diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 89a4f8f810..b6eacd5baa 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -438,14 +438,8 @@ BeginCopyTo(ParseState *pstate,
 		/*
 		 * Run parse analysis and rewrite.  Note this also acquires sufficient
 		 * locks on the source table(s).
-		 *
-		 * Because the parser and planner tend to scribble on their input, we
-		 * make a preliminary copy of the source querytree.  This prevents
-		 * problems in the case that the COPY is in a portal or plpgsql
-		 * function and is executed repeatedly.  (See also the same hack in
-		 * DECLARE CURSOR and PREPARE.)  XXX FIXME someday.
 		 */
-		rewritten = pg_analyze_and_rewrite(copyObject(raw_query),
+		rewritten = pg_analyze_and_rewrite(raw_query,
 										   pstate->p_sourcetext, NULL, 0,
 										   NULL);
 
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index dce882012e..0982851715 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -299,14 +299,8 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		 * rewriter.  We do not do AcquireRewriteLocks: we assume the query
 		 * either came straight from the parser, or suitable locks were
 		 * acquired by plancache.c.
-		 *
-		 * Because the rewriter and planner tend to scribble on the input, we
-		 * make a preliminary copy of the source querytree.  This prevents
-		 * problems in the case that CTAS is in a portal or plpgsql function
-		 * and is executed repeatedly.  (See also the same hack in EXPLAIN and
-		 * PREPARE.)
 		 */
-		rewritten = QueryRewrite(copyObject(query));
+		rewritten = QueryRewrite(query);
 
 		/* SELECT should never rewrite to more or less than one SELECT query */
 		if (list_length(rewritten) != 1)
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 9a60865d19..7045f6ad55 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -256,14 +256,8 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
 	 * rewriter.  We do not do AcquireRewriteLocks: we assume the query either
 	 * came straight from the parser, or suitable locks were acquired by
 	 * plancache.c.
-	 *
-	 * Because the rewriter and planner tend to scribble on the input, we make
-	 * a preliminary copy of the source querytree.  This prevents problems in
-	 * the case that the EXPLAIN is in a portal or plpgsql function and is
-	 * executed repeatedly.  (See also the same hack in DECLARE CURSOR and
-	 * PREPARE.)  XXX FIXME someday.
 	 */
-	rewritten = QueryRewrite(castNode(Query, copyObject(stmt->query)));
+	rewritten = QueryRewrite(castNode(Query, stmt->query));
 
 	/* emit opening boilerplate */
 	ExplainBeginOutput(es);
@@ -441,8 +435,7 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 	{
 		/*
 		 * We have to rewrite the contained SELECT and then pass it back to
-		 * ExplainOneQuery.  It's probably not really necessary to copy the
-		 * contained parsetree another time, but let's be safe.
+		 * ExplainOneQuery.
 		 */
 		CreateTableAsStmt *ctas = (CreateTableAsStmt *) utilityStmt;
 		List	   *rewritten;
@@ -463,7 +456,7 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 			return;
 		}
 
-		rewritten = QueryRewrite(castNode(Query, copyObject(ctas->query)));
+		rewritten = QueryRewrite(castNode(Query, ctas->query));
 		Assert(list_length(rewritten) == 1);
 		ExplainOneQuery(linitial_node(Query, rewritten),
 						CURSOR_OPT_PARALLEL_OK, ctas->into, es,
@@ -482,7 +475,7 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 		DeclareCursorStmt *dcs = (DeclareCursorStmt *) utilityStmt;
 		List	   *rewritten;
 
-		rewritten = QueryRewrite(castNode(Query, copyObject(dcs->query)));
+		rewritten = QueryRewrite(castNode(Query, dcs->query));
 		Assert(list_length(rewritten) == 1);
 		ExplainOneQuery(linitial_node(Query, rewritten),
 						dcs->options, NULL, es,
diff --git a/src/backend/commands/policy.c b/src/backend/commands/policy.c
index 5cacc088cd..5d469309ce 100644
--- a/src/backend/commands/policy.c
+++ b/src/backend/commands/policy.c
@@ -747,12 +747,12 @@ CreatePolicy(CreatePolicyStmt *stmt)
 	addNSItemToQuery(with_check_pstate, nsitem, false, true, true);
 
 	qual = transformWhereClause(qual_pstate,
-								copyObject(stmt->qual),
+								stmt->qual,
 								EXPR_KIND_POLICY,
 								"POLICY");
 
 	with_check_qual = transformWhereClause(with_check_pstate,
-										   copyObject(stmt->with_check),
+										   stmt->with_check,
 										   EXPR_KIND_POLICY,
 										   "POLICY");
 
@@ -922,7 +922,7 @@ AlterPolicy(AlterPolicyStmt *stmt)
 
 		addNSItemToQuery(qual_pstate, nsitem, false, true, true);
 
-		qual = transformWhereClause(qual_pstate, copyObject(stmt->qual),
+		qual = transformWhereClause(qual_pstate, stmt->qual,
 									EXPR_KIND_POLICY,
 									"POLICY");
 
@@ -946,7 +946,7 @@ AlterPolicy(AlterPolicyStmt *stmt)
 		addNSItemToQuery(with_check_pstate, nsitem, false, true, true);
 
 		with_check_qual = transformWhereClause(with_check_pstate,
-											   copyObject(stmt->with_check),
+											   stmt->with_check,
 											   EXPR_KIND_POLICY,
 											   "POLICY");
 
diff --git a/src/backend/commands/portalcmds.c b/src/backend/commands/portalcmds.c
index d34cc39fde..3ea30bcbc9 100644
--- a/src/backend/commands/portalcmds.c
+++ b/src/backend/commands/portalcmds.c
@@ -76,14 +76,8 @@ PerformCursorOpen(ParseState *pstate, DeclareCursorStmt *cstmt, ParamListInfo pa
 	 * rewriter.  We do not do AcquireRewriteLocks: we assume the query either
 	 * came straight from the parser, or suitable locks were acquired by
 	 * plancache.c.
-	 *
-	 * Because the rewriter and planner tend to scribble on the input, we make
-	 * a preliminary copy of the source querytree.  This prevents problems in
-	 * the case that the DECLARE CURSOR is in a portal or plpgsql function and
-	 * is executed repeatedly.  (See also the same hack in EXPLAIN and
-	 * PREPARE.)  XXX FIXME someday.
 	 */
-	rewritten = QueryRewrite((Query *) copyObject(query));
+	rewritten = QueryRewrite(query);
 
 	/* SELECT should never rewrite to more or less than one query */
 	if (list_length(rewritten) != 1)
diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 65d8ac65b1..5e03c7c5aa 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -78,12 +78,9 @@ PrepareQuery(ParseState *pstate, PrepareStmt *stmt,
 	/*
 	 * Need to wrap the contained statement in a RawStmt node to pass it to
 	 * parse analysis.
-	 *
-	 * Because parse analysis scribbles on the raw querytree, we must make a
-	 * copy to ensure we don't modify the passed-in tree.  FIXME someday.
 	 */
 	rawstmt = makeNode(RawStmt);
-	rawstmt->stmt = (Node *) copyObject(stmt->query);
+	rawstmt->stmt = stmt->query;
 	rawstmt->stmt_location = stmt_location;
 	rawstmt->stmt_len = stmt_len;
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 028e8ac46b..4e23c7fce5 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -4408,8 +4408,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 	 * Copy the original subcommand for each table.  This avoids conflicts
 	 * when different child tables need to make different parse
 	 * transformations (for example, the same column may have different column
-	 * numbers in different children).  It also ensures that we don't corrupt
-	 * the original parse tree, in case it is saved in plancache.
+	 * numbers in different children).
 	 */
 	cmd = copyObject(cmd);
 
diff --git a/src/backend/commands/view.c b/src/backend/commands/view.c
index f2642dba6c..4df05a0b33 100644
--- a/src/backend/commands/view.c
+++ b/src/backend/commands/view.c
@@ -417,12 +417,9 @@ DefineView(ViewStmt *stmt, const char *queryString,
 	/*
 	 * Run parse analysis to convert the raw parse tree to a Query.  Note this
 	 * also acquires sufficient locks on the source table(s).
-	 *
-	 * Since parse analysis scribbles on its input, copy the raw parse tree;
-	 * this ensures we don't corrupt a prepared statement, for example.
 	 */
 	rawstmt = makeNode(RawStmt);
-	rawstmt->stmt = (Node *) copyObject(stmt->query);
+	rawstmt->stmt = stmt->query;
 	rawstmt->stmt_location = stmt_location;
 	rawstmt->stmt_len = stmt_len;
 
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index b8bd05e894..70800a649e 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -2532,6 +2532,14 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
 				ProcessUtilityContext context;
 				QueryCompletion qc;
 
+				/*
+				 * Copy the utility statement out of the plan cache, in case
+				 * its processing scribbles on the statement's node tree.
+				 * (This could be refined if we knew which utility statements
+				 * do that.)
+				 */
+				stmt = copyObject(stmt);
+
 				/*
 				 * If the SPI context is atomic, or we were not told to allow
 				 * nonatomic operations, tell ProcessUtility this is an atomic
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index c9708e38f4..81d3e7990c 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -11,10 +11,6 @@
  * Hence these functions are now called at the start of execution of their
  * respective utility commands.
  *
- * NOTE: in general we must avoid scribbling on the passed-in raw parse
- * tree, since it might be in a plan cache.  The simplest solution is
- * a quick copyObject() call before manipulating the query tree.
- *
  *
  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -177,12 +173,6 @@ transformCreateStmt(CreateStmt *stmt, const char *queryString)
 	Oid			existing_relid;
 	ParseCallbackState pcbstate;
 
-	/*
-	 * We must not scribble on the passed-in CreateStmt, so copy it.  (This is
-	 * overkill, but easy.)
-	 */
-	stmt = copyObject(stmt);
-
 	/* Set up pstate */
 	pstate = make_parsestate(NULL);
 	pstate->p_sourcetext = queryString;
@@ -2824,12 +2814,6 @@ transformIndexStmt(Oid relid, IndexStmt *stmt, const char *queryString)
 	if (stmt->transformed)
 		return stmt;
 
-	/*
-	 * We must not scribble on the passed-in IndexStmt, so copy it.  (This is
-	 * overkill, but easy.)
-	 */
-	stmt = copyObject(stmt);
-
 	/* Set up pstate */
 	pstate = make_parsestate(NULL);
 	pstate->p_sourcetext = queryString;
@@ -2925,12 +2909,6 @@ transformStatsStmt(Oid relid, CreateStatsStmt *stmt, const char *queryString)
 	if (stmt->transformed)
 		return stmt;
 
-	/*
-	 * We must not scribble on the passed-in CreateStatsStmt, so copy it.
-	 * (This is overkill, but easy.)
-	 */
-	stmt = copyObject(stmt);
-
 	/* Set up pstate */
 	pstate = make_parsestate(NULL);
 	pstate->p_sourcetext = queryString;
@@ -2993,9 +2971,6 @@ transformStatsStmt(Oid relid, CreateStatsStmt *stmt, const char *queryString)
  *
  * actions and whereClause are output parameters that receive the
  * transformed results.
- *
- * Note that we must not scribble on the passed-in RuleStmt, so we do
- * copyObject() on the actions and WHERE clause.
  */
 void
 transformRuleStmt(RuleStmt *stmt, const char *queryString,
@@ -3070,7 +3045,7 @@ transformRuleStmt(RuleStmt *stmt, const char *queryString,
 
 	/* take care of the where clause */
 	*whereClause = transformWhereClause(pstate,
-										(Node *) copyObject(stmt->whereClause),
+										stmt->whereClause,
 										EXPR_KIND_WHERE,
 										"WHERE");
 	/* we have to fix its collations too */
@@ -3142,8 +3117,7 @@ transformRuleStmt(RuleStmt *stmt, const char *queryString,
 			addNSItemToQuery(sub_pstate, newnsitem, false, true, false);
 
 			/* Transform the rule action statement */
-			top_subqry = transformStmt(sub_pstate,
-									   (Node *) copyObject(action));
+			top_subqry = transformStmt(sub_pstate, action);
 
 			/*
 			 * We cannot support utility-statement actions (eg NOTIFY) with
@@ -3325,12 +3299,6 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 	AlterTableCmd *newcmd;
 	ParseNamespaceItem *nsitem;
 
-	/*
-	 * We must not scribble on the passed-in AlterTableStmt, so copy it. (This
-	 * is overkill, but easy.)
-	 */
-	stmt = copyObject(stmt);
-
 	/* Caller is responsible for locking the relation */
 	rel = relation_open(relid, NoLock);
 	tupdesc = RelationGetDescr(rel);
diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c
index f7f08e6c05..4e02e1821c 100644
--- a/src/backend/tcop/pquery.c
+++ b/src/backend/tcop/pquery.c
@@ -1144,6 +1144,15 @@ PortalRunUtility(Portal portal, PlannedStmt *pstmt,
 	else
 		portal->portalSnapshot = NULL;
 
+	/*
+	 * If the Portal's statement list belongs to a cached plan, we must not
+	 * damage the original statement node tree.  Processing of the statement
+	 * might scribble on the node tree, so copy the statement.  (This could be
+	 * refined if we knew which utility statements do that.)
+	 */
+	if (portal->cplan)
+		pstmt = copyObject(pstmt);
+
 	ProcessUtility(pstmt,
 				   portal->sourceText,
 				   isTopLevel ? PROCESS_UTILITY_TOPLEVEL : PROCESS_UTILITY_QUERY,
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 1a8fc16773..81f34dfb69 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -485,6 +485,10 @@ CheckRestrictedOperation(const char *cmdname)
  *	qc: where to store command completion status data.  May be NULL,
  *		but if not, then caller must have initialized it.
  *
+ * Some utility statement execution functions will scribble on the passed
+ * "pstmt" node tree.  It is caller's responsibility that that tree not be
+ * something that must be preserved.
+ *
  * Caller MUST supply a queryString; it is not allowed (anymore) to pass NULL.
  * If you really don't have source text, you can pass a constant string,
  * perhaps "(query not available)".