test: fix OPT_STEP_ADAMW for test-backend-ops (ggml/974)

ggml/include/ggml.h

@@ -2052,6 +2052,7 @@ extern "C" {
     GGML_API struct ggml_tensor * ggml_opt_step_adamw(
             struct ggml_context * ctx,
             struct ggml_tensor  * a,
+            struct ggml_tensor  * grad,
             float                 alpha,
             float                 beta1,
             float                 beta2,

ggml/src/ggml.c

@@ -7818,12 +7818,14 @@ struct ggml_tensor * ggml_cross_entropy_loss_back(
 struct ggml_tensor * ggml_opt_step_adamw(
         struct ggml_context * ctx,
         struct ggml_tensor  * a,
+        struct ggml_tensor  * grad,
         float                 alpha,
         float                 beta1,
         float                 beta2,
         float                 eps,
         float                 wd) {
     GGML_ASSERT(a->flags & GGML_TENSOR_FLAG_PARAM);
+    GGML_ASSERT(ggml_are_same_shape(a, grad));
     GGML_ASSERT(alpha >  0.0f);
     GGML_ASSERT(beta1 >= 0.0f && beta1 <= 1.0f);
     GGML_ASSERT(beta2 >= 0.0f && beta2 <= 1.0f);
@@ -7842,9 +7844,9 @@ struct ggml_tensor * ggml_opt_step_adamw(
 
     result->op     = GGML_OP_OPT_STEP_ADAMW;
     result->src[0] = a;
-    result->src[1] = a->grad;
-    result->src[2] = ggml_dup_tensor(ctx, a);
-    result->src[3] = ggml_dup_tensor(ctx, a);
+    result->src[1] = grad;
+    result->src[2] = ggml_dup_tensor(ctx, grad);
+    result->src[3] = ggml_dup_tensor(ctx, grad);
 
     return result;
 }
@@ -18769,7 +18771,7 @@ void ggml_build_opt_adamw(
 
         if (node->flags & GGML_TENSOR_FLAG_PARAM) {
             GGML_PRINT_DEBUG("%s: found root node %p\n", __func__, (void *) node);
-            struct ggml_tensor * opt_step = ggml_opt_step_adamw(ctx, node, alpha, beta1, beta2, eps, wd);
+            struct ggml_tensor * opt_step = ggml_opt_step_adamw(ctx, node, node->grad, alpha, beta1, beta2, eps, wd);
             ggml_build_forward_expand(gb, opt_step);
         }
     }