4 files changed, 106 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/CMakeLists.txt b/llvm/lib/CodeGen/CMakeLists.txt
index 48bf3545e73..672b6bae2dd 100644
--- a/llvm/lib/CodeGen/CMakeLists.txt
+++ b/llvm/lib/CodeGen/CMakeLists.txt
@@ -71,6 +71,7 @@ add_llvm_library(LLVMCodeGen
   MachineSink.cpp
   MachineTraceMetrics.cpp
   MachineVerifier.cpp
+  NoopInsertion.cpp
   OcamlGC.cpp
   OptimizePHIs.cpp
   PHIElimination.cpp
diff --git a/llvm/lib/CodeGen/CodeGen.cpp b/llvm/lib/CodeGen/CodeGen.cpp
index 307dec548fc..fdb89438115 100644
--- a/llvm/lib/CodeGen/CodeGen.cpp
+++ b/llvm/lib/CodeGen/CodeGen.cpp
@@ -51,6 +51,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeMachineSchedulerPass(Registry);
   initializeMachineSinkingPass(Registry);
   initializeMachineVerifierPassPass(Registry);
+  initializeNoopInsertionPass(Registry);
   initializeOptimizePHIsPass(Registry);
   initializePHIEliminationPass(Registry);
   initializePeepholeOptimizerPass(Registry);
diff --git a/llvm/lib/CodeGen/NoopInsertion.cpp b/llvm/lib/CodeGen/NoopInsertion.cpp
new file mode 100644
index 00000000000..f2291b8e99c
--- /dev/null
+++ b/llvm/lib/CodeGen/NoopInsertion.cpp
@@ -0,0 +1,101 @@
+//===- NoopInsertion.cpp - Noop Insertion ---------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass adds fine-grained diversity by displacing code using randomly
+// placed (optionally target supplied) Noop instructions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/NoopInsertion.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/RandomNumberGenerator.h"
+#include "llvm/Target/TargetInstrInfo.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "noop-insertion"
+
+static cl::opt<unsigned> NoopInsertionPercentage(
+    "noop-insertion-percentage",
+    cl::desc("Percentage of instructions that have Noops prepended"),
+    cl::init(25)); // Default is a good balance between entropy and
+                   // performance impact
+
+static cl::opt<unsigned> MaxNoopsPerInstruction(
+    "max-noops-per-instruction",
+    llvm::cl::desc("Maximum number of Noops per instruction"),
+    llvm::cl::init(1));
+
+STATISTIC(InsertedNoops,
+          "Total number of noop type instructions inserted for diversity");
+
+char NoopInsertion::ID = 0;
+char &llvm::NoopInsertionID = NoopInsertion::ID;
+INITIALIZE_PASS(NoopInsertion, "noop-insertion",
+                "Noop Insertion for fine-grained code randomization", false,
+                false)
+
+NoopInsertion::NoopInsertion() : MachineFunctionPass(ID) {
+  initializeNoopInsertionPass(*PassRegistry::getPassRegistry());
+
+  // clamp percentage to 100
+  if (NoopInsertionPercentage > 100)
+    NoopInsertionPercentage = 100;
+}
+
+void NoopInsertion::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.setPreservesCFG();
+  MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+bool NoopInsertion::runOnMachineFunction(MachineFunction &Fn) {
+  // The RNG must be initialized on first use so we have a Module to
+  // construct it from
+  if (!RNG)
+    RNG.reset(Fn.getFunction()->getParent()->createRNG(this));
+
+  const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
+
+  unsigned FnInsertedNoopCount = 0;
+
+  for (auto &BB : Fn) {
+    MachineBasicBlock::iterator FirstTerm = BB.getFirstTerminator();
+
+    for (MachineBasicBlock::iterator I = BB.begin(), E = BB.end(); I != E;
+         ++I) {
+      if (I->isPseudo())
+        continue;
+
+      // Insert random number of Noop-like instructions.
+      for (unsigned i = 0; i < MaxNoopsPerInstruction; i++) {
+        if (Distribution(*RNG) >= NoopInsertionPercentage)
+          continue;
+
+        TII->insertNoop(BB, I, *RNG);
+
+        ++FnInsertedNoopCount;
+      }
+
+      if (I == FirstTerm)
+        break;
+    }
+  }
+
+  InsertedNoops += FnInsertedNoopCount;
+
+  return FnInsertedNoopCount > 0;
+}
diff --git a/llvm/lib/CodeGen/Passes.cpp b/llvm/lib/CodeGen/Passes.cpp
index 28e9f847a9d..a5d32103d7c 100644
--- a/llvm/lib/CodeGen/Passes.cpp
+++ b/llvm/lib/CodeGen/Passes.cpp
@@ -583,6 +583,9 @@ void TargetPassConfig::addMachinePasses() {
       addPass(createGCInfoPrinter(dbgs()), false, false);
   }
 
+  if (TM->Options.NoopInsertion)
+    addPass(&NoopInsertionID);
+
   // Basic block placement.
   if (getOptLevel() != CodeGenOpt::None)
     addBlockPlacement();