Adding upstream version 14.5.upstream/14.5upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 898 insertions, 0 deletions

diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
new file mode 100644
index 0000000..4e0b533
--- /dev/null
+++ b/src/backend/optimizer/util/var.c
@@ -0,0 +1,898 @@
+/*-------------------------------------------------------------------------
+ *
+ * var.c
+ *	  Var node manipulation routines
+ *
+ * Note: for most purposes, PlaceHolderVar is considered a Var too,
+ * even if its contained expression is variable-free.  Also, CurrentOfExpr
+ * is treated as a Var for purposes of determining whether an expression
+ * contains variables.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/optimizer/util/var.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/sysattr.h"
+#include "nodes/nodeFuncs.h"
+#include "optimizer/optimizer.h"
+#include "optimizer/placeholder.h"
+#include "optimizer/prep.h"
+#include "parser/parsetree.h"
+#include "rewrite/rewriteManip.h"
+
+
+typedef struct
+{
+	Relids		varnos;
+	PlannerInfo *root;
+	int			sublevels_up;
+} pull_varnos_context;
+
+typedef struct
+{
+	Bitmapset  *varattnos;
+	Index		varno;
+} pull_varattnos_context;
+
+typedef struct
+{
+	List	   *vars;
+	int			sublevels_up;
+} pull_vars_context;
+
+typedef struct
+{
+	int			var_location;
+	int			sublevels_up;
+} locate_var_of_level_context;
+
+typedef struct
+{
+	List	   *varlist;
+	int			flags;
+} pull_var_clause_context;
+
+typedef struct
+{
+	Query	   *query;			/* outer Query */
+	int			sublevels_up;
+	bool		possible_sublink;	/* could aliases include a SubLink? */
+	bool		inserted_sublink;	/* have we inserted a SubLink? */
+} flatten_join_alias_vars_context;
+
+static bool pull_varnos_walker(Node *node,
+							   pull_varnos_context *context);
+static bool pull_varattnos_walker(Node *node, pull_varattnos_context *context);
+static bool pull_vars_walker(Node *node, pull_vars_context *context);
+static bool contain_var_clause_walker(Node *node, void *context);
+static bool contain_vars_of_level_walker(Node *node, int *sublevels_up);
+static bool locate_var_of_level_walker(Node *node,
+									   locate_var_of_level_context *context);
+static bool pull_var_clause_walker(Node *node,
+								   pull_var_clause_context *context);
+static Node *flatten_join_alias_vars_mutator(Node *node,
+											 flatten_join_alias_vars_context *context);
+static Relids alias_relid_set(Query *query, Relids relids);
+
+
+/*
+ * pull_varnos
+ *		Create a set of all the distinct varnos present in a parsetree.
+ *		Only varnos that reference level-zero rtable entries are considered.
+ *
+ * NOTE: this is used on not-yet-planned expressions.  It may therefore find
+ * bare SubLinks, and if so it needs to recurse into them to look for uplevel
+ * references to the desired rtable level!	But when we find a completed
+ * SubPlan, we only need to look at the parameters passed to the subplan.
+ */
+Relids
+pull_varnos(PlannerInfo *root, Node *node)
+{
+	pull_varnos_context context;
+
+	context.varnos = NULL;
+	context.root = root;
+	context.sublevels_up = 0;
+
+	/*
+	 * Must be prepared to start with a Query or a bare expression tree; if
+	 * it's a Query, we don't want to increment sublevels_up.
+	 */
+	query_or_expression_tree_walker(node,
+									pull_varnos_walker,
+									(void *) &context,
+									0);
+
+	return context.varnos;
+}
+
+/*
+ * pull_varnos_of_level
+ *		Create a set of all the distinct varnos present in a parsetree.
+ *		Only Vars of the specified level are considered.
+ */
+Relids
+pull_varnos_of_level(PlannerInfo *root, Node *node, int levelsup)
+{
+	pull_varnos_context context;
+
+	context.varnos = NULL;
+	context.root = root;
+	context.sublevels_up = levelsup;
+
+	/*
+	 * Must be prepared to start with a Query or a bare expression tree; if
+	 * it's a Query, we don't want to increment sublevels_up.
+	 */
+	query_or_expression_tree_walker(node,
+									pull_varnos_walker,
+									(void *) &context,
+									0);
+
+	return context.varnos;
+}
+
+static bool
+pull_varnos_walker(Node *node, pull_varnos_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		Var		   *var = (Var *) node;
+
+		if (var->varlevelsup == context->sublevels_up)
+			context->varnos = bms_add_member(context->varnos, var->varno);
+		return false;
+	}
+	if (IsA(node, CurrentOfExpr))
+	{
+		CurrentOfExpr *cexpr = (CurrentOfExpr *) node;
+
+		if (context->sublevels_up == 0)
+			context->varnos = bms_add_member(context->varnos, cexpr->cvarno);
+		return false;
+	}
+	if (IsA(node, PlaceHolderVar))
+	{
+		PlaceHolderVar *phv = (PlaceHolderVar *) node;
+
+		/*
+		 * If a PlaceHolderVar is not of the target query level, ignore it,
+		 * instead recursing into its expression to see if it contains any
+		 * vars that are of the target level.
+		 */
+		if (phv->phlevelsup == context->sublevels_up)
+		{
+			/*
+			 * Ideally, the PHV's contribution to context->varnos is its
+			 * ph_eval_at set.  However, this code can be invoked before
+			 * that's been computed.  If we cannot find a PlaceHolderInfo,
+			 * fall back to the conservative assumption that the PHV will be
+			 * evaluated at its syntactic level (phv->phrels).
+			 *
+			 * There is a second hazard: this code is also used to examine
+			 * qual clauses during deconstruct_jointree, when we may have a
+			 * PlaceHolderInfo but its ph_eval_at value is not yet final, so
+			 * that theoretically we could obtain a relid set that's smaller
+			 * than we'd see later on.  That should never happen though,
+			 * because we deconstruct the jointree working upwards.  Any outer
+			 * join that forces delay of evaluation of a given qual clause
+			 * will be processed before we examine that clause here, so the
+			 * ph_eval_at value should have been updated to include it.
+			 *
+			 * Another problem is that a PlaceHolderVar can appear in quals or
+			 * tlists that have been translated for use in a child appendrel.
+			 * Typically such a PHV is a parameter expression sourced by some
+			 * other relation, so that the translation from parent appendrel
+			 * to child doesn't change its phrels, and we should still take
+			 * ph_eval_at at face value.  But in corner cases, the PHV's
+			 * original phrels can include the parent appendrel itself, in
+			 * which case the translated PHV will have the child appendrel in
+			 * phrels, and we must translate ph_eval_at to match.
+			 */
+			PlaceHolderInfo *phinfo = NULL;
+
+			if (phv->phlevelsup == 0)
+			{
+				ListCell   *lc;
+
+				foreach(lc, context->root->placeholder_list)
+				{
+					phinfo = (PlaceHolderInfo *) lfirst(lc);
+					if (phinfo->phid == phv->phid)
+						break;
+					phinfo = NULL;
+				}
+			}
+			if (phinfo == NULL)
+			{
+				/* No PlaceHolderInfo yet, use phrels */
+				context->varnos = bms_add_members(context->varnos,
+												  phv->phrels);
+			}
+			else if (bms_equal(phv->phrels, phinfo->ph_var->phrels))
+			{
+				/* Normal case: use ph_eval_at */
+				context->varnos = bms_add_members(context->varnos,
+												  phinfo->ph_eval_at);
+			}
+			else
+			{
+				/* Translated PlaceHolderVar: translate ph_eval_at to match */
+				Relids		newevalat,
+							delta;
+
+				/* remove what was removed from phv->phrels ... */
+				delta = bms_difference(phinfo->ph_var->phrels, phv->phrels);
+				newevalat = bms_difference(phinfo->ph_eval_at, delta);
+				/* ... then if that was in fact part of ph_eval_at ... */
+				if (!bms_equal(newevalat, phinfo->ph_eval_at))
+				{
+					/* ... add what was added */
+					delta = bms_difference(phv->phrels, phinfo->ph_var->phrels);
+					newevalat = bms_join(newevalat, delta);
+				}
+				context->varnos = bms_join(context->varnos,
+										   newevalat);
+			}
+			return false;		/* don't recurse into expression */
+		}
+	}
+	else if (IsA(node, Query))
+	{
+		/* Recurse into RTE subquery or not-yet-planned sublink subquery */
+		bool		result;
+
+		context->sublevels_up++;
+		result = query_tree_walker((Query *) node, pull_varnos_walker,
+								   (void *) context, 0);
+		context->sublevels_up--;
+		return result;
+	}
+	return expression_tree_walker(node, pull_varnos_walker,
+								  (void *) context);
+}
+
+
+/*
+ * pull_varattnos
+ *		Find all the distinct attribute numbers present in an expression tree,
+ *		and add them to the initial contents of *varattnos.
+ *		Only Vars of the given varno and rtable level zero are considered.
+ *
+ * Attribute numbers are offset by FirstLowInvalidHeapAttributeNumber so that
+ * we can include system attributes (e.g., OID) in the bitmap representation.
+ *
+ * Currently, this does not support unplanned subqueries; that is not needed
+ * for current uses.  It will handle already-planned SubPlan nodes, though,
+ * looking into only the "testexpr" and the "args" list.  (The subplan cannot
+ * contain any other references to Vars of the current level.)
+ */
+void
+pull_varattnos(Node *node, Index varno, Bitmapset **varattnos)
+{
+	pull_varattnos_context context;
+
+	context.varattnos = *varattnos;
+	context.varno = varno;
+
+	(void) pull_varattnos_walker(node, &context);
+
+	*varattnos = context.varattnos;
+}
+
+static bool
+pull_varattnos_walker(Node *node, pull_varattnos_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		Var		   *var = (Var *) node;
+
+		if (var->varno == context->varno && var->varlevelsup == 0)
+			context->varattnos =
+				bms_add_member(context->varattnos,
+							   var->varattno - FirstLowInvalidHeapAttributeNumber);
+		return false;
+	}
+
+	/* Should not find an unplanned subquery */
+	Assert(!IsA(node, Query));
+
+	return expression_tree_walker(node, pull_varattnos_walker,
+								  (void *) context);
+}
+
+
+/*
+ * pull_vars_of_level
+ *		Create a list of all Vars (and PlaceHolderVars) referencing the
+ *		specified query level in the given parsetree.
+ *
+ * Caution: the Vars are not copied, only linked into the list.
+ */
+List *
+pull_vars_of_level(Node *node, int levelsup)
+{
+	pull_vars_context context;
+
+	context.vars = NIL;
+	context.sublevels_up = levelsup;
+
+	/*
+	 * Must be prepared to start with a Query or a bare expression tree; if
+	 * it's a Query, we don't want to increment sublevels_up.
+	 */
+	query_or_expression_tree_walker(node,
+									pull_vars_walker,
+									(void *) &context,
+									0);
+
+	return context.vars;
+}
+
+static bool
+pull_vars_walker(Node *node, pull_vars_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		Var		   *var = (Var *) node;
+
+		if (var->varlevelsup == context->sublevels_up)
+			context->vars = lappend(context->vars, var);
+		return false;
+	}
+	if (IsA(node, PlaceHolderVar))
+	{
+		PlaceHolderVar *phv = (PlaceHolderVar *) node;
+
+		if (phv->phlevelsup == context->sublevels_up)
+			context->vars = lappend(context->vars, phv);
+		/* we don't want to look into the contained expression */
+		return false;
+	}
+	if (IsA(node, Query))
+	{
+		/* Recurse into RTE subquery or not-yet-planned sublink subquery */
+		bool		result;
+
+		context->sublevels_up++;
+		result = query_tree_walker((Query *) node, pull_vars_walker,
+								   (void *) context, 0);
+		context->sublevels_up--;
+		return result;
+	}
+	return expression_tree_walker(node, pull_vars_walker,
+								  (void *) context);
+}
+
+
+/*
+ * contain_var_clause
+ *	  Recursively scan a clause to discover whether it contains any Var nodes
+ *	  (of the current query level).
+ *
+ *	  Returns true if any varnode found.
+ *
+ * Does not examine subqueries, therefore must only be used after reduction
+ * of sublinks to subplans!
+ */
+bool
+contain_var_clause(Node *node)
+{
+	return contain_var_clause_walker(node, NULL);
+}
+
+static bool
+contain_var_clause_walker(Node *node, void *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		if (((Var *) node)->varlevelsup == 0)
+			return true;		/* abort the tree traversal and return true */
+		return false;
+	}
+	if (IsA(node, CurrentOfExpr))
+		return true;
+	if (IsA(node, PlaceHolderVar))
+	{
+		if (((PlaceHolderVar *) node)->phlevelsup == 0)
+			return true;		/* abort the tree traversal and return true */
+		/* else fall through to check the contained expr */
+	}
+	return expression_tree_walker(node, contain_var_clause_walker, context);
+}
+
+
+/*
+ * contain_vars_of_level
+ *	  Recursively scan a clause to discover whether it contains any Var nodes
+ *	  of the specified query level.
+ *
+ *	  Returns true if any such Var found.
+ *
+ * Will recurse into sublinks.  Also, may be invoked directly on a Query.
+ */
+bool
+contain_vars_of_level(Node *node, int levelsup)
+{
+	int			sublevels_up = levelsup;
+
+	return query_or_expression_tree_walker(node,
+										   contain_vars_of_level_walker,
+										   (void *) &sublevels_up,
+										   0);
+}
+
+static bool
+contain_vars_of_level_walker(Node *node, int *sublevels_up)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		if (((Var *) node)->varlevelsup == *sublevels_up)
+			return true;		/* abort tree traversal and return true */
+		return false;
+	}
+	if (IsA(node, CurrentOfExpr))
+	{
+		if (*sublevels_up == 0)
+			return true;
+		return false;
+	}
+	if (IsA(node, PlaceHolderVar))
+	{
+		if (((PlaceHolderVar *) node)->phlevelsup == *sublevels_up)
+			return true;		/* abort the tree traversal and return true */
+		/* else fall through to check the contained expr */
+	}
+	if (IsA(node, Query))
+	{
+		/* Recurse into subselects */
+		bool		result;
+
+		(*sublevels_up)++;
+		result = query_tree_walker((Query *) node,
+								   contain_vars_of_level_walker,
+								   (void *) sublevels_up,
+								   0);
+		(*sublevels_up)--;
+		return result;
+	}
+	return expression_tree_walker(node,
+								  contain_vars_of_level_walker,
+								  (void *) sublevels_up);
+}
+
+
+/*
+ * locate_var_of_level
+ *	  Find the parse location of any Var of the specified query level.
+ *
+ * Returns -1 if no such Var is in the querytree, or if they all have
+ * unknown parse location.  (The former case is probably caller error,
+ * but we don't bother to distinguish it from the latter case.)
+ *
+ * Will recurse into sublinks.  Also, may be invoked directly on a Query.
+ *
+ * Note: it might seem appropriate to merge this functionality into
+ * contain_vars_of_level, but that would complicate that function's API.
+ * Currently, the only uses of this function are for error reporting,
+ * and so shaving cycles probably isn't very important.
+ */
+int
+locate_var_of_level(Node *node, int levelsup)
+{
+	locate_var_of_level_context context;
+
+	context.var_location = -1;	/* in case we find nothing */
+	context.sublevels_up = levelsup;
+
+	(void) query_or_expression_tree_walker(node,
+										   locate_var_of_level_walker,
+										   (void *) &context,
+										   0);
+
+	return context.var_location;
+}
+
+static bool
+locate_var_of_level_walker(Node *node,
+						   locate_var_of_level_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		Var		   *var = (Var *) node;
+
+		if (var->varlevelsup == context->sublevels_up &&
+			var->location >= 0)
+		{
+			context->var_location = var->location;
+			return true;		/* abort tree traversal and return true */
+		}
+		return false;
+	}
+	if (IsA(node, CurrentOfExpr))
+	{
+		/* since CurrentOfExpr doesn't carry location, nothing we can do */
+		return false;
+	}
+	/* No extra code needed for PlaceHolderVar; just look in contained expr */
+	if (IsA(node, Query))
+	{
+		/* Recurse into subselects */
+		bool		result;
+
+		context->sublevels_up++;
+		result = query_tree_walker((Query *) node,
+								   locate_var_of_level_walker,
+								   (void *) context,
+								   0);
+		context->sublevels_up--;
+		return result;
+	}
+	return expression_tree_walker(node,
+								  locate_var_of_level_walker,
+								  (void *) context);
+}
+
+
+/*
+ * pull_var_clause
+ *	  Recursively pulls all Var nodes from an expression clause.
+ *
+ *	  Aggrefs are handled according to these bits in 'flags':
+ *		PVC_INCLUDE_AGGREGATES		include Aggrefs in output list
+ *		PVC_RECURSE_AGGREGATES		recurse into Aggref arguments
+ *		neither flag				throw error if Aggref found
+ *	  Vars within an Aggref's expression are included in the result only
+ *	  when PVC_RECURSE_AGGREGATES is specified.
+ *
+ *	  WindowFuncs are handled according to these bits in 'flags':
+ *		PVC_INCLUDE_WINDOWFUNCS		include WindowFuncs in output list
+ *		PVC_RECURSE_WINDOWFUNCS		recurse into WindowFunc arguments
+ *		neither flag				throw error if WindowFunc found
+ *	  Vars within a WindowFunc's expression are included in the result only
+ *	  when PVC_RECURSE_WINDOWFUNCS is specified.
+ *
+ *	  PlaceHolderVars are handled according to these bits in 'flags':
+ *		PVC_INCLUDE_PLACEHOLDERS	include PlaceHolderVars in output list
+ *		PVC_RECURSE_PLACEHOLDERS	recurse into PlaceHolderVar arguments
+ *		neither flag				throw error if PlaceHolderVar found
+ *	  Vars within a PHV's expression are included in the result only
+ *	  when PVC_RECURSE_PLACEHOLDERS is specified.
+ *
+ *	  GroupingFuncs are treated exactly like Aggrefs, and so do not need
+ *	  their own flag bits.
+ *
+ *	  CurrentOfExpr nodes are ignored in all cases.
+ *
+ *	  Upper-level vars (with varlevelsup > 0) should not be seen here,
+ *	  likewise for upper-level Aggrefs and PlaceHolderVars.
+ *
+ *	  Returns list of nodes found.  Note the nodes themselves are not
+ *	  copied, only referenced.
+ *
+ * Does not examine subqueries, therefore must only be used after reduction
+ * of sublinks to subplans!
+ */
+List *
+pull_var_clause(Node *node, int flags)
+{
+	pull_var_clause_context context;
+
+	/* Assert that caller has not specified inconsistent flags */
+	Assert((flags & (PVC_INCLUDE_AGGREGATES | PVC_RECURSE_AGGREGATES))
+		   != (PVC_INCLUDE_AGGREGATES | PVC_RECURSE_AGGREGATES));
+	Assert((flags & (PVC_INCLUDE_WINDOWFUNCS | PVC_RECURSE_WINDOWFUNCS))
+		   != (PVC_INCLUDE_WINDOWFUNCS | PVC_RECURSE_WINDOWFUNCS));
+	Assert((flags & (PVC_INCLUDE_PLACEHOLDERS | PVC_RECURSE_PLACEHOLDERS))
+		   != (PVC_INCLUDE_PLACEHOLDERS | PVC_RECURSE_PLACEHOLDERS));
+
+	context.varlist = NIL;
+	context.flags = flags;
+
+	pull_var_clause_walker(node, &context);
+	return context.varlist;
+}
+
+static bool
+pull_var_clause_walker(Node *node, pull_var_clause_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		if (((Var *) node)->varlevelsup != 0)
+			elog(ERROR, "Upper-level Var found where not expected");
+		context->varlist = lappend(context->varlist, node);
+		return false;
+	}
+	else if (IsA(node, Aggref))
+	{
+		if (((Aggref *) node)->agglevelsup != 0)
+			elog(ERROR, "Upper-level Aggref found where not expected");
+		if (context->flags & PVC_INCLUDE_AGGREGATES)
+		{
+			context->varlist = lappend(context->varlist, node);
+			/* we do NOT descend into the contained expression */
+			return false;
+		}
+		else if (context->flags & PVC_RECURSE_AGGREGATES)
+		{
+			/* fall through to recurse into the aggregate's arguments */
+		}
+		else
+			elog(ERROR, "Aggref found where not expected");
+	}
+	else if (IsA(node, GroupingFunc))
+	{
+		if (((GroupingFunc *) node)->agglevelsup != 0)
+			elog(ERROR, "Upper-level GROUPING found where not expected");
+		if (context->flags & PVC_INCLUDE_AGGREGATES)
+		{
+			context->varlist = lappend(context->varlist, node);
+			/* we do NOT descend into the contained expression */
+			return false;
+		}
+		else if (context->flags & PVC_RECURSE_AGGREGATES)
+		{
+			/* fall through to recurse into the GroupingFunc's arguments */
+		}
+		else
+			elog(ERROR, "GROUPING found where not expected");
+	}
+	else if (IsA(node, WindowFunc))
+	{
+		/* WindowFuncs have no levelsup field to check ... */
+		if (context->flags & PVC_INCLUDE_WINDOWFUNCS)
+		{
+			context->varlist = lappend(context->varlist, node);
+			/* we do NOT descend into the contained expressions */
+			return false;
+		}
+		else if (context->flags & PVC_RECURSE_WINDOWFUNCS)
+		{
+			/* fall through to recurse into the windowfunc's arguments */
+		}
+		else
+			elog(ERROR, "WindowFunc found where not expected");
+	}
+	else if (IsA(node, PlaceHolderVar))
+	{
+		if (((PlaceHolderVar *) node)->phlevelsup != 0)
+			elog(ERROR, "Upper-level PlaceHolderVar found where not expected");
+		if (context->flags & PVC_INCLUDE_PLACEHOLDERS)
+		{
+			context->varlist = lappend(context->varlist, node);
+			/* we do NOT descend into the contained expression */
+			return false;
+		}
+		else if (context->flags & PVC_RECURSE_PLACEHOLDERS)
+		{
+			/* fall through to recurse into the placeholder's expression */
+		}
+		else
+			elog(ERROR, "PlaceHolderVar found where not expected");
+	}
+	return expression_tree_walker(node, pull_var_clause_walker,
+								  (void *) context);
+}
+
+
+/*
+ * flatten_join_alias_vars
+ *	  Replace Vars that reference JOIN outputs with references to the original
+ *	  relation variables instead.  This allows quals involving such vars to be
+ *	  pushed down.  Whole-row Vars that reference JOIN relations are expanded
+ *	  into RowExpr constructs that name the individual output Vars.  This
+ *	  is necessary since we will not scan the JOIN as a base relation, which
+ *	  is the only way that the executor can directly handle whole-row Vars.
+ *
+ * This also adjusts relid sets found in some expression node types to
+ * substitute the contained base rels for any join relid.
+ *
+ * If a JOIN contains sub-selects that have been flattened, its join alias
+ * entries might now be arbitrary expressions, not just Vars.  This affects
+ * this function in one important way: we might find ourselves inserting
+ * SubLink expressions into subqueries, and we must make sure that their
+ * Query.hasSubLinks fields get set to true if so.  If there are any
+ * SubLinks in the join alias lists, the outer Query should already have
+ * hasSubLinks = true, so this is only relevant to un-flattened subqueries.
+ *
+ * NOTE: this is used on not-yet-planned expressions.  We do not expect it
+ * to be applied directly to the whole Query, so if we see a Query to start
+ * with, we do want to increment sublevels_up (this occurs for LATERAL
+ * subqueries).
+ */
+Node *
+flatten_join_alias_vars(Query *query, Node *node)
+{
+	flatten_join_alias_vars_context context;
+
+	context.query = query;
+	context.sublevels_up = 0;
+	/* flag whether join aliases could possibly contain SubLinks */
+	context.possible_sublink = query->hasSubLinks;
+	/* if hasSubLinks is already true, no need to work hard */
+	context.inserted_sublink = query->hasSubLinks;
+
+	return flatten_join_alias_vars_mutator(node, &context);
+}
+
+static Node *
+flatten_join_alias_vars_mutator(Node *node,
+								flatten_join_alias_vars_context *context)
+{
+	if (node == NULL)
+		return NULL;
+	if (IsA(node, Var))
+	{
+		Var		   *var = (Var *) node;
+		RangeTblEntry *rte;
+		Node	   *newvar;
+
+		/* No change unless Var belongs to a JOIN of the target level */
+		if (var->varlevelsup != context->sublevels_up)
+			return node;		/* no need to copy, really */
+		rte = rt_fetch(var->varno, context->query->rtable);
+		if (rte->rtekind != RTE_JOIN)
+			return node;
+		if (var->varattno == InvalidAttrNumber)
+		{
+			/* Must expand whole-row reference */
+			RowExpr    *rowexpr;
+			List	   *fields = NIL;
+			List	   *colnames = NIL;
+			AttrNumber	attnum;
+			ListCell   *lv;
+			ListCell   *ln;
+
+			attnum = 0;
+			Assert(list_length(rte->joinaliasvars) == list_length(rte->eref->colnames));
+			forboth(lv, rte->joinaliasvars, ln, rte->eref->colnames)
+			{
+				newvar = (Node *) lfirst(lv);
+				attnum++;
+				/* Ignore dropped columns */
+				if (newvar == NULL)
+					continue;
+				newvar = copyObject(newvar);
+
+				/*
+				 * If we are expanding an alias carried down from an upper
+				 * query, must adjust its varlevelsup fields.
+				 */
+				if (context->sublevels_up != 0)
+					IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
+				/* Preserve original Var's location, if possible */
+				if (IsA(newvar, Var))
+					((Var *) newvar)->location = var->location;
+				/* Recurse in case join input is itself a join */
+				/* (also takes care of setting inserted_sublink if needed) */
+				newvar = flatten_join_alias_vars_mutator(newvar, context);
+				fields = lappend(fields, newvar);
+				/* We need the names of non-dropped columns, too */
+				colnames = lappend(colnames, copyObject((Node *) lfirst(ln)));
+			}
+			rowexpr = makeNode(RowExpr);
+			rowexpr->args = fields;
+			rowexpr->row_typeid = var->vartype;
+			rowexpr->row_format = COERCE_IMPLICIT_CAST;
+			rowexpr->colnames = colnames;
+			rowexpr->location = var->location;
+
+			return (Node *) rowexpr;
+		}
+
+		/* Expand join alias reference */
+		Assert(var->varattno > 0);
+		newvar = (Node *) list_nth(rte->joinaliasvars, var->varattno - 1);
+		Assert(newvar != NULL);
+		newvar = copyObject(newvar);
+
+		/*
+		 * If we are expanding an alias carried down from an upper query, must
+		 * adjust its varlevelsup fields.
+		 */
+		if (context->sublevels_up != 0)
+			IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
+
+		/* Preserve original Var's location, if possible */
+		if (IsA(newvar, Var))
+			((Var *) newvar)->location = var->location;
+
+		/* Recurse in case join input is itself a join */
+		newvar = flatten_join_alias_vars_mutator(newvar, context);
+
+		/* Detect if we are adding a sublink to query */
+		if (context->possible_sublink && !context->inserted_sublink)
+			context->inserted_sublink = checkExprHasSubLink(newvar);
+
+		return newvar;
+	}
+	if (IsA(node, PlaceHolderVar))
+	{
+		/* Copy the PlaceHolderVar node with correct mutation of subnodes */
+		PlaceHolderVar *phv;
+
+		phv = (PlaceHolderVar *) expression_tree_mutator(node,
+														 flatten_join_alias_vars_mutator,
+														 (void *) context);
+		/* now fix PlaceHolderVar's relid sets */
+		if (phv->phlevelsup == context->sublevels_up)
+		{
+			phv->phrels = alias_relid_set(context->query,
+										  phv->phrels);
+		}
+		return (Node *) phv;
+	}
+
+	if (IsA(node, Query))
+	{
+		/* Recurse into RTE subquery or not-yet-planned sublink subquery */
+		Query	   *newnode;
+		bool		save_inserted_sublink;
+
+		context->sublevels_up++;
+		save_inserted_sublink = context->inserted_sublink;
+		context->inserted_sublink = ((Query *) node)->hasSubLinks;
+		newnode = query_tree_mutator((Query *) node,
+									 flatten_join_alias_vars_mutator,
+									 (void *) context,
+									 QTW_IGNORE_JOINALIASES);
+		newnode->hasSubLinks |= context->inserted_sublink;
+		context->inserted_sublink = save_inserted_sublink;
+		context->sublevels_up--;
+		return (Node *) newnode;
+	}
+	/* Already-planned tree not supported */
+	Assert(!IsA(node, SubPlan));
+	/* Shouldn't need to handle these planner auxiliary nodes here */
+	Assert(!IsA(node, SpecialJoinInfo));
+	Assert(!IsA(node, PlaceHolderInfo));
+	Assert(!IsA(node, MinMaxAggInfo));
+
+	return expression_tree_mutator(node, flatten_join_alias_vars_mutator,
+								   (void *) context);
+}
+
+/*
+ * alias_relid_set: in a set of RT indexes, replace joins by their
+ * underlying base relids
+ */
+static Relids
+alias_relid_set(Query *query, Relids relids)
+{
+	Relids		result = NULL;
+	int			rtindex;
+
+	rtindex = -1;
+	while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
+	{
+		RangeTblEntry *rte = rt_fetch(rtindex, query->rtable);
+
+		if (rte->rtekind == RTE_JOIN)
+			result = bms_join(result, get_relids_for_join(query, rtindex));
+		else
+			result = bms_add_member(result, rtindex);
+	}
+	return result;
+}