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This module runs after the grammar has been analyzed but before the
automaton is constructed.

[--random-sentence-concrete].

[--random-sentence-concrete], and obey them.

Specialize atomic and sparse sets equality and comparison

See merge request !16

In Tarjan, add rev_topological_iter to iterate SCCs in reverse topological ordering

See merge request !15

They were not showing in the profile (the grammar is too big for them to
be useful), but for "symmetry", I do the same optimization.

(Also this remove the abstraction breaking use of generic comparison that
relied on the representation of AtomicBitSet to be structurally unique
for a given set of bits)

For AtomicBitSet, the lack of type annotation caused the generic
implementations to be used (the typechecker generalizes before
applying the module coercion, and codegen picks the generic code).

For SparseBitSet, a specialized implementation is now used. It should be
semantically equivalent to the generic one.

Both optimizations allowed to reduce the runtime by around ~5% when
applying the new `--list-errors` to cca_cpp.mly.  Lookahead classes
partition refinement was particularly affected.
(generic compare function would show up in profile, taking a bit more
than 7% of the total run time; it is now down below 1%, while the new
implementation performs a bit better).

This is used by the new implementation of `--list-errors` to compute
lookahead classes as a backward data-flow problem.