Introduce a new pass MandatoryTempRValueElimination, which works as the original TempRValueElimination, except that it does not remove any alloc_stack instruction which are associated with source variables.
Running this pass at Onone helps to reduce copies of large structs, e.g. InlineArrays or structs containing InlineArrays.
Copying large structs can be a performance problem, even at Onone.
rdar://151629149
This corresponds to the parameter-passing convention of the Itanium C++
ABI, in which the argument is passed indirectly and possibly modified,
but not destroyed, by the callee.
@in_cxx is handled the same way as @in in callers and @in_guaranteed in
callees. OwnershipModelEliminator emits the call to destroy_addr that is
needed to destroy the argument in the caller.
rdar://122707697
When instantiating C++ types who contain ARC types in the past either
their default constructors are skipped or they are synthesized with
Unmanged<> wrappers. This has made it more cumbersome to instantiate
these from Swift and often requires a static C++ build method to
manually shim the synthesized constructor. The following change drops
the Unmanaged<> so that for the time being these types can be
instantiated directly even if types like Swift -> NSString are not
bridged completely.
(cherry picked from commit accdace5f0438860a0d6760d9598402a9998a324)
(cherry picked from commit 567763c9ec76e14b0d6af5707e50b1674b2c2cbf)
