IRGen: add a function suitable for emitting linker directive as global variable

Author: nkcsgexi

lib/IRGen/GenDecl.cpp

@@ -1929,6 +1929,49 @@ llvm::GlobalVariable *swift::irgen::createVariable(
   return var;
 }
 
+llvm::GlobalVariable *
+swift::irgen::createLinkerDirectiveVariable(IRGenModule &IGM, StringRef name) {
+
+  // A prefix of \1 can avoid further mangling of the symbol (prefixing _).
+  llvm::SmallString<32> NameWithFlag;
+  NameWithFlag.push_back('\1');
+  NameWithFlag.append(name);
+  name = NameWithFlag.str();
+  static const uint8_t Size = 8;
+  static const uint8_t Alignment = 8;
+
+  // Use a char type as the type for this linker directive.
+  auto ProperlySizedIntTy = SILType::getBuiltinIntegerType(
+      Size, IGM.getSwiftModule()->getASTContext());
+  auto storageType = IGM.getStorageType(ProperlySizedIntTy);
+
+  llvm::GlobalValue *existingValue = IGM.Module.getNamedGlobal(name);
+  if (existingValue) {
+    auto existingVar = dyn_cast<llvm::GlobalVariable>(existingValue);
+    if (existingVar && isPointerTo(existingVar->getType(), storageType))
+      return existingVar;
+
+    IGM.error(SourceLoc(),
+              "program too clever: variable collides with existing symbol " +
+                  name);
+
+    // Note that this will implicitly unique if the .unique name is also taken.
+    existingValue->setName(name + ".unique");
+  }
+
+  llvm::GlobalValue::LinkageTypes Linkage =
+    llvm::GlobalValue::LinkageTypes::ExternalLinkage;
+  auto var = new llvm::GlobalVariable(IGM.Module, storageType, /*constant*/true,
+    Linkage, /*Init to zero*/llvm::Constant::getNullValue(storageType), name);
+  ApplyIRLinkage({Linkage,
+                  llvm::GlobalValue::VisibilityTypes::DefaultVisibility,
+        llvm::GlobalValue::DLLStorageClassTypes::DefaultStorageClass}).to(var);
+  var->setAlignment(Alignment);
+  disableAddressSanitizer(IGM, var);
+  IGM.addUsedGlobal(var);
+  return var;
+}
+
 void swift::irgen::disableAddressSanitizer(IRGenModule &IGM, llvm::GlobalVariable *var) {
   // Add an operand to llvm.asan.globals blacklisting this global variable.
   llvm::Metadata *metadata[] = {

lib/IRGen/GenDecl.h

@@ -52,6 +52,9 @@ namespace irgen {
                  Optional<SILLocation> DebugLoc = None,
                  StringRef DebugName = StringRef(), bool heapAllocated = false);
 
+  llvm::GlobalVariable *
+  createLinkerDirectiveVariable(IRGenModule &IGM, StringRef Name);
+
   void disableAddressSanitizer(IRGenModule &IGM, llvm::GlobalVariable *var);
 }
 }

test/attr/Inputs/SymbolMove/LowLevel.swift

@@ -1,8 +1,10 @@
+@available(OSX 10.8, *)
 @_originallyDefinedIn(module: "HighLevel", OSX 10.10)
 public func printMessageMoved() {
   print("Hello from LowLevel")
 }
 
+@available(OSX 10.8, *)
 @_originallyDefinedIn(module: "HighLevel", OSX 10.10)
 public struct Entity {
     public let value = "LowLevel"
@@ -11,6 +13,7 @@ public struct Entity {
 }
 
 // =================== Move protocol =================================//
+@available(OSX 10.8, *)
 @_originallyDefinedIn(module: "HighLevel", OSX 10.10)
 public protocol Box {
   associatedtype Item
@@ -19,18 +22,21 @@ public protocol Box {
   func shape() -> String
 }
 
+@available(OSX 10.8, *)
 @_originallyDefinedIn(module: "HighLevel", OSX 10.10)
 extension Box {
   public func shape() -> String { return "round"}
 }
 
+@available(OSX 10.8, *)
 @_originallyDefinedIn(module: "HighLevel", OSX 10.10)
 public struct Candy {
   public var kind = "candy"
   public init() {}
 }
 
 // =================== Move enum ============================ //
+@available(OSX 10.8, *)
 @_originallyDefinedIn(module: "HighLevel", OSX 10.10)
 public enum LanguageKind: Int {
   case Cpp = 1
@@ -39,6 +45,7 @@ public enum LanguageKind: Int {
 }
 
 // =================== Move class ============================ //
+@available(OSX 10.8, *)
 @_originallyDefinedIn(module: "HighLevel", OSX 10.10)
 open class Vehicle {
     public init() {}