method_meta add uses_backend function (#8198)

Summary:

For a runtime that supports models of a couple different types it helps to be able to check ahead of time whether certain backend types are present. In our case, there are processors that can use this information to make scheduling decisions without having the actual required backend implementations present.

Reviewed By: dbort

Differential Revision: D69143825

Author: cmt0

runtime/executor/method_meta.cpp

@@ -228,6 +228,17 @@ Result<int64_t> MethodMeta::memory_planned_buffer_size(size_t index) const {
   return s_plan_->non_const_buffer_sizes()->Get(index + 1);
 }
 
+bool MethodMeta::uses_backend(const char* backend_name) const {
+  const auto delegates = s_plan_->delegates();
+  for (size_t i = 0; i < delegates->size(); i++) {
+    auto delegate = delegates->Get(i);
+    if (strcmp(delegate->id()->c_str(), backend_name) == 0) {
+      return true;
+    }
+  }
+  return false;
+}
+
 size_t MethodMeta::num_instructions() const {
   const auto chains = s_plan_->chains();
   if (chains == nullptr) {

runtime/executor/method_meta.h

@@ -180,11 +180,19 @@ class MethodMeta final {
   /**
    * Get the size in bytes of the specified memory-planned buffer.
    *
-   * @param[in] index The index of the buffer to look up.
+   * [in] index The index of the buffer to look up.
    * @returns The size in bytes on success, or an error on failure.
    */
   Result<int64_t> memory_planned_buffer_size(size_t index) const;
 
+  /**
+   * Check to see if a backend is used in this method.
+   *
+   * @param[in] backend_name The name of the backend to search for.
+   * @returns true if a backend is used in this method, otherwise false.
+   */
+  bool uses_backend(const char* backend_name) const;
+
   /**
    * Get the number of instructions in this method.
    *

runtime/executor/test/backend_integration_test.cpp

@@ -338,6 +338,10 @@ TEST_P(BackendIntegrationTest, BasicInitSucceeds) {
   Result<Program> program = Program::load(&loader.get());
   ASSERT_EQ(program.error(), Error::Ok);
 
+  auto method_meta = program->method_meta("forward");
+  EXPECT_EQ(method_meta->uses_backend(StubBackend::kName), true);
+  EXPECT_EQ(method_meta->uses_backend("INVALID_BACKEND_NAME"), false);
+
   ManagedMemoryManager mmm(kDefaultNonConstMemBytes, kDefaultRuntimeMemBytes);
   Result<Method> method_res = program->load_method("forward", &mmm.get());
   EXPECT_EQ(method_res.error(), Error::Ok);