swift234

Support struct_element_addr and tuple_element_addr in SILMem2Reg.

SILMem2Reg can now optimize sequences like:
  alloc_stack
  store whole struct to stack
  get struct_element_addr
  load struct member from stack

This pattern occurs quite often. And this change can reduce the number of SIL instructions in some functions significantly.
The effect on the benchmarks is not significant (only a few small improvements).



Swift SVN r24917