[FuzzMutate] Don't crash when mutator is unable to find operation

include/llvm/FuzzMutate/IRMutator.h

 // configurable set of strategies. Some common strategies are also included
 // here.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_FUZZMUTATE_IRMUTATOR_H
 #define LLVM_FUZZMUTATE_IRMUTATOR_H
 
+#include "llvm/ADT/Optional.h"
 #include "llvm/FuzzMutate/OpDescriptor.h"
 #include "llvm/Support/ErrorHandling.h"
 
 namespace llvm {
 class BasicBlock;
 class Function;
 class Instruction;
 class Module;
public:
 
   void mutateModule(Module &M, int Seed, size_t CurSize, size_t MaxSize);
 };
 
 /// Strategy that injects operations into the function.
 class InjectorIRStrategy : public IRMutationStrategy {
   std::vector<fuzzerop::OpDescriptor> Operations;
 
-  fuzzerop::OpDescriptor chooseOperation(Value *Src, RandomIRBuilder &IB);
+  Optional<fuzzerop::OpDescriptor> chooseOperation(Value *Src,
+                                                   RandomIRBuilder &IB);
 
 public:
   InjectorIRStrategy(std::vector<fuzzerop::OpDescriptor> &&Operations)
       : Operations(std::move(Operations)) {}
   static std::vector<fuzzerop::OpDescriptor> getDefaultOps();
 
   uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
                      uint64_t CurrentWeight) override {

lib/FuzzMutate/IRMutator.cpp

 //===-- IRMutator.cpp -----------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/FuzzMutate/IRMutator.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/FuzzMutate/Operations.h"
 #include "llvm/FuzzMutate/Random.h"
 #include "llvm/FuzzMutate/RandomIRBuilder.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Function.h"
-#include "llvm/IR/Instructions.h"
 #include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
 #include "llvm/IR/Module.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Transforms/Scalar/DCE.h"
 
 using namespace llvm;
 
 static void createEmptyFunction(Module &M) {
   // TODO: Some arguments and a return value would probably be more interesting.
   LLVMContext &Context = M.getContext();
   Function *F = Function::Create(FunctionType::get(Type::getVoidTy(Context), {},
std::vector<fuzzerop::OpDescriptor> InjectorIRStrategy::getDefaultOps() {
   describeFuzzerFloatOps(Ops);
   describeFuzzerControlFlowOps(Ops);
   describeFuzzerPointerOps(Ops);
   describeFuzzerAggregateOps(Ops);
   describeFuzzerVectorOps(Ops);
   return Ops;
 }
 
-fuzzerop::OpDescriptor
+Optional<fuzzerop::OpDescriptor>
 InjectorIRStrategy::chooseOperation(Value *Src, RandomIRBuilder &IB) {
   auto OpMatchesPred = [&Src](fuzzerop::OpDescriptor &Op) {
     return Op.SourcePreds[0].matches({}, Src);
   };
   auto RS = makeSampler(IB.Rand, make_filter_range(Operations, OpMatchesPred));
   if (RS.isEmpty())
-    report_fatal_error("No available operations for src type");
+    return None;
   return *RS;
 }
 
 void InjectorIRStrategy::mutate(BasicBlock &BB, RandomIRBuilder &IB) {
   SmallVector<Instruction *, 32> Insts;
   for (auto I = BB.getFirstInsertionPt(), E = BB.end(); I != E; ++I)
     Insts.push_back(&*I);
   if (Insts.size() < 1)
     return;
 
   // Choose an insertion point for our new instruction.
   size_t IP = uniform<size_t>(IB.Rand, 0, Insts.size() - 1);
 
   auto InstsBefore = makeArrayRef(Insts).slice(0, IP);
   auto InstsAfter = makeArrayRef(Insts).slice(IP);
 
   // Choose a source, which will be used to constrain the operation selection.
   SmallVector<Value *, 2> Srcs;
   Srcs.push_back(IB.findOrCreateSource(BB, InstsBefore));
 
   // Choose an operation that's constrained to be valid for the type of the
   // source, collect any other sources it needs, and then build it.
-  fuzzerop::OpDescriptor OpDesc = chooseOperation(Srcs[0], IB);
-  for (const auto &Pred : makeArrayRef(OpDesc.SourcePreds).slice(1))
+  auto OpDesc = chooseOperation(Srcs[0], IB);
+  // Bail if no operation was found
+  if (!OpDesc)
+    return;
+
+  for (const auto &Pred : makeArrayRef(OpDesc->SourcePreds).slice(1))
     Srcs.push_back(IB.findOrCreateSource(BB, InstsBefore, Srcs, Pred));
-  if (Value *Op = OpDesc.BuilderFunc(Srcs, Insts[IP])) {
+
+  if (Value *Op = OpDesc->BuilderFunc(Srcs, Insts[IP])) {
     // Find a sink and wire up the results of the operation.
     IB.connectToSink(BB, InstsAfter, Op);
   }
 }
 
 uint64_t InstDeleterIRStrategy::getWeight(size_t CurrentSize, size_t MaxSize,
                                           uint64_t CurrentWeight) {
   // If we have less than 200 bytes, panic and try to always delete.