Fix wrong idx bug in invertible LayerNormBackward1 (#692)

* fix wrong idx bug in invertible LayerNormBackward1

this index bug cause wrong scale grad

* fix unexpected deletion

* fix idx for LayerNormBackward1_fused_add

* move pos defination in LayerNormBackward1 kernels

* fix format error
Co-authored-by: NReza Yazdani <reyazda@microsoft.com>

csrc/transformer/normalize_kernels.cu

@@ -624,9 +624,8 @@ __global__ void LayerNormBackward1(const T* __restrict__ out_grad,
     int offset = threadIdx.y * width + idx;
     int y_stride = width * TILE_DIM;
 
-    int pos = blockIdx.x * TILE_DIM + threadIdx.y;
-    float betta_reg = (invertible ? (float)betta[pos] : 0.0f);
-    float gamma_reg = (float)gamma[pos];
+    float betta_reg = (invertible ? (float)betta[idx] : 0.0f);
+    float gamma_reg = (float)gamma[idx];
 
     // Loop across matrix height
     float betta_tmp = 0;
@@ -660,6 +659,7 @@ __global__ void LayerNormBackward1(const T* __restrict__ out_grad,
     }
 
     if (threadIdx.x == 0) {
+        int pos = blockIdx.x * TILE_DIM + threadIdx.y;
         betta_grad[pos] = s1;
         gamma_grad[pos] = s2;
     }
@@ -1368,9 +1368,8 @@ __global__ void LayerNormBackward1_fused_add(const T* __restrict__ out_grad1,
     int offset = threadIdx.y * width + idx;
     int y_stride = width * TILE_DIM;
 
-    int pos = blockIdx.x * TILE_DIM + threadIdx.y;
-    float betta_reg = (invertible ? (float)betta[pos] : 0.0f);
-    float gamma_reg = (float)gamma[pos];
+    float betta_reg = (invertible ? (float)betta[idx] : 0.0f);
+    float gamma_reg = (float)gamma[idx];
 
     // Loop across matrix height
     float betta_tmp = 0;
@@ -1404,6 +1403,7 @@ __global__ void LayerNormBackward1_fused_add(const T* __restrict__ out_grad1,
     }
 
     if (threadIdx.x == 0) {
+        int pos = blockIdx.x * TILE_DIM + threadIdx.y;
         betta_grad[pos] = s1;
         gamma_grad[pos] = s2;
     }