[llvm-exegesis] Allow measuring several instructions in a single run.

[courbet]

Summary

We try to recover gracefully on instructions that would crash the
program.

This includes some refactoring of runMeasurement() implementations.

[courbet]

revert debug code

[lebedev.ri]

How do you plan to deal with opcodes that crash (assertion failure) the llvm as a whole?
I.e. not when the snippet crashes, but the generation of the snippet itself crashes.
I *believe* there are some cases.

[gchatelet]

In D53371#1267732, @lebedev.ri wrote:

How do you plan to deal with opcodes that crash (assertion failure) the llvm as a whole?
I.e. not when the snippet crashes, but the generation of the snippet itself crashes.
I *believe* there are some cases.

We were looking at those as I speak. The plan is to not crash :)

tools/llvm-exegesis/lib/BenchmarkRunner.cpp

59

This is not very useful, is it?

63

Probably more than 2 counter names.

77

As discussed, lets store the result in a bool and return after the state is restored

CrashRecoveryContext CRC;
CrashRecoveryContext::Enable();
Counter.start();
const bool IsSuccess = CRC.RunSafely(...
Counter.stop();
CrashRecoveryContext::Disable();
if(!IsSuccess) return ....

[lebedev.ri]

In D53371#1267734, @gchatelet wrote:

In D53371#1267732, @lebedev.ri wrote:

How do you plan to deal with opcodes that crash (assertion failure) the llvm as a whole?
I.e. not when the snippet crashes, but the generation of the snippet itself crashes.
I *believe* there are some cases.

We were looking at those as I speak. The plan is to not crash :)

Ok, sounds great :)

[courbet]

address comments.

[courbet]

tools/llvm-exegesis/lib/BenchmarkRunner.cpp

63

The current max is 2, for SNB.

[gchatelet]

tools/llvm-exegesis/lib/BenchmarkRunner.cpp

58

Return an int64_t here.

tools/llvm-exegesis/lib/Latency.cpp

91

Can you please rename MinLatency to MinValue?

96

ExpectedCounterValue? so it's easier to understand the next lines

97

remove the braces

101

Now you don't need to cast anymore.

tools/llvm-exegesis/lib/Uops.cpp

236

remove the braces

245

ditto

tools/llvm-exegesis/llvm-exegesis.cpp

121

Let's go with a for loop so it's easier to reason about the last element.

125

can you specify the lambda return type so it's explicit.

[courbet]

address comments

[courbet]

Start/stop the counter inside the lambda to avoid measuring events from RunSafely().

[courbet]

rebase

docs/CommandGuide/llvm-exegesis.rst

 
  Print a summary of command line options.
 
 .. option:: -opcode-index=<LLVM opcode index>
 
  Specify the opcode to measure, by index. See example 1 for details.
  Either `opcode-index`, `opcode-name` or `snippets-file` must be set.
 
-.. option:: -opcode-name=<LLVM opcode name>
+.. option:: -opcode-name=<opcode name 1>,<opcode name 2>,...
 
- Specify the opcode to measure, by name. See example 1 for details.
+ Specify the opcode to measure, by name. Several opcodes can be specified as
+ a comma-separated list. See example 1 for details.
  Either `opcode-index`, `opcode-name` or `snippets-file` must be set.
 
  .. option:: -snippets-file=<filename>
 
   Specify the custom code snippet to measure. See example 2 for details.
   Either `opcode-index`, `opcode-name` or `snippets-file` must be set.
 
 .. option:: -mode=[latency|uops|analysis]

tools/llvm-exegesis/lib/BenchmarkRunner.h

struct ScratchSpace {
     char *ptr() const { return AlignedPtr; }
     void clear() { std::memset(ptr(), 0, kSize); }
 
   private:
     const std::unique_ptr<char[]> UnalignedPtr;
     char *const AlignedPtr;
   };
 
+  // A helper to measure counters while executing a function in a sandboxed
+  // context.
+  class FunctionExecutor {
+  public:
+    ~FunctionExecutor();
+    virtual llvm::Expected<double>
+    runAndMeasure(const char *Counters) const = 0;
+  };
+
 protected:
   const LLVMState &State;
 
 private:
-  virtual std::vector<BenchmarkMeasure>
-  runMeasurements(const ExecutableFunction &EF,
-                  ScratchSpace &Scratch) const = 0;
+  virtual llvm::Expected<std::vector<BenchmarkMeasure>>
+  runMeasurements(const FunctionExecutor &Executor) const = 0;
 
   llvm::Expected<std::string>
   writeObjectFile(const BenchmarkCode &Configuration,
                   llvm::ArrayRef<llvm::MCInst> Code) const;
 
   const InstructionBenchmark::ModeE Mode;
 
   const std::unique_ptr<ScratchSpace> Scratch;
 };
 
 } // namespace exegesis
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_BENCHMARKRUNNER_H

tools/llvm-exegesis/lib/BenchmarkRunner.cpp

 //===-- BenchmarkRunner.cpp -------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include <array>
 #include <string>
 
 #include "Assembler.h"
 #include "BenchmarkRunner.h"
 #include "MCInstrDescView.h"
+#include "PerfHelper.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Program.h"
 
 namespace exegesis {
 
 BenchmarkFailure::BenchmarkFailure(const llvm::Twine &S)
     : llvm::StringError(S, llvm::inconvertibleErrorCode()) {}
GenerateInstructions(const BenchmarkCode &BC, const size_t MinInstructions) {
   if (BC.Instructions.empty())
     return {};
   std::vector<llvm::MCInst> Code = BC.Instructions;
   for (int I = 0; Code.size() < MinInstructions; ++I)
     Code.push_back(BC.Instructions[I % BC.Instructions.size()]);
   return Code;
 }
 
+namespace {
+class FunctionExecutorImpl : public BenchmarkRunner::FunctionExecutor {
+public:
+  FunctionExecutorImpl(const LLVMState &State,
+                       llvm::object::OwningBinary<llvm::object::ObjectFile> Obj,
+                       BenchmarkRunner::ScratchSpace *Scratch)
+      : Function(State.createTargetMachine(), std::move(Obj)),
+        Scratch(Scratch) {}
+
+private:
+  llvm::Expected<double> runAndMeasure(const char *Counters) const override {
+    using llvm::CrashRecoveryContext;
+    // We sum counts when there are several counters for a single ProcRes
+    // (e.g. P23 on SandyBridge).
+    int64_t CounterValue = 0;
+    llvm::SmallVector<llvm::StringRef, 2> CounterNames;
+    llvm::StringRef(Counters).split(CounterNames, ',');
+    char *const ScratchPtr = Scratch->ptr();
+    for (const auto &CounterName : CounterNames) {
+      pfm::PerfEvent PerfEvent(CounterName);
+      if (!PerfEvent.valid())
+        llvm::report_fatal_error(
+            llvm::Twine("invalid perf event ").concat(Counters));
+      pfm::Counter Counter(PerfEvent);
+      Scratch->clear();
+      {
+        CrashRecoveryContext CRC;
+        CrashRecoveryContext::Enable();
+        Counter.start();
+        if (!CRC.RunSafely([this, ScratchPtr]() { Function(ScratchPtr); })) {
+          // FIXME: Better diagnosis.
+          return llvm::make_error<BenchmarkFailure>(
+              "snippet crashed while running");
+        }
+        Counter.stop();
+        CrashRecoveryContext::Disable();
+      }
+      CounterValue += Counter.read();
+    }
+    return CounterValue;
+  }
+
+  const ExecutableFunction Function;
+  BenchmarkRunner::ScratchSpace *const Scratch;
+};
+} // namespace
+
 InstructionBenchmark
 BenchmarkRunner::runConfiguration(const BenchmarkCode &BC,
                                   unsigned NumRepetitions) const {
   InstructionBenchmark InstrBenchmark;
   InstrBenchmark.Mode = Mode;
   InstrBenchmark.CpuName = State.getTargetMachine().getTargetCPU();
   InstrBenchmark.LLVMTriple =
       State.getTargetMachine().getTargetTriple().normalize();
BenchmarkRunner::runConfiguration(const BenchmarkCode &BC,
   auto ObjectFilePath = writeObjectFile(
       BC, GenerateInstructions(BC, InstrBenchmark.NumRepetitions));
   if (llvm::Error E = ObjectFilePath.takeError()) {
     InstrBenchmark.Error = llvm::toString(std::move(E));
     return InstrBenchmark;
   }
   llvm::outs() << "Check generated assembly with: /usr/bin/objdump -d "
                << *ObjectFilePath << "\n";
-  const ExecutableFunction EF(State.createTargetMachine(),
-                              getObjectFromFile(*ObjectFilePath));
-  InstrBenchmark.Measurements = runMeasurements(EF, *Scratch);
+  const FunctionExecutorImpl Executor(State, getObjectFromFile(*ObjectFilePath),
+                                      Scratch.get());
+  auto Measurements = runMeasurements(Executor);
+  if (llvm::Error E = Measurements.takeError()) {
+    InstrBenchmark.Error = llvm::toString(std::move(E));
+    return InstrBenchmark;
+  }
+  InstrBenchmark.Measurements = std::move(*Measurements);
   assert(InstrBenchmark.NumRepetitions > 0 && "invalid NumRepetitions");
   for (BenchmarkMeasure &BM : InstrBenchmark.Measurements) {
     // Scale the measurements by instruction.
     BM.PerInstructionValue /= InstrBenchmark.NumRepetitions;
     // Scale the measurements by snippet.
     BM.PerSnippetValue *= static_cast<double>(BC.Instructions.size()) /
                           InstrBenchmark.NumRepetitions;
   }
 
   return InstrBenchmark;
 }
 
 llvm::Expected<std::string>
 BenchmarkRunner::writeObjectFile(const BenchmarkCode &BC,
                                  llvm::ArrayRef<llvm::MCInst> Code) const {
   int ResultFD = 0;
   llvm::SmallString<256> ResultPath;
   if (llvm::Error E = llvm::errorCodeToError(llvm::sys::fs::createTemporaryFile(
           "snippet", "o", ResultFD, ResultPath)))
     return std::move(E);
   llvm::raw_fd_ostream OFS(ResultFD, true /*ShouldClose*/);
   assembleToStream(State.getExegesisTarget(), State.createTargetMachine(),
                    BC.LiveIns, BC.RegisterInitialValues, Code, OFS);
   return ResultPath.str();
 }
 
+BenchmarkRunner::FunctionExecutor::~FunctionExecutor() {}
+
 } // namespace exegesis

tools/llvm-exegesis/lib/Latency.h

 
 class LatencyBenchmarkRunner : public BenchmarkRunner {
 public:
   LatencyBenchmarkRunner(const LLVMState &State)
       : BenchmarkRunner(State, InstructionBenchmark::Latency) {}
   ~LatencyBenchmarkRunner() override;
 
 private:
-  std::vector<BenchmarkMeasure>
-  runMeasurements(const ExecutableFunction &EF,
-                  ScratchSpace &Scratch) const override;
+  llvm::Expected<std::vector<BenchmarkMeasure>>
+  runMeasurements(const FunctionExecutor &Executor) const override;
 
   virtual const char *getCounterName() const;
 };
 } // namespace exegesis
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_LATENCY_H

tools/llvm-exegesis/lib/Latency.cpp

 //===-- Latency.cpp ---------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "Latency.h"
 
 #include "Assembler.h"
 #include "BenchmarkRunner.h"
 #include "MCInstrDescView.h"
-#include "PerfHelper.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCInstBuilder.h"
 #include "llvm/Support/FormatVariadic.h"
 
 namespace exegesis {
 
 LatencySnippetGenerator::~LatencySnippetGenerator() = default;
const char *CounterName = State.getSubtargetInfo()
                                 .PfmCounters.CycleCounter;
   if (!CounterName)
     llvm::report_fatal_error("sched model does not define a cycle counter");
   return CounterName;
 }
 
 LatencyBenchmarkRunner::~LatencyBenchmarkRunner() = default;
 
-std::vector<BenchmarkMeasure>
-LatencyBenchmarkRunner::runMeasurements(const ExecutableFunction &Function,
-                                        ScratchSpace &Scratch) const {
+llvm::Expected<std::vector<BenchmarkMeasure>>
+LatencyBenchmarkRunner::runMeasurements(
+    const FunctionExecutor &Executor) const {
   // Cycle measurements include some overhead from the kernel. Repeat the
   // measure several times and take the minimum value.
   constexpr const int NumMeasurements = 30;
   int64_t MinLatency = std::numeric_limits<int64_t>::max();
   const char *CounterName = getCounterName();
   if (!CounterName)
     llvm::report_fatal_error("could not determine cycle counter name");
-  const pfm::PerfEvent CyclesPerfEvent(CounterName);
-  if (!CyclesPerfEvent.valid())
-    llvm::report_fatal_error("invalid perf event");
   for (size_t I = 0; I < NumMeasurements; ++I) {
-    pfm::Counter Counter(CyclesPerfEvent);
-    Scratch.clear();
-    Counter.start();
-    Function(Scratch.ptr());
-    Counter.stop();
-    const int64_t Value = Counter.read();
-    if (Value < MinLatency)
-      MinLatency = Value;
-  }
-  return {BenchmarkMeasure::Create("latency", MinLatency)};
+    auto CounterValue = Executor.runAndMeasure(CounterName);
+    if (!CounterValue) {
+      return CounterValue.takeError();
+    }
+    if (*CounterValue < MinLatency)
+      MinLatency = static_cast<int64_t>(*CounterValue);
+  }
+  std::vector<BenchmarkMeasure> Result = {
+      BenchmarkMeasure::Create("latency", MinLatency)};
+  return std::move(Result);
 }
 
 } // namespace exegesis

tools/llvm-exegesis/lib/Uops.h

 public:
   UopsBenchmarkRunner(const LLVMState &State)
       : BenchmarkRunner(State, InstructionBenchmark::Uops) {}
   ~UopsBenchmarkRunner() override;
 
   static constexpr const size_t kMinNumDifferentAddresses = 6;
 
 private:
-  std::vector<BenchmarkMeasure>
-  runMeasurements(const ExecutableFunction &EF,
-                  ScratchSpace &Scratch) const override;
+  llvm::Expected<std::vector<BenchmarkMeasure>>
+  runMeasurements(const FunctionExecutor &Executor) const override;
 };
 
 } // namespace exegesis
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_UOPS_H

tools/llvm-exegesis/lib/Uops.cpp

 //===-- Uops.cpp ------------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "Uops.h"
 
 #include "Assembler.h"
 #include "BenchmarkRunner.h"
 #include "MCInstrDescView.h"
-#include "PerfHelper.h"
 #include "Target.h"
 
 // FIXME: Load constants into registers (e.g. with fld1) to not break
 // instructions like x87.
 
 // Ideally we would like the only limitation on executing uops to be the issue
 // ports. Maximizing port pressure increases the likelihood that the load is
 // distributed evenly across possible ports.
UopsSnippetGenerator::generateCodeTemplates(const Instruction &Instr) const {
   }
   CT.Info =
       "instruction has no tied variables picking Uses different from defs";
   CT.Instructions.push_back(std::move(IT));
   instantiateMemoryOperands(CT.ScratchSpacePointerInReg, CT.Instructions);
   return getSingleton(CT);
 }
 
-std::vector<BenchmarkMeasure>
-UopsBenchmarkRunner::runMeasurements(const ExecutableFunction &Function,
-                                     ScratchSpace &Scratch) const {
+llvm::Expected<std::vector<BenchmarkMeasure>>
+UopsBenchmarkRunner::runMeasurements(const FunctionExecutor &Executor) const {
   const auto &SchedModel = State.getSubtargetInfo().getSchedModel();
 
-  const auto RunMeasurement = [&Function,
-                               &Scratch](const char *const Counters) {
-    // We sum counts when there are several counters for a single ProcRes
-    // (e.g. P23 on SandyBridge).
-    int64_t CounterValue = 0;
-    llvm::SmallVector<llvm::StringRef, 2> CounterNames;
-    llvm::StringRef(Counters).split(CounterNames, ',');
-    for (const auto &CounterName : CounterNames) {
-      pfm::PerfEvent UopPerfEvent(CounterName);
-      if (!UopPerfEvent.valid())
-        llvm::report_fatal_error(
-            llvm::Twine("invalid perf event ").concat(Counters));
-      pfm::Counter Counter(UopPerfEvent);
-      Scratch.clear();
-      Counter.start();
-      Function(Scratch.ptr());
-      Counter.stop();
-      CounterValue += Counter.read();
-    }
-    return CounterValue;
-  };
-
   std::vector<BenchmarkMeasure> Result;
   const auto &PfmCounters = SchedModel.getExtraProcessorInfo().PfmCounters;
   // Uops per port.
   for (unsigned ProcResIdx = 1;
        ProcResIdx < SchedModel.getNumProcResourceKinds(); ++ProcResIdx) {
     const char *const Counters = PfmCounters.IssueCounters[ProcResIdx];
     if (!Counters)
       continue;
-    const double CounterValue = RunMeasurement(Counters);
+    auto CounterValue = Executor.runAndMeasure(Counters);
+    if (!CounterValue) {
+      return CounterValue.takeError();
+    }
     Result.push_back(BenchmarkMeasure::Create(
-        SchedModel.getProcResource(ProcResIdx)->Name, CounterValue));
+        SchedModel.getProcResource(ProcResIdx)->Name, *CounterValue));
   }
   // NumMicroOps.
   if (const char *const UopsCounter = PfmCounters.UopsCounter) {
-    const double CounterValue = RunMeasurement(UopsCounter);
-    Result.push_back(BenchmarkMeasure::Create("NumMicroOps", CounterValue));
+    auto CounterValue = Executor.runAndMeasure(UopsCounter);
+    if (!CounterValue) {
+      return CounterValue.takeError();
     }
-  return Result;
+    Result.push_back(BenchmarkMeasure::Create("NumMicroOps", *CounterValue));
+  }
+  return std::move(Result);
 }
 
 constexpr const size_t UopsSnippetGenerator::kMinNumDifferentAddresses;
 
 } // namespace exegesis

tools/llvm-exegesis/llvm-exegesis.cpp

 #include "llvm/Support/Format.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/TargetSelect.h"
 #include <algorithm>
 #include <string>
 
-static llvm::cl::opt<unsigned>
+static llvm::cl::opt<int>
     OpcodeIndex("opcode-index", llvm::cl::desc("opcode to measure, by index"),
                 llvm::cl::init(0));
 
-static llvm::cl::opt<std::string>
-    OpcodeName("opcode-name", llvm::cl::desc("opcode to measure, by name"),
-               llvm::cl::init(""));
+static llvm::cl::opt<std::string> OpcodeNames(
+    "opcode-name",
+    llvm::cl::desc("comma-separated list of opcodes to measure, by name"),
 
 static llvm::cl::opt<std::string>
     SnippetsFile("snippets-file", llvm::cl::desc("code snippets to measure"),
                  llvm::cl::init(""));
 
 static llvm::cl::opt<std::string>
     BenchmarkFile("benchmarks-file", llvm::cl::desc(""), llvm::cl::init(""));
 

 namespace exegesis {
 
 static llvm::ExitOnError ExitOnErr;
 
 #ifdef LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET
 void LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET();
 #endif
 
-// Checks that only one of OpcodeName, OpcodeIndex or SnippetsFile is provided,
-// and returns the opcode index or 0 if snippets should be read from
+// Checks that only one of OpcodeNames, OpcodeIndex or SnippetsFile is provided,
+// and returns the opcode indices or {} if snippets should be read from
 // `SnippetsFile`.
-static unsigned getOpcodeOrDie(const llvm::MCInstrInfo &MCInstrInfo) {
-  const size_t NumSetFlags = (OpcodeName.empty() ? 0 : 1) +
+static std::vector<unsigned>
+getOpcodesOrDie(const llvm::MCInstrInfo &MCInstrInfo) {
+  const size_t NumSetFlags = (OpcodeNames.empty() ? 0 : 1) +
                              (OpcodeIndex == 0 ? 0 : 1) +
                              (SnippetsFile.empty() ? 0 : 1);
   if (NumSetFlags != 1)
     llvm::report_fatal_error(
         "please provide one and only one of 'opcode-index', 'opcode-name' or "
         "'snippets-file'");
   if (!SnippetsFile.empty())
-    return 0;
+    return {};
   if (OpcodeIndex > 0)
-    return OpcodeIndex;
+    return {static_cast<unsigned>(OpcodeIndex)};
+  if (OpcodeIndex < 0) {
+    std::vector<unsigned> Result(MCInstrInfo.getNumOpcodes());
+    std::iota(Result.begin(), Result.end(), 1);
+    return Result;
+  }
   // Resolve opcode name -> opcode.
-  for (unsigned I = 0, E = MCInstrInfo.getNumOpcodes(); I < E; ++I)
+  const auto ResolveName = [&MCInstrInfo](llvm::StringRef OpcodeName) {
+    for (unsigned I = 1, E = MCInstrInfo.getNumOpcodes(); I < E; ++I)
       if (MCInstrInfo.getName(I) == OpcodeName)
         return I;
-  llvm::report_fatal_error(llvm::Twine("unknown opcode ").concat(OpcodeName));
+    return 0u;
+  };
+  llvm::SmallVector<llvm::StringRef, 2> Pieces;
+  llvm::StringRef(OpcodeNames.getValue())
+      .split(Pieces, ",", /* MaxSplit */ -1, /* KeepEmpty */ false);
+  std::vector<unsigned> Result;
+  for (const llvm::StringRef OpcodeName : Pieces) {
+    if (unsigned Opcode = ResolveName(OpcodeName))
+      Result.push_back(Opcode);
+    else
+      llvm::report_fatal_error(
+          llvm::Twine("unknown opcode ").concat(OpcodeName));
+  }
+  return Result;
 }
 
 // Generates code snippets for opcode `Opcode`.
 static llvm::Expected<std::vector<BenchmarkCode>>
 generateSnippets(const LLVMState &State, unsigned Opcode) {
   const Instruction Instr(State, Opcode);
   const llvm::MCInstrDesc &InstrDesc = *Instr.Description;
   // Ignore instructions that we cannot run.
void benchmarkMain() {
   llvm::InitializeNativeTarget();
   llvm::InitializeNativeTargetAsmPrinter();
   llvm::InitializeNativeTargetAsmParser();
 #ifdef LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET
   LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET();
 #endif
 
   const LLVMState State;
-  const auto Opcode = getOpcodeOrDie(State.getInstrInfo());
+  const auto Opcodes = getOpcodesOrDie(State.getInstrInfo());
 
   std::vector<BenchmarkCode> Configurations;
-  if (Opcode > 0) {
-    // Ignore instructions without a sched class if -ignore-invalid-sched-class
-    // is passed.
+  if (!Opcodes.empty()) {
+    for (const unsigned Opcode : Opcodes) {
+      // Ignore instructions without a sched class if
+      // -ignore-invalid-sched-class is passed.
       if (IgnoreInvalidSchedClass &&
           State.getInstrInfo().get(Opcode).getSchedClass() == 0) {
-      llvm::errs() << "ignoring instruction without sched class\n";
-      return;
+        llvm::errs() << State.getInstrInfo().getName(Opcode)
+                     << ": ignoring instruction without sched class\n";
+        continue;
+      }
+      auto ConfigsForInstr = generateSnippets(State, Opcode);
+      if (!ConfigsForInstr) {
+        llvm::logAllUnhandledErrors(
+            ConfigsForInstr.takeError(), llvm::errs(),
+            llvm::Twine(State.getInstrInfo().getName(Opcode)).concat(": "));
+        continue;
+      }
+      std::move(ConfigsForInstr->begin(), ConfigsForInstr->end(),
+                std::back_inserter(Configurations));
     }
-    Configurations = ExitOnErr(generateSnippets(State, Opcode));
   } else {
     Configurations = ExitOnErr(readSnippets(State, SnippetsFile));
   }
 
   const std::unique_ptr<BenchmarkRunner> Runner =
       State.getExegesisTarget().createBenchmarkRunner(BenchmarkMode, State);
   if (!Runner) {
     llvm::report_fatal_error("cannot create benchmark runner");