Faster expression evaluation and targetlist projection.

This replaces the old, recursive tree-walk based evaluation, with
non-recursive, opcode dispatch based, expression evaluation.
Projection is now implemented as part of expression evaluation.

This both leads to significant performance improvements, and makes
future just-in-time compilation of expressions easier.

The speed gains primarily come from:
- non-recursive implementation reduces stack usage / overhead
- simple sub-expressions are implemented with a single jump, without
  function calls
- sharing some state between different sub-expressions
- reduced amount of indirect/hard to predict memory accesses by laying
  out operation metadata sequentially; including the avoidance of
  nearly all of the previously used linked lists
- more code has been moved to expression initialization, avoiding
  constant re-checks at evaluation time

Future just-in-time compilation (JIT) has become easier, as
demonstrated by released patches intended to be merged in a later
release, for primarily two reasons: Firstly, due to a stricter split
between expression initialization and evaluation, less code has to be
handled by the JIT. Secondly, due to the non-recursive nature of the
generated "instructions", less performance-critical code-paths can
easily be shared between interpreted and compiled evaluation.

The new framework allows for significant future optimizations. E.g.:
- basic infrastructure for to later reduce the per executor-startup
  overhead of expression evaluation, by caching state in prepared
  statements.  That'd be helpful in OLTPish scenarios where
  initialization overhead is measurable.
- optimizing the generated "code". A number of proposals for potential
  work has already been made.
- optimizing the interpreter. Similarly a number of proposals have
  been made here too.

The move of logic into the expression initialization step leads to some
backward-incompatible changes:
- Function permission checks are now done during expression
  initialization, whereas previously they were done during
  execution. In edge cases this can lead to errors being raised that
  previously wouldn't have been, e.g. a NULL array being coerced to a
  different array type previously didn't perform checks.
- The set of domain constraints to be checked, is now evaluated once
  during expression initialization, previously it was re-built
  every time a domain check was evaluated. For normal queries this
  doesn't change much, but e.g. for plpgsql functions, which caches
  ExprStates, the old set could stick around longer.  The behavior
  around might still change.

Author: Andres Freund, with significant changes by Tom Lane,
	changes by Heikki Linnakangas
Reviewed-By: Tom Lane, Heikki Linnakangas
Discussion: https://postgr.es/m/20161206034955.bh33paeralxbtluv@alap3.anarazel.de

src/backend/commands/analyze.c

@@ -713,7 +713,7 @@ compute_index_stats(Relation onerel, double totalrows,
 		TupleTableSlot *slot;
 		EState	   *estate;
 		ExprContext *econtext;
-		List	   *predicate;
+		ExprState  *predicate;
 		Datum	   *exprvals;
 		bool	   *exprnulls;
 		int			numindexrows,
@@ -739,9 +739,7 @@ compute_index_stats(Relation onerel, double totalrows,
 		econtext->ecxt_scantuple = slot;
 
 		/* Set up execution state for predicate. */
-		predicate = castNode(List,
-							 ExecPrepareExpr((Expr *) indexInfo->ii_Predicate,
-											 estate));
+		predicate = ExecPrepareQual(indexInfo->ii_Predicate, estate);
 
 		/* Compute and save index expression values */
 		exprvals = (Datum *) palloc(numrows * attr_cnt * sizeof(Datum));
@@ -764,9 +762,9 @@ compute_index_stats(Relation onerel, double totalrows,
 			ExecStoreTuple(heapTuple, slot, InvalidBuffer, false);
 
 			/* If index is partial, check predicate */
-			if (predicate != NIL)
+			if (predicate != NULL)
 			{
-				if (!ExecQual(predicate, econtext, false))
+				if (!ExecQual(predicate, econtext))
 					continue;
 			}
 			numindexrows++;

src/backend/commands/explain.c

@@ -2890,7 +2890,7 @@ ExplainSubPlans(List *plans, List *ancestors,
 	foreach(lst, plans)
 	{
 		SubPlanState *sps = (SubPlanState *) lfirst(lst);
-		SubPlan    *sp = (SubPlan *) sps->xprstate.expr;
+		SubPlan    *sp = sps->subplan;
 
 		/*
 		 * There can be multiple SubPlan nodes referencing the same physical

src/backend/commands/indexcmds.c

@@ -179,7 +179,7 @@ CheckIndexCompatible(Oid oldId,
 	indexInfo = makeNode(IndexInfo);
 	indexInfo->ii_Expressions = NIL;
 	indexInfo->ii_ExpressionsState = NIL;
-	indexInfo->ii_PredicateState = NIL;
+	indexInfo->ii_PredicateState = NULL;
 	indexInfo->ii_ExclusionOps = NULL;
 	indexInfo->ii_ExclusionProcs = NULL;
 	indexInfo->ii_ExclusionStrats = NULL;
@@ -551,7 +551,7 @@ DefineIndex(Oid relationId,
 	indexInfo->ii_Expressions = NIL;	/* for now */
 	indexInfo->ii_ExpressionsState = NIL;
 	indexInfo->ii_Predicate = make_ands_implicit((Expr *) stmt->whereClause);
-	indexInfo->ii_PredicateState = NIL;
+	indexInfo->ii_PredicateState = NULL;
 	indexInfo->ii_ExclusionOps = NULL;
 	indexInfo->ii_ExclusionProcs = NULL;
 	indexInfo->ii_ExclusionStrats = NULL;

src/backend/commands/prepare.c

@@ -391,7 +391,7 @@ EvaluateParams(PreparedStatement *pstmt, List *params,
 	}
 
 	/* Prepare the expressions for execution */
-	exprstates = (List *) ExecPrepareExpr((Expr *) params, estate);
+	exprstates = ExecPrepareExprList(params, estate);
 
 	paramLI = (ParamListInfo)
 		palloc(offsetof(ParamListInfoData, params) +
@@ -407,7 +407,7 @@ EvaluateParams(PreparedStatement *pstmt, List *params,
 	i = 0;
 	foreach(l, exprstates)
 	{
-		ExprState  *n = lfirst(l);
+		ExprState  *n = (ExprState *) lfirst(l);
 		ParamExternData *prm = &paramLI->params[i];
 
 		prm->ptype = param_types[i];

src/backend/commands/tablecmds.c

@@ -185,7 +185,7 @@ typedef struct NewConstraint
 	Oid			refindid;		/* OID of PK's index, if FOREIGN */
 	Oid			conid;			/* OID of pg_constraint entry, if FOREIGN */
 	Node	   *qual;			/* Check expr or CONSTR_FOREIGN Constraint */
-	List	   *qualstate;		/* Execution state for CHECK */
+	ExprState  *qualstate;		/* Execution state for CHECK expr */
 } NewConstraint;
 
 /*
@@ -4262,7 +4262,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 	CommandId	mycid;
 	BulkInsertState bistate;
 	int			hi_options;
-	List	   *partqualstate = NIL;
+	ExprState  *partqualstate = NULL;
 
 	/*
 	 * Open the relation(s).  We have surely already locked the existing
@@ -4315,8 +4315,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 		{
 			case CONSTR_CHECK:
 				needscan = true;
-				con->qualstate = (List *)
-					ExecPrepareExpr((Expr *) con->qual, estate);
+				con->qualstate = ExecPrepareExpr((Expr *) con->qual, estate);
 				break;
 			case CONSTR_FOREIGN:
 				/* Nothing to do here */
@@ -4331,9 +4330,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 	if (tab->partition_constraint)
 	{
 		needscan = true;
-		partqualstate = (List *)
-			ExecPrepareExpr((Expr *) tab->partition_constraint,
-							estate);
+		partqualstate = ExecPrepareCheck(tab->partition_constraint, estate);
 	}
 
 	foreach(l, tab->newvals)
@@ -4508,7 +4505,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 				switch (con->contype)
 				{
 					case CONSTR_CHECK:
-						if (!ExecQual(con->qualstate, econtext, true))
+						if (!ExecCheck(con->qualstate, econtext))
 							ereport(ERROR,
 									(errcode(ERRCODE_CHECK_VIOLATION),
 									 errmsg("check constraint \"%s\" is violated by some row",
@@ -4524,7 +4521,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 				}
 			}
 
-			if (partqualstate && !ExecQual(partqualstate, econtext, true))
+			if (partqualstate && !ExecCheck(partqualstate, econtext))
 				ereport(ERROR,
 						(errcode(ERRCODE_CHECK_VIOLATION),
 					errmsg("partition constraint is violated by some row")));
@@ -6607,8 +6604,7 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 			newcon = (NewConstraint *) palloc0(sizeof(NewConstraint));
 			newcon->name = ccon->name;
 			newcon->contype = ccon->contype;
-			/* ExecQual wants implicit-AND format */
-			newcon->qual = (Node *) make_ands_implicit((Expr *) ccon->expr);
+			newcon->qual = ccon->expr;
 
 			tab->constraints = lappend(tab->constraints, newcon);
 		}
@@ -7786,7 +7782,7 @@ validateCheckConstraint(Relation rel, HeapTuple constrtup)
 	Datum		val;
 	char	   *conbin;
 	Expr	   *origexpr;
-	List	   *exprstate;
+	ExprState  *exprstate;
 	TupleDesc	tupdesc;
 	HeapScanDesc scan;
 	HeapTuple	tuple;
@@ -7817,8 +7813,7 @@ validateCheckConstraint(Relation rel, HeapTuple constrtup)
 			 HeapTupleGetOid(constrtup));
 	conbin = TextDatumGetCString(val);
 	origexpr = (Expr *) stringToNode(conbin);
-	exprstate = (List *)
-		ExecPrepareExpr((Expr *) make_ands_implicit(origexpr), estate);
+	exprstate = ExecPrepareExpr(origexpr, estate);
 
 	econtext = GetPerTupleExprContext(estate);
 	tupdesc = RelationGetDescr(rel);
@@ -7838,7 +7833,7 @@ validateCheckConstraint(Relation rel, HeapTuple constrtup)
 	{
 		ExecStoreTuple(tuple, slot, InvalidBuffer, false);
 
-		if (!ExecQual(exprstate, econtext, true))
+		if (!ExecCheck(exprstate, econtext))
 			ereport(ERROR,
 					(errcode(ERRCODE_CHECK_VIOLATION),
 					 errmsg("check constraint \"%s\" is violated by some row",

src/backend/commands/trigger.c

@@ -3057,7 +3057,7 @@ TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
 	if (trigger->tgqual)
 	{
 		TupleDesc	tupdesc = RelationGetDescr(relinfo->ri_RelationDesc);
-		List	  **predicate;
+		ExprState **predicate;
 		ExprContext *econtext;
 		TupleTableSlot *oldslot = NULL;
 		TupleTableSlot *newslot = NULL;
@@ -3078,7 +3078,7 @@ TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
 		 * nodetrees for it.  Keep them in the per-query memory context so
 		 * they'll survive throughout the query.
 		 */
-		if (*predicate == NIL)
+		if (*predicate == NULL)
 		{
 			Node	   *tgqual;
 
@@ -3087,9 +3087,9 @@ TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
 			/* Change references to OLD and NEW to INNER_VAR and OUTER_VAR */
 			ChangeVarNodes(tgqual, PRS2_OLD_VARNO, INNER_VAR, 0);
 			ChangeVarNodes(tgqual, PRS2_NEW_VARNO, OUTER_VAR, 0);
-			/* ExecQual wants implicit-AND form */
+			/* ExecPrepareQual wants implicit-AND form */
 			tgqual = (Node *) make_ands_implicit((Expr *) tgqual);
-			*predicate = (List *) ExecPrepareExpr((Expr *) tgqual, estate);
+			*predicate = ExecPrepareQual((List *) tgqual, estate);
 			MemoryContextSwitchTo(oldContext);
 		}
 
@@ -3137,7 +3137,7 @@ TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
 		 */
 		econtext->ecxt_innertuple = oldslot;
 		econtext->ecxt_outertuple = newslot;
-		if (!ExecQual(*predicate, econtext, false))
+		if (!ExecQual(*predicate, econtext))
 			return false;
 	}