Re-commit r139643.

Make clang use Acquire loads and Release stores where necessary.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@139650 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 20 insertions, 30 deletions

diff --git a/lib/CodeGen/CGBuiltin.cpp b/lib/CodeGen/CGBuiltin.cpp
index 0c93ed36c1..271fe66ffe 100644
--- a/lib/CodeGen/CGBuiltin.cpp
+++ b/lib/CodeGen/CGBuiltin.cpp
@@ -900,13 +900,14 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
   case Builtin::BI__sync_lock_release_8:
   case Builtin::BI__sync_lock_release_16: {
     Value *Ptr = EmitScalarExpr(E->getArg(0));
-    llvm::Type *ElTy =
+    llvm::Type *ElLLVMTy =
       cast<llvm::PointerType>(Ptr->getType())->getElementType();
     llvm::StoreInst *Store = 
-      Builder.CreateStore(llvm::Constant::getNullValue(ElTy), Ptr);
-    // FIXME: This is completely, utterly wrong; it only even sort-of works
-    // on x86.
-    Store->setVolatile(true);
+      Builder.CreateStore(llvm::Constant::getNullValue(ElLLVMTy), Ptr);
+    QualType ElTy = E->getArg(0)->getType()->getPointeeType();
+    CharUnits StoreSize = getContext().getTypeSizeInChars(ElTy);
+    Store->setAlignment(StoreSize.getQuantity());
+    Store->setAtomic(llvm::Release);
     return RValue::get(0);
   }
 
diff --git a/lib/CodeGen/ItaniumCXXABI.cpp b/lib/CodeGen/ItaniumCXXABI.cpp
index cbcc4491c5..d0ec3eb4fa 100644
--- a/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/lib/CodeGen/ItaniumCXXABI.cpp
@@ -1130,20 +1130,27 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
   } else {
     // Load the first byte of the guard variable.
     llvm::Type *PtrTy = Builder.getInt8PtrTy();
-    llvm::Value *V = 
+    llvm::LoadInst *LI = 
       Builder.CreateLoad(Builder.CreateBitCast(GuardVariable, PtrTy), "tmp");
-
-    IsInitialized = Builder.CreateIsNull(V, "guard.uninitialized");
+    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");
   }
 
   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, NoCheckBlock);
+  Builder.CreateCondBr(IsInitialized, InitCheckBlock, EndBlock);
 
   CGF.EmitBlock(InitCheckBlock);
 
@@ -1177,23 +1184,5 @@ 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);
 }