From 1ebee48b90d54290573134df33a20332cf886fa3 Mon Sep 17 00:00:00 2001
From: fis <jm.yuan@outlook.com>
Date: Mon, 25 May 2020 14:24:07 +0800
Subject: [PATCH] Fix IsDense.

---
 src/data/device_dmatrix.cu            | 11 ++++++-----
 tests/cpp/data/test_device_dmatrix.cu | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/src/data/device_dmatrix.cu b/src/data/device_dmatrix.cu
index 6173ec913995..d11d01b16f2a 100644
--- a/src/data/device_dmatrix.cu
+++ b/src/data/device_dmatrix.cu
@@ -33,16 +33,17 @@ DeviceDMatrix::DeviceDMatrix(AdapterT* adapter, float missing, int nthread, int
   size_t row_stride =
       GetRowCounts(batch, row_counts_span, adapter->DeviceIdx(), missing);
 
-  ellpack_page_.reset(new EllpackPage());
-  *ellpack_page_->Impl() =
-      EllpackPageImpl(adapter, missing, this->IsDense(), nthread, max_bin,
-                      row_counts_span, row_stride);
-
   dh::XGBCachingDeviceAllocator<char> alloc;
   info_.num_nonzero_ = thrust::reduce(thrust::cuda::par(alloc),
                                       row_counts.begin(), row_counts.end());
   info_.num_col_ = adapter->NumColumns();
   info_.num_row_ = adapter->NumRows();
+
+  ellpack_page_.reset(new EllpackPage());
+  *ellpack_page_->Impl() =
+      EllpackPageImpl(adapter, missing, this->IsDense(), nthread, max_bin,
+                      row_counts_span, row_stride);
+
   // Synchronise worker columns
   rabit::Allreduce<rabit::op::Max>(&info_.num_col_, 1);
 }
diff --git a/tests/cpp/data/test_device_dmatrix.cu b/tests/cpp/data/test_device_dmatrix.cu
index 1634cea3c46e..db29cc574342 100644
--- a/tests/cpp/data/test_device_dmatrix.cu
+++ b/tests/cpp/data/test_device_dmatrix.cu
@@ -129,3 +129,22 @@ TEST(DeviceDMatrix, Equivalent) {
     }
   }
 }
+
+TEST(DeviceDMatrix, IsDense) {
+  int num_bins = 16;
+  auto test = [num_bins] (float sparsity) {
+    HostDeviceVector<float> data;
+    std::string interface_str = RandomDataGenerator{10, 10, sparsity}
+      .Device(0).GenerateArrayInterface(&data);
+    data::CupyAdapter x{interface_str};
+    std::unique_ptr<data::DeviceDMatrix> device_dmat{ new data::DeviceDMatrix(
+        &x, std::numeric_limits<float>::quiet_NaN(), 1, num_bins) };
+    if (sparsity == 0.0) {
+      ASSERT_TRUE(device_dmat->IsDense()) << sparsity;
+    } else {
+      ASSERT_FALSE(device_dmat->IsDense());
+    }
+  };
+  test(0.0);
+  test(0.1);
+}