reduce shared library file size

setup.py

@@ -21,8 +21,8 @@ BUILD_DOCS = os.getenv('BUILD_DOCS', '0') == '1'
 def get_extensions():
     Extension = CppExtension
     define_macros = []
-    extra_compile_args = {'cxx': []}
-    extra_link_args = []
+    extra_compile_args = {'cxx': ['-O2']}
+    extra_link_args = ['-s']
 
     info = parallel_info()
     if 'parallel backend: OpenMP' in info and 'OpenMP not found' not in info:
@@ -39,7 +39,7 @@ def get_extensions():
         define_macros += [('WITH_CUDA', None)]
         nvcc_flags = os.getenv('NVCC_FLAGS', '')
         nvcc_flags = [] if nvcc_flags == '' else nvcc_flags.split(' ')
-        nvcc_flags += ['-arch=sm_35', '--expt-relaxed-constexpr']
+        nvcc_flags += ['-arch=sm_35', '--expt-relaxed-constexpr', '-O2']
         extra_compile_args['nvcc'] = nvcc_flags
 
     extensions_dir = osp.join(osp.dirname(osp.abspath(__file__)), 'csrc')