Simplify the planner's new representation of indexable clauses a little.

In commit 1a8d5afb, I thought it'd be a good idea to define
IndexClause.indexquals as NIL in the most common case where the given
clause (IndexClause.rinfo) is usable exactly as-is.  It'd be more
consistent to define the indexquals in that case as being a one-element
list containing IndexClause.rinfo, but I thought saving the palloc
overhead for making such a list would be worthwhile.

In hindsight, that was a great example of "premature optimization is the
root of all evil": it's complicated everyplace that needs to deal with
the indexquals, requiring duplicative code to handle both the simple
case and the not-simple case.  I'd initially found that tolerable but
it's getting less so as I mop up some areas that I'd not touched in
1a8d5afb.  In any case, two more pallocs during a planner run are
surely at the noise level (a conclusion confirmed by a bit of
microbenchmarking).  So let's change this decision before it becomes
set in stone, and insist that IndexClause.indexquals always be a valid
list of the actual index quals for the clause.

Discussion: https://postgr.es/m/24586.1550106354@sss.pgh.pa.us

src/backend/optimizer/path/indxpath.c

@@ -2435,7 +2435,7 @@ match_clause_to_indexcol(PlannerInfo *root,
 		{
 			iclause = makeNode(IndexClause);
 			iclause->rinfo = rinfo;
-			iclause->indexquals = NIL;
+			iclause->indexquals = list_make1(rinfo);
 			iclause->lossy = false;
 			iclause->indexcol = indexcol;
 			iclause->indexcols = NIL;
@@ -2599,7 +2599,7 @@ match_opclause_to_indexcol(PlannerInfo *root,
 		{
 			iclause = makeNode(IndexClause);
 			iclause->rinfo = rinfo;
-			iclause->indexquals = NIL;
+			iclause->indexquals = list_make1(rinfo);
 			iclause->lossy = false;
 			iclause->indexcol = indexcol;
 			iclause->indexcols = NIL;
@@ -2819,7 +2819,7 @@ match_saopclause_to_indexcol(RestrictInfo *rinfo,
 			IndexClause *iclause = makeNode(IndexClause);
 
 			iclause->rinfo = rinfo;
-			iclause->indexquals = NIL;
+			iclause->indexquals = list_make1(rinfo);
 			iclause->lossy = false;
 			iclause->indexcol = indexcol;
 			iclause->indexcols = NIL;
@@ -3078,7 +3078,7 @@ expand_indexqual_rowcompare(RestrictInfo *rinfo,
 	 * usable as index quals.
 	 */
 	if (var_on_left && !iclause->lossy)
-		iclause->indexquals = NIL;
+		iclause->indexquals = list_make1(rinfo);
 	else
 	{
 		/*

src/backend/optimizer/plan/createplan.c

@@ -3075,11 +3075,8 @@ create_bitmap_subplan(PlannerInfo *root, Path *bitmapqual,
 
 			Assert(!rinfo->pseudoconstant);
 			subquals = lappend(subquals, rinfo->clause);
-			if (iclause->indexquals)
 			subindexquals = list_concat(subindexquals,
 										get_actual_clauses(iclause->indexquals));
-			else
-				subindexquals = lappend(subindexquals, rinfo->clause);
 			if (rinfo->parent_ec)
 				subindexECs = lappend(subindexECs, rinfo->parent_ec);
 		}
@@ -4491,20 +4488,6 @@ fix_indexqual_references(PlannerInfo *root, IndexPath *index_path,
 	{
 		IndexClause *iclause = lfirst_node(IndexClause, lc);
 		int			indexcol = iclause->indexcol;
-
-		if (iclause->indexquals == NIL)
-		{
-			/* rinfo->clause is directly usable as an indexqual */
-			Node	   *clause = (Node *) iclause->rinfo->clause;
-
-			stripped_indexquals = lappend(stripped_indexquals, clause);
-			clause = fix_indexqual_clause(root, index, indexcol,
-										  clause, iclause->indexcols);
-			fixed_indexquals = lappend(fixed_indexquals, clause);
-		}
-		else
-		{
-			/* Process the derived indexquals */
 		ListCell   *lc2;
 
 		foreach(lc2, iclause->indexquals)
@@ -4518,7 +4501,6 @@ fix_indexqual_references(PlannerInfo *root, IndexPath *index_path,
 			fixed_indexquals = lappend(fixed_indexquals, clause);
 		}
 	}
-	}
 
 	*stripped_indexquals_p = stripped_indexquals;
 	*fixed_indexquals_p = fixed_indexquals;

src/backend/utils/adt/selfuncs.c

@@ -197,8 +197,6 @@ static bool get_actual_variable_range(PlannerInfo *root,
 						  Oid sortop,
 						  Datum *min, Datum *max);
 static RelOptInfo *find_join_input_rel(PlannerInfo *root, Relids relids);
-static IndexQualInfo *deconstruct_indexqual(RestrictInfo *rinfo,
-					  IndexOptInfo *index, int indexcol);
 static List *add_predicate_to_quals(IndexOptInfo *index, List *indexQuals);
 
 
@@ -5263,16 +5261,13 @@ get_index_quals(List *indexclauses)
 	foreach(lc, indexclauses)
 	{
 		IndexClause *iclause = lfirst_node(IndexClause, lc);
+		ListCell   *lc2;
 
-		if (iclause->indexquals == NIL)
-		{
-			/* rinfo->clause is directly usable as an indexqual */
-			result = lappend(result, iclause->rinfo);
-		}
-		else
+		foreach(lc2, iclause->indexquals)
 		{
-			/* report the derived indexquals */
-			result = list_concat(result, list_copy(iclause->indexquals));
+			RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc2);
+
+			result = lappend(result, rinfo);
 		}
 	}
 	return result;
@@ -5282,47 +5277,20 @@ List *
 deconstruct_indexquals(IndexPath *path)
 {
 	List	   *result = NIL;
-	IndexOptInfo *index = path->indexinfo;
 	ListCell   *lc;
 
 	foreach(lc, path->indexclauses)
 	{
 		IndexClause *iclause = lfirst_node(IndexClause, lc);
 		int			indexcol = iclause->indexcol;
-		IndexQualInfo *qinfo;
-
-		if (iclause->indexquals == NIL)
-		{
-			/* rinfo->clause is directly usable as an indexqual */
-			qinfo = deconstruct_indexqual(iclause->rinfo, index, indexcol);
-			result = lappend(result, qinfo);
-		}
-		else
-		{
-			/* Process the derived indexquals */
 		ListCell   *lc2;
 
 		foreach(lc2, iclause->indexquals)
 		{
 			RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc2);
-
-				qinfo = deconstruct_indexqual(rinfo, index, indexcol);
-				result = lappend(result, qinfo);
-			}
-		}
-	}
-	return result;
-}
-
-static IndexQualInfo *
-deconstruct_indexqual(RestrictInfo *rinfo, IndexOptInfo *index, int indexcol)
-{
-	{
-		Expr	   *clause;
+			Expr	   *clause = rinfo->clause;
 			IndexQualInfo *qinfo;
 
-		clause = rinfo->clause;
-
 			qinfo = (IndexQualInfo *) palloc(sizeof(IndexQualInfo));
 			qinfo->rinfo = rinfo;
 			qinfo->indexcol = indexcol;
@@ -5357,8 +5325,10 @@ deconstruct_indexqual(RestrictInfo *rinfo, IndexOptInfo *index, int indexcol)
 					 (int) nodeTag(clause));
 			}
 
-		return qinfo;
+			result = lappend(result, qinfo);
+		}
 	}
+	return result;
 }
 
 /*

src/include/nodes/pathnodes.h

@@ -1185,26 +1185,20 @@ typedef struct IndexPath
  * conditions is done by a planner support function attached to the
  * indexclause's top-level function or operator.
  *
- * If indexquals is NIL, it means that rinfo->clause is directly usable as
- * an indexqual.  Otherwise indexquals contains one or more directly-usable
- * indexqual conditions extracted from the given clause.  The 'lossy' flag
- * indicates whether the indexquals are semantically equivalent to the
- * original clause, or form a weaker condition.
- *
- * Currently, entries in indexquals are RestrictInfos, but they could perhaps
- * be bare clauses instead; the only advantage of making them RestrictInfos
- * is the possibility of caching cost and selectivity information across
- * multiple uses, and it's not clear that that's really worth the price of
- * constructing RestrictInfos for them.  Note however that the extended-stats
- * machinery won't do anything with non-RestrictInfo clauses, so that would
- * have to be fixed.
+ * indexquals is a list of RestrictInfos for the directly-usable index
+ * conditions associated with this IndexClause.  In the simplest case
+ * it's a one-element list whose member is iclause->rinfo.  Otherwise,
+ * it contains one or more directly-usable indexqual conditions extracted
+ * from the given clause.  The 'lossy' flag indicates whether the
+ * indexquals are semantically equivalent to the original clause, or
+ * represent a weaker condition.
  *
  * Normally, indexcol is the index of the single index column the clause
  * works on, and indexcols is NIL.  But if the clause is a RowCompareExpr,
  * indexcol is the index of the leading column, and indexcols is a list of
  * all the affected columns.  (Note that indexcols matches up with the
- * columns of the actual indexable RowCompareExpr, which might be in
- * indexquals rather than rinfo.)
+ * columns of the actual indexable RowCompareExpr in indexquals, which
+ * might be different from the original in rinfo.)
  *
  * An IndexPath's IndexClause list is required to be ordered by index
  * column, i.e. the indexcol values must form a nondecreasing sequence.
@@ -1214,7 +1208,7 @@ typedef struct IndexClause
 {
 	NodeTag		type;
 	struct RestrictInfo *rinfo; /* original restriction or join clause */
-	List	   *indexquals;		/* indexqual(s) derived from it, or NIL */
+	List	   *indexquals;		/* indexqual(s) derived from it */
 	bool		lossy;			/* are indexquals a lossy version of clause? */
 	AttrNumber	indexcol;		/* index column the clause uses (zero-based) */
 	List	   *indexcols;		/* multiple index columns, if RowCompare */