swift234

Change silgen to lower non-inout-self arguments as simple values, instead of
allocating a box for them.  When self is not marked inout (which will be
the default for structs someday) it changes the codegen of:

struct Foo {
  ...

  func testfunction() -> Foo {
    return self
  }
}

To:

sil @_TV1t3Foo12testfunctionfS0_FT_S0_ : $@cc(method) @thin (Foo) -> Foo {
bb0(%0 : $Foo):
  %1 = tuple ()
  return %0 : $Foo                                // id: %2
}

instead of allocating a box, doing a store to it, etc.

Also included: don't maintain references into VarLoc where a simple copy
of the element would suffice.  This isn't important, but was part of my
silvtable debugging and seems like the right thing.



Swift SVN r11307