Improvements and changes in dialect conversion APIs. Type conversion
and op rewriting are now a bit more independent mechanisms. Dialect
conversion now requires a target object with the legal transformations
to be applied. Legality checks to detect illegal operations after
dialect conversion have been strengthened significantly.

MLIR LLVM commit:
commit 82d5084cf28bca7a0eebec283cdeae118dfa1d11 (HEAD)
Author: Jacques Pienaar <jpienaar@google.com>
Date:   Wed Jun 26 11:12:40 2019 -0700

    Split out TranslateClParser and add new parse method that reuses
    SourceMgr.

MLIR commit:
commit 82d5084cf28bca7a0eebec283cdeae118dfa1d11 (HEAD)
Author: Jacques Pienaar <jpienaar@google.com>
Date:   Wed Jun 26 11:12:40 2019 -0700

    Split out TranslateClParser and add new parse method that reuses
    SourceMgr.

* Move dialect and types to mlir namespace

* PR fixes and some cleanup

* Merge fix

* Use NGRAPH export macros instead of CPU

* Move code to ngmlir namespace

* Move MLIR to src/contrib/mlir

* Create MLIR as cmake external project. Clone and build via ngraph cmake

* Moved code and enabled compilation. Need to clone and build MLIR/LLVM during cmake step, so find_package can work

* clone and build llvm/mlir during configuration. Compiles now. Needs more testing

* Force DEX only if MLIR is ON

* Remove extra cmake file. Style-apply

* Remove redundant files in cpu/mlir

* Update CODEOWNERS. Check for ninja and fail if not found

* Fixing post merge issues

* Link MLIR static libs to cpu backend

* Use LLVMConfig.cmake

* Initial commit. Link fails with undefined reference to typeinfo for mlir::Dialect

* Added AddOp

* initial compiler class

* Initialize module/function, and map tensors to arguments

* Code compiles. Moved MLIR building to correct DEX handler

* NGDialect code-gen working

* Use vector instead of sets for i/o tensors. Use functor in executor

* Misc fixes

* style-apply

* WIP: Adding support for dialect lowering.

* WIP: Lowered to affine. Crash on constant ops have side effects in Constant Folding

* Fixed missing whole package linkage.

* Removed fake instruction and update func type

*  Enable lowering to LLVM dialect and IR

* Made loop nest builder handle any rank

* Fixes per PR feedback. Major ones:
- Removed ngdialect namespace
- renamed dialect classes to start with NG prefixwq:w

* Add unreachable assert

* Add reading of LLVM options from an env var MLIR_LLVM_OPTIONS (#5)

* update licenses for 2019

* style

Primitive CPU Executor for managing thread pools and executing kernels across partitioned resources (#1858)

* Add arena support to DEX kernels

* Add CPUExecutionContext to pass executor information to kernels

* Removed eigen_thread_pool. Functionality moved to cpu_executor

* Moved MKLDNN engine to CPU executor

* Added TBB arenas for node affinitization

* Fixed missing arena in one hot kernel

* Style fixes

* update test to verify all header files are complete, meaning they include what they use.

* disable

* use line comments instead of multiline comments for license header

* update more

* update new files

* more header updates

* style

* CPU: Direct Execution
Part 1 with bare minimum infrastructure

* Refactor: Move build related functionality to a separate TU
and external function method

* Add TU back after merge

* Remove an assert

* Remove commented-out code

* rename directories to be consistent
* rename reference namespace to match directory

* CPU: Eigen-based Pad kernel

* CPU: Create a global Eigen thread pool and use it for padding

* Formatting fixes

* cleanup

* cleanup

* fix all headers to be standalone as far as includes go

* include cleanup

* cleanup includes

* cleanup

* include tester

* wip

* cleanup

* cleanup

* cleanup

* cleanup

* fix node includes

* port functions from funky passman branch

* update pass tests

* wip

* fixed

* remove obsolete test

* remove debug prints

add tensor buffer size unit test

fix warnings when building mkldnn test

get tensor is_output set. Add Manager state and Function to pass manager

use pass manager internal state

* Done to achieve goal of having our #include directives all start
  with `"ngraph/`, like LLVM does.

Add memory layout and liveness passes.

* Fixed the paths in the include statements

* absolute path include, relative to /src

* fix invalid use of incomplete type

* Fixed a compilation error.

add test framework

stuff wired up

benchmark segfault for 5M nodes. fun

make traverse_nodes not recursive

print timings on benchmark

unit test for pass manager

Element types needed some reorganization to allow literals to know what kind of values to hold.