Recognize "match-all" NFAs within the regex engine.

This builds on the previous "rainbow" patch to detect NFAs that will
match any string, though possibly with constraints on the string length.
This definition is chosen to match constructs such as ".*", ".+", and
".{1,100}".  Recognizing such an NFA after the optimization pass is
fairly cheap, since we basically just have to verify that all arcs
are RAINBOW arcs and count the number of steps to the end state.
(Well, there's a bit of complication with pseudo-color arcs for string
boundary conditions, but not much.)

Once we have these markings, the regex executor functions longest(),
shortest(), and matchuntil() don't have to expend per-character work
to determine whether a given substring satisfies such an NFA; they
just need to check its length against the bounds.  Since some matching
problems require O(N) invocations of these functions, we've reduced
the runtime for an N-character string from O(N^2) to O(N).  Of course,
this is no help for non-matchall sub-patterns, but those usually have
constraints that allow us to avoid needing O(N) substring checks in the
first place.  It's precisely the unconstrained "match-all" cases that
cause the most headaches.

This is part of a patch series that in total reduces the regex engine's
runtime by about a factor of four on a large corpus of real-world regexes.

Patch by me, reviewed by Joel Jacobson

Discussion: https://postgr.es/m/1340281.1613018383@sss.pgh.pa.us

1 files changed, 5 insertions, 0 deletions

diff --git a/src/backend/regex/regcomp.c b/src/backend/regex/regcomp.c
index ae8dbe58191..39e837adc2a 100644
--- a/src/backend/regex/regcomp.c
+++ b/src/backend/regex/regcomp.c
@@ -175,6 +175,11 @@ static void cleanup(struct nfa *);
 static void markreachable(struct nfa *, struct state *, struct state *, struct state *);
 static void markcanreach(struct nfa *, struct state *, struct state *, struct state *);
 static long analyze(struct nfa *);
+static void checkmatchall(struct nfa *);
+static bool checkmatchall_recurse(struct nfa *, struct state *,
+								  bool, int, bool *);
+static bool check_out_colors_match(struct state *, color, color);
+static bool check_in_colors_match(struct state *, color, color);
 static void compact(struct nfa *, struct cnfa *);
 static void carcsort(struct carc *, size_t);
 static int	carc_cmp(const void *, const void *);