Bug#37662 nested if() inside sum() is parsed in exponential time

      
min() and max() functions are implemented in MySQL as macros.
This means that max(a,b) is expanded to: ((a) > (b) ? (a) : (b))
Note how 'a' is quoted two times.
Now imagine 'a' is a recursive function call that's several 10s of levels deep.
And the recursive function does max() with a function arg as well to dive into
recursion.
This means that simple function call can take most of the clock time.
Identified and fixed several such calls to max()/min() : including the IF() 
sql function implementation.

mysql-test/r/func_if.result:
  Bug#37662 test case
mysql-test/t/func_if.test:
  Bug#37662 test case
sql/item.cc:
  Bug#37662 don't call expensive functions as arguments to min/max
sql/item_cmpfunc.cc:
  Bug#37662 don't call expensive functions as arguments to min/max
sql/item_func.cc:
  Bug#37662 don't call expensive functions as arguments to min/max

mysql-test/r/func_if.result

@@ -131,3 +131,49 @@ drop table t1;
 select if(0, 18446744073709551610, 18446744073709551610);
 if(0, 18446744073709551610, 18446744073709551610)
 18446744073709551610
+CREATE TABLE t1(a DECIMAL(10,3));
+SELECT t1.a,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,0)))))))))))))))))))))))))))))) + 1
+FROM t1;
+a	IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((ROUND(t1.a,2)=1), 2,
+IF((R
+DROP TABLE t1;
+End of 5.0 tests

mysql-test/t/func_if.test

@@ -108,3 +108,46 @@ drop table t1;
 select if(0, 18446744073709551610, 18446744073709551610);
 
 
+#
+# Bug #37662: nested if() inside sum() is parsed in exponential time
+#
+
+CREATE TABLE t1(a DECIMAL(10,3));
+
+# check : should be fast. more than few secs means failure.
+SELECT t1.a,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,
+ IF((ROUND(t1.a,2)=1), 2,0)))))))))))))))))))))))))))))) + 1
+FROM t1;
+
+DROP TABLE t1;
+
+--echo End of 5.0 tests

sql/item.cc

@@ -429,8 +429,11 @@ uint Item::decimal_precision() const
   Item_result restype= result_type();
 
   if ((restype == DECIMAL_RESULT) || (restype == INT_RESULT))
-    return min(my_decimal_length_to_precision(max_length, decimals, unsigned_flag),
-               DECIMAL_MAX_PRECISION);
+  {
+    uint prec= 
+      my_decimal_length_to_precision(max_length, decimals, unsigned_flag);
+    return min(prec, DECIMAL_MAX_PRECISION);
+  }
   return min(max_length, DECIMAL_MAX_PRECISION);
 }
 
@@ -6838,8 +6841,9 @@ bool Item_type_holder::join_types(THD *thd, Item *item)
   if (Field::result_merge_type(fld_type) == DECIMAL_RESULT)
   {
     decimals= min(max(decimals, item->decimals), DECIMAL_MAX_SCALE);
-    int precision= min(max(prev_decimal_int_part, item->decimal_int_part())
-                       + decimals, DECIMAL_MAX_PRECISION);
+    int item_int_part= item->decimal_int_part();
+    int item_prec = max(prev_decimal_int_part, item_int_part) + decimals;
+    int precision= min(item_prec, DECIMAL_MAX_PRECISION);
     unsigned_flag&= item->unsigned_flag;
     max_length= my_decimal_precision_to_length(precision, decimals,
                                                unsigned_flag);

sql/item_cmpfunc.cc

@@ -2098,8 +2098,11 @@ Item_func_ifnull::fix_length_and_dec()
 
 uint Item_func_ifnull::decimal_precision() const
 {
-  int max_int_part=max(args[0]->decimal_int_part(),args[1]->decimal_int_part());
-  return min(max_int_part + decimals, DECIMAL_MAX_PRECISION);
+  int arg0_int_part= args[0]->decimal_int_part();
+  int arg1_int_part= args[1]->decimal_int_part();
+  int max_int_part= max(arg0_int_part, arg1_int_part);
+  int precision= max_int_part + decimals;
+  return min(precision, DECIMAL_MAX_PRECISION);
 }
 
 
@@ -2281,8 +2284,9 @@ Item_func_if::fix_length_and_dec()
 
 uint Item_func_if::decimal_precision() const
 {
-  int precision=(max(args[1]->decimal_int_part(),args[2]->decimal_int_part())+
-                 decimals);
+  int arg1_prec= args[1]->decimal_int_part();
+  int arg2_prec= args[2]->decimal_int_part();
+  int precision=max(arg1_prec,arg2_prec) + decimals;
   return min(precision, DECIMAL_MAX_PRECISION);
 }
 

sql/item_func.cc

@@ -1156,9 +1156,10 @@ my_decimal *Item_func_plus::decimal_op(my_decimal *decimal_value)
 void Item_func_additive_op::result_precision()
 {
   decimals= max(args[0]->decimals, args[1]->decimals);
-  int max_int_part= max(args[0]->decimal_precision() - args[0]->decimals,
-                        args[1]->decimal_precision() - args[1]->decimals);
-  int precision= min(max_int_part + 1 + decimals, DECIMAL_MAX_PRECISION);
+  int arg1_int= args[0]->decimal_precision() - args[0]->decimals;
+  int arg2_int= args[1]->decimal_precision() - args[1]->decimals;
+  int est_prec= max(arg1_int, arg2_int) + 1 + decimals;
+  int precision= min(est_prec, DECIMAL_MAX_PRECISION);
 
   /* Integer operations keep unsigned_flag if one of arguments is unsigned */
   if (result_type() == INT_RESULT)
@@ -1267,8 +1268,8 @@ void Item_func_mul::result_precision()
   else
     unsigned_flag= args[0]->unsigned_flag & args[1]->unsigned_flag;
   decimals= min(args[0]->decimals + args[1]->decimals, DECIMAL_MAX_SCALE);
-  int precision= min(args[0]->decimal_precision() + args[1]->decimal_precision(),
-                     DECIMAL_MAX_PRECISION);
+  uint est_prec = args[0]->decimal_precision() + args[1]->decimal_precision();
+  uint precision= min(est_prec, DECIMAL_MAX_PRECISION);
   max_length= my_decimal_precision_to_length(precision, decimals,unsigned_flag);
 }
 
@@ -1315,8 +1316,8 @@ my_decimal *Item_func_div::decimal_op(my_decimal *decimal_value)
 
 void Item_func_div::result_precision()
 {
-  uint precision=min(args[0]->decimal_precision() + prec_increment,
-                     DECIMAL_MAX_PRECISION);
+  uint arg_prec= args[0]->decimal_precision() + prec_increment;
+  uint precision=min(arg_prec, DECIMAL_MAX_PRECISION);
   /* Integer operations keep unsigned_flag if one of arguments is unsigned */
   if (result_type() == INT_RESULT)
     unsigned_flag= args[0]->unsigned_flag | args[1]->unsigned_flag;