ZJIT: We use as_heap and fields_obj to mean the same thing sometimes

[tekknolagi]

Looking at this HIR dump from optcarrot:

Optimized HIR:
fn wait_one_clock@/Users/emacs/Documents/code/yjit-bench/benchmarks/optcarrot/lib/optcarrot/ppu.rb:906:
bb1():
  EntryPoint interpreter
  v1:HeapBasicObject = LoadSelf
  Jump bb3(v1)
bb2():
  EntryPoint JIT(0)
  v4:HeapBasicObject = LoadArg :self@0
  Jump bb3(v4)
bb3(v6:HeapBasicObject):
  PatchPoint SingleRactorMode
  v12:CShape = LoadField v6, :shape_id@0x4
  v13:CShape[0x4040017a] = GuardBitEquals v12, CShape(0x4040017a) recompile
  v14:RubyValue = LoadField v6, :fields_obj@0x10
  v15:BasicObject = LoadField v14, :@hclk@0x68
  v17:Fixnum[1] = Const Value(1)
  PatchPoint MethodRedefined(Integer@0x1013844e0, +@0x2b, cme:0x10136bfd0)
  v72:Fixnum = GuardType v15, Fixnum recompile
  v73:Fixnum = FixnumAdd v72, v17
  v26:BasicObject = LoadField v6, :as_heap@0x10
  StoreField v26, :@hclk@0x68, v73
  WriteBarrier v26, v73
  PatchPoint SingleRactorMode
  v37:BasicObject = LoadField v14, :@hclk_target@0x78
  v44:BasicObject = LoadField v14, :@hclk@0x68
  PatchPoint MethodRedefined(Integer@0x1013844e0, <=@0x8a, cme:0x10136c2a0)
  v76:Fixnum = GuardType v37, Fixnum recompile
  v77:Fixnum = GuardType v44, Fixnum
  v78:BoolExact = FixnumLe v76, v77
  v49:CBool = Test v78
  CondBranch v49, bb5(), bb4(v6)
bb5():
  v54:BasicObject = GetConstantPath 0x8dc425800
  SideExit NoProfileSend recompile
bb4(v61:HeapBasicObject):
  v64:NilClass = Const Value(nil)
  CheckInterrupts
  Return v64

v14:RubyValue = LoadField v6, :fields_obj@0x10 and v26:BasicObject = LoadField v6, :as_heap@0x10 seem to be doing the same thing with different names which is really confusing.

[tekknolagi]

I think this is a subtle naming difference between getivar and setivar