volatile access optimization (C++ / x86_64)

[DJ Delorie]

> What is involved with the auditing?

Each pattern that (directly or indirectly) uses general_operand,
memory_operand, or nonimmediate_operand needs to be checked to see if
it's volatile-safe.  If so, you need to change the predicate to
something that explicitly accepts volatiles.

There's been talk about adding direct support for a "volatile-clean"
flag that avoids this for targets where you know it's correct, which
bypasses the volatile check in those functions, but it hasn't happened
yet.