make reverse op support negative axis (#21925)

* make reverse op support negative axis

paddle/fluid/operators/reverse_op.cc

@@ -31,7 +31,13 @@ class ReverseOp : public framework::OperatorWithKernel {
     PADDLE_ENFORCE(!axis.empty(), "'axis' can not be empty.");
     for (int a : axis) {
       PADDLE_ENFORCE_LT(a, x_dims.size(),
-                        "The axis must be less than input tensor's rank.");
+                        paddle::platform::errors::OutOfRange(
+                            "The axis must be less than input tensor's rank."));
+      PADDLE_ENFORCE_GE(
+          a, -x_dims.size(),
+          paddle::platform::errors::OutOfRange(
+              "The axis must be greater than the negative number of "
+              "input tensor's rank."));
     }
     ctx->SetOutputDim("Out", x_dims);
   }

paddle/fluid/operators/reverse_op.h

@@ -28,7 +28,11 @@ struct ReverseFunctor {
       reverse_axis[i] = false;
     }
     for (int a : axis) {
+      if (a >= 0) {
         reverse_axis[a] = true;
+      } else {
+        reverse_axis[Rank + a] = true;
+      }
     }
 
     auto in_eigen = framework::EigenTensor<T, Rank>::From(in);

python/paddle/fluid/tests/unittests/test_reverse_op.py

@@ -47,23 +47,47 @@ class TestCase0(TestReverseOp):
         self.axis = [1]
 
 
+class TestCase0(TestReverseOp):
+    def initTestCase(self):
+        self.x = np.random.random((3, 40)).astype('float64')
+        self.axis = [-1]
+
+
 class TestCase1(TestReverseOp):
     def initTestCase(self):
         self.x = np.random.random((3, 40)).astype('float64')
         self.axis = [0, 1]
 
 
+class TestCase0(TestReverseOp):
+    def initTestCase(self):
+        self.x = np.random.random((3, 40)).astype('float64')
+        self.axis = [0, -1]
+
+
 class TestCase2(TestReverseOp):
     def initTestCase(self):
         self.x = np.random.random((3, 4, 10)).astype('float64')
         self.axis = [0, 2]
 
 
+class TestCase2(TestReverseOp):
+    def initTestCase(self):
+        self.x = np.random.random((3, 4, 10)).astype('float64')
+        self.axis = [0, -2]
+
+
 class TestCase3(TestReverseOp):
     def initTestCase(self):
         self.x = np.random.random((3, 4, 10)).astype('float64')
         self.axis = [1, 2]
 
 
+class TestCase3(TestReverseOp):
+    def initTestCase(self):
+        self.x = np.random.random((3, 4, 10)).astype('float64')
+        self.axis = [-1, -2]
+
+
 if __name__ == '__main__':
     unittest.main()