Fix bug: In dynamic mode, if start or end is negetive, __getitem__ return wrong result(#30003)

1. when slice_item is a slice: 
 1) the start of __getitem__ should be std::max(start, 0) if slice
 2) the start of __getitem__ should be std::min(end, dim) 
2. when slice_item is an integer, it should be in [-dim_len, dim_len) 
3. Fix error message to use accurate data

paddle/fluid/operators/slice_op.cc

@@ -121,8 +121,11 @@ class SliceOp : public framework::OperatorWithKernel {
           start = std::max(start, 0);
           end = std::max(end, 0);
           end = std::min(end, dim_value);
-          PADDLE_ENFORCE_GT(end, start, platform::errors::InvalidArgument(
+          PADDLE_ENFORCE_GT(end, start,
-                                            "end should greater than start"));
+                            platform::errors::InvalidArgument(
+                                "end should greater than start, but received "
+                                "end = %d, start = %d.",
+                                ends[i], starts[i]));
           out_dims[axes[i]] = end - start;
         }
       }

paddle/fluid/operators/slice_op.h

@@ -122,8 +122,8 @@ class SliceKernel : public framework::OpKernel<T> {
       PADDLE_ENFORCE_GT(end, start,
                         platform::errors::InvalidArgument(
                             "Attr(ends) should be greater than attr(starts) in "
-                            "slice op. But received ends = %d, starts = %d.",
+                            "slice op. But received end = %d, start = %d.",
-                            end, start));
+                            ends[0], starts[0]));
       int64_t out_size = end - start;
 
       if (out_is_tensor_array) {
@@ -181,8 +181,8 @@ class SliceKernel : public framework::OpKernel<T> {
               end, start,
               platform::errors::InvalidArgument(
                   "Attr(ends) should be greater than attr(starts) in "
-                  "slice op. But received ends = %d, starts = %d.",
+                  "slice op. But received end = %d, start = %d.",
-                  end, start));
+                  ends[i], starts[i]));
           out_dims[axes[i]] = end - start;
         }
       }

paddle/fluid/pybind/imperative.cc

@@ -20,6 +20,7 @@ limitations under the License. */
 #include <pybind11/functional.h>
 #include <pybind11/stl.h>
 
+#include <algorithm>
 #include <memory>
 #include <set>
 #include <string>
@@ -322,6 +323,7 @@ static int _PySlice_GetIndices(PySliceObject *r, Py_ssize_t length,
           std::string(Py_TYPE(r->start)->tp_name)));
     }
     if (*start < 0) *start += length;
+    *start = std::max(*start, static_cast<Py_ssize_t>(0));
   }
   if (r->stop == Py_None) {
     *stop = *step < 0 ? -1 : length;
@@ -335,6 +337,7 @@ static int _PySlice_GetIndices(PySliceObject *r, Py_ssize_t length,
           std::string(Py_TYPE(r->stop)->tp_name)));
     }
     if (*stop < 0) *stop += length;
+    *stop = std::min(*stop, length);
   }
   if (*stop > length) return -1;
   if (*start >= length) return -1;
@@ -380,7 +383,7 @@ static void ParseIndexingSlice(framework::LoDTensor *tensor, PyObject *_index,
       int start = static_cast<int>(PyLong_AsLong(slice_item));
       auto s_t = start;
       start = start < 0 ? start + dim_len : start;
-      if (start >= dim_len) {
+      if (start >= dim_len || start < 0) {
         std::string str_error_message =
             "The starting index " + std::to_string(s_t) +
             " of slice is out of bounds in tensor " + std::to_string(dim) +

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

@@ -413,10 +413,11 @@ class TestVarBase(unittest.TestCase):
         var13 = var[2:10, 2:, -2:-1]
         var14 = var[1:-1, 0:2, ::-1]
         var15 = var[::-1, ::-1, ::-1]
+        var16 = var[-4:4]
 
         vars = [
             var, var1, var2, var3, var4, var5, var6, var7, var8, var9, var10,
-            var11, var12, var13, var14, var15
+            var11, var12, var13, var14, var15, var16
         ]
         local_out = [var.numpy() for var in vars]
 
@@ -444,6 +445,7 @@ class TestVarBase(unittest.TestCase):
             np.array_equal(local_out[14], tensor_array[1:-1, 0:2, ::-1]))
         self.assertTrue(
             np.array_equal(local_out[15], tensor_array[::-1, ::-1, ::-1]))
+        self.assertTrue(np.array_equal(local_out[16], tensor_array[-4:4]))
 
     def _test_for_var(self):
         np_value = np.random.random((30, 100, 100)).astype('float32')
@@ -464,6 +466,9 @@ class TestVarBase(unittest.TestCase):
             with self.assertRaises(IndexError):
                 y = var[self.shape[0]]
 
+            with self.assertRaises(IndexError):
+                y = var[0 - self.shape[0] - 1]
+
     def test_var_base_to_np(self):
         with fluid.dygraph.guard():
             var = fluid.dygraph.to_variable(self.array)