Allow matchingsel() to be used with operators that might return NULL.

Although selfuncs.c will never call a target operator with null inputs,
some functions might return null anyway.  The existing coding will fail
if that happens (since FunctionCall2Coll will punt), which seems
undesirable given that matchingsel() has such a broad range of potential
applicability --- in fact, we already have a problem because we apply it
to jsonb_path_exists_opr, which can return null.  Hence, rejigger the
underlying functions mcv_selectivity and histogram_selectivity to cope,
treating a null result as false.

While we are at it, we can move the InitFunctionCallInfoData overhead
out of the inner loops, which isn't a huge number of cycles but might
save something considering we are likely calling functions as cheap
as int4eq().  Plus, the number of loop cycles to be expected is much
more than it was when this code was written, since typical settings
of default_statistics_target are higher.

In view of that consideration, let's apply the same change to
var_eq_const, eqjoinsel_inner, and eqjoinsel_semi.  We do not expect
equality functions to ever return null for non-null inputs (and
certainly that code has been that way a long time without complaints),
but the cycle savings seem attractive, especially in the eqjoinsel loops
where there's potentially an O(N^2) savings.

Similar code exists in ineq_histogram_selectivity and
get_variable_range, but I forebore from changing those for now.
The performance argument for changing ineq_histogram_selectivity
is really weak anyway, since that will only iterate log2(N) times.

Nikita Glukhov and Tom Lane

Discussion: https://postgr.es/m/9d3b0959-95d6-c37e-2c0b-287bcfe5c705@postgrespro.ru

src/backend/utils/adt/selfuncs.c

@@ -345,25 +345,42 @@ var_eq_const(VariableStatData *vardata, Oid operator,
 							 STATISTIC_KIND_MCV, InvalidOid,
 							 ATTSTATSSLOT_VALUES | ATTSTATSSLOT_NUMBERS))
 		{
+			LOCAL_FCINFO(fcinfo, 2);
 			FmgrInfo	eqproc;
 
 			fmgr_info(opfuncoid, &eqproc);
 
+			/*
+			 * Save a few cycles by setting up the fcinfo struct just once.
+			 * Using FunctionCallInvoke directly also avoids failure if the
+			 * eqproc returns NULL, though really equality functions should
+			 * never do that.
+			 */
+			InitFunctionCallInfoData(*fcinfo, &eqproc, 2, sslot.stacoll,
+									 NULL, NULL);
+			fcinfo->args[0].isnull = false;
+			fcinfo->args[1].isnull = false;
+			/* be careful to apply operator right way 'round */
+			if (varonleft)
+				fcinfo->args[1].value = constval;
+			else
+				fcinfo->args[0].value = constval;
+
 			for (i = 0; i < sslot.nvalues; i++)
 			{
-				/* be careful to apply operator right way 'round */
+				Datum		fresult;
+
 				if (varonleft)
-					match = DatumGetBool(FunctionCall2Coll(&eqproc,
-														   sslot.stacoll,
-														   sslot.values[i],
-														   constval));
+					fcinfo->args[0].value = sslot.values[i];
 				else
-					match = DatumGetBool(FunctionCall2Coll(&eqproc,
-														   sslot.stacoll,
-														   constval,
-														   sslot.values[i]));
-				if (match)
+					fcinfo->args[1].value = sslot.values[i];
+				fcinfo->isnull = false;
+				fresult = FunctionCallInvoke(fcinfo);
+				if (!fcinfo->isnull && DatumGetBool(fresult))
+				{
+					match = true;
 					break;
+				}
 			}
 		}
 		else
@@ -723,17 +740,36 @@ mcv_selectivity(VariableStatData *vardata, FmgrInfo *opproc,
 						 STATISTIC_KIND_MCV, InvalidOid,
 						 ATTSTATSSLOT_VALUES | ATTSTATSSLOT_NUMBERS))
 	{
+		LOCAL_FCINFO(fcinfo, 2);
+
+		/*
+		 * We invoke the opproc "by hand" so that we won't fail on NULL
+		 * results.  Such cases won't arise for normal comparison functions,
+		 * but generic_restriction_selectivity could perhaps be used with
+		 * operators that can return NULL.  A small side benefit is to not
+		 * need to re-initialize the fcinfo struct from scratch each time.
+		 */
+		InitFunctionCallInfoData(*fcinfo, opproc, 2, sslot.stacoll,
+								 NULL, NULL);
+		fcinfo->args[0].isnull = false;
+		fcinfo->args[1].isnull = false;
+		/* be careful to apply operator right way 'round */
+		if (varonleft)
+			fcinfo->args[1].value = constval;
+		else
+			fcinfo->args[0].value = constval;
+
 		for (i = 0; i < sslot.nvalues; i++)
 		{
-			if (varonleft ?
-				DatumGetBool(FunctionCall2Coll(opproc,
-											   sslot.stacoll,
-											   sslot.values[i],
-											   constval)) :
-				DatumGetBool(FunctionCall2Coll(opproc,
-											   sslot.stacoll,
-											   constval,
-											   sslot.values[i])))
+			Datum		fresult;
+
+			if (varonleft)
+				fcinfo->args[0].value = sslot.values[i];
+			else
+				fcinfo->args[1].value = sslot.values[i];
+			fcinfo->isnull = false;
+			fresult = FunctionCallInvoke(fcinfo);
+			if (!fcinfo->isnull && DatumGetBool(fresult))
 				mcv_selec += sslot.numbers[i];
 			sumcommon += sslot.numbers[i];
 		}
@@ -798,20 +834,39 @@ histogram_selectivity(VariableStatData *vardata, FmgrInfo *opproc,
 		*hist_size = sslot.nvalues;
 		if (sslot.nvalues >= min_hist_size)
 		{
+			LOCAL_FCINFO(fcinfo, 2);
 			int			nmatch = 0;
 			int			i;
 
+			/*
+			 * We invoke the opproc "by hand" so that we won't fail on NULL
+			 * results.  Such cases won't arise for normal comparison
+			 * functions, but generic_restriction_selectivity could perhaps be
+			 * used with operators that can return NULL.  A small side benefit
+			 * is to not need to re-initialize the fcinfo struct from scratch
+			 * each time.
+			 */
+			InitFunctionCallInfoData(*fcinfo, opproc, 2, sslot.stacoll,
+									 NULL, NULL);
+			fcinfo->args[0].isnull = false;
+			fcinfo->args[1].isnull = false;
+			/* be careful to apply operator right way 'round */
+			if (varonleft)
+				fcinfo->args[1].value = constval;
+			else
+				fcinfo->args[0].value = constval;
+
 			for (i = n_skip; i < sslot.nvalues - n_skip; i++)
 			{
-				if (varonleft ?
-					DatumGetBool(FunctionCall2Coll(opproc,
-												   sslot.stacoll,
-												   sslot.values[i],
-												   constval)) :
-					DatumGetBool(FunctionCall2Coll(opproc,
-												   sslot.stacoll,
-												   constval,
-												   sslot.values[i])))
+				Datum		fresult;
+
+				if (varonleft)
+					fcinfo->args[0].value = sslot.values[i];
+				else
+					fcinfo->args[1].value = sslot.values[i];
+				fcinfo->isnull = false;
+				fresult = FunctionCallInvoke(fcinfo);
+				if (!fcinfo->isnull && DatumGetBool(fresult))
 					nmatch++;
 			}
 			result = ((double) nmatch) / ((double) (sslot.nvalues - 2 * n_skip));
@@ -2292,6 +2347,7 @@ eqjoinsel_inner(Oid opfuncoid,
 		 * results", Technical Report 1018, Computer Science Dept., University
 		 * of Wisconsin, Madison, March 1991 (available from ftp.cs.wisc.edu).
 		 */
+		LOCAL_FCINFO(fcinfo, 2);
 		FmgrInfo	eqproc;
 		bool	   *hasmatch1;
 		bool	   *hasmatch2;
@@ -2310,6 +2366,18 @@ eqjoinsel_inner(Oid opfuncoid,
 					nmatches;
 
 		fmgr_info(opfuncoid, &eqproc);
+
+		/*
+		 * Save a few cycles by setting up the fcinfo struct just once. Using
+		 * FunctionCallInvoke directly also avoids failure if the eqproc
+		 * returns NULL, though really equality functions should never do
+		 * that.
+		 */
+		InitFunctionCallInfoData(*fcinfo, &eqproc, 2, sslot1->stacoll,
+								 NULL, NULL);
+		fcinfo->args[0].isnull = false;
+		fcinfo->args[1].isnull = false;
+
 		hasmatch1 = (bool *) palloc0(sslot1->nvalues * sizeof(bool));
 		hasmatch2 = (bool *) palloc0(sslot2->nvalues * sizeof(bool));
 
@@ -2325,14 +2393,18 @@ eqjoinsel_inner(Oid opfuncoid,
 		{
 			int			j;
 
+			fcinfo->args[0].value = sslot1->values[i];
+
 			for (j = 0; j < sslot2->nvalues; j++)
 			{
+				Datum		fresult;
+
 				if (hasmatch2[j])
 					continue;
-				if (DatumGetBool(FunctionCall2Coll(&eqproc,
-												   sslot1->stacoll,
-												   sslot1->values[i],
-												   sslot2->values[j])))
+				fcinfo->args[1].value = sslot2->values[j];
+				fcinfo->isnull = false;
+				fresult = FunctionCallInvoke(fcinfo);
+				if (!fcinfo->isnull && DatumGetBool(fresult))
 				{
 					hasmatch1[i] = hasmatch2[j] = true;
 					matchprodfreq += sslot1->numbers[i] * sslot2->numbers[j];
@@ -2502,6 +2574,7 @@ eqjoinsel_semi(Oid opfuncoid,
 		 * lists.  We still have to estimate for the remaining population, but
 		 * in a skewed distribution this gives us a big leg up in accuracy.
 		 */
+		LOCAL_FCINFO(fcinfo, 2);
 		FmgrInfo	eqproc;
 		bool	   *hasmatch1;
 		bool	   *hasmatch2;
@@ -2523,6 +2596,18 @@ eqjoinsel_semi(Oid opfuncoid,
 		clamped_nvalues2 = Min(sslot2->nvalues, nd2);
 
 		fmgr_info(opfuncoid, &eqproc);
+
+		/*
+		 * Save a few cycles by setting up the fcinfo struct just once. Using
+		 * FunctionCallInvoke directly also avoids failure if the eqproc
+		 * returns NULL, though really equality functions should never do
+		 * that.
+		 */
+		InitFunctionCallInfoData(*fcinfo, &eqproc, 2, sslot1->stacoll,
+								 NULL, NULL);
+		fcinfo->args[0].isnull = false;
+		fcinfo->args[1].isnull = false;
+
 		hasmatch1 = (bool *) palloc0(sslot1->nvalues * sizeof(bool));
 		hasmatch2 = (bool *) palloc0(clamped_nvalues2 * sizeof(bool));
 
@@ -2537,14 +2622,18 @@ eqjoinsel_semi(Oid opfuncoid,
 		{
 			int			j;
 
+			fcinfo->args[0].value = sslot1->values[i];
+
 			for (j = 0; j < clamped_nvalues2; j++)
 			{
+				Datum		fresult;
+
 				if (hasmatch2[j])
 					continue;
-				if (DatumGetBool(FunctionCall2Coll(&eqproc,
-												   sslot1->stacoll,
-												   sslot1->values[i],
-												   sslot2->values[j])))
+				fcinfo->args[1].value = sslot2->values[j];
+				fcinfo->isnull = false;
+				fresult = FunctionCallInvoke(fcinfo);
+				if (!fcinfo->isnull && DatumGetBool(fresult))
 				{
 					hasmatch1[i] = hasmatch2[j] = true;
 					nmatches++;
@@ -3687,8 +3776,9 @@ double
 estimate_hashagg_tablesize(Path *path, const AggClauseCosts *agg_costs,
 						   double dNumGroups)
 {
-	Size		hashentrysize = hash_agg_entry_size(
-		agg_costs->numAggs, path->pathtarget->width, agg_costs->transitionSpace);
+	Size		hashentrysize = hash_agg_entry_size(agg_costs->numAggs,
+													path->pathtarget->width,
+													agg_costs->transitionSpace);
 
 	/*
 	 * Note that this disregards the effect of fill-factor and growth policy