Most of these are "we know we can just ignore this instruction", but
also sanity check for the lowering passes applied before this -- if any
of those instructions remain, then we're very likely to do the wrong
thing.

Bug: b/124388146
Change-Id: I3f8f66121f57f20cc93abdbd26c575baf03d9c94
Reviewed-on: https://swiftshader-review.googlesource.com/c/24597Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Chris Forbes <chrisforbes@google.com>