[AutoScheduler] Improve warning messages (apache#6935)

* [AutoScheduler] Improve warning messages

* fix lint

python/tvm/auto_scheduler/dispatcher.py

@@ -258,10 +258,11 @@ def query(self, target, workload_key, has_complex_op, dag):
 
         if self.verbose == 2 or (has_complex_op and self.verbose == 1):
             msg = (
-                "Cannot find tuned schedules for target=%s, workload_key=%s, compute:\n%s"
+                "-----------------------------------\n"
+                "Cannot find tuned schedules for target=%s, workload_key=%s. "
                 "A fallback TOPI schedule is used, "
-                "which may bring great performance regression or even compilation failure."
-                % (target, workload_key, dag)
+                "which may bring great performance regression or even compilation failure. "
+                "Compute DAG info:\n%s" % (target, workload_key, dag)
             )
             if msg not in self.messages:
                 self.messages.add(msg)

python/tvm/relay/op/strategy/cuda.py

@@ -101,6 +101,18 @@ def schedule_lrn_cuda(attrs, outs, target):
         return topi.cuda.schedule_lrn(outs)
 
 
+def naive_schedule(_, outs, target):
+    """Return the naive default schedule"""
+    if "gpu" in target.keys:
+        # For GPU, we at least need thread binding to make a valid schedule.
+        # So the naive schedule cannot be compiled.
+        raise RuntimeError(
+            "Cannot compile for GPU targets if no tuned schedule is found."
+            "Please see the warning messages above for more information about the failed workloads."
+        )
+    return tvm.te.create_schedule(outs[-1].op)
+
+
 @conv2d_strategy.register(["cuda", "gpu"])
 def conv2d_strategy_cuda(attrs, inputs, out_type, target):
     """conv2d cuda strategy"""
@@ -224,7 +236,7 @@ def conv2d_strategy_cuda(attrs, inputs, out_type, target):
             if use_auto_scheduler and judge_winograd_auto_scheduler:
                 strategy.add_implementation(
                     wrap_compute_conv2d(topi.nn.conv2d_winograd_nhwc),
-                    wrap_topi_schedule(tvm.te.create_schedule),
+                    naive_schedule,  # this implementation should never be picked by autotvm
                     name="conv2d_nhwc.winograd",
                     plevel=15,
                 )
@@ -451,7 +463,7 @@ def conv2d_winograd_without_weight_transfrom_strategy_cuda(attrs, inputs, out_ty
         if PassContext.current().config.get("relay.backend.use_auto_scheduler", False):
             strategy.add_implementation(
                 wrap_compute_conv2d(topi.nn.conv2d_winograd_nhwc_without_weight_transform),
-                wrap_topi_schedule(tvm.te.create_schedule),
+                naive_schedule,  # this implementation should never be picked by autotvm
                 name="conv2d_nhwc_winograd_without_weight_transform",
                 plevel=15,
             )