Fix empty output tensor and add an unitest case

paddle/operators/ctc_align_op.cu

@@ -80,6 +80,14 @@ class CTCAlignOpCUDAKernel : public framework::OpKernel<T> {
 
     // resize output dims
     output->Resize({static_cast<int64_t>(host_out_lod0.back()), 1});
+
+    if (host_out_lod0.back() == 0) {
+      output->Resize({1});
+      output->mutable_data<T>(ctx.GetPlace());
+      math::SetConstant<platform::CUDADeviceContext, T> set_constant;
+      set_constant(ctx.template device_context<platform::CUDADeviceContext>(),
+                   output, -1);
+    }
   }
 };
 

paddle/operators/ctc_align_op.h

@@ -16,6 +16,8 @@ limitations under the License. */
 
 #include <string.h>
 #include "paddle/framework/op_registry.h"
+#include "paddle/operators/math/math_function.h"
+
 namespace paddle {
 namespace operators {
 
@@ -65,9 +67,14 @@ class CTCAlignKernel : public framework::OpKernel<T> {
     framework::LoD output_lod;
     output_lod.push_back(output_lod0);
     output->set_lod(output_lod);
-
     // resize output dims
     output->Resize({static_cast<int64_t>(output_lod0.back()), 1});
+    // for empty sequence
+    if (output_lod0.back() == 0) {
+      output->Resize({1});
+      output_data = output->mutable_data<T>(ctx.GetPlace());
+      output_data[0] = -1;
+    }
   }
 };
 

python/paddle/v2/fluid/tests/test_ctc_align.py

@@ -31,6 +31,8 @@ def CTCAlign(input, lod, blank, merge_repeated):
                 result.append(token)
             prev_token = token
     result = np.array(result).reshape([len(result), 1]).astype("int32")
+    if len(result) == 0:
+        result = np.array([-1])
     return result
 
 
@@ -72,5 +74,14 @@ class TestCTCAlignOpCase1(TestCTCAlignOp):
                 [19, 1]).astype("int32")
 
 
+class TestCTCAlignOpCase2(TestCTCAlignOp):
+    def config(self):
+        self.op_type = "ctc_align"
+        self.input_lod = [[0, 4]]
+        self.blank = 0
+        self.merge_repeated = True
+        self.input = np.array([0, 0, 0, 0]).reshape([4, 1]).astype("int32")
+
+
 if __name__ == "__main__":
     unittest.main()