item_cmp_type: simplier for a faster codepath

The common case for this function is that both types are the same. The Item_result defination from include/mysql.h.pp is the following enum enum Item_result { STRING_RESULT=0, REAL_RESULT, INT_RESULT, ROW_RESULT, DECIMAL_RESULT, TIME_RESULT }; The compilers aren't quite smart enough to optimize to this shortcut so this makes it quicker. Before the change: 0000000000012730 <item_cmp_type(Item_result, Item_result)>: 12730: 89 f0 mov %esi,%eax 12732: 09 f8 or %edi,%eax 12734: 74 4c je 12782 <item_cmp_type(Item_result, Item_result)+0x52> 12736: 83 ff 02 cmp $0x2,%edi 12739: 75 0a jne 12745 <item_cmp_type(Item_result, Item_result)+0x15> 1273b: b8 02 00 00 00 mov $0x2,%eax 12740: 83 fe 02 cmp $0x2,%esi 12743: 74 3c je 12781 <item_cmp_type(Item_result, Item_result)+0x51> 12745: 83 ff 03 cmp $0x3,%edi 12748: b8 03 00 00 00 mov $0x3,%eax 1274d: 74 32 je 12781 <item_cmp_type(Item_result, Item_result)+0x51> 1274f: 83 fe 03 cmp $0x3,%esi 12752: 74 2d je 12781 <item_cmp_type(Item_result, Item_result)+0x51> 12754: 83 ff 05 cmp $0x5,%edi 12757: b8 05 00 00 00 mov $0x5,%eax 1275c: 74 23 je 12781 <item_cmp_type(Item_result, Item_result)+0x51> 1275e: 83 fe 05 cmp $0x5,%esi 12761: 74 1e je 12781 <item_cmp_type(Item_result, Item_result)+0x51> 12763: 83 ff 04 cmp $0x4,%edi 12766: 74 05 je 1276d <item_cmp_type(Item_result, Item_result)+0x3d> 12768: 83 ff 02 cmp $0x2,%edi 1276b: 75 0f jne 1277c <item_cmp_type(Item_result, Item_result)+0x4c> 1276d: b8 04 00 00 00 mov $0x4,%eax 12772: 83 fe 02 cmp $0x2,%esi 12775: 74 0a je 12781 <item_cmp_type(Item_result, Item_result)+0x51> 12777: 83 fe 04 cmp $0x4,%esi 1277a: 74 05 je 12781 <item_cmp_type(Item_result, Item_result)+0x51> 1277c: b8 01 00 00 00 mov $0x1,%eax 12781: c3 retq 12782: 31 c0 xor %eax,%eax 12784: c3 retq After, noting the short cut and the beginning of the function: 0000000000012730 <item_cmp_type(Item_result, Item_result)>: 12730: 39 f7 cmp %esi,%edi 12732: 75 03 jne 12737 <item_cmp_type(Item_result, Item_result)+0x7> 12734: 89 f8 mov %edi,%eax 12736: c3 retq 12737: 83 ff 03 cmp $0x3,%edi 1273a: b8 03 00 00 00 mov $0x3,%eax 1273f: 74 32 je 12773 <item_cmp_type(Item_result, Item_result)+0x43> 12741: 83 fe 03 cmp $0x3,%esi 12744: 74 2d je 12773 <item_cmp_type(Item_result, Item_result)+0x43> 12746: 83 ff 05 cmp $0x5,%edi 12749: b8 05 00 00 00 mov $0x5,%eax 1274e: 74 23 je 12773 <item_cmp_type(Item_result, Item_result)+0x43> 12750: 83 fe 05 cmp $0x5,%esi 12753: 74 1e je 12773 <item_cmp_type(Item_result, Item_result)+0x43> 12755: 83 ff 04 cmp $0x4,%edi 12758: 74 05 je 1275f <item_cmp_type(Item_result, Item_result)+0x2f> 1275a: 83 ff 02 cmp $0x2,%edi 1275d: 75 0f jne 1276e <item_cmp_type(Item_result, Item_result)+0x3e> 1275f: b8 04 00 00 00 mov $0x4,%eax 12764: 83 fe 02 cmp $0x2,%esi 12767: 74 0a je 12773 <item_cmp_type(Item_result, Item_result)+0x43> 12769: 83 fe 04 cmp $0x4,%esi 1276c: 74 05 je 12773 <item_cmp_type(Item_result, Item_result)+0x43> 1276e: b8 01 00 00 00 mov $0x1,%eax 12773: c3 retq Signed-off-by: Daniel Black <daniel@linux.vnet.ibm.com>

Author: grooverdan

sql/item.cc

@@ -8719,13 +8719,11 @@ void Item_trigger_field::cleanup()
 
 Item_result item_cmp_type(Item_result a,Item_result b)
 {
- if (a == STRING_RESULT && b == STRING_RESULT)
- return STRING_RESULT;
- if (a == INT_RESULT && b == INT_RESULT)
- return INT_RESULT;
- else if (a == ROW_RESULT || b == ROW_RESULT)
+ if (a == b)
+ return a;
+ if (a == ROW_RESULT || b == ROW_RESULT)
  return ROW_RESULT;
- else if (a == TIME_RESULT || b == TIME_RESULT)
+ if (a == TIME_RESULT || b == TIME_RESULT)
  return TIME_RESULT;
  if ((a == INT_RESULT || a == DECIMAL_RESULT) &&
  (b == INT_RESULT || b == DECIMAL_RESULT))