[OpenMP] Fix initializer not working on AMDGPU

[jhuber6]

Summary

The RAII class used for debugging RTL entry used a shared variable to
keep track of the current depth. This used a global initializer, which
isn't supported on AMDGPU. This patch removes the initializer and
instead sets it to zero when the state is initialized in the runtime.

[jhuber6]

Put the debug init call in the wrong init function.

[jdoerfert]

LG, though racy, see comment.

openmp/libomptarget/DeviceRTL/src/State.cpp

370–372

Put it under this guard.

[JonChesterfield]

There's a recent (amdgpu specific I think) llvm pass that gathers ctor/dtor into one or more kernels that expect to be executed with one wavefront, possibly one thread active at the entry point. I'm aware of two bugs in it, one fixed and one with a patch outstanding. These aren't actually run by the amdgpu plugin yet but probably will be shortly. At least the constructors, I'm not clear how we would know when to run the destructors. At that point we could optionally revert this, looks good for now.

Moving one-off initialisation to a global ctor, once said ctor is actually executed by the plugin, is probably a minor performance win. Do some work once instead of once per kernel.

openmp/libomptarget/DeviceRTL/include/Debug.h

#define FunctionTracingRAII()                                                  \
   DebugEntryRAII Entry(__FILE__, __LINE__, __PRETTY_FUNCTION__);
 
 /// An RAII class for handling entries to debug locations. The current location
 /// and function will be printed on entry. Nested levels increase the
 /// indentation shown in the debugging output.
 struct DebugEntryRAII {
   DebugEntryRAII(const char *File, const unsigned Line, const char *Function);
   ~DebugEntryRAII();
+
+  static void init();
 };
 
 #endif

openmp/libomptarget/DeviceRTL/src/Debug.cpp

 #pragma omp end declare variant
 
 int32_t __llvm_omp_vprintf(const char *Format, void *Arguments, uint32_t Size) {
   return impl::omp_vprintf(Format, Arguments, Size);
 }
 }
 
 /// Current indentation level for the function trace. Only accessed by thread 0.
-static uint32_t Level = 0;
+static uint32_t Level;
 #pragma omp allocate(Level) allocator(omp_pteam_mem_alloc)
 
 DebugEntryRAII::DebugEntryRAII(const char *File, const unsigned Line,
                                const char *Function) {
   if (config::isDebugMode(config::DebugKind::FunctionTracing) &&
       mapping::getThreadIdInBlock() == 0 && mapping::getBlockId() == 0) {
 
     for (int I = 0; I < Level; ++I)
       PRINTF("%s", "  ");
 
     PRINTF("%s:%u: Thread %u Entering %s\n", File, Line,
            mapping::getThreadIdInBlock(), Function);
     Level++;
   }
 }
 
 DebugEntryRAII::~DebugEntryRAII() {
   if (config::isDebugMode(config::DebugKind::FunctionTracing) &&
       mapping::getThreadIdInBlock() == 0 && mapping::getBlockId() == 0)
     Level--;
 }
 
+void DebugEntryRAII::init() { Level = 0; }
+
 #pragma omp end declare target

openmp/libomptarget/DeviceRTL/src/State.cpp

void *&state::lookupPtr(ValueKind Kind, bool IsReadonly) {
   default:
     break;
   }
   __builtin_unreachable();
 }
 
 void state::init(bool IsSPMD) {
   SharedMemorySmartStack.init(IsSPMD);
-  if (mapping::isInitialThreadInLevel0(IsSPMD))
+  if (mapping::isInitialThreadInLevel0(IsSPMD)) {
     TeamState.init(IsSPMD);
+    DebugEntryRAII::init();
+  }
 
   ThreadStates[mapping::getThreadIdInBlock()] = nullptr;
 }
 
 void state::enterDataEnvironment() {
   unsigned TId = mapping::getThreadIdInBlock();
   ThreadStateTy *NewThreadState =
       static_cast<ThreadStateTy *>(__kmpc_alloc_shared(sizeof(ThreadStateTy)));