c++-mode dreadfully slow?

[Miles Bader]

Has anyone noticed c++-mode being really slow recently?  Recently I've
noticed that sometimes even just scrolling to a new screen can take on
the order of 5 seconds in some C++ files.

[The file I'm looking at currently is a "medium-sized" source file, ~3K
lines, and uses no particularly weird constructs (for instance, no
templates), and has no long functions.]

-Miles

-- 
Carefully crafted initial estimates reward you not only with
reduced computational effort, but also with understanding and
increased self-esteem.         -- Numerical methods in C,
  Chapter 9. "Root Finding and Nonlinear Sets of Equations"