V4: Only start JITting after a minimum of 3 calls

Change-Id: I748e06041f3085980ce48391ba2d829a9d86a727
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

4 files changed, 27 insertions, 14 deletions

diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index c57f39f61c..c97ba38dec 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -168,6 +168,15 @@ ExecutionEngine::ExecutionEngine()
                                              /* writable */ true, /* executable */ false,
                                              /* includesGuardPages */ true);
 
+    {
+        bool ok = false;
+        jitCallCountThreshold = qEnvironmentVariableIntValue("QV4_JIT_CALL_THRESHOLD", &ok);
+        if (!ok)
+            jitCallCountThreshold = 3;
+        if (qEnvironmentVariableIsSet("QV4_FORCE_INTERPRETER"))
+            jitCallCountThreshold = std::numeric_limits<int>::max();
+    }
+
     exceptionValue = jsAlloca(1);
     globalObject = static_cast<Object *>(jsAlloca(1));
     jsObjects = jsAlloca(NJSObjects);
@@ -1545,15 +1554,6 @@ QV4::ReturnedValue ExecutionEngine::metaTypeToJS(int type, const void *data)
     return 0;
 }
 
-bool ExecutionEngine::canJIT()
-{
-#ifdef V4_ENABLE_JIT
-    return true;
-#else
-    return false;
-#endif
-}
-
 // Converts a JS value to a meta-type.
 // data must point to a place that can store a value of the given type.
 // Returns true if conversion succeeded, false otherwise.
diff --git a/src/qml/jsruntime/qv4engine_p.h b/src/qml/jsruntime/qv4engine_p.h
index 346f290feb..61efe0c41e 100644
--- a/src/qml/jsruntime/qv4engine_p.h
+++ b/src/qml/jsruntime/qv4engine_p.h
@@ -56,7 +56,9 @@
 #include <private/qintrusivelist_p.h>
 #include "qv4enginebase_p.h"
 
+
 #ifndef V4_BOOTSTRAP
+#  include "qv4function_p.h"
 #  include <private/qv8engine_p.h>
 #  include <private/qv4compileddata_p.h>
 #endif
@@ -85,6 +87,7 @@ namespace CompiledData {
 struct CompilationUnit;
 }
 
+struct Function;
 struct InternalClass;
 struct InternalClassPool;
 
@@ -481,13 +484,22 @@ public:
 
     bool checkStackLimits();
 
-    static bool canJIT();
+    bool canJIT(Function *f)
+    {
+#if defined(V4_ENABLE_JIT) && !defined(V4_BOOTSTRAP)
+        return f->interpreterCallCount > jitCallCountThreshold;
+#else
+        Q_UNUSED(f);
+        return false;
+#endif
+    }
 
 private:
 #if QT_CONFIG(qml_debug)
     QScopedPointer<QV4::Debugging::Debugger> m_debugger;
     QScopedPointer<QV4::Profiling::Profiler> m_profiler;
 #endif
+    int jitCallCountThreshold;
 };
 
 // This is a trick to tell the code generators that functions taking a NoThrowContext won't
diff --git a/src/qml/jsruntime/qv4function_p.h b/src/qml/jsruntime/qv4function_p.h
index 0e61be5115..dcbd41f2e6 100644
--- a/src/qml/jsruntime/qv4function_p.h
+++ b/src/qml/jsruntime/qv4function_p.h
@@ -83,6 +83,7 @@ struct Q_QML_EXPORT Function {
     // first nArguments names in internalClass are the actual arguments
     InternalClass *internalClass;
     uint nFormals;
+    int interpreterCallCount = 0;
     bool hasQmlDependencies;
 
     Function(ExecutionEngine *engine, CompiledData::CompilationUnit *unit, const CompiledData::Function *function, Code codePtr);
diff --git a/src/qml/jsruntime/qv4vme_moth.cpp b/src/qml/jsruntime/qv4vme_moth.cpp
index c21d992e98..6956112718 100644
--- a/src/qml/jsruntime/qv4vme_moth.cpp
+++ b/src/qml/jsruntime/qv4vme_moth.cpp
@@ -552,17 +552,17 @@ QV4::ReturnedValue VME::exec(const FunctionObject *fo, const Value *thisObject,
 
     Profiling::FunctionCallProfiler profiler(engine, function); // start execution profiling
     QV4::Debugging::Debugger *debugger = engine->debugger();
-
     const uchar *exceptionHandler = 0;
 
     QV4::Value &accumulator = frame.jsFrame->accumulator;
     QV4::ReturnedValue acc = Encode::undefined();
 
 #ifdef V4_ENABLE_JIT
-    static const bool forceInterpreter = qEnvironmentVariableIsSet("QV4_FORCE_INTERPRETER");
-    if (function->jittedCode == nullptr) {
-        if (ExecutionEngine::canJIT() && debugger == nullptr && !forceInterpreter)
+    if (function->jittedCode == nullptr && debugger == nullptr) {
+        if (engine->canJIT(function))
             QV4::JIT::BaselineJIT(function).generate();
+        else
+            ++function->interpreterCallCount;
     }
 #endif // V4_ENABLE_JIT