swift234

[sil-combine] (struct_extract (load %x) #vardecl) -> (load (struct_element_addr %x #vardecl))

This peephole transforms struct_extract of a load into a load of a
struct_element_addr. This eliminates unnecessary creation of a non-trivial
non-reference counted types and additionally reduces the size of loads.
An example of this from RC4 is:

  %24 = struct_element_addr %1 : $*RC4, #State    // user: %25
  %25 = struct_element_addr %24 : $*Slice<UInt8>, #count // user: %26
  %26 = load %25 : $*Int64                        // user: %29
...
  %29 = struct_extract %26 : $Int64, #value       // user: %30
  %30 = apply %28(%29, %27) : $@thin (Builtin.Int64, Builtin.Int64) -> %Builtin.Int1 // user: %33

In this case there is no use of the load besides the struct_extract. This
becomes even more interesting when the type one is attempting to retrieve from
the non-trivial non-reference counted type is reference counted itself.

Swift SVN r10605