Fixed bug in 'GetBinding' when doing the lookup of stored values.  We now use ImmutableMap::SlimFind(), which returns the correct value.
Fixed bug in 'GetBinding' when doing the lookup of stored values.  We now
use ImmutableMap::SlimFind(), which returns the correct value.

Added pruning of dead block-level expressions and Decls from our value map
using liveness information.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@46154 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang