[SYCL] Fix LastDeviceIds assignment for Platform w/o device (#5695)

When platform has no devices LastDeviceIds[] for the platform will stay 0 that will affect device enumeration for the next platforms.
Now we do adjustment if no devices for platform was obtained from backend.

Testing: issue is found/partly covered by E2E test in llvm-test_suite/SYCL/Regression/device_num.cpp
Signed-off-by: Tikhomirova, Kseniya <[email protected]>

Author: KseniyaTikhomirova

sycl/source/detail/platform_impl.cpp

@@ -255,8 +255,23 @@ platform_impl::get_devices(info::device_type DeviceType) const {
       MPlatform, pi::cast<RT::PiDeviceType>(DeviceType), 0,
       pi::cast<RT::PiDevice *>(nullptr), &NumDevices);
 
-  if (NumDevices == 0)
+  if (NumDevices == 0) {
+    // If platform doesn't have devices (even without filter)
+    // LastDeviceIds[PlatformId] stay 0 that affects next platform devices num
+    // analysis. Doing adjustment by simple copy of last device num from
+    // previous platform.
+    // Needs non const plugin reference.
+    std::vector<plugin> &Plugins = RT::initialize();
+    auto It = std::find_if(Plugins.begin(), Plugins.end(),
+                           [&Platform = MPlatform](plugin &Plugin) {
+                             return Plugin.containsPiPlatform(Platform);
+                           });
+    if (It != Plugins.end()) {
+      std::lock_guard<std::mutex> Guard(*(It->getPluginMutex()));
+      (*It).adjustLastDeviceId(MPlatform);
+    }
     return Res;
+  }
 
   std::vector<RT::PiDevice> PiDevices(NumDevices);
   // TODO catch an exception and put it to list of asynchronous exceptions

sycl/source/detail/plugin.hpp

@@ -238,6 +238,16 @@ class plugin {
     LastDeviceIds[PlatformId] = Id;
   }
 
+  // Adjust the id of the last device for the given platform.
+  // Involved when there is no device on that platform at all.
+  // The function is expected to be called in a thread safe manner.
+  void adjustLastDeviceId(RT::PiPlatform Platform) {
+    int PlatformId = getPlatformId(Platform);
+    if (PlatformId > 0 &&
+        LastDeviceIds[PlatformId] < LastDeviceIds[PlatformId - 1])
+      LastDeviceIds[PlatformId] = LastDeviceIds[PlatformId - 1];
+  }
+
   bool containsPiPlatform(RT::PiPlatform Platform) {
     auto It = std::find(PiPlatforms.begin(), PiPlatforms.end(), Platform);
     return It != PiPlatforms.end();