1 files changed, 25 insertions, 14 deletions

diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index d0ec3eb4fa3..cbcc4491c5a 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -1130,27 +1130,20 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
   } else {
     // Load the first byte of the guard variable.
     llvm::Type *PtrTy = Builder.getInt8PtrTy();
-    llvm::LoadInst *LI = 
+    llvm::Value *V = 
       Builder.CreateLoad(Builder.CreateBitCast(GuardVariable, PtrTy), "tmp");
-    LI->setAlignment(1);
-
-    // Itanium ABI:
-    //   An implementation supporting thread-safety on multiprocessor
-    //   systems must also guarantee that references to the initialized
-    //   object do not occur before the load of the initialization flag.
-    //
-    // In LLVM, we do this by marking the load Acquire.
-    if (threadsafe)
-      LI->setAtomic(llvm::Acquire);
-
-    IsInitialized = Builder.CreateIsNull(LI, "guard.uninitialized");
+
+    IsInitialized = Builder.CreateIsNull(V, "guard.uninitialized");
   }
 
   llvm::BasicBlock *InitCheckBlock = CGF.createBasicBlock("init.check");
   llvm::BasicBlock *EndBlock = CGF.createBasicBlock("init.end");
 
+  llvm::BasicBlock *NoCheckBlock = EndBlock;
+  if (threadsafe) NoCheckBlock = CGF.createBasicBlock("init.barrier");
+
   // Check if the first byte of the guard variable is zero.
-  Builder.CreateCondBr(IsInitialized, InitCheckBlock, EndBlock);
+  Builder.CreateCondBr(IsInitialized, InitCheckBlock, NoCheckBlock);
 
   CGF.EmitBlock(InitCheckBlock);
 
@@ -1184,5 +1177,23 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
     Builder.CreateStore(llvm::ConstantInt::get(GuardTy, 1), GuardVariable);
   }
 
+  // Emit an acquire memory barrier if using thread-safe statics:
+  // Itanium ABI:
+  //   An implementation supporting thread-safety on multiprocessor
+  //   systems must also guarantee that references to the initialized
+  //   object do not occur before the load of the initialization flag.
+  if (threadsafe) {
+    Builder.CreateBr(EndBlock);
+    CGF.EmitBlock(NoCheckBlock);
+
+    llvm::Value *_false = Builder.getFalse();
+    llvm::Value *_true = Builder.getTrue();
+
+    Builder.CreateCall5(CGM.getIntrinsic(llvm::Intrinsic::memory_barrier),
+                        /* load-load, load-store */ _true, _true,
+                        /* store-load, store-store */ _false, _false,
+                        /* device or I/O */ _false);
+  }
+
   CGF.EmitBlock(EndBlock);
 }