[clang] [llvm] [HLSL] Add handle initialization for simple resource declarations (PR #111207)

[Damyan Pepper via cfe-commits]

================
@@ -489,3 +494,100 @@ void CGHLSLRuntime::generateGlobalCtorDtorCalls() {
       GV->eraseFromParent();
   }
 }
+
+// Returns handle type of a resource, if the type is a resource
+// or an array of resources
+static const HLSLAttributedResourceType *findHandleTypeOnResource(QualType QT) {
+  // If the type is a resource class, the first field must
+  // be the resource handle of type HLSLAttributedResourceType
+  const clang::Type *Ty = QT->getUnqualifiedDesugaredType();
+  if (RecordDecl *RD = Ty->getAsCXXRecordDecl()) {
+    if (!RD->fields().empty()) {
+      const auto &FirstFD = RD->fields().begin();
+      return dyn_cast<HLSLAttributedResourceType>(
+          FirstFD->getType().getTypePtr());
+    }
+  }
+  return nullptr;
+}
+
+void CGHLSLRuntime::handleGlobalVarDefinition(const VarDecl *VD,
+                                              llvm::GlobalVariable *Var) {
+  // If the global variable has resource binding, add it to the list of globals
+  // that need resource binding initialization.
+  const HLSLResourceBindingAttr *RBA = VD->getAttr<HLSLResourceBindingAttr>();
+  if (!RBA)
+    return;
+
+  if (!findHandleTypeOnResource(VD->getType()))
+    // FIXME: Only simple declarations of resources are supported for now.
+    // Arrays of resources or resources in user defined classes are
+    // not implemented yet.
+    return;
+
+  ResourcesToBind.emplace_back(std::make_pair(VD, Var));
+}
+
+llvm::Function *CGHLSLRuntime::createResourceBindingInitFn() {
+  // No resources to bind
+  if (ResourcesToBind.empty())
+    return nullptr;
+
+  LLVMContext &Ctx = CGM.getLLVMContext();
+
+  llvm::Function *InitResBindingsFunc =
+      llvm::Function::Create(llvm::FunctionType::get(CGM.VoidTy, false),
+                             llvm::GlobalValue::InternalLinkage,
+                             "_init_resource_bindings", CGM.getModule());
+
+  llvm::BasicBlock *EntryBB =
+      llvm::BasicBlock::Create(Ctx, "entry", InitResBindingsFunc);
+  CGBuilderTy Builder(CGM, Ctx);
+  const DataLayout &DL = CGM.getModule().getDataLayout();
+  Builder.SetInsertPoint(EntryBB);
+
+  for (auto I : ResourcesToBind) {
----------------
damyanp wrote:

```suggestion
  for (const auto &I : ResourcesToBind) {
```

Since ResourcesToBind's element type is a pair of pointers it probably doesn't make a real performance difference here, but whenever I see a `for (auto X : Foo)` pattern it rings alarm bells for me that someone might accidentally be copying values they didn't intend to copy, so I have to go look.

https://github.com/llvm/llvm-project/pull/111207