[Devirtualization] insert placement new barrier with -O0

Summary:
To not break LTO with different optimizations levels, we should insert
the barrier regardles of optimization level.

Reviewers: rjmccall, rsmith, mehdi_amini

Reviewed By: mehdi_amini

Subscribers: mehdi_amini, cfe-commits

Differential Revision: https://reviews.llvm.org/D32401

llvm-svn: 303488

clang/lib/CodeGen/CGExprCXX.cpp

@@ -1658,8 +1658,9 @@ llvm::Value *CodeGenFunction::EmitCXXNewExpr(const CXXNewExpr *E) {
 
   // Passing pointer through invariant.group.barrier to avoid propagation of
   // vptrs information which may be included in previous type.
+  // To not break LTO with different optimizations levels, we do it regardless
+  // of optimization level.
   if (CGM.getCodeGenOpts().StrictVTablePointers &&
-      CGM.getCodeGenOpts().OptimizationLevel > 0 &&
       allocator->isReservedGlobalPlacementOperator())
     result = Address(Builder.CreateInvariantGroupBarrier(result.getPointer()),
                      result.getAlignment());