Sync patternsel_common's operator selection logic with pattern_prefix's.

Make patternsel_common() select the comparison operators to use with
hardwired logic that matches pattern_prefix()'s new logic, eliminating
its dependencies on particular index opfamilies.

This shouldn't change any behavior, as it's just replacing runtime
operator lookups with the same values hard-wired.  But it makes these
closely-related functions look more alike, and saving some runtime
syscache lookups is worth something.

Actually, it's not quite true that this is zero behavioral change:
when estimating for a column of type "name", the comparison constant
will be kept as "text" not coerced to "name".  But that's more correct
anyway, and it allows additional simplification of the coercion logic,
again syncing this more closely with pattern_prefix().

Per consideration of a report from Manuel Rigger.

Discussion: https://postgr.es/m/CA+u7OA7nnGYy8rY0vdTe811NuA+Frr9nbcBO9u2Z+JxqNaud+g@mail.gmail.com

src/backend/utils/adt/like_support.c

@@ -91,7 +91,8 @@ static Pattern_Prefix_Status pattern_fixed_prefix(Const *patt,
 												  Selectivity *rest_selec);
 static Selectivity prefix_selectivity(PlannerInfo *root,
 									  VariableStatData *vardata,
-									  Oid vartype, Oid opfamily, Const *prefixcon);
+									  Oid eqopr, Oid ltopr, Oid geopr,
+									  Const *prefixcon);
 static Selectivity like_selectivity(const char *patt, int pattlen,
 									bool case_insensitive);
 static Selectivity regex_selectivity(const char *patt, int pattlen,
@@ -470,7 +471,10 @@ patternsel_common(PlannerInfo *root,
 	Datum		constval;
 	Oid			consttype;
 	Oid			vartype;
-	Oid			opfamily;
+	Oid			rdatatype;
+	Oid			eqopr;
+	Oid			ltopr;
+	Oid			geopr;
 	Pattern_Prefix_Status pstatus;
 	Const	   *patt;
 	Const	   *prefix = NULL;
@@ -527,29 +531,51 @@ patternsel_common(PlannerInfo *root,
 	/*
 	 * Similarly, the exposed type of the left-hand side should be one of
 	 * those we know.  (Do not look at vardata.atttype, which might be
-	 * something binary-compatible but different.)	We can use it to choose
-	 * the index opfamily from which we must draw the comparison operators.
+	 * something binary-compatible but different.)	We can use it to identify
+	 * the comparison operators and the required type of the comparison
+	 * constant, much as in match_pattern_prefix().
 	 *
-	 * NOTE: It would be more correct to use the PATTERN opfamilies than the
-	 * simple ones, but at the moment ANALYZE will not generate statistics for
-	 * the PATTERN operators.  But our results are so approximate anyway that
-	 * it probably hardly matters.
+	 * NOTE: this logic does not consider collations.  Ideally we'd force use
+	 * of "C" collation, but since ANALYZE only generates statistics for the
+	 * column's specified collation, we have little choice but to use those.
+	 * But our results are so approximate anyway that it probably hardly
+	 * matters.
 	 */
 	vartype = vardata.vartype;
 
 	switch (vartype)
 	{
 		case TEXTOID:
+			eqopr = TextEqualOperator;
+			ltopr = TextLessOperator;
+			geopr = TextGreaterEqualOperator;
+			rdatatype = TEXTOID;
+			break;
 		case NAMEOID:
-			opfamily = TEXT_BTREE_FAM_OID;
+
+			/*
+			 * Note that here, we need the RHS type to be text, so that the
+			 * comparison value isn't improperly truncated to NAMEDATALEN.
+			 */
+			eqopr = NameEqualTextOperator;
+			ltopr = NameLessTextOperator;
+			geopr = NameGreaterEqualTextOperator;
+			rdatatype = TEXTOID;
 			break;
 		case BPCHAROID:
-			opfamily = BPCHAR_BTREE_FAM_OID;
+			eqopr = BpcharEqualOperator;
+			ltopr = BpcharLessOperator;
+			geopr = BpcharGreaterEqualOperator;
+			rdatatype = BPCHAROID;
 			break;
 		case BYTEAOID:
-			opfamily = BYTEA_BTREE_FAM_OID;
+			eqopr = ByteaEqualOperator;
+			ltopr = ByteaLessOperator;
+			geopr = ByteaGreaterEqualOperator;
+			rdatatype = BYTEAOID;
 			break;
 		default:
+			/* Can't get here unless we're attached to the wrong operator */
 			ReleaseVariableStats(vardata);
 			return result;
 	}
@@ -579,41 +605,23 @@ patternsel_common(PlannerInfo *root,
 								   &prefix, &rest_selec);
 
 	/*
-	 * If necessary, coerce the prefix constant to the right type.
+	 * If necessary, coerce the prefix constant to the right type.  The only
+	 * case where we need to do anything is when converting text to bpchar.
+	 * Those two types are binary-compatible, so relabeling the Const node is
+	 * sufficient.
 	 */
-	if (prefix && prefix->consttype != vartype)
+	if (prefix && prefix->consttype != rdatatype)
 	{
-		char	   *prefixstr;
-
-		switch (prefix->consttype)
-		{
-			case TEXTOID:
-				prefixstr = TextDatumGetCString(prefix->constvalue);
-				break;
-			case BYTEAOID:
-				prefixstr = DatumGetCString(DirectFunctionCall1(byteaout,
-																prefix->constvalue));
-				break;
-			default:
-				elog(ERROR, "unrecognized consttype: %u",
-					 prefix->consttype);
-				ReleaseVariableStats(vardata);
-				return result;
-		}
-		prefix = string_to_const(prefixstr, vartype);
-		pfree(prefixstr);
+		Assert(prefix->consttype == TEXTOID &&
+			   rdatatype == BPCHAROID);
+		prefix->consttype = rdatatype;
 	}
 
 	if (pstatus == Pattern_Prefix_Exact)
 	{
 		/*
-		 * Pattern specifies an exact match, so pretend operator is '='
+		 * Pattern specifies an exact match, so estimate as for '='
 		 */
-		Oid			eqopr = get_opfamily_member(opfamily, vartype, vartype,
-												BTEqualStrategyNumber);
-
-		if (eqopr == InvalidOid)
-			elog(ERROR, "no = operator for opfamily %u", opfamily);
 		result = var_eq_const(&vardata, eqopr, prefix->constvalue,
 							  false, true, false);
 	}
@@ -656,8 +664,9 @@ patternsel_common(PlannerInfo *root,
 			Selectivity prefixsel;
 
 			if (pstatus == Pattern_Prefix_Partial)
-				prefixsel = prefix_selectivity(root, &vardata, vartype,
-											   opfamily, prefix);
+				prefixsel = prefix_selectivity(root, &vardata,
+											   eqopr, ltopr, geopr,
+											   prefix);
 			else
 				prefixsel = 1.0;
 			heursel = prefixsel * rest_selec;
@@ -1181,15 +1190,14 @@ pattern_fixed_prefix(Const *patt, Pattern_Type ptype, Oid collation,
  * Estimate the selectivity of a fixed prefix for a pattern match.
  *
  * A fixed prefix "foo" is estimated as the selectivity of the expression
- * "variable >= 'foo' AND variable < 'fop'" (see also indxpath.c).
+ * "variable >= 'foo' AND variable < 'fop'".
  *
  * The selectivity estimate is with respect to the portion of the column
  * population represented by the histogram --- the caller must fold this
  * together with info about MCVs and NULLs.
  *
- * We use the >= and < operators from the specified btree opfamily to do the
- * estimation.  The given variable and Const must be of the associated
- * datatype.
+ * We use the specified btree comparison operators to do the estimation.
+ * The given variable and Const must be of the associated datatype(s).
  *
  * XXX Note: we make use of the upper bound to estimate operator selectivity
  * even if the locale is such that we cannot rely on the upper-bound string.
@@ -1198,20 +1206,17 @@ pattern_fixed_prefix(Const *patt, Pattern_Type ptype, Oid collation,
  */
 static Selectivity
 prefix_selectivity(PlannerInfo *root, VariableStatData *vardata,
-				   Oid vartype, Oid opfamily, Const *prefixcon)
+				   Oid eqopr, Oid ltopr, Oid geopr,
+				   Const *prefixcon)
 {
 	Selectivity prefixsel;
-	Oid			cmpopr;
 	FmgrInfo	opproc;
 	AttStatsSlot sslot;
 	Const	   *greaterstrcon;
 	Selectivity eq_sel;
 
-	cmpopr = get_opfamily_member(opfamily, vartype, vartype,
-								 BTGreaterEqualStrategyNumber);
-	if (cmpopr == InvalidOid)
-		elog(ERROR, "no >= operator for opfamily %u", opfamily);
-	fmgr_info(get_opcode(cmpopr), &opproc);
+	/* Estimate the selectivity of "x >= prefix" */
+	fmgr_info(get_opcode(geopr), &opproc);
 
 	prefixsel = ineq_histogram_selectivity(root, vardata,
 										   &opproc, true, true,
@@ -1237,11 +1242,7 @@ prefix_selectivity(PlannerInfo *root, VariableStatData *vardata,
 		 /* sslot.stacoll is set up */ ;
 	else
 		sslot.stacoll = DEFAULT_COLLATION_OID;
-	cmpopr = get_opfamily_member(opfamily, vartype, vartype,
-								 BTLessStrategyNumber);
-	if (cmpopr == InvalidOid)
-		elog(ERROR, "no < operator for opfamily %u", opfamily);
-	fmgr_info(get_opcode(cmpopr), &opproc);
+	fmgr_info(get_opcode(ltopr), &opproc);
 	greaterstrcon = make_greater_string(prefixcon, &opproc, sslot.stacoll);
 	if (greaterstrcon)
 	{
@@ -1277,11 +1278,7 @@ prefix_selectivity(PlannerInfo *root, VariableStatData *vardata,
 	 * probably off the end of the histogram, and thus we probably got a very
 	 * small estimate from the >= condition; so we still need to clamp.
 	 */
-	cmpopr = get_opfamily_member(opfamily, vartype, vartype,
-								 BTEqualStrategyNumber);
-	if (cmpopr == InvalidOid)
-		elog(ERROR, "no = operator for opfamily %u", opfamily);
-	eq_sel = var_eq_const(vardata, cmpopr, prefixcon->constvalue,
+	eq_sel = var_eq_const(vardata, eqopr, prefixcon->constvalue,
 						  false, true, false);
 
 	prefixsel = Max(prefixsel, eq_sel);