rename gelu_backward to gelu_backward_inplace, and made it obvious in…

… the code that this is an inplace operation

train_gpt2.cu

@@ -942,12 +942,12 @@ __global__ void gelu_forward_kernel2(floatX* out, const floatX* inp) {
     store128(out + idx, packed_out);
 }
 
-__global__ void gelu_backward_kernel(floatX* dinp, const floatX* inp, const floatX* dout) {
+__global__ void gelu_backward_inplace_kernel(floatX* d_in_out, const floatX* inp) {
     int idx = (blockIdx.x * blockDim.x + threadIdx.x) * x128::size;
 
     x128 packed_dinp;
     x128 packed_inp = load128cs(inp + idx);
-    x128 packed_dout = load128cs(dout + idx);
+    x128 packed_dout = load128(d_in_out + idx);
     for (int k = 0; k < packed_inp.size; ++k) {
         float x = (float)packed_inp[k];
         float cube = 0.044715f * x * x * x;
@@ -958,7 +958,7 @@ __global__ void gelu_backward_kernel(floatX* dinp, const floatX* inp, const floa
         float local_grad = 0.5f * (1.0f + tanh_out) + x * 0.5f * sech_out * GELU_SCALING_FACTOR * (1.0f + 3.0f * 0.044715f * x * x);
         packed_dinp[k] = (floatX)(local_grad * (float)packed_dout[k]);
     }
-    store128(dinp + idx, packed_dinp);
+    store128(d_in_out + idx, packed_dinp);
 }
 
 template<typename OutFloat, bool UseAuxBuffer>
@@ -1747,12 +1747,12 @@ void gelu_forward(floatX* out, const floatX* inp, int N) {
     cudaCheck(cudaGetLastError());
 }
 
-void gelu_backward(floatX* dinp, const floatX* inp, const floatX* dout, const int N) {
+void gelu_backward_inplace(floatX* d_in_out, const floatX* inp, const int N) {
     NVTX_RANGE_FN();
     const int block_size = 128;
     assert(N % block_size == 0);
     const int grid_size = CEIL_DIV(N, block_size * x128::size);
-    gelu_backward_kernel<<<grid_size, block_size>>>(dinp, inp, dout);
+    gelu_backward_inplace_kernel<<<grid_size, block_size>>>(d_in_out, inp);
     cudaCheck(cudaGetLastError());
 }
 
@@ -2660,7 +2660,7 @@ void gpt2_backward(GPT2 *model, int* inputs) {
             gelu_forward(l_fch_gelu, l_fch, B*T*4*C);
         }
         matmul_backward(dl_bt4c, dl_fcprojw, dl_fcprojb, dresidual, l_fch_gelu, l_fcprojw, scratchF, B, T, 4*C, C);
-        gelu_backward(dl_bt4c, l_fch, dl_bt4c, B*T*4*C);
+        gelu_backward_inplace(dl_bt4c, l_fch, B*T*4*C);
         if(model->recompute >= 2) {
             // same as gelu above, l_ln1 and l_ln2 are just buffers if recompute >= 2, recompute them here on demand
             layernorm_forward(l_ln2, l_ln2_mean, l_ln2_rstd, l_residual2, l_ln2w, l_ln2b, B, T, C);