vsir_program_normalise() has function calls to basically everything in
ir.c, so it's useful to have it in an easily reachable place to
quickly jump to wherever you need using your favorite code editor's
features.
The label itself is certainly an unsigned integer, but the register
has no meaningful data type. It cannot be evaluated to anything.
The goal of this is to reduce cluttering in the internal ASM dumps.
The new structurizer therefore reaches feature parity with the
older simple one, except for a couple of points:
* the old structurizer accepts any CFG, without requiring reducibility;
however, the DXIL specification requires the CFG to be reducible
anyway, so we're not really losing anything;
* the new structurizer additionally requires that no block has two
incoming back arrows; AFAIK this is condition that can happen,
but in practice it seems to be rare; also, it's not hard to add
support for it, as soon as it is decided it is useful.
On the other hand, the new structurizer makes use of the merging
information that are reconstructed from the CFG, which is important
for downstream optimization and fundamental for correctly emitting
tangled instructions.
Taking these considerations into account, the old structurizer is
considered superseded and is therefore removed.
