Fill the map from fields to bitmap infos. This is called for all fields in each transformed class (by the fields info transformer), after the fields inherited from traits have been added.

bitmaps for checkinit fields are not inherited

The compute method (slow path) looks like:

def l$compute() = {
  synchronized(this) {
    if ((bitmap$n & MASK) == 0) {
     init // l$ = <rhs>
     bitmap$n = bimap$n | MASK
    }
  }
  ...
  this.f1 = null
  ...
  this.fn = null
  l$
}

bitmap$n is a byte, int or long value acting as a bitmap of initialized values. The kind of the bitmap determines how many bit indicators for lazy vals are stored in it. For Int bitmap it is 32 and then 'n' in the above code is: (offset / 32), the MASK is (1 << (offset % 32)).

If the class contains only a single lazy val then the bitmap is represented as a Boolean and the condition checking is a simple bool test.

Private fields used only in this initializer are subsequently set to null.

For performance reasons the double-checked locking is split into two parts, the first (fast) path checks the bitmap without synchronizing, and if that fails it initializes the lazy val within the synchronization block (slow path).

This way the inliner should optimize the fast path because the method body is small enough.

Return an (untyped) tree of the form 'Clazz.this.bmp = Clazz.this.bmp | mask'.

Return an (untyped) tree of the form 'clazz.this.bitmapSym & mask (==|!=) 0', the precise comparison operator depending on the value of 'equalToZero'.