enable O3 build

setup.py

@@ -44,7 +44,7 @@ def get_extensions():
         if sys.platform == 'win32':
             define_macros += [('torchscatter_EXPORTS', None)]
 
-        extra_compile_args = {'cxx': ['-O2']}
+        extra_compile_args = {'cxx': ['-O3']}
         if not os.name == 'nt':  # Not on Windows:
             extra_compile_args['cxx'] += ['-Wno-sign-compare']
         extra_link_args = [] if WITH_SYMBOLS else ['-s']
@@ -69,14 +69,14 @@ def get_extensions():
             define_macros += [('WITH_CUDA', None)]
             nvcc_flags = os.getenv('NVCC_FLAGS', '')
             nvcc_flags = [] if nvcc_flags == '' else nvcc_flags.split(' ')
-            if torch.version.hip:
             nvcc_flags += ['-O3']
-                # USE_ROCM was added to later versons of rocm pytorch
-                # define here to support older pytorch versions
+            if torch.version.hip:
+                # USE_ROCM was added to later versions of PyTorch.
+                # Define here to support older PyTorch versions as well:
                 define_macros += [('USE_ROCM', None)]
                 undef_macros += ['__HIP_NO_HALF_CONVERSIONS__']
             else:
-                nvcc_flags += ['--expt-relaxed-constexpr', '-O2']
+                nvcc_flags += ['--expt-relaxed-constexpr']
             extra_compile_args['nvcc'] = nvcc_flags
 
         name = main.split(os.sep)[-1][:-4]