Disable running the preamble during replay of trace

Summary: The preamble of activity should be skipped when running from a replay of a trace. This is because that activity will already be in the trace itself, so executing it again would result in duplicated trace records.

Reviewed By: neildhar

Differential Revision: D37662040

fbshipit-source-id: 3722cb332f9df21467a99430070963c56f166239

API/hermes/TracingRuntime.cpp

@@ -27,7 +27,8 @@ TracingRuntime::TracingRuntime(
     std::unique_ptr<llvh::raw_ostream> traceStream)
     : RuntimeDecorator<jsi::Runtime>(*runtime),
       runtime_(std::move(runtime)),
-      trace_(globalID, conf, std::move(traceStream)) {}
+      trace_(globalID, conf, std::move(traceStream)),
+      numPreambleRecords_(0) {}
 
 void TracingRuntime::replaceNondeterministicFuncs() {
   insertHostForwarder({"Math", "random"});
@@ -736,9 +737,7 @@ TracingHermesRuntime::TracingHermesRuntime(
           runtimeConfig,
           std::move(traceStream),
           std::move(commitAction),
-          std::move(rollbackAction)) {
-  replaceNondeterministicFuncs();
-}
+          std::move(rollbackAction)) {}
 
 TracingHermesRuntime::~TracingHermesRuntime() {
   if (crashCallbackKey_) {
@@ -870,10 +869,13 @@ static std::unique_ptr<TracingHermesRuntime> makeTracingHermesRuntimeImpl(
       std::move(traceStream),
       commitAction,
       rollbackAction);
-  // In non-replay executions, add the __nativeRecordTraceMarker function.
-  // In replay executions, this will be simulated from the trace.
   if (!forReplay) {
+    // In non-replay executions, add the __nativeRecordTraceMarker function.
+    // In replay executions, this will be simulated from the trace.
     addRecordMarker(*ret);
+    // In replay executions, the trace will contain the instructions for
+    // replacing the nondeterministic functions.
+    ret->replaceNondeterministicFuncs();
   }
   return ret;
 }

unittests/API/SynthTraceSerializationTest.cpp

@@ -350,24 +350,23 @@ TEST_F(SynthTraceSerializationTest, FullTrace) {
 
   auto records = optTrace.getPropertyAsObject(*rt, "trace").asArray(*rt);
 
-  auto offset = rt->getNumPreambleRecordsForTest();
-  auto record = records.getValueAtIndex(*rt, 0 + offset).asObject(*rt);
+  auto record = records.getValueAtIndex(*rt, 0).asObject(*rt);
   EXPECT_EQ(
       "CreateObjectRecord",
       record.getProperty(*rt, "type").asString(*rt).utf8(*rt));
   EXPECT_TRUE(record.getProperty(*rt, "time").isNumber());
   EXPECT_EQ(objID, record.getProperty(*rt, "objID").asNumber());
 
   // The obj.getProperty(*rt, "a") creates a string primitive for "a".
-  record = records.getValueAtIndex(*rt, 1 + offset).asObject(*rt);
+  record = records.getValueAtIndex(*rt, 1).asObject(*rt);
   EXPECT_EQ(
       "CreateStringRecord",
       record.getProperty(*rt, "type").asString(*rt).utf8(*rt));
   EXPECT_TRUE(record.getProperty(*rt, "time").isNumber());
   EXPECT_TRUE(record.getProperty(*rt, "objID").isNumber());
   auto stringID = record.getProperty(*rt, "objID").asNumber();
 
-  record = records.getValueAtIndex(*rt, 2 + offset).asObject(*rt);
+  record = records.getValueAtIndex(*rt, 2).asObject(*rt);
   EXPECT_EQ(
       "GetPropertyRecord",
       record.getProperty(*rt, "type").asString(*rt).utf8(*rt));

unittests/API/SynthTraceTest.cpp

@@ -64,9 +64,8 @@ struct SynthTraceTest : public ::testing::Test {
   }
 
   llvh::ArrayRef<std::unique_ptr<SynthTrace::Record>> getRecords() {
-    auto n = rt->getNumPreambleRecordsForTest();
     auto &recs = rt->trace().records();
-    return llvh::makeArrayRef(recs.data() + n, recs.size() - n);
+    return llvh::makeArrayRef(recs.data(), recs.size());
   }
 };
 
@@ -1003,7 +1002,7 @@ struct SynthTraceReplayTest : public ::testing::Test {
             config,
             /* traceStream */
             std::make_unique<llvh::raw_string_ostream>(traceResult),
-            /* forReplay */ true)) {}
+            /* forReplay */ false)) {}
 
   SynthTraceReplayTest()
       : SynthTraceReplayTest(::hermes::vm::RuntimeConfig::Builder()
@@ -1020,6 +1019,12 @@ struct SynthTraceReplayTest : public ::testing::Test {
   jsi::Value eval(jsi::Runtime &rt, const char *code) {
     return rt.global().getPropertyAsFunction(rt, "eval").call(rt, code);
   }
+
+  llvh::ArrayRef<std::unique_ptr<SynthTrace::Record>> getRecords() {
+    auto n = traceRt->getNumPreambleRecordsForTest();
+    auto &recs = traceRt->trace().records();
+    return llvh::makeArrayRef(recs.data() + n, recs.size() - n);
+  }
 };
 
 TEST_F(SynthTraceReplayTest, CreateObjectReplay) {