Avoid recursion while processing ELSIF lists in plpgsql.

The original implementation of ELSIF in plpgsql converted the construct
into nested simple IF statements.  This was prone to stack overflow with
long ELSIF lists, in two different ways.  First, it's difficult to generate
the parsetree without using right-recursion in the bison grammar, and
that's prone to parser stack overflow since nothing can be reduced until
the whole list has been read.  Second, we'd recurse during execution, thus
creating an unnecessary risk of execution-time stack overflow.  Rewrite
so that the ELSIF list is represented as a flat list, scanned via iteration
not recursion, and generated through left-recursion in the grammar.
Per a gripe from Håvard Kongsgård.

diff --git a/src/pl/plpgsql/src/gram.y b/src/pl/plpgsql/src/gram.y
index f8e956b2a423de75fe7dcef58d4901e184438303..fb3a54646f08c02a771f22ac94ad88fb47e3c1a2 100644 (file)
--- a/src/pl/plpgsql/src/gram.y
+++ b/src/pl/plpgsql/src/gram.y
@@ -186,7 +186,7 @@ static      List                    *read_raise_options(void);
 
 %type <str>            any_identifier opt_block_label opt_label
 
-%type <list>   proc_sect proc_stmts stmt_else
+%type <list>   proc_sect proc_stmts stmt_elsifs stmt_else
 %type <loop_body>      loop_body
 %type <stmt>   proc_stmt pl_block
 %type <stmt>   stmt_assign stmt_if stmt_loop stmt_while stmt_exit
@@ -1007,7 +1007,7 @@ assign_var                : T_DATUM
                                        }
                                ;
 
-stmt_if                        : K_IF expr_until_then proc_sect stmt_else K_END K_IF ';'
+stmt_if                        : K_IF expr_until_then proc_sect stmt_elsifs stmt_else K_END K_IF ';'
                                        {
                                                PLpgSQL_stmt_if *new;
 
@@ -1015,47 +1015,35 @@ stmt_if                 : K_IF expr_until_then proc_sect stmt_else K_END K_IF ';'
                                                new->cmd_type   = PLPGSQL_STMT_IF;
                                                new->lineno             = plpgsql_location_to_lineno(@1);
                                                new->cond               = $2;
-                                               new->true_body  = $3;
-                                               new->false_body = $4;
+                                               new->then_body  = $3;
+                                               new->elsif_list = $4;
+                                               new->else_body  = $5;
 
                                                $$ = (PLpgSQL_stmt *)new;
                                        }
                                ;
 
-stmt_else              :
+stmt_elsifs            :
                                        {
                                                $$ = NIL;
                                        }
-                               | K_ELSIF expr_until_then proc_sect stmt_else
-                                       {
-                                               /*----------
-                                                * Translate the structure:        into:
-                                                *
-                                                * IF c1 THEN                              IF c1 THEN
-                                                *       ...                                               ...
-                                                * ELSIF c2 THEN                           ELSE
-                                                *                                                                 IF c2 THEN
-                                                *       ...                                                       ...
-                                                * ELSE                                                    ELSE
-                                                *       ...                                                       ...
-                                                * END IF                                                  END IF
-                                                *                                                         END IF
-                                                *----------
-                                                */
-                                               PLpgSQL_stmt_if *new_if;
+                               | stmt_elsifs K_ELSIF expr_until_then proc_sect
+                                       {
+                                               PLpgSQL_if_elsif *new;
 
-                                               /* first create a new if-statement */
-                                               new_if = palloc0(sizeof(PLpgSQL_stmt_if));
-                                               new_if->cmd_type        = PLPGSQL_STMT_IF;
-                                               new_if->lineno          = plpgsql_location_to_lineno(@1);
-                                               new_if->cond            = $2;
-                                               new_if->true_body       = $3;
-                                               new_if->false_body      = $4;
+                                               new = palloc0(sizeof(PLpgSQL_if_elsif));
+                                               new->lineno = plpgsql_location_to_lineno(@2);
+                                               new->cond   = $3;
+                                               new->stmts  = $4;
 
-                                               /* wrap the if-statement in a "container" list */
-                                               $$ = list_make1(new_if);
+                                               $$ = lappend($1, new);
                                        }
+                               ;
 
+stmt_else              :
+                                       {
+                                               $$ = NIL;
+                                       }
                                | K_ELSE proc_sect
                                        {
                                                $$ = $2;

diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index b1ed3c3167c6120bd6d0d30998c6f006077e9791..387362a59a2de3b77e51301439e00b5e294600cb 100644 (file)
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -1510,22 +1510,24 @@ exec_stmt_if(PLpgSQL_execstate *estate, PLpgSQL_stmt_if *stmt)
 {
        bool            value;
        bool            isnull;
+       ListCell   *lc;
 
        value = exec_eval_boolean(estate, stmt->cond, &isnull);
        exec_eval_cleanup(estate);
-
        if (!isnull && value)
+               return exec_stmts(estate, stmt->then_body);
+
+       foreach(lc, stmt->elsif_list)
        {
-               if (stmt->true_body != NIL)
-                       return exec_stmts(estate, stmt->true_body);
-       }
-       else
-       {
-               if (stmt->false_body != NIL)
-                       return exec_stmts(estate, stmt->false_body);
+               PLpgSQL_if_elsif *elif = (PLpgSQL_if_elsif *) lfirst(lc);
+
+               value = exec_eval_boolean(estate, elif->cond, &isnull);
+               exec_eval_cleanup(estate);
+               if (!isnull && value)
+                       return exec_stmts(estate, elif->stmts);
        }
 
-       return PLPGSQL_RC_OK;
+       return exec_stmts(estate, stmt->else_body);
 }
 
 

diff --git a/src/pl/plpgsql/src/pl_funcs.c b/src/pl/plpgsql/src/pl_funcs.c
index 030ed07ac55f999af6160bbac9294a4a2f360a42..18ca885e806dabe274eb798777760f9e92f3c7a2 100644 (file)
--- a/src/pl/plpgsql/src/pl_funcs.c
+++ b/src/pl/plpgsql/src/pl_funcs.c
@@ -446,9 +446,18 @@ free_assign(PLpgSQL_stmt_assign *stmt)
 static void
 free_if(PLpgSQL_stmt_if *stmt)
 {
+       ListCell   *l;
+
        free_expr(stmt->cond);
-       free_stmts(stmt->true_body);
-       free_stmts(stmt->false_body);
+       free_stmts(stmt->then_body);
+       foreach(l, stmt->elsif_list)
+       {
+               PLpgSQL_if_elsif *elif = (PLpgSQL_if_elsif *) lfirst(l);
+
+               free_expr(elif->cond);
+               free_stmts(elif->stmts);
+       }
+       free_stmts(stmt->else_body);
 }
 
 static void
@@ -877,20 +886,29 @@ dump_assign(PLpgSQL_stmt_assign *stmt)
 static void
 dump_if(PLpgSQL_stmt_if *stmt)
 {
+       ListCell   *l;
+
        dump_ind();
        printf("IF ");
        dump_expr(stmt->cond);
        printf(" THEN\n");
+       dump_stmts(stmt->then_body);
+       foreach(l, stmt->elsif_list)
+       {
+               PLpgSQL_if_elsif *elif = (PLpgSQL_if_elsif *) lfirst(l);
 
-       dump_stmts(stmt->true_body);
-
-       if (stmt->false_body != NIL)
+               dump_ind();
+               printf("    ELSIF ");
+               dump_expr(elif->cond);
+               printf(" THEN\n");
+               dump_stmts(elif->stmts);
+       }
+       if (stmt->else_body != NIL)
        {
                dump_ind();
                printf("    ELSE\n");
-               dump_stmts(stmt->false_body);
+               dump_stmts(stmt->else_body);
        }
-
        dump_ind();
        printf("    ENDIF\n");
 }

diff --git a/src/pl/plpgsql/src/plpgsql.h b/src/pl/plpgsql/src/plpgsql.h
index 61503f10a786b18765893185721e12ff2587e8b8..c638f4323f442dbfd6ec86a7b4367dabe2649e77 100644 (file)
--- a/src/pl/plpgsql/src/plpgsql.h
+++ b/src/pl/plpgsql/src/plpgsql.h
@@ -396,11 +396,19 @@ typedef struct
 {                                                              /* IF statement                         */
        int                     cmd_type;
        int                     lineno;
-       PLpgSQL_expr *cond;
-       List       *true_body;          /* List of statements */
-       List       *false_body;         /* List of statements */
+       PLpgSQL_expr *cond;                     /* boolean expression for THEN */
+       List       *then_body;          /* List of statements */
+       List       *elsif_list;         /* List of PLpgSQL_if_elsif structs */
+       List       *else_body;          /* List of statements */
 } PLpgSQL_stmt_if;
 
+typedef struct                                 /* one ELSIF arm of IF statement */
+{
+       int                     lineno;
+       PLpgSQL_expr *cond;                     /* boolean expression for this case */
+       List       *stmts;                      /* List of statements */
+} PLpgSQL_if_elsif;
+
 
 typedef struct                                 /* CASE statement */
 {