[IDAG] do not select devices from multiple platforms

include/device_selection.h

@@ -67,7 +67,8 @@ auto pick_devices(const config& cfg, const DevicesOrSelector& user_devices_or_se
 		}
 
 		const auto select_all = [platforms](auto& selector) {
-			std::unordered_map<BackendT, std::vector<std::pair<DeviceT, size_t>>> scored_devices_by_backend;
+			std::unordered_map<std::pair<size_t /* index in platforms[] */, BackendT>, std::vector<std::pair<DeviceT, size_t /* score */>>, utils::pair_hash>
+			    scored_devices_by_platform_and_backend;
 			for(size_t i = 0; i < platforms.size(); ++i) {
 				const auto devices = platforms[i].get_devices(sycl::info::device_type::all);
 				for(size_t j = 0; j < devices.size(); ++j) {
@@ -79,12 +80,12 @@ auto pick_devices(const config& cfg, const DevicesOrSelector& user_devices_or_se
 					}
 					const auto score = selector(devices[j]);
 					if(score < 0) continue;
-					scored_devices_by_backend[devices[j].get_backend()].push_back(std::pair{devices[j], score});
+					scored_devices_by_platform_and_backend[{i, devices[j].get_backend()}].push_back(std::pair{devices[j], score});
 				}
 			}
 			size_t max_score = 0;
 			std::vector<DeviceT> max_score_devices;
-			for(auto& [backend, scored_devices] : scored_devices_by_backend) {
+			for(auto& [platform_and_backend, scored_devices] : scored_devices_by_platform_and_backend) {
 				size_t sum_score = 0;
 				std::vector<DeviceT> devices;
 				for(auto& [d, score] : scored_devices) {