Consistently handle algorithm selection in GemmAlgorithmPicker

PiperOrigin-RevId: 618789520

xla/service/gpu/gemm_algorithm_picker.cc

@@ -417,15 +417,28 @@ absl::StatusOr<bool> RunOnInstruction(HloInstruction* gemm,
                  config.GetGpuComputeCapability());
 
   if (update_algorithm) {
+    int64_t new_algorithm{};
     if (algorithm.has_gemm()) {
-      backend_config.set_selected_algorithm(algorithm.gemm().algorithm());
+      new_algorithm = algorithm.gemm().algorithm();
     } else {
       // NOTE: runtime autotuning is no longer available => set to default
-      backend_config.set_selected_algorithm(se::blas::kDefaultAlgorithm);
+      new_algorithm = se::blas::kDefaultAlgorithm;
     }
+
+    if (new_algorithm == old_algorithm &&
+        backend_config.has_selected_algorithm()) {
+      // We don't need to update the backend config if
+      // the algorithm hasn't changed unless previously
+      // the algorithm wasn't set explicitly.
+      return false;
+    }
+
+    backend_config.set_selected_algorithm(new_algorithm);
+    TF_RETURN_IF_ERROR(gemm->set_backend_config(gpu_config));
+    return true;  // We changed `gemm`
   }
-  TF_RETURN_IF_ERROR(gemm->set_backend_config(gpu_config));
-  return old_algorithm != backend_config.selected_algorithm();
+
+  return false;  // No change to `gemm`
 }
 
 absl::StatusOr<bool> RunOnComputation(HloComputation* computation,