remove a bunch of locking from LLVMContextImpl. Since only one thread

can be banging on a context at a time, this isn't needed.  Owen, please
review.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85728 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SimplifyCFGPass.cpp

@@ -126,6 +126,9 @@ static bool MarkAliveBlocks(BasicBlock *BB,
         }
       }
       
+      // Store to undef and store to null are undefined and used to signal that
+      // they should be changed to unreachable by passes that can't modify the
+      // CFG.
       if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
         Value *Ptr = SI->getOperand(1);