Bug 126075 – Deconstruction patterns in parameter list don't create local variables (wut?)

• Status: NEW
• Component: JavaScriptCore

[Oliver Hunt]

>>> function f([a,b]){}
<global>#CaPZ5W:[0x7f90c9d08a70->0x11245f770, NoneGlobal]: 6 m_instructions; 48 bytes; 1 parameter(s); 2 callee register(s); 0 variable(s)
[   0] enter             
[   1] mov               loc0, Undefined(@k0)
[   4] end               loc0

Constants:
   k0 = Undefined

undefined
>>> f([1,2])
<global>#CMJCpr:[0x7f90c9c104c0->0x11245f6f0, NoneGlobal]: 33 m_instructions; 264 bytes; 1 parameter(s); 10 callee register(s); 0 variable(s)
[   0] enter             
[   1] mov               loc0, Undefined(@k0)
[   4] resolve_scope     loc3, f(@id0), 1
[  10] get_from_scope    loc1, loc3, f(@id0), 1
[  18] new_array_buffer  loc2, 0, 2
[  23] call              loc0, loc1, 2, 10 status(Not Set)    Original; predicting None
[  31] end               loc0

Identifiers:
  id0 = f

Constants:
   k0 = Undefined

f#EQKQNp:[0x7f90cc0070c0->0x110ecf570, NoneFunctionCall]: 47 m_instructions; 376 bytes; 2 parameter(s); 2 callee register(s); 0 variable(s)
[   0] enter             
[   1] mov               loc0, Int32: 0(@k0)
[   4] get_by_val        loc0, arg1, loc0    Original; predicting None
[  10] resolve_scope     loc1, a(@id0), 0 <- wit? *******
[  16] put_to_scope      loc1, a(@id0), loc0, 65536
[  23] mov               loc0, Int32: 1(@k1)
[  26] get_by_val        loc0, arg1, loc0    Original; predicting None
[  32] resolve_scope     loc1, b(@id1), 0
[  38] put_to_scope      loc1, b(@id1), loc0, 65536
[  45] ret               Undefined(@k2)

Identifiers:
  id0 = a
  id1 = b

Constants:
   k0 = Int32: 0
   k1 = Int32: 1
   k2 = Undefined

undefined