kv-cache : support layer reuse (#15504)

* kv-cache : support layer reuse

ggml-ci

* cont : update comments [no ci]

src/llama-hparams.cpp

@@ -153,3 +153,28 @@ bool llama_hparams::is_swa(uint32_t il) const {
 
     GGML_ABORT("fatal error");
 }
+
+bool llama_hparams::has_kv(uint32_t il) const {
+    if (n_layer_kv_from_start >= 0) {
+        if (il < (uint32_t) n_layer_kv_from_start) {
+            return true;
+        }
+
+        return false;
+    }
+
+    // by default, all layers have kv
+    return true;
+}
+
+uint32_t llama_hparams::n_layer_kv() const {
+    uint32_t res = 0;
+
+    for (uint32_t il = 0; il < n_layer; ++il) {
+        if (has_kv(il)) {
+            res++;
+        }
+    }
+
+    return res;
+}