This is a sorted interval map data structure for small keys and values with
automatic coalescing and bidirectional iteration over coalesced intervals.

Except for coalescing intervals, it provides similar functionality to std::map.
It is however much more compact for small keys and values, and hopefully faster
too.

The container object itself can hold the first few intervals without any
allocations, then it switches to a cache conscious B+-tree representation. A
recycling allocator can be shared between many containers, even between
containers holding different types.

The IntervalMap is initially intended to be used with SlotIndex intervals for:

- Backing store for LiveIntervalUnion that is smaller and faster than std::set.

- Backing store for LiveInterval with less overhead than std::vector for typical
  intervals and O(N log N) merging of large intervals. 99% of virtual registers
  need 4 entries or less and would benefit from the small object optimization.

- Backing store for LiveDebugVariable which doesn't exist yet, but will track
  debug variables during register allocation.

This is a work in progress. Missing items are:

- Performance metrics.
- erase().
- insert() shrinkage.
- clear().
- More performance metrics.
- Simplification and detemplatization.

llvm-svn: 119772

llvm-svn: 119040

llvm-svn: 117646

UnitTests for building all the unit tests.

llvm-svn: 117545

llvm-svn: 117057

llvm-svn: 116834

This time correctly.

llvm-svn: 116247

This reverts commit 116234.

It compiled just fine with MSVC and clang...

llvm-svn: 116242

llvm-svn: 116235

llvm-svn: 116234

llvm-svn: 114835

available targets unless LLVM_INCLUDE_X is ON. LLVM_BUILD_X implies
LLVM_INCLUDE_X"

It breaks the configuration phase when cmake is invoked without
parameters, it is too complex for the purpose and introduces an
incovenience for the user (as both LLVM_BUILD_X and LLVM_INCLUDE_X
must set to OFF for not including X on the build)

llvm-svn: 114795

unless LLVM_INCLUDE_X is ON. LLVM_BUILD_X implies LLVM_INCLUDE_X

llvm-svn: 114747

llvm-svn: 114725