[Quantization, Calibrate] Fix context creation when current_target is…

… explicity set (apache#4582)

python/tvm/relay/quantize/_calibrate.py

@@ -53,11 +53,18 @@ def collect_stats(mod, dataset):
     logging.info("collecting statistics for calibration...")
     func = mod['main']
     func = _quantize.CreateStatsCollector(func)
-    target = tvm.target.current_target() or 'llvm'
+
+    if tvm.target.current_target():
+        target = tvm.target.current_target()
+        ctx = tvm.context(target.target_name)
+    else:
+        target = 'llvm'
+        ctx = tvm.context(target)
+
     with _transform.build_config(opt_level=3):
         graph, lib, params = _build_module.build(func, target=target)
     outputs = []
-    runtime = graph_runtime.create(graph, lib, tvm.context(target))
+    runtime = graph_runtime.create(graph, lib, ctx)
     runtime.set_input(**params)
 
     num_outputs = runtime.get_num_outputs()

tests/python/relay/test_pass_auto_quantize.py

@@ -14,6 +14,7 @@
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
+import numpy as np
 import tvm
 from tvm import relay
 from tvm.relay import testing
@@ -45,5 +46,28 @@ def test_mul_rewrite():
 
     quantize_and_build(act * pool)
 
+
+def get_calibration_dataset(input_name):
+    dataset = []
+    for i in range(5):
+        data = np.random.uniform(size=(1, 3, 224, 224))
+        dataset.append({input_name: data})
+    return dataset
+
+
+def test_calibrate_target(create_target=False):
+    mod, params = testing.resnet.get_workload(num_layers=18)
+    dataset = get_calibration_dataset("data")
+    with relay.quantize.qconfig(calibrate_mode="kl_divergence"):
+        if create_target:
+            with tvm.target.create("llvm"):
+                relay.quantize.quantize(mod, params, dataset)
+        else:
+            # current_target = None
+            relay.quantize.quantize(mod, params, dataset)
+
+
 if __name__ == "__main__":
     test_mul_rewrite()
+    test_calibrate_target(False)
+    test_calibrate_target(True)