[clang] [llvm] [Offload] Change unregister library to use `atexit` instead of destructor (PR #86830)

[Joseph Huber via cfe-commits]

================
@@ -186,57 +186,62 @@ GlobalVariable *createBinDesc(Module &M, ArrayRef<ArrayRef<char>> Bufs,
                             ".omp_offloading.descriptor" + Suffix);
 }
 
-void createRegisterFunction(Module &M, GlobalVariable *BinDesc,
-                            StringRef Suffix) {
+Function *createUnregisterFunction(Module &M, GlobalVariable *BinDesc,
+                                   StringRef Suffix) {
   LLVMContext &C = M.getContext();
   auto *FuncTy = FunctionType::get(Type::getVoidTy(C), /*isVarArg*/ false);
-  auto *Func = Function::Create(FuncTy, GlobalValue::InternalLinkage,
-                                ".omp_offloading.descriptor_reg" + Suffix, &M);
+  auto *Func =
+      Function::Create(FuncTy, GlobalValue::InternalLinkage,
+                       ".omp_offloading.descriptor_unreg" + Suffix, &M);
   Func->setSection(".text.startup");
 
-  // Get __tgt_register_lib function declaration.
-  auto *RegFuncTy = FunctionType::get(Type::getVoidTy(C), getBinDescPtrTy(M),
-                                      /*isVarArg*/ false);
-  FunctionCallee RegFuncC =
-      M.getOrInsertFunction("__tgt_register_lib", RegFuncTy);
+  // Get __tgt_unregister_lib function declaration.
+  auto *UnRegFuncTy = FunctionType::get(Type::getVoidTy(C), getBinDescPtrTy(M),
+                                        /*isVarArg*/ false);
+  FunctionCallee UnRegFuncC =
+      M.getOrInsertFunction("__tgt_unregister_lib", UnRegFuncTy);
 
   // Construct function body
   IRBuilder<> Builder(BasicBlock::Create(C, "entry", Func));
-  Builder.CreateCall(RegFuncC, BinDesc);
+  Builder.CreateCall(UnRegFuncC, BinDesc);
   Builder.CreateRetVoid();
 
-  // Add this function to constructors.
-  // Set priority to 1 so that __tgt_register_lib is executed AFTER
-  // __tgt_register_requires (we want to know what requirements have been
-  // asked for before we load a libomptarget plugin so that by the time the
-  // plugin is loaded it can report how many devices there are which can
-  // satisfy these requirements).
-  appendToGlobalCtors(M, Func, /*Priority*/ 1);
+  return Func;
 }
 
-void createUnregisterFunction(Module &M, GlobalVariable *BinDesc,
-                              StringRef Suffix) {
+void createRegisterFunction(Module &M, GlobalVariable *BinDesc,
+                            StringRef Suffix) {
   LLVMContext &C = M.getContext();
   auto *FuncTy = FunctionType::get(Type::getVoidTy(C), /*isVarArg*/ false);
-  auto *Func =
-      Function::Create(FuncTy, GlobalValue::InternalLinkage,
-                       ".omp_offloading.descriptor_unreg" + Suffix, &M);
+  auto *Func = Function::Create(FuncTy, GlobalValue::InternalLinkage,
+                                ".omp_offloading.descriptor_reg" + Suffix, &M);
   Func->setSection(".text.startup");
 
-  // Get __tgt_unregister_lib function declaration.
-  auto *UnRegFuncTy = FunctionType::get(Type::getVoidTy(C), getBinDescPtrTy(M),
-                                        /*isVarArg*/ false);
-  FunctionCallee UnRegFuncC =
-      M.getOrInsertFunction("__tgt_unregister_lib", UnRegFuncTy);
+  // Get __tgt_register_lib function declaration.
+  auto *RegFuncTy = FunctionType::get(Type::getVoidTy(C), getBinDescPtrTy(M),
+                                      /*isVarArg*/ false);
+  FunctionCallee RegFuncC =
+      M.getOrInsertFunction("__tgt_register_lib", RegFuncTy);
+
+  auto *AtExitTy = FunctionType::get(
+      Type::getInt32Ty(C), PointerType::getUnqual(C), /*isVarArg=*/false);
+  FunctionCallee AtExit = M.getOrInsertFunction("atexit", AtExitTy);
+
+  Function *UnregFunc = createUnregisterFunction(M, BinDesc, Suffix);
 
   // Construct function body
   IRBuilder<> Builder(BasicBlock::Create(C, "entry", Func));
-  Builder.CreateCall(UnRegFuncC, BinDesc);
+
+  // Register the destructors with 'atexit', This is expected by the CUDA
----------------
jhuber6 wrote:

I think that's actually in this file somewhere for the CUDA wrapper portion.

https://github.com/llvm/llvm-project/pull/86830