which GCC detects and Clang does not!

llvm-svn: 208033

llvm-svn: 208030

Add llvm::function_ref (and a couple of uses of it), representing a type-erased reference to a callable object.

llvm-svn: 208025

This moves most of GlobalOpt's constructor optimization
code out of GlobalOpt into Transforms/Utils/CDtorUtils.{h,cpp}. The
public interface is a single function OptimizeGlobalCtorsList() that
takes a predicate returning which constructors to remove.

GlobalOpt calls this with a function that statically evaluates all
constructors, just like it did before. This part of the change is
behavior-preserving.

Also add a call to this from GlobalDCE with a filter that removes global
constructors that contain a "ret" instruction and nothing else – this
fixes PR19590.

llvm-svn: 207856