branch! produces wrong target block numbers?

I'm trying to write a no-op transform:
```
function block_transform(ir)
ir = copy(ir)
n_ir = IR()
for (i, bb) in enumerate(ir.blocks)
new_bb = block!(n_ir, i)
for arg in bb.args
argument!(new_bb, arg)
end
for stmt in bb.stmts
push!(new_bb, stmt)
end
if !isempty(bb.branches)
for branch in bb.branches
branch.condition isa Nothing ? branch!(new_bb, branch.block, branch.args...; unless = nothing) : branch!(new_bb, branch.block, branch.args...; unless = branch.condition)
end
end
end
return n_ir
end
```
but the result is something weird when I use branch!
```
--- IR (foo2) ---
1: (%1)
br 2 (0.0)
2: (%2)
%3 = Main.BlockManip.Normal(0, 1)
%4 = Main.BlockManip.rand(%3)
%5 = %4 > 0.0
br 4 unless %5
br 3
3:
%6 = Main.BlockManip.Normal(0, 1)
%7 = Main.BlockManip.rand(%6)
%8 = %2 + %7
br 2 (%8)
4:
return %2

--- Transformed ---
1: (%1)
br 5 (0.0)
2: (%2)
%3 = Main.BlockManip.Normal(0, 1)
%4 = Main.BlockManip.rand(%3)
%5 = %4 > 0.0
br 6 unless %5
br 5
3:
%6 = Main.BlockManip.Normal(0, 1)
%7 = Main.BlockManip.rand(%6)
%8 = %2 + %7
br 2 (%8)
4:
return %2
5:
```
i.e. the block numbers produced in the branch statement by branch! seem to be off and I'm not sure where/if I made a mistake.

Edit: I also know this is inefficient, but can I use `Pipe` here and work with blocks like this?

Edit2: I think I see the crux of the issue - `branch.block` is referring to a branch in the original IR, not the new IR.