Add passes for applying SFI sandboxing at the LLVM IR level

lib/Transforms/NaCl/ReplacePtrsWithInts.cpp

 //===- ReplacePtrsWithInts.cpp - Convert pointer values to integer values--===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This pass strips out aggregate pointer types and replaces them with
@@ skipping 495 matching lines @@
 // Convert ptrtoint+inttoptr to a bitcast because it's shorter and
 // because some intrinsics work on bitcasts but not on
 // ptrtoint+inttoptr, in particular:
 //  * llvm.lifetime.start/end (although we strip these out)
 //  * llvm.eh.typeid.for
 static void SimplifyCasts(Instruction *Inst, Type *IntPtrType) {
   if (IntToPtrInst *Cast1 = dyn_cast<IntToPtrInst>(Inst)) {
     if (PtrToIntInst *Cast2 = dyn_cast<PtrToIntInst>(Cast1->getOperand(0))) {
       assert(Cast2->getType() == IntPtrType);
       Value *V = Cast2->getPointerOperand();
-      if (V->getType() != Cast1->getType())
+      if (V->getType() != Cast1->getType()) {
+        // Hack: don't convert to bitcast.
+        return;
         V = new BitCastInst(V, Cast1->getType(), V->getName() + ".bc", Cast1);
+      }
       Cast1->replaceAllUsesWith(V);
       if (Cast1->use_empty())
         Cast1->eraseFromParent();
       if (Cast2->use_empty())
         Cast2->eraseFromParent();
     }
   }
 }
 
 static void CleanUpFunction(Function *Func, Type *IntPtrType) {
@@ skipping 101 matching lines @@
     // Delete the now-unused bitcast ConstantExprs that we created so
     // that they don't interfere with StripDeadPrototypes.
     Func->removeDeadConstantUsers();
   }
   return true;
 }
 
 ModulePass *llvm::createReplacePtrsWithIntsPass() {
   return new ReplacePtrsWithInts();
 }