[CINN]fix bug in cinn stack op_mapper (PaddlePaddle#57307)

fix bug in cinn stack op_mapper, the output shape is wrong when axis < 0

paddle/cinn/frontend/op_mappers/paddle/concat.cc

@@ -67,11 +67,23 @@ void StackOpMapper(const paddle::cpp::OpDesc& op_desc,
                   "but here cannot found! Please check.";
   }
 
+  cinn::utils::ShapeType input_shape(ctx.GetVar(x_names.front())->shape);
   auto axis = utils::GetAttrOrDefault<int>(op_desc, "axis", 0);
+  axis = axis >= 0 ? axis : axis + input_shape.size() + 1;
+  cinn::utils::ShapeType output_shape(input_shape);
+  output_shape.insert(output_shape.begin() + axis, 1);
 
   std::vector<Variable> xs;
   for (const auto& name : x_names) {
-    xs.emplace_back(ctx.GetVar(name));
+    auto x = ctx.GetVar(name);
+    CHECK(x->shape == input_shape)
+        << "All input shape of [stack] should be the same, be the input "
+        << x->id << "'s shape [" << cinn::utils::Join(x->shape, ", ")
+        << "] not equal to "
+        << "the first input " << ctx.GetVar(x_names.front())->id << "'s shape ["
+        << cinn::utils::Join(input_shape, ", ") << "]";
+
+    xs.emplace_back(ctx.Builder()->Reshape(x, output_shape));
   }
 
   auto err_x = std::find_if(xs.begin(), xs.end(), [&](Variable x) {
@@ -83,39 +95,10 @@ void StackOpMapper(const paddle::cpp::OpDesc& op_desc,
       << "] not equal to the first input " << xs.front()->id << "'s dtype ["
       << xs.front()->type << "]";
 
-  err_x = std::find_if(xs.begin(), xs.end(), [&](Variable x) {
-    return x->shape != xs.front()->shape;
-  });
-  CHECK(err_x == xs.end())
-      << "All input shape of [stack] should be the same, be the input "
-      << (*err_x)->id << "'s shape ["
-      << cinn::utils::Join((*err_x)->shape, ", ") << "] not equal to "
-      << "the first input " << xs.front()->id << "'s shape ["
-      << cinn::utils::Join(xs.front()->shape, ", ") << "]";
-
   auto concat_out = ctx.Builder()->Concat(xs, axis);
 
-  int rank = concat_out->shape.size();
-  axis = axis >= 0 ? axis : axis + rank;
-  CHECK(axis >= 0 && axis < rank)
-      << "The axis of stack should >=0 and <rank(x)! Please check.";
-
-  // N * [A, B] with axis=0 --> [N, A, B]; N * [A, B] with axis=1 --> [A, N, B];
-  cinn::utils::ShapeType new_shape;
-  for (int i = 0; i < rank; ++i) {
-    auto dim = concat_out->shape[i];
-    if (i != axis) {
-      new_shape.emplace_back(dim);
-    } else {
-      new_shape.emplace_back(xs.size());
-      // the shape same ensure `dim % xs.size() == 0`
-      new_shape.emplace_back(dim / xs.size());
-    }
-  }
-  auto out = ctx.Builder()->Reshape(concat_out, new_shape);
-
-  ctx.AddVar(out_name, out);
-  ctx.AddVarModelToProgram(out_name, out->id);
+  ctx.AddVar(out_name, concat_out);
+  ctx.AddVarModelToProgram(out_name, concat_out->id);
 }
 
 void SplitOpMapper(const paddle::cpp::OpDesc& op_desc,

test/cinn/op_mappers/test_stack_op.py

@@ -52,5 +52,10 @@ def test_check_results(self):
         self.check_outputs_and_grads()
 
 
+class TestStackOpAxisNegative(TestStackOp):
+    def set_op_attrs(self):
+        return {"axis": -1}
+
+
 if __name__ == "__main__":
     unittest.main()