[Relay] C++ GraphRuntimeCodegen, Deprecate Python2 (apache#2986)

* [Relay] C++ GraphRuntimeCodegen

* [Test] Deprecate Python2

* [Python3] Add Py2 check

* Update _pyversion.py

* [Python3] Update test

CMakeLists.txt

@@ -85,6 +85,7 @@ else(MSVC)
   include(CheckCXXCompilerFlag)
   check_cxx_compiler_flag("-std=c++11"    SUPPORT_CXX11)
   if ("${CMAKE_BUILD_TYPE}" STREQUAL "Debug")
+    message("Build in Debug mode")
     set(CMAKE_C_FLAGS "-O0 -g -Wall -fPIC ${CMAKE_C_FLAGS} -rdynamic")
     set(CMAKE_CXX_FLAGS "-O0 -g -Wall -fPIC -std=c++11 ${CMAKE_CXX_FLAGS} -rdynamic")
   else()

Jenkinsfile

@@ -214,7 +214,7 @@ stage('Build') {
 }
 
 stage('Unit Test') {
-  parallel 'python2/3: GPU': {
+  parallel 'python3: GPU': {
     node('GPU') {
       ws('workspace/tvm/ut-python-gpu') {
         init_git()
@@ -226,7 +226,7 @@ stage('Unit Test') {
       }
     }
   },
-  'python2/3: i386': {
+  'python3: i386': {
     node('CPU') {
       ws('workspace/tvm/ut-python-i386') {
         init_git()

python/tvm/__init__.py

@@ -18,6 +18,8 @@
 """TVM: Low level DSL/IR stack for tensor computation."""
 from __future__ import absolute_import as _abs
 
+from . import _pyversion
+
 from . import tensor
 from . import arith
 from . import expr

python/tvm/_pyversion.py

@@ -0,0 +1,25 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+"""Python2 version check
+"""
+import sys
+
+if not (sys.version_info[0] >= 3 and sys.version_info[1] >= 5):
+    PY3STATEMENT = """TVM project proudly dropped support of Python2.
+    The minimal Python requirement is Python 3.5
+    """
+    raise Exception(PY3STATEMENT)