[Bug middle-end/83653] [6/7/8 Regression] GCC fails to remove a can't-happen call on ia64

[matthew at wil dot cx]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83653

--- Comment #9 from Matthew Wilcox <matthew at wil dot cx> ---
Maybe I'm a little slow, but I don't see what the path is that sets 'nr' to 0. 
It's 1UL << compound_order.  Typically, compound_order is 0, although it may be
anything up to log2(number of pages in the machine).  Are you saying that nr
could be 0 because DOM2 thinks compound_order() could be larger than 64, and
thus undefined?