PNaCl: Add NoAlias attributes in ExpandByVal and ExpandVarArgs passes

lib/Transforms/NaCl/ExpandVarArgs.cpp

 //===- ExpandVarArgs.cpp - Expand out variable argument function calls-----===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This pass expands out all use of variable argument functions.
@@ skipping 69 matching lines @@
 
   // In order to change the function's arguments, we have to recreate
   // the function.
   Function *NewFunc = Function::Create(NFTy, Func->getLinkage());
   NewFunc->copyAttributesFrom(Func);
   Func->getParent()->getFunctionList().insert(Func, NewFunc);
   NewFunc->takeName(Func);
   NewFunc->getBasicBlockList().splice(NewFunc->begin(),
                                       Func->getBasicBlockList());
 
+  // Declare the new argument as "noalias".
+  NewFunc->setAttributes(
+      Func->getAttributes().addAttribute(
+          Func->getContext(), FTy->getNumParams() + 1, Attribute::NoAlias));
+
   // Move the arguments across to the new function.
   for (Function::arg_iterator Arg = Func->arg_begin(), E = Func->arg_end(),
          NewArg = NewFunc->arg_begin();
        Arg != E; ++Arg, ++NewArg) {
     Arg->replaceAllUsesWith(NewArg);
     NewArg->takeName(Arg);
   }
 
   Func->replaceAllUsesWith(
       ConstantExpr::getBitCast(NewFunc, FTy->getPointerTo()));
@@ skipping 230 matching lines @@
       ExpandVarArgFunc(Func);
     }
   }
 
   return Changed;
 }
 
 ModulePass *llvm::createExpandVarArgsPass() {
   return new ExpandVarArgs();
 }