[analyzer] check for now possibly null predecessor edge.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@202434 91177308-0d34-0410-b5e6-96231b3b80d8
[CFG] record the original (now unreachable) block of 'case:' and 'default:' cases.

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[-Wunreachable-code] always treat 'case:' and 'default:' cases as reachable.

This is a heuristic.  Many switch statements, although they look covered
over an enum, may actually handle at runtime more values than in the enum.

This is overly conservative, as there are some cases that clearly
can be ruled as being clearly unreachable, e.g. 'switch (42) { case 1: ... }'.
We can refine this later.

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Remove an assertion that no longer holds. <rdar://problem/16135814>

In r201528, I changed the PGO instrumentation counter for a "do" loop to not
include the fall-through count. That fall-through count is included later, b
it means that this assertion may fail for "do" loops.

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Reapply r202420 hopefully fixed for other STLs

Keep the copy constructor around, and add a FIXME that we should really
remove it as soon as we have C++11 std::map's emplace function.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@202439 91177308-0d34-0410-b5e6-96231b3b80d8
MS ABI: Attempt to fix DenseMap entry reference invalidation

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