Add option to force GC before printing stats

Summary:
Add option to force GC before printing stats when running a synth trace on the command-line. This allows measuring the live data when execution stopped at some interesting marker (under "heapInfo"->"Allocated bytes"). This enables estimating the impact of a diff on the live size of an application (rather than just total allocation, or allocated after the last organic collection).

Also add it for the hermes command-line tool, mostly for consistency.

Reviewed By: dulinriley

Differential Revision: D16603771

fbshipit-source-id: 69421e623a0cdc72e2071ee980fa100d0b2d6ded

API/hermes/TraceInterpreter.cpp

@@ -1179,6 +1179,9 @@ void TraceInterpreter::addObjectToDefs(
 }
 
 std::string TraceInterpreter::printStats() {
+  if (options.forceGCBeforeStats) {
+    rt.instrumentation().collectGarbage();
+  }
   std::string stats = rt.instrumentation().getRecordedGCStats();
   ::hermes::vm::instrumentation::PerfEvents::endAndInsertStats(stats);
 #ifdef HERMESVM_PROFILER_OPCODE

API/hermes/TraceInterpreter.h

@@ -109,6 +109,7 @@ class TraceInterpreter final {
     ::hermes::vm::gcheapsize_t maxHeapSize{0};
     bool allocInYoung{true};
     bool revertToYGAtTTI{true};
+    bool forceGCBeforeStats{false};
     bool shouldPrintGCStats{false};
     bool shouldTrackIO{false};
     uint8_t bytecodeWarmupPercent{0};

include/hermes/ConsoleHost/ConsoleHost.h

@@ -64,6 +64,9 @@ struct ExecuteOptions {
 
   /// Fatally crash on any JIT compilation error.
   bool jitCrashOnError{false};
+
+  /// Perform a full GC just before printing any statistics.
+  bool forceGCBeforeStats{false};
 };
 
 /// Executes the HBC bytecode provided in HermesVM.

lib/ConsoleHost/ConsoleHost.cpp

@@ -286,6 +286,9 @@ bool executeHBCBytecode(
     llvm::errs() << "Process stats:\n";
     statSampler->stop().printJSON(llvm::errs());
 
+    if (options.forceGCBeforeStats) {
+      runtime->collect();
+    }
     printStats(runtime.get(), llvm::errs());
   }
 

tools/hermes/hermes.cpp

@@ -66,6 +66,12 @@ static opt<bool> GCRevertToYGAtTTI(
     cat(GCCategory),
     init(false));
 
+static opt<bool> GCBeforeStats(
+    "gc-before-stats",
+    desc("Perform a full GC just before printing statistics at exit"),
+    cat(GCCategory),
+    init(false));
+
 static opt<bool> GCPrintStats(
     "gc-print-stats",
     desc("Output summary garbage collection statistics at exit"),
@@ -97,7 +103,7 @@ static int executeHBCBytecodeFromCL(
                           .withRandomSeed(cl::GCSanitizeRandomSeed)
                           .build())
                   .withShouldRandomizeAllocSpace(cl::GCRandomizeAllocSpace)
-                  .withShouldRecordStats(cl::GCPrintStats)
+                  .withShouldRecordStats(cl::GCPrintStats || cl::GCBeforeStats)
                   .withShouldReleaseUnused(false)
                   .withAllocInYoung(cl::GCAllocYoung)
                   .withRevertToYGAtTTI(cl::GCRevertToYGAtTTI)
@@ -123,6 +129,7 @@ static int executeHBCBytecodeFromCL(
   options.dumpJITCode = cl::DumpJITCode;
   options.jitCrashOnError = cl::JITCrashOnError;
   options.stopAfterInit = cl::StopAfterInit;
+  options.forceGCBeforeStats = cl::GCBeforeStats;
 
   bool success;
   if (cl::Repeat <= 1) {

tools/synth/synth.cpp

@@ -80,6 +80,12 @@ static opt<bool> GCRevertToYGAtTTI(
     cat(GCCategory),
     init(true));
 
+static opt<bool> GCBeforeStats(
+    "gc-before-stats",
+    desc("Perform a full GC just before printing statistics at exit"),
+    cat(GCCategory),
+    init(false));
+
 static opt<bool> GCPrintStats(
     "gc-print-stats",
     desc("Output summary garbage collection statistics at exit"),
@@ -111,7 +117,8 @@ int main(int argc, char **argv) {
     options.maxHeapSize = cl::MaxHeapSize.bytes;
     options.allocInYoung = cl::GCAllocYoung;
     options.revertToYGAtTTI = cl::GCRevertToYGAtTTI;
-    options.shouldPrintGCStats = cl::GCPrintStats;
+    options.forceGCBeforeStats = cl::GCBeforeStats;
+    options.shouldPrintGCStats = cl::GCPrintStats || cl::GCBeforeStats;
     options.shouldTrackIO = cl::TrackBytecodeIO;
     options.bytecodeWarmupPercent = cl::BytecodeWarmupPercent;
     options.sanitizeRate = cl::GCSanitizeRate;