Live range splitting in new allocator

[dewar@gnat.com]

<<Indeed.  If -g subtly changes the code generated by
"-O99 -fdiscombobulate", it can be a real nightmare
finding a compiler bug.
>>

Or a user bug. We see all the time cases of erroneous programs,
e.g. from the use of an uninitialized variable, that work "fine"
in -O0, but blow up in -O2. Of course these often get reported
as compiler bugs, and they kind of look like compiler bugs to the
app programmer, but they are not!