swift234

Extend MemberRefExpr in a fairly substantial way: now it is ok, when applied to a
struct rvalue, to produce a struct element directly, without converting the rvalue
to an lvalue.

This means that it no longer materializes an lvalue when applied to a let declaration
or other rvalue.  For example, this testcase:

struct X { var a,b : Int} 
func g() -> X { return X(1,2) }

func f() {
  let a = g().a
}

used to sema into:

       (load_expr implicit type='Int'
          (member_ref_expr type='@inout (implicit, nonsettable)Int' decl=t.(file).X.a@t.swift:2:16
            (materialize_expr implicit type='@inout (implicit)X'
              (call_expr type='X'

and silgen into:

  %1 = function_ref @_TF1t1gFT_VS_1X : $@thin () -> X // user: %2
  %2 = apply %1() : $@thin () -> X                // user: %4
  %3 = alloc_stack $X                             // users: %7, %5, %4
  store %2 to %3#1 : $*X                          // id: %4
  %5 = struct_element_addr %3#1 : $*X, #a         // user: %6
  %6 = load %5 : $*Int64

It now sema's into:
        (member_ref_expr type='Int' decl=t.(file).X.a@t.swift:1:16
          (call_expr type='X'

and silgens into:

  %1 = function_ref @_TF1t1gFT_VS_1X : $@thin () -> X // user: %2
  %2 = apply %1() : $@thin () -> X                // user: %3
  %3 = struct_extract %2 : $X, #a

I think I'm finally starting to grok Doug's crazy typechecker magic.



Swift SVN r11599