This implements the second half of the fix for PR3290, handling

This implements the second half of the fix for PR3290, handling
loads from allocas that cover the entire aggregate.  This handles
some memcpy/byval cases that are produced by llvm-gcc.  This triggers
a few times in kc++ (with std::pair<std::_Rb_tree_const_iterator
<kc::impl_abstract_phylum*>,bool>) and once in 176.gcc (with %struct..0anon).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61915 91177308-0d34-0410-b5e6-96231b3b80d8