[C++] Use 'nullptr'. Tools edition.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207176 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Use a std::list for Loops

As pointed out by David Blaikie in code review, a `std::list<T>` is
simpler than a `std::vector<std::unique_ptr<T>>`.  Another option is a
`std::deque<T>` (which allocates in chunks), but I'd like to leave open
the option of inserting in the middle of the sequence for handling
irreducible control flow on the fly.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207177 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Stop using range-based for to traverse Loops

A follow-up commit will need the actual iterators.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207178 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Use LoopData directly

Instead of passing around loop headers, pass around `LoopData` directly.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207179 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Embed Loop hierarchy in LoopData

Continue refactoring to make `LoopData` first-class.  Here I'm making
the `LoopData` hierarchy explicit, instead of bouncing back and forth
with `WorkingData`.  This simplifies the logic and better matches the
`LoopInfo` design.  (Eventually, `LoopInfo` should be restructured so
that it supports this pass, and `LoopData` can be removed.)

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207180 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Encapsulate LoopData::Header

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207181 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Store the header with the members

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207182 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Expose getPackagedNode()

Make `getPackagedNode()` a member function of
`BlockFrequencyInfoImplBase` so that it's available for templated code.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207183 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: LoopData::MemberList => NodeList

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207184 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Separate unwrapLoops() from finalizeMetrics()

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207185 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Unwrap from Loops

When unwrapping loops, just visit the loops rather than all nodes.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207186 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Pass the Loop directly into unwrapLoopPackage()

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207187 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: unwrapLoopPackage() => unwrapLoop()

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207188 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Scale LoopData::Scale on the way down

Rather than scaling loop headers and then scaling all the loop members
by the header frequency, scale `LoopData::Scale` itself, and scale the
loop members by it.  It's much more obvious what's going on this way,
and doesn't cost any extra multiplies.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207189 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Remove dead code

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207190 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Document high-level functions

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207191 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Clean up irreducible testcases

Strip irreducible testcases to pure control flow.  The function calls
made the branch weights more believable but cluttered it up a lot.
There isn't going to be any constant analysis here, so just use dumb
branch logic to clarify the important parts.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207192 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Use better branch weights in multiexit test

The branch weights were even before.  Make them different.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207193 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Document assertion

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207194 91177308-0d34-0410-b5e6-96231b3b80d8
blockfreq: Only one mass distribution per node

Remove the concepts of "forward" and "general" mass distributions, which
was wrong.  The split might have made sense in an early version of the
algorithm, but it's definitely wrong now.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207195 91177308-0d34-0410-b5e6-96231b3b80d8