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

1 files changed, 8 insertions, 4 deletions

diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index 16f3e51d615..1994f6bf1a5 100644
--- a/sql/item_cmpfunc.cc
+++ b/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);
 }