precision integers.  This won't actually work
(and most of the code is dead) unless the new
legalization machinery is turned on.  While
there, I rationalized the handling of i1, and
removed some bogus (and unused) sextload patterns.
For i1, this could result in microscopically
better code for some architectures (not X86).
It might also result in worse code if annotating
with AssertZExt nodes turns out to be more harmful
than helpful.

llvm-svn: 46280