fix(gopt): using new_inp for build_chain in DelayBroadcast pass

GitOrigin-RevId: efc6377197

imperative/python/megengine/functional/nn.py

@@ -784,10 +784,10 @@ def sync_batch_norm(
 
         if is_distributed():
             # reduce all nodes' data to calculate mean and variance
-            reduce_size = broadcast_to(Tensor(reduce_size, dtype=_dtype), [1] * _ndim)
-            stat = concat(
-                [reduce_size.astype(_dtype), channel_x1s, channel_x2s], axis=1
+            reduce_size = broadcast_to(
+                Tensor(reduce_size).astype(dtype=_dtype), [1] * _ndim
             )
+            stat = concat([reduce_size, channel_x1s, channel_x2s], axis=1)
             stat = all_reduce_sum(stat, group)
             reduce_size = stat[:, :1].reshape(1)
             channel_x1s = stat[:, 1 : 1 + _channels]

imperative/python/megengine/tensor.py

@@ -18,6 +18,7 @@ from .core._wrap import device as as_device
 from .core.ops.builtin import Copy, GetVarShape
 from .core.tensor.array_method import ArrayMethodMixin
 from .device import _valid_device, get_default_device
+from .logger import get_logger
 from .utils.deprecation import deprecated
 
 
@@ -41,6 +42,10 @@ class Tensor(_Tensor, ArrayMethodMixin):
                 cn = device._cn
 
         if isinstance(data, _Tensor):
+            if dtype is not None:
+                get_logger().warning(
+                    "dtype does not work when creating a new Tensor with another Tensor"
+                )
             obj = _Tensor.__new__(cls, data)
         else:
             if isinstance(data, np.ndarray):

imperative/python/test/integration/test_bn.py

@@ -17,7 +17,7 @@ import megengine.optimizer as optimizer
 from megengine import Parameter, tensor
 from megengine.distributed.helper import get_device_count_by_fork
 from megengine.jit import trace
-from megengine.module import BatchNorm2d, Module, SyncBatchNorm
+from megengine.module import BatchNorm2d, Conv2d, Module, Sequential, SyncBatchNorm
 
 
 def run_frozen_bn(BNModule, use_trace=False, use_symbolic=False):
@@ -68,7 +68,7 @@ def test_frozen_bn():
     run_frozen_bn(BatchNorm2d, True, True)
 
 
-@pytest.mark.skipif(get_device_count_by_fork("gpu") < 2, reason="need more gpu device")
+@pytest.mark.require_ngpu(2)
 @pytest.mark.isolated_distributed
 def test_frozen_synced_bn():
     @dist.launcher(n_gpus=2)
@@ -151,6 +151,45 @@ def test_trace_bn_forward_twice():
     np.testing.assert_equal(y.numpy(), 0)
 
 
+def run_syncbn(trace_mode):
+    x = F.ones([2, 16, 4, 4], dtype="float32")
+
+    net = Sequential(
+        Conv2d(16, 16, 1), SyncBatchNorm(16), Conv2d(16, 16, 1), SyncBatchNorm(16),
+    )
+
+    gm = ad.GradManager().attach(
+        net.parameters(), callbacks=dist.make_allreduce_cb("MEAN")
+    )
+    opt = optimizer.SGD(net.parameters(), 1e-3)
+
+    def train_func(x):
+        with gm:
+            y = net(x)
+            loss = y.mean()
+            gm.backward(loss)
+            opt.step().clear_grad()
+        return loss
+
+    if trace_mode is not None:
+        train_func = trace(train_func, symbolic=trace_mode)
+
+    for _ in range(3):
+        loss = train_func(x)
+        loss.numpy()
+
+
+@pytest.mark.require_ngpu(2)
+@pytest.mark.isolated_distributed
+@pytest.mark.parametrize("trace_mode", [None, True, False])
+def test_trace_several_syncbn(trace_mode):
+    @dist.launcher(n_gpus=2)
+    def worker():
+        run_syncbn(trace_mode)
+
+    worker()
+
+
 # https://github.com/MegEngine/MegEngine/issues/145
 def test_frozen_bn_no_affine():
     nchannel = 3

src/gopt/impl/misc.cpp

@@ -226,8 +226,14 @@ void DelayBroadcastPass::apply(OptState& opt) const {
             if (!prev)
                 prev = rewriter.get_var(opr->input(inp_idx));
             if (!opr->same_type<opr::Broadcast>()) {
-                VarNodeArray new_inp = opr->input();
-                new_inp.at(inp_idx) = prev;
+                VarNodeArray new_inp(opr->input().size());
+                for (size_t i = 0; i < opr->input().size(); i++) {
+                    if (i == inp_idx) {
+                        new_inp[i] = prev;
+                    } else {
+                        new_inp[i] = rewriter.get_var(opr->input(i));
+                    }
+                }
                 opt.call_with_opr(opr, [&] {
                     // create new opr with the original opr's properties
                     auto new_opr = serialization::copy_opr_shallow(

src/gopt/test/misc.cpp

@@ -177,6 +177,32 @@ TEST_PASS(DelayBroadcastPass, LongChain) {
     ASSERT_EQ(bcast(bcast(relu(relu(x)), y), z), out);
 }
 
+TEST_PASS(DelayBroadcastPass, ElemwiseChain) {
+    auto typecvt = [](SymbolVar x) {
+        return opr::TypeCvt::make(x, dtype::Int32());
+    };
+
+    auto reduce = [](SymbolVar x) {
+        SymbolVar tshp = x.make_scalar(1);
+        opr::Reduce::Param param_default{opr::Reduce::Mode::SUM, INT_MAX,
+                                    opr::Reduce::Param::DataType::DEFAULT};
+        return opr::Reduce::make(x, param_default, tshp);
+    };
+
+    auto shp = TensorShape{2, 2};
+
+    auto x = mkvar("x", {1, 1});
+    auto val = x.make_scalar(3);
+
+    auto out = reduce(typecvt(x.broadcast(shp))) + val.broadcast(shp);
+    out = gopt::GraphOptimizer{}.
+        add_pass<gopt::DelayBroadcastPass>().
+        apply({{out}}).endpoint_vars()[0];
+
+    auto expected = (reduce(typecvt(x).broadcast(shp)) + val).broadcast(shp);
+    ASSERT_EQ(out, expected);
+}
+
 TEST_PASS(ExpandVirtualGradPass, Simple) {
     auto x = mkvar("x");
     check(x * 2,