use IndexList to improve performance of instance_norm op (#25132)

* use IndexList to improve performance, test=develop

* remove EIGEN_HAS_INDEX_LIST, test=develop

* use IndexList only when EIGEN_HAS_INDEX_LIST is true

paddle/fluid/operators/instance_norm_op.cc

@@ -181,10 +181,22 @@ class InstanceNormKernel<platform::CPUDeviceContext, T>
     auto &dev_ctx = ctx.template device_context<platform::CPUDeviceContext>();
     auto *place = dev_ctx.eigen_device();
 
+    Eigen::DSizes<int, 2> shape(NxC, sample_size);
+// Once eigen on Windows is updated, the if branch can be removed.
+#ifndef EIGEN_HAS_INDEX_LIST
     Eigen::DSizes<int, 2> bcast(1, sample_size);
     Eigen::DSizes<int, 2> C_shape(C, 1);
     Eigen::DSizes<int, 2> NxC_shape(NxC, 1);
-    Eigen::DSizes<int, 2> shape(NxC, sample_size);
+    Eigen::DSizes<int, 1> rdims(1);
+#else
+    Eigen::IndexList<Eigen::type2index<1>, int> bcast;
+    bcast.set(1, sample_size);
+    Eigen::IndexList<int, Eigen::type2index<1>> C_shape;
+    C_shape.set(0, C);
+    Eigen::IndexList<int, Eigen::type2index<1>> NxC_shape;
+    NxC_shape.set(0, NxC);
+    Eigen::IndexList<Eigen::type2index<1>> rdims;
+#endif
 
     math::SetConstant<platform::CPUDeviceContext, T> set_constant;
 
@@ -201,8 +213,6 @@ class InstanceNormKernel<platform::CPUDeviceContext, T>
     auto x_e = framework::EigenVector<T>::Flatten(*x);
     auto x_arr = x_e.reshape(shape);
 
-    Eigen::DSizes<int, 1> rdims(1);
-
     saved_mean_e.device(*place) = x_arr.mean(rdims);
     auto saved_variance_arr =
         (x_arr - saved_mean_e.broadcast(bcast)).square().mean(rdims) + epsilon;
@@ -316,14 +326,25 @@ class InstanceNormGradKernel<platform::CPUDeviceContext, T>
     auto &dev_ctx = ctx.template device_context<platform::CPUDeviceContext>();
     auto *place = dev_ctx.eigen_device();
 
+    Eigen::DSizes<int, 2> rshape(NxC, sample_size);
+    Eigen::DSizes<int, 2> param_shape(N, C);
+    Eigen::DSizes<int, 2> shape(NxC, sample_size);
+#ifndef EIGEN_HAS_INDEX_LIST
     Eigen::DSizes<int, 1> rdims(0);
     Eigen::DSizes<int, 1> mean_rdims(1);
-    Eigen::DSizes<int, 2> rshape(NxC, sample_size);
     Eigen::DSizes<int, 2> bcast(1, sample_size);
     Eigen::DSizes<int, 2> C_shape(C, 1);
     Eigen::DSizes<int, 2> NxC_shape(NxC, 1);
-    Eigen::DSizes<int, 2> param_shape(N, C);
-    Eigen::DSizes<int, 2> shape(NxC, sample_size);
+#else
+    Eigen::IndexList<Eigen::type2index<0>> rdims;
+    Eigen::IndexList<Eigen::type2index<1>> mean_rdims;
+    Eigen::IndexList<Eigen::type2index<1>, int> bcast;
+    bcast.set(1, sample_size);
+    Eigen::IndexList<int, Eigen::type2index<1>> C_shape;
+    C_shape.set(0, C);
+    Eigen::IndexList<int, Eigen::type2index<1>> NxC_shape;
+    NxC_shape.set(0, NxC);
+#endif
 
     math::SetConstant<platform::CPUDeviceContext, T> set_constant;