From 65b0561637511d3565c4b6f3d48dac4e28690241 Mon Sep 17 00:00:00 2001
From: xaedes <xaedes@gmail.com>
Date: Fri, 18 Aug 2023 20:25:03 +0200
Subject: [PATCH] remove unnecessary src tensor from ggml_get_rows_back

we don't need data of src[2] for computation, only to setup the correct output shape.
remove dependency on src[2], so that allocator can work more freely.

the computational graph is still completely determined, because the output shape is naturally included.
this is similar to how ggml_reshape does it.
---
 ggml.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/ggml.c b/ggml.c
index 90b610721..24f06b4ca 100644
--- a/ggml.c
+++ b/ggml.c
@@ -6564,7 +6564,9 @@ struct ggml_tensor * ggml_get_rows_back(
     result->grad = is_node ? ggml_dup_tensor(ctx, result) : NULL;
     result->src[0] = a;
     result->src[1] = b;
-    result->src[2] = c;
+    // we don't need data of c for computation, only to setup the correct output shape.
+    // break dependency on c, so that allocator can work more freely.
+    //result->src[2] = c;
 
     return result;
 }
@@ -11282,14 +11284,15 @@ static void ggml_compute_forward_get_rows_back_f32_f16(
         const struct ggml_compute_params * params,
         const struct ggml_tensor * src0,
         const struct ggml_tensor * src1,
-        const struct ggml_tensor * opt0,
               struct ggml_tensor * dst) {
     GGML_ASSERT(params->ith == 0);
-    GGML_ASSERT(ggml_are_same_shape(opt0, dst));
-    GGML_ASSERT(ggml_is_contiguous(opt0));
     GGML_ASSERT(ggml_is_contiguous(dst));
 
-    ggml_compute_forward_dup_same_cont(params, opt0, dst);
+    // ggml_compute_forward_dup_same_cont(params, opt0, dst);
+
+    if (params->type == GGML_TASK_INIT) {
+        memset(dst->data, 0, ggml_nbytes(dst));
+    }
 
     if (params->type == GGML_TASK_INIT || params->type == GGML_TASK_FINALIZE) {
         return;
@@ -11315,11 +11318,8 @@ static void ggml_compute_forward_get_rows_back_f32(
         const struct ggml_compute_params * params,
         const struct ggml_tensor * src0,
         const struct ggml_tensor * src1,
-        const struct ggml_tensor * opt0,
               struct ggml_tensor * dst) {
     GGML_ASSERT(params->ith == 0);
-    GGML_ASSERT(ggml_are_same_shape(opt0, dst));
-    GGML_ASSERT(ggml_is_contiguous(opt0));
     GGML_ASSERT(ggml_is_contiguous(dst));
 
     // ggml_compute_forward_dup_same_cont(params, opt0, dst);
@@ -11353,16 +11353,15 @@ static void ggml_compute_forward_get_rows_back(
         const struct ggml_compute_params * params,
         const struct ggml_tensor * src0,
         const struct ggml_tensor * src1,
-        const struct ggml_tensor * opt0,
         struct ggml_tensor * dst) {
     switch (src0->type) {
         case GGML_TYPE_F16:
             {
-                ggml_compute_forward_get_rows_back_f32_f16(params, src0, src1, opt0, dst);
+                ggml_compute_forward_get_rows_back_f32_f16(params, src0, src1, dst);
             } break;
         case GGML_TYPE_F32:
             {
-                ggml_compute_forward_get_rows_back_f32(params, src0, src1, opt0, dst);
+                ggml_compute_forward_get_rows_back_f32(params, src0, src1, dst);
             } break;
         default:
             {
@@ -14867,7 +14866,7 @@ static void ggml_compute_forward(struct ggml_compute_params * params, struct ggm
             } break;
         case GGML_OP_GET_ROWS_BACK:
             {
-                ggml_compute_forward_get_rows_back(params, tensor->src[0], tensor->src[1], tensor->src[2], tensor);
+                ggml_compute_forward_get_rows_back(params, tensor->src[0], tensor->src[1], tensor);
             } break;
         case GGML_OP_DIAG:
             {
@@ -15524,6 +15523,8 @@ static void ggml_compute_backward(struct ggml_context * ctx, struct ggml_tensor
                 if (src0->grad) {
                     src0->grad =
                         ggml_add_or_set(ctx, src0->grad,
+                            // last ggml_get_rows_back argument src0->grad is only 
+                            // necessary to setup correct output shape
                             ggml_get_rows_back(ctx, tensor->grad, src1, src0->grad),
                         zero_table);
                 }