metal : allow ops to run concurrently (#15929)

* metal : run graphs ops concurrently

ggml-ci

* cont : add flags for debugging and disabling concurrency

ggml-ci

* cont : refactor and handle fusing

ggml-ci

* cont : simplify - no need to use GPU address

ggml-ci

* cont : prepare mem ranges for reuse + add ggml-metal-common.cpp

ggml-ci

* cont : avoid redundant keywords in cpp [no ci]

* metal : reorder graph for better concurrency

ggml-ci

* metal : fix race on mem pool buffers

ggml-ci

* cont : add env GGML_METAL_GRAPH_OPTIMIZE_DISABLE

ggml-ci

* cont : refactor, optimize, add comments

ggml-ci

* cont : refactor ggml-metal.m

ggml-ci

* minor : update logs [no ci]

ggml/src/ggml-metal/ggml-metal-common.h

@@ -0,0 +1,52 @@
+// helper functions for ggml-metal that are too difficult to implement in Objective-C
+
+#pragma once
+
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct ggml_tensor;
+struct ggml_cgraph;
+
+enum ggml_mem_range_type {
+    MEM_RANGE_TYPE_SRC = 0,
+    MEM_RANGE_TYPE_DST = 1,
+};
+
+// a helper object that can be used for reordering operations to improve concurrency
+//
+// the fundamental idea is that a set of tasks (either ggml ops, or something else) can run concurrently if they
+//   don't write to a memory that is being read by another task or written to by another task in the set
+//
+// with this structure, we can add tasks to the set, setting memory constraints. we can also check if a new task
+//   can be added to the set without violating the constraints (i.e. if it can be executed concurrently with the
+//   tasks already in the set)
+//
+struct ggml_mem_ranges;
+
+struct ggml_mem_ranges * ggml_mem_ranges_init(int debug);
+void ggml_mem_ranges_free(struct ggml_mem_ranges * mrs);
+
+// remove all ranges from the set
+void ggml_mem_ranges_reset(struct ggml_mem_ranges * mrs);
+
+// add src or dst ranges to track
+bool ggml_mem_ranges_add(struct ggml_mem_ranges * mrs, const struct ggml_tensor * tensor);
+
+// return false if:
+// - new src range overlaps with any existing dst range
+// - new dst range overlaps with any existing range (src or dst)
+bool ggml_mem_ranges_check(const struct ggml_mem_ranges * mrs, const struct ggml_tensor * tensor);
+
+// reorder the nodes in the graph to improve concurrency, while respecting fusion
+//
+// note: this implementation is generic and not specific to metal
+//       if it proves to work well, we can start using it for other backends in the future
+void ggml_metal_graph_optimize(struct ggml_cgraph * gf);
+
+#ifdef __cplusplus
+}
+#endif