Simplify memory management for regex DFAs a little.

Coverity complained that functions in regexec.c might leak DFA
storage.  It's wrong, but this logic is confusing enough that it's
not so surprising Coverity couldn't make sense of it.  Rewrite
in hopes of making it more legible to humans as well as machines.

src/backend/regex/rege_dfa.c

@@ -499,7 +499,7 @@ newdfa(struct vars *v,
 	struct dfa *d;
 	size_t		nss = cnfa->nstates * 2;
 	int			wordsper = (cnfa->nstates + UBITS - 1) / UBITS;
-	struct smalldfa *smallwas = sml;
+	bool		ismalloced = false;
 
 	assert(cnfa != NULL && cnfa->nstates != 0);
 
@@ -514,6 +514,7 @@ newdfa(struct vars *v,
 				ERR(REG_ESPACE);
 				return NULL;
 			}
+			ismalloced = true;
 		}
 		d = &sml->dfa;
 		d->ssets = sml->ssets;
@@ -521,8 +522,8 @@ newdfa(struct vars *v,
 		d->work = &d->statesarea[nss];
 		d->outsarea = sml->outsarea;
 		d->incarea = sml->incarea;
-		d->cptsmalloced = 0;
-		d->mallocarea = (smallwas == NULL) ? (char *) sml : NULL;
+		d->ismalloced = ismalloced;
+		d->arraysmalloced = false;	/* not separately allocated, anyway */
 	}
 	else
 	{
@@ -540,8 +541,9 @@ newdfa(struct vars *v,
 											  sizeof(struct sset *));
 		d->incarea = (struct arcp *) MALLOC(nss * cnfa->ncolors *
 											sizeof(struct arcp));
-		d->cptsmalloced = 1;
-		d->mallocarea = (char *) d;
+		d->ismalloced = true;
+		d->arraysmalloced = true;
+		/* now freedfa() will behave sanely */
 		if (d->ssets == NULL || d->statesarea == NULL ||
 			d->outsarea == NULL || d->incarea == NULL)
 		{
@@ -573,7 +575,7 @@ newdfa(struct vars *v,
 static void
 freedfa(struct dfa *d)
 {
-	if (d->cptsmalloced)
+	if (d->arraysmalloced)
 	{
 		if (d->ssets != NULL)
 			FREE(d->ssets);
@@ -585,8 +587,8 @@ freedfa(struct dfa *d)
 			FREE(d->incarea);
 	}
 
-	if (d->mallocarea != NULL)
-		FREE(d->mallocarea);
+	if (d->ismalloced)
+		FREE(d);
 }
 
 /*

src/backend/regex/regexec.c

@@ -77,8 +77,8 @@ struct dfa
 	chr		   *lastpost;		/* location of last cache-flushed success */
 	chr		   *lastnopr;		/* location of last cache-flushed NOPROGRESS */
 	struct sset *search;		/* replacement-search-pointer memory */
-	int			cptsmalloced;	/* were the areas individually malloced? */
-	char	   *mallocarea;		/* self, or master malloced area, or NULL */
+	bool		ismalloced;		/* should this struct dfa be freed? */
+	bool		arraysmalloced; /* should its subsidiary arrays be freed? */
 };
 
 #define WORK	1				/* number of work bitvectors needed */
@@ -88,7 +88,7 @@ struct dfa
 #define FEWCOLORS	15
 struct smalldfa
 {
-	struct dfa	dfa;
+	struct dfa	dfa;			/* must be first */
 	struct sset ssets[FEWSTATES * 2];
 	unsigned	statesarea[FEWSTATES * 2 + WORK];
 	struct sset *outsarea[FEWSTATES * 2 * FEWCOLORS];