with a load of all "abnormal" vars.

Anyway, not sure why the gimplify code is disabled for -O0 (or why we
don't re-use formal temps more aggressively as they become anonymous
SSA names later anyway).