This assumes that the set of valid node IDs is exactly `0..num_nodes`.
In practice, we have a lot of graph-algorithm code that already assumes that
nodes are densely numbered, by using `num_nodes` to allocate per-node indexed
data structures.
By removing all methods from this struct and treating it as a collection of
data fields, we make it easier for a future PR to store that data in a query
result, without having to move all of its methods into `rustc_middle`.
Using `SmallVec` here was fine when it was a module-private detail, but if we
want to pass these terms across query boundaries then it's not worth the extra
hassle.
Replacing a method call with direct field access is slightly simpler.
Using the name `counter_terms` is more consistent with other code that tries to
maintain a distinction between (physical) "counters" and "expressions".
Making these separate types from `CovTerm` and `Expression` was historically
very helpful, but now that most of the counter-creation work is handled by
`node_flow` they are no longer needed.
- Move `make_bcb_counters` out of `CoverageCounters`
- Split out `make_node_counter_priority_list`
- Flatten `Transcriber` into the function `transcribe_counters`
This makes it possible for other parts of counter-assignment to check whether a
node is guaranteed to end up with some kind of counter.
Switching from `impl Fn` to a concrete `&BitSet` just avoids the hassle of
trying to store a closure in a struct field, and currently there's no
foreseeable need for this information to not be a bitset.
Given that we directly access the graph predecessors/successors in so many
other places, and sometimes must do so to satisfy the borrow checker, there is
little value in having this trivial helper method.
- Look up the node's predecessors only once
- Get rid of some overly verbose logging
- Explain why some nodes need physical counters
- Extract a helper method to create and set a physical node counter
These tests might have originally been useful as an implementation aid, but now
they don't provide enough value to justify the burden of updating them as the
underlying code changes.
The code they test is still exercised by the main end-to-end coverage tests.
Some of these cases currently don't occur in practice, but are included for
completeness, and to avoid having to add them later as branch coverage and
MC/DC coverage start building more complex expressions.
These assertions detect situations where a BCB node would have both a physical
counter and one or more in-edge counters/expressions.
For most BCBs that situation would indicate an implementation bug. However,
it's perfectly fine in the case of a BCB having an edge that loops back to
itself.
Given the complexity and risk involved in fixing the assertions, and the fact
that nothing relies on them actually being true, this patch just removes them
instead.
This makes it possible for two nodes/edges in the coverage graph to share the
same counter, without causing the instrumentor to inject unwanted duplicate
counter-increment statements.
`BcbBranch` represented an out-edge of a coverage graph node, but would
silently refer to a node instead in cases where that node only had one in-edge.
Instead we now refer to a graph edge as a `(from_bcb, to_bcb)` pair, or
sometimes as just one of those nodes when the other node is implied by the
surrounding context. The case of sole in-edges is handled by special code added
directly to `get_or_make_edge_counter_operand`.
This was previously a helper method in `MakeBcbCounters`, but putting it in the
graph lets us call it from `BcbBranch`, and gives us a more fine-grained
borrow.
In some cases we need to prepare a coverage expression that is the sum of an
arbitrary number of other terms. This patch simplifies the code paths that
build those sums.
This causes some churn in the mappings, because the previous code was building
its sums in a somewhat idiosyncratic order.
