Teach eval_const_expressions() to simplify an ArrayCoerceExpr to a constant

when its input is constant and the element coercion function is immutable
(or nonexistent, ie, binary-coercible case).  This is an oversight in the
8.3 implementation of ArrayCoerceExpr, and its result is that certain cases
involving IN or NOT IN with constants don't get optimized as they should be.
Per experimentation with an example from Ow Mun Heng.

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 26857dcd08c655464e6c090ec2735ac859141173..30b42f01096903bd7c74bc6618228c7567ee7a72 100644 (file)
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2160,6 +2160,41 @@ eval_const_expressions_mutator(Node *node,
                newexpr->coerceformat = expr->coerceformat;
                return (Node *) newexpr;
        }
+       if (IsA(node, ArrayCoerceExpr))
+       {
+               ArrayCoerceExpr *expr = (ArrayCoerceExpr *) node;
+               Expr       *arg;
+               ArrayCoerceExpr *newexpr;
+
+               /*
+                * Reduce constants in the ArrayCoerceExpr's argument, then build
+                * a new ArrayCoerceExpr.
+                */
+               arg = (Expr *) eval_const_expressions_mutator((Node *) expr->arg,
+                                                                                                         context);
+
+               newexpr = makeNode(ArrayCoerceExpr);
+               newexpr->arg = arg;
+               newexpr->elemfuncid = expr->elemfuncid;
+               newexpr->resulttype = expr->resulttype;
+               newexpr->resulttypmod = expr->resulttypmod;
+               newexpr->isExplicit = expr->isExplicit;
+               newexpr->coerceformat = expr->coerceformat;
+
+               /*
+                * If constant argument and it's a binary-coercible or immutable
+                * conversion, we can simplify it to a constant.
+                */
+               if (arg && IsA(arg, Const) &&
+                       (!OidIsValid(newexpr->elemfuncid) ||
+                        func_volatile(newexpr->elemfuncid) == PROVOLATILE_IMMUTABLE))
+                       return (Node *) evaluate_expr((Expr *) newexpr,
+                                                                                 newexpr->resulttype,
+                                                                                 newexpr->resulttypmod);
+
+               /* Else we must return the partially-simplified node */
+               return (Node *) newexpr;
+       }
        if (IsA(node, CaseExpr))
        {
                /*----------