flags and modes in 754R

[David Hough 754R work <754r@xxxxxxxxxxx>]

754R tried to make it as explicit as possible that a global set of flags
is not a required implementation.    It wasn't in 754 either,
but because everybody
implemented flags as global hardware, many people supposed it was mandatory.

In 754R, nothing guarantees that you can "look at the flags" in places where
you haven't said "I'm going to look at the flags" in advance.     Those places
where you said you might look at the flags 
might well run the normal case slower.

The actual implementation might be distributed with flags accompanying data
and only OR'ed together to satisfy an explicit inquiry in the source code.
In particular asynchronous events like debugger inquiries might not have
a single set of global flags to look at.

Likewise the scope of mode declarations is language-defined and might
not be discernible by looking at a global mode bit,
except where a program says in advance that it's going to look at 
the mode.

Having taken these steps to uninhibit future architectures, it remains true
that the installed-base momentum will probably continue to encourage global
flags and modes implementations that will continue to threaten to
impede optimization of the normal cases.