[Fixbug][Hidet Script] Fix a bug that hidet script does not recognize…

… return type (#329)

Fix hidet script transpiler to run recognize the following code
```python
def test_unroll():
    from hidet.lang import printf, attrs
    from hidet.ir.dtypes import float32x8, float32
    from hidet.ir import primitives
    from hidet.lang import address, cast

    with hidet.script_module() as script_module:

        @hidet.script
        def example() -> float32x8:
            attrs.func_kind = 'cpu_internal'
            return primitives.cpu.avx_f32x8_setzero()

        @hidet.script
        def main():
            attrs.func_kind = 'cpu_kernel'

            a = example()
            a_unpacked = cast(address(a), ~float32)
            for i in range(8):
                printf("%f ", a_unpacked[i])
            printf("\n")

    func = script_module.build()
    func()

    return func
```
Previously, hidet can not recognize the `float32x8` return type.

python/hidet/ir/tools/printer.py

@@ -75,6 +75,8 @@ def visit_Function(self, func: Function):
             else:
                 head_doc += NewLine()
         head_doc += ')'
+        if not func.ret_type.is_void():
+            head_doc += ' -> ' + self(func.ret_type) + ':'
 
         # attributes
         attr_doc = Doc()

python/hidet/lang/transpiler.py

@@ -501,7 +501,8 @@ def visit_FunctionDef(self, func_def: FunctionDef):
                 # the default return type is void
                 ret_type = ir.VoidType()
             else:
-                ret_type = self.visit(func_def.returns)
+                # ret_type = self.visit(func_def.returns)
+                ret_type = self.func_annotations['return']
                 if not isinstance(ret_type, ir.BaseType):
                     if ret_type is bool:
                         ret_type = ir.data_type('bool')

tests/script/test_return_type.py

@@ -0,0 +1,46 @@
+# Licensed 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.
+import pytest
+import hidet
+
+
+def test_return_type():
+    from hidet.lang import printf, attrs
+    from hidet.ir.dtypes import float32x8, float32
+    from hidet.ir import primitives
+    from hidet.lang import address, cast
+
+    with hidet.script_module() as script_module:
+
+        @hidet.script
+        def example() -> float32x8:
+            attrs.func_kind = 'cpu_internal'
+            return primitives.cpu.avx_f32x8_setzero()
+
+        @hidet.script
+        def main():
+            attrs.func_kind = 'cpu_kernel'
+
+            a = example()
+            a_unpacked = cast(address(a), ~float32)
+            for i in range(8):
+                printf("%f ", a_unpacked[i])
+            printf("\n")
+
+    func = script_module.build()
+    func()
+
+    return func
+
+
+if __name__ == '__main__':
+    pytest.main([__file__])