swift234

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

This reapplies commit r10605 with the relevant fixes. The specific bug
had to do with the original code inserting the new
load/struct_element_addr at the struct_extract instead of at the load
instruction. As an example of this consider the following:

%y = (load %x)
(do_stuff)
(struct_extract %y #vardecl)

if (do_stuff) modifies the memory at %x that aliases what we would be
extracting from %y, then transforming the code to:

  (do_stuff)
  %y = (struct_element_addr %x #vardecl)
  (load %y)

would yield an incorrect value. This patch changes the transformation so that we
perform the following transformation instead:

  %y = (struct_element_addr %x #vardecl)
  (load %y)
  (do_stuff)

which will resolve the issue.

This peephole triggers 365 times in the stdlib.

Swift SVN r10619