From 2dd6733108f2bea07b0a3469e768bd900c0808b3 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 14 Feb 2021 19:53:28 -0500
Subject: [PATCH] Minor fixes to improve regex debugging code.

When REG_DEBUG is defined, ensure that an un-filled "struct cnfa"
is all-zeroes, not just that it has nstates == 0.  This is mainly
so that looking at "struct subre" structs in gdb doesn't distract
one with a lot of garbage fields during regex compilation.

Adjust some places that print debug output to have suitable fflush
calls afterwards.

In passing, correct an erroneous ancient comment: the concatenation
subre-s created by parsebranch() have op == '.' not ','.

Noted while fooling around with some regex performance improvements.
---
 src/backend/regex/regc_nfa.c | 6 +++---
 src/backend/regex/regcomp.c  | 5 ++++-
 src/include/regex/regguts.h  | 8 ++++++++
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/backend/regex/regc_nfa.c b/src/backend/regex/regc_nfa.c
index 92c9c4d795d..cde82625c85 100644
--- a/src/backend/regex/regc_nfa.c
+++ b/src/backend/regex/regc_nfa.c
@@ -2951,11 +2951,11 @@ carc_cmp(const void *a, const void *b)
 static void
 freecnfa(struct cnfa *cnfa)
 {
-	assert(cnfa->nstates != 0); /* not empty already */
-	cnfa->nstates = 0;
+	assert(!NULLCNFA(*cnfa));	/* not empty already */
 	FREE(cnfa->stflags);
 	FREE(cnfa->states);
 	FREE(cnfa->arcs);
+	ZAPCNFA(*cnfa);
 }
 
 /*
@@ -3012,13 +3012,13 @@ dumpstate(struct state *s,
 		fprintf(f, "\tno out arcs\n");
 	else
 		dumparcs(s, f);
-	fflush(f);
 	for (a = s->ins; a != NULL; a = a->inchain)
 	{
 		if (a->to != s)
 			fprintf(f, "\tlink from %d to %d on %d's in-chain\n",
 					a->from->no, a->to->no, s->no);
 	}
+	fflush(f);
 }
 
 /*
diff --git a/src/backend/regex/regcomp.c b/src/backend/regex/regcomp.c
index 91078dcd806..f0896d2db14 100644
--- a/src/backend/regex/regcomp.c
+++ b/src/backend/regex/regcomp.c
@@ -479,7 +479,10 @@ pg_regcomp(regex_t *re,
 
 #ifdef REG_DEBUG
 	if (flags & REG_DUMP)
+	{
 		dump(re, stdout);
+		fflush(stdout);
+	}
 #endif
 
 	assert(v->err == 0);
@@ -721,7 +724,7 @@ parse(struct vars *v,
  *
  * This mostly manages concatenation, working closely with parseqatom().
  * Concatenated things are bundled up as much as possible, with separate
- * ',' nodes introduced only when necessary due to substructure.
+ * '.' nodes introduced only when necessary due to substructure.
  */
 static struct subre *
 parsebranch(struct vars *v,
diff --git a/src/include/regex/regguts.h b/src/include/regex/regguts.h
index 5d0e7a961c9..0a616562d03 100644
--- a/src/include/regex/regguts.h
+++ b/src/include/regex/regguts.h
@@ -368,7 +368,15 @@ struct cnfa
 	struct carc *arcs;			/* the area for the lists */
 };
 
+/*
+ * When debugging, it's helpful if an un-filled CNFA is all-zeroes.
+ * In production, though, we only require nstates to be zero.
+ */
+#ifdef REG_DEBUG
+#define ZAPCNFA(cnfa)	memset(&(cnfa), 0, sizeof(cnfa))
+#else
 #define ZAPCNFA(cnfa)	((cnfa).nstates = 0)
+#endif
 #define NULLCNFA(cnfa)	((cnfa).nstates == 0)
 
 /*