SILGen: Stub initializer functions for unavailable global vars.

Part of rdar://107388493

Author: tshortli

lib/SILGen/SILGenGlobalVariable.cpp

@@ -240,6 +240,10 @@ void SILGenFunction::emitLazyGlobalInitializer(PatternBindingDecl *binding,
 
   // Add unused context pointer argument required to pass to `Builtin.once`
   SILBasicBlock &entry = *F.begin();
+
+  if (shouldLowerToUnavailableCodeStub(binding))
+    emitApplyOfUnavailableCodeReached();
+
   SILType rawPointerSILTy =
       getLoweredLoadableType(getASTContext().TheRawPointerType);
   entry.createFunctionArgument(rawPointerSILTy);
@@ -279,6 +283,9 @@ static void emitOnceCall(SILGenFunction &SGF, VarDecl *global,
 void SILGenFunction::emitGlobalAccessor(VarDecl *global,
                                         SILGlobalVariable *onceToken,
                                         SILFunction *onceFunc) {
+  if (shouldLowerToUnavailableCodeStub(global))
+    emitApplyOfUnavailableCodeReached();
+
   emitOnceCall(*this, global, onceToken, onceFunc);
 
   // Return the address of the global variable.

test/SILGen/unavailable_decl_optimization_stub.swift

@@ -23,3 +23,19 @@ enum SomeError: Error { case generic }
 public func unavailableThrowingFunc() throws {
   throw SomeError.generic
 }
+
+// one-time initialization function for globalVar
+// CHECK-LABEL: sil {{.*}} @$s4Test9globalVar_WZ
+// CHECK:         [[FNREF:%.*]] = function_ref @$ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+// CHECK-NEXT:    [[APPLY:%.*]] = apply [[FNREF]]()
+// CHECK:         alloc_global
+// CHECK:       } // end sil function '$s4Test9globalVar_WZ'
+//
+// globalVar.unsafeMutableAddressor
+// CHECK-LABEL: sil {{.*}} @$s4Test9globalVarAA1SVvau
+// CHECK:         [[FNREF:%.*]] = function_ref @$ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+// CHECK-NEXT:    [[APPLY:%.*]] = apply [[FNREF]]()
+// CHECK:         global_addr @$s4Test9globalVar_Wz
+// CHECK:       } // end sil function '$s4Test9globalVarAA1SVvau'
+@available(*, unavailable)
+public var globalVar = S()