[SYCL] Add SYCL_PI_TRACE on loadOsLibrary (#5628)

Author: aobolensk

sycl/source/detail/posix_pi.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include <CL/sycl/detail/defines.hpp>
+#include <CL/sycl/detail/pi.hpp>
 
 #include <dlfcn.h>
 #include <string>
@@ -19,7 +20,12 @@ namespace pi {
 void *loadOsLibrary(const std::string &PluginPath) {
   // TODO: Check if the option RTLD_NOW is correct. Explore using
   // RTLD_DEEPBIND option when there are multiple plugins.
-  return dlopen(PluginPath.c_str(), RTLD_NOW);
+  void *so = dlopen(PluginPath.c_str(), RTLD_NOW);
+  if (!so && trace(TraceLevel::PI_TRACE_ALL)) {
+    std::cerr << "SYCL_PI_TRACE[-1]: dlopen(" << PluginPath << ") failed with <"
+              << dlerror() << ">" << std::endl;
+  }
+  return so;
 }
 
 int unloadOsLibrary(void *Library) { return dlclose(Library); }

sycl/test/basic_tests/library_loading.cpp

@@ -0,0 +1,16 @@
+// REQUIRES: linux
+// RUN: %clangxx -fsycl -fsycl-targets=%sycl_triple %s -o %t.out
+// RUN: env SYCL_PI_TRACE=-1 %t.out 2>&1 | FileCheck %s
+
+// Checks pi traces on library loading
+#include <CL/sycl.hpp>
+
+using namespace cl::sycl;
+
+int main() {
+  // CHECK: {{(SYCL_PI_TRACE\[-1\]: dlopen\(libpi_cuda.so\) failed with)|(SYCL_PI_TRACE\[basic\]: Plugin found and successfully loaded: libpi_cuda.so)}}
+  // CHECK: {{(SYCL_PI_TRACE\[-1\]: dlopen\(libpi_hip.so\) failed with)|(SYCL_PI_TRACE\[basic\]: Plugin found and successfully loaded: libpi_hip.so)}}
+  // CHECK: {{(SYCL_PI_TRACE\[-1\]: dlopen\(libpi_esimd_emulator.so\) failed with)|(SYCL_PI_TRACE\[basic\]: Plugin found and successfully loaded: libpi_esimd_emulator.so)}}
+  queue q;
+  q.submit([&](handler &cgh) {});
+}