This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.
This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.
This doesn't actually modify StringRef yet, I'll do that in a follow-up.
Summary:
In the DFAPacketizer we copy the Transitions array
into a map in order to later access the transitions
based on a "Current State/Action" pair as a key.
This map lives in the Automaton object used by the DFAPacketizer.
It is never changed during the life of the object after
having been created during the creation of the Automaton
itself.
This map creation can make the creation of a DFAPacketizer
quite expensive if the target contains a considerable
amount of transition states.
Considering that TableGen already generates a
sorted list of transitions by State/Action pairs
we could just use that directly in our Automaton
and search entries with std::lower_bound instead of copying
it in a map and paying the execution time and memory cost.
Reviewers: jmolloy, ThomasRaoux
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72682
Summary:
This patch introduces -gen-automata, a backend for generating deterministic finite-state automata.
DFAs are already generated by the -gen-dfa-packetizer backend. This backend is more generic and will
hopefully be used to implement the DFA generation (and determinization) for the packetizer in the
future.
This backend allows not only generation of a DFA from an NFA (nondeterministic finite-state
automaton), it also emits sidetables that allow a path through the DFA under a sequence of inputs to
be analyzed, and the equivalent set of all possible NFA transitions extracted.
This allows a user to not just answer "can my problem be solved?" but also "what is the
solution?". Clearly this analysis is more expensive than just playing a DFA forwards so is
opt-in. The DFAPacketizer has this behaviour already but this is a more compact and generic
representation.
Examples are bundled in unittests/TableGen/Automata.td. Some are trivial, but the BinPacking example
is a stripped-down version of the original target problem I set out to solve, where we pack values
(actually immediates) into bins (an immediate pool in a VLIW bundle) subject to a set of esoteric
constraints.
Reviewers: t.p.northover
Subscribers: mgorny, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D67968
llvm-svn: 373718
Kazu Hirata