[SYCL] Fix ESIMD_EMULATOR being picked as default device (#6870)

This commit attempts to fix the problem that occurs when the default
device selector picks the ESIMD_EMULATOR when other devices are
available.

Author: lbushi25

sycl/source/detail/filter_selector_impl.cpp

@@ -76,6 +76,8 @@ filter create_filter(const std::string &Input) {
       Result.Backend = backend::ext_oneapi_cuda;
     } else if (Token == "hip" && !Result.Backend) {
       Result.Backend = backend::ext_oneapi_hip;
+    } else if (Token == "esimd_emulator" && !Result.Backend) {
+      Result.Backend = backend::ext_intel_esimd_emulator;
     } else if (std::regex_match(Token, IntegerExpr) && !Result.DeviceNum) {
       try {
         Result.DeviceNum = std::stoi(Token);

sycl/source/detail/pi.cpp

@@ -283,8 +283,6 @@ std::vector<std::pair<std::string, backend>> findPlugins() {
                              backend::ext_oneapi_level_zero);
     PluginNames.emplace_back(__SYCL_CUDA_PLUGIN_NAME, backend::ext_oneapi_cuda);
     PluginNames.emplace_back(__SYCL_HIP_PLUGIN_NAME, backend::ext_oneapi_hip);
-    PluginNames.emplace_back(__SYCL_ESIMD_EMULATOR_PLUGIN_NAME,
-                             backend::ext_intel_esimd_emulator);
   } else {
     std::vector<device_filter> Filters = FilterList->get();
     bool OpenCLFound = false;
@@ -311,8 +309,7 @@ std::vector<std::pair<std::string, backend>> findPlugins() {
                                  backend::ext_oneapi_cuda);
         CudaFound = true;
       }
-      if (!EsimdCpuFound && (Backend == backend::ext_intel_esimd_emulator ||
-                             Backend == backend::all)) {
+      if (!EsimdCpuFound && Backend == backend::ext_intel_esimd_emulator) {
         PluginNames.emplace_back(__SYCL_ESIMD_EMULATOR_PLUGIN_NAME,
                                  backend::ext_intel_esimd_emulator);
         EsimdCpuFound = true;

sycl/source/device_selector.cpp

@@ -164,14 +164,22 @@ static void traceDeviceSelector(const std::string &DeviceType) {
   bool ShouldTrace = false;
   ShouldTrace = detail::pi::trace(detail::pi::TraceLevel::PI_TRACE_BASIC);
   if (ShouldTrace) {
-    std::cout << "SYCL_PI_TRACE[all]: Requested device_type: " << DeviceType << std::endl;
+    std::cout << "SYCL_PI_TRACE[all]: Requested device_type: " << DeviceType
+              << std::endl;
   }
 }
 
 __SYCL_EXPORT int default_selector_v(const device &dev) {
   // The default selector doesn't reject any devices.
   int Score = 0;
 
+  // we give the esimd_emulator device a score of zero to prevent it from being
+  // chosen among other devices. The same thing is done for gpu_selector_v
+  // below.
+  if (dev.get_backend() == backend::ext_intel_esimd_emulator) {
+    return 0;
+  }
+
   traceDeviceSelector("info::device_type::automatic");
   if (dev.get_info<info::device::device_type>() == detail::get_forced_type())
     Score += 2000;
@@ -197,6 +205,10 @@ __SYCL_EXPORT int default_selector_v(const device &dev) {
 __SYCL_EXPORT int gpu_selector_v(const device &dev) {
   int Score = detail::REJECT_DEVICE_SCORE;
 
+  if (dev.get_backend() == backend::ext_intel_esimd_emulator) {
+    return 0;
+  }
+
   traceDeviceSelector("info::device_type::gpu");
   if (dev.is_gpu()) {
     Score = 1000;