Introduce ExecQualAndReset() helper.

It's a common task to evaluate a qual and reset the corresponding
expression context. Currently that requires storing the result of the
qual eval, resetting the context, and then reacting on the result. As
that's awkward several places only reset the context next time through
a node. That's not great, so introduce a helper that evaluates and
resets.

It's a bit ugly that it currently uses MemoryContextReset() instead of
ResetExprContext(), but that seems easier than reordering all of
executor.h.

Author: Andres Freund
Discussion: https://postgr.es/m/20180109222544.f7loxrunqh3xjl5f@alap3.anarazel.de

src/backend/executor/nodeBitmapHeapscan.c

@@ -352,9 +352,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			if (tbmres->recheck)
 			{
 				econtext->ecxt_scantuple = slot;
-				ResetExprContext(econtext);
-
-				if (!ExecQual(node->bitmapqualorig, econtext))
+				if (!ExecQualAndReset(node->bitmapqualorig, econtext))
 				{
 					/* Fails recheck, so drop it and loop back for another */
 					InstrCountFiltered2(node, 1);
@@ -717,10 +715,7 @@ BitmapHeapRecheck(BitmapHeapScanState *node, TupleTableSlot *slot)
 
 	/* Does the tuple meet the original qual conditions? */
 	econtext->ecxt_scantuple = slot;
-
-	ResetExprContext(econtext);
-
-	return ExecQual(node->bitmapqualorig, econtext);
+	return ExecQualAndReset(node->bitmapqualorig, econtext);
 }
 
 /* ----------------------------------------------------------------

src/backend/executor/nodeHash.c

@@ -1942,10 +1942,7 @@ ExecScanHashBucket(HashJoinState *hjstate,
 											 false);	/* do not pfree */
 			econtext->ecxt_innertuple = inntuple;
 
-			/* reset temp memory each time to avoid leaks from qual expr */
-			ResetExprContext(econtext);
-
-			if (ExecQual(hjclauses, econtext))
+			if (ExecQualAndReset(hjclauses, econtext))
 			{
 				hjstate->hj_CurTuple = hashTuple;
 				return true;
@@ -2002,10 +1999,7 @@ ExecParallelScanHashBucket(HashJoinState *hjstate,
 											 false);	/* do not pfree */
 			econtext->ecxt_innertuple = inntuple;
 
-			/* reset temp memory each time to avoid leaks from qual expr */
-			ResetExprContext(econtext);
-
-			if (ExecQual(hjclauses, econtext))
+			if (ExecQualAndReset(hjclauses, econtext))
 			{
 				hjstate->hj_CurTuple = hashTuple;
 				return true;

src/backend/executor/nodeIndexonlyscan.c

@@ -214,8 +214,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
 		if (scandesc->xs_recheck)
 		{
 			econtext->ecxt_scantuple = slot;
-			ResetExprContext(econtext);
-			if (!ExecQual(node->indexqual, econtext))
+			if (!ExecQualAndReset(node->indexqual, econtext))
 			{
 				/* Fails recheck, so drop it and loop back for another */
 				InstrCountFiltered2(node, 1);

src/backend/executor/nodeIndexscan.c

@@ -152,8 +152,7 @@ IndexNext(IndexScanState *node)
 		if (scandesc->xs_recheck)
 		{
 			econtext->ecxt_scantuple = slot;
-			ResetExprContext(econtext);
-			if (!ExecQual(node->indexqualorig, econtext))
+			if (!ExecQualAndReset(node->indexqualorig, econtext))
 			{
 				/* Fails recheck, so drop it and loop back for another */
 				InstrCountFiltered2(node, 1);
@@ -300,8 +299,7 @@ next_indextuple:
 		if (scandesc->xs_recheck)
 		{
 			econtext->ecxt_scantuple = slot;
-			ResetExprContext(econtext);
-			if (!ExecQual(node->indexqualorig, econtext))
+			if (!ExecQualAndReset(node->indexqualorig, econtext))
 			{
 				/* Fails recheck, so drop it and loop back for another */
 				InstrCountFiltered2(node, 1);
@@ -420,10 +418,7 @@ IndexRecheck(IndexScanState *node, TupleTableSlot *slot)
 
 	/* Does the tuple meet the indexqual condition? */
 	econtext->ecxt_scantuple = slot;
-
-	ResetExprContext(econtext);
-
-	return ExecQual(node->indexqualorig, econtext);
+	return ExecQualAndReset(node->indexqualorig, econtext);
 }
 
 

src/include/executor/executor.h

@@ -17,6 +17,7 @@
 #include "catalog/partition.h"
 #include "executor/execdesc.h"
 #include "nodes/parsenodes.h"
+#include "utils/memutils.h"
 
 
 /*
@@ -381,6 +382,22 @@ ExecQual(ExprState *state, ExprContext *econtext)
 }
 #endif
 
+/*
+ * ExecQualAndReset() - evaluate qual with ExecQual() and reset expression
+ * context.
+ */
+#ifndef FRONTEND
+static inline bool
+ExecQualAndReset(ExprState *state, ExprContext *econtext)
+{
+	bool		ret = ExecQual(state, econtext);
+
+	/* inline ResetExprContext, to avoid ordering issue in this file */
+	MemoryContextReset(econtext->ecxt_per_tuple_memory);
+	return ret;
+}
+#endif
+
 extern bool ExecCheck(ExprState *state, ExprContext *context);
 
 /*