Speed up exception propagation

Avoid catch (...) with re-throw as it turns that this is very slow because it
throws a new exception and the unwinder starts from scratch. Instead use stack
allocated objects and cleaning destructors to restore state before continuing
with the propagation of exceptions.

Change-Id: I6d95026bcd60b58cb6258a9dae28623a46739532
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

10 files changed, 136 insertions, 163 deletions

diff --git a/src/imports/localstorage/plugin.cpp b/src/imports/localstorage/plugin.cpp
index 84bcb756e8..9a0528a28f 100644
--- a/src/imports/localstorage/plugin.cpp
+++ b/src/imports/localstorage/plugin.cpp
@@ -322,6 +322,35 @@ static ReturnedValue qmlsqldatabase_executeSql(SimpleCallContext *ctx)
     return result.asReturnedValue();
 }
 
+struct TransactionRollback {
+    QSqlDatabase *db;
+    bool *inTransactionFlag;
+
+    TransactionRollback(QSqlDatabase *database, bool *transactionFlag)
+        : db(database)
+        , inTransactionFlag(transactionFlag)
+    {
+        if (inTransactionFlag)
+            *inTransactionFlag = true;
+    }
+
+    ~TransactionRollback()
+    {
+        if (inTransactionFlag)
+            *inTransactionFlag = false;
+        if (db)
+            db->rollback();
+    }
+
+    void clear() {
+        db = 0;
+        if (inTransactionFlag)
+            *inTransactionFlag = false;
+        inTransactionFlag = 0;
+    }
+};
+
+
 static ReturnedValue qmlsqldatabase_changeVersion(SimpleCallContext *ctx)
 {
     if (ctx->callData->argc < 2)
@@ -349,7 +378,6 @@ static ReturnedValue qmlsqldatabase_changeVersion(SimpleCallContext *ctx)
     w->type = QQmlSqlDatabaseWrapper::Query;
     w->database = db;
     w->version = r->version;
-    w->inTransaction = true;
 
     bool ok = true;
     if (!!callback) {
@@ -359,12 +387,10 @@ static ReturnedValue qmlsqldatabase_changeVersion(SimpleCallContext *ctx)
         ScopedCallData callData(scope, 1);
         callData->thisObject = engine->global();
         callData->args[0] = w;
-        try {
-            callback->call(callData);
-        } catch (...) {
-            db.rollback();
-            ctx->rethrowException();
-        }
+
+        TransactionRollback rollbackOnException(&db, &w->inTransaction);
+        callback->call(callData);
+        rollbackOnException.clear();
         if (!db.commit()) {
             db.rollback();
             V4THROW_SQL(SQLEXCEPTION_UNKNOWN_ERR,QQmlEngine::tr("SQL transaction failed"));
@@ -373,8 +399,6 @@ static ReturnedValue qmlsqldatabase_changeVersion(SimpleCallContext *ctx)
         }
     }
 
-    w->inTransaction = false;
-
     if (ok) {
         w->version = to_version;
 #ifndef QT_NO_SETTINGS
@@ -408,22 +432,15 @@ static ReturnedValue qmlsqldatabase_transaction_shared(SimpleCallContext *ctx, b
     w->database = db;
     w->version = r->version;
     w->readonly = readOnly;
-    w->inTransaction = true;
 
     db.transaction();
     if (callback) {
         ScopedCallData callData(scope, 1);
         callData->thisObject = engine->global();
         callData->args[0] = w;
-        try {
-            callback->call(callData);
-        } catch (...) {
-            w->inTransaction = false;
-            db.rollback();
-            ctx->rethrowException();
-        }
-
-        w->inTransaction = false;
+        TransactionRollback rollbackOnException(&db, &w->inTransaction);
+        callback->call(callData);
+        rollbackOnException.clear();
 
         if (!db.commit())
             db.rollback();
diff --git a/src/qml/jsruntime/qv4context.cpp b/src/qml/jsruntime/qv4context.cpp
index be6e1649cf..f3d2ab66ed 100644
--- a/src/qml/jsruntime/qv4context.cpp
+++ b/src/qml/jsruntime/qv4context.cpp
@@ -649,11 +649,6 @@ ReturnedValue ExecutionContext::catchException(StackTrace *trace)
     return engine->catchException(this, trace);
 }
 
-void ExecutionContext::rethrowException()
-{
-    engine->rethrowException(this);
-}
-
 void ExecutionContext::throwReferenceError(const ValueRef value)
 {
     Scope scope(this);
diff --git a/src/qml/jsruntime/qv4context_p.h b/src/qml/jsruntime/qv4context_p.h
index d44c7d25f9..e5b0c431ca 100644
--- a/src/qml/jsruntime/qv4context_p.h
+++ b/src/qml/jsruntime/qv4context_p.h
@@ -147,7 +147,6 @@ struct Q_QML_EXPORT ExecutionContext
 
     // Can only be called from within catch(...), rethrows if no JS exception.
     ReturnedValue catchException(StackTrace *trace = 0);
-    void Q_NORETURN rethrowException();
 
     void mark();
 
diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index 23faa43ac7..d312db272c 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -826,19 +826,9 @@ void ExecutionEngine::throwException(const ValueRef value)
     throwInternal();
 }
 
-void ExecutionEngine::rethrowException(ExecutionContext *intermediateCatchingContext)
-{
-    if (hasException) {
-        while (current != intermediateCatchingContext)
-            popContext();
-    }
-    rethrowInternal();
-}
-
 ReturnedValue ExecutionEngine::catchException(ExecutionContext *catchingContext, StackTrace *trace)
 {
-    if (!hasException)
-        rethrowInternal();
+    Q_ASSERT(hasException);
     while (current != catchingContext)
         popContext();
     if (trace)
@@ -858,11 +848,6 @@ void ExecutionEngine::throwInternal()
 {
     throw DummyException();
 }
-
-void ExecutionEngine::rethrowInternal()
-{
-    throw;
-}
 #endif
 
 QT_END_NAMESPACE
diff --git a/src/qml/jsruntime/qv4engine_cxxabi.cpp b/src/qml/jsruntime/qv4engine_cxxabi.cpp
index dfe1db8fe3..f29af5a284 100644
--- a/src/qml/jsruntime/qv4engine_cxxabi.cpp
+++ b/src/qml/jsruntime/qv4engine_cxxabi.cpp
@@ -118,22 +118,6 @@ void ExecutionEngine::throwInternal()
     std::terminate();
 }
 
-void ExecutionEngine::rethrowInternal()
-{
-    cxa_eh_globals *globals = __cxa_get_globals();
-    cxa_exception *exception = globals->caughtExceptions;
-
-    // Make sure we only re-throw our foreign exceptions. For general re-throw
-    // we'd need different code.
-#ifndef __ARM_EABI_UNWINDER__
-    Q_ASSERT(exception->unwindHeader.exception_class == 0x514d4c4a53563400); // QMLJSV40
-#endif
-
-    globals->caughtExceptions = 0;
-    _Unwind_RaiseException(&exception->unwindHeader);
-    std::terminate();
-}
-
 QT_END_NAMESPACE
 
 /*
diff --git a/src/qml/jsruntime/qv4engine_p.h b/src/qml/jsruntime/qv4engine_p.h
index 5da556452e..e49b6a4ebf 100644
--- a/src/qml/jsruntime/qv4engine_p.h
+++ b/src/qml/jsruntime/qv4engine_p.h
@@ -326,11 +326,9 @@ struct Q_QML_EXPORT ExecutionEngine
     StackTrace exceptionStackTrace;
 
     void Q_NORETURN throwException(const ValueRef value);
-    void Q_NORETURN rethrowException(ExecutionContext *intermediateCatchingContext);
     ReturnedValue catchException(ExecutionContext *catchingContext, StackTrace *trace);
 
     void Q_NORETURN throwInternal();
-    void Q_NORETURN rethrowInternal();
     // ----
 
 
@@ -351,6 +349,23 @@ inline ExecutionContext *ExecutionEngine::popContext()
     return current;
 }
 
+struct ExecutionContextSaver
+{
+    ExecutionEngine *engine;
+    ExecutionContext *savedContext;
+
+    ExecutionContextSaver(ExecutionContext *context)
+        : engine(context->engine)
+        , savedContext(context)
+    {
+    }
+    ~ExecutionContextSaver()
+    {
+        while (engine->current != savedContext)
+            engine->popContext();
+    }
+};
+
 } // namespace QV4
 
 QT_END_NAMESPACE
diff --git a/src/qml/jsruntime/qv4function_p.h b/src/qml/jsruntime/qv4function_p.h
index 34ab5df73a..35c98897a0 100644
--- a/src/qml/jsruntime/qv4function_p.h
+++ b/src/qml/jsruntime/qv4function_p.h
@@ -86,13 +86,24 @@ struct Function {
     const CompiledData::Function *compiledFunction;
     CompiledData::CompilationUnit *compilationUnit;
     inline ReturnedValue code(ExecutionContext *ctx, const uchar *data) {
-        SafeValue *stack = ctx->engine->jsStackTop;
-        try {
-            return codePtr(ctx, data);
-        } catch (...) {
-            ctx->engine->jsStackTop = stack;
-            ctx->rethrowException();
-        }
+
+        struct StackSaver {
+            ExecutionEngine *engine;
+            SafeValue *stack;
+
+            StackSaver(ExecutionEngine *engine)
+                : engine(engine)
+                , stack(engine->jsStackTop)
+            {}
+
+            ~StackSaver()
+            {
+                engine->jsStackTop = stack;
+            }
+        };
+
+        StackSaver(ctx->engine);
+        return codePtr(ctx, data);
     }
 
     ReturnedValue (*codePtr)(ExecutionContext *, const uchar *);
diff --git a/src/qml/jsruntime/qv4functionobject.cpp b/src/qml/jsruntime/qv4functionobject.cpp
index 8faf2a74b6..55baef06db 100644
--- a/src/qml/jsruntime/qv4functionobject.cpp
+++ b/src/qml/jsruntime/qv4functionobject.cpp
@@ -443,16 +443,8 @@ ReturnedValue ScriptFunction::construct(Managed *that, CallData *callData)
     callData->thisObject = obj.asReturnedValue();
     ExecutionContext *ctx = context->newCallContext(f.getPointer(), callData);
 
-    ScopedValue result(scope);
-    SAVE_JS_STACK(f->scope);
-    try {
-        result = f->function->code(ctx, f->function->codeData);
-    } catch (...) {
-        context->rethrowException();
-    }
-    CHECK_JS_STACK(f->scope);
-    ctx->engine->popContext();
-
+    ExecutionContextSaver ctxSaver(context);
+    ScopedValue result(scope, f->function->code(ctx, f->function->codeData));
     if (result->isObject())
         return result.asReturnedValue();
     return obj.asReturnedValue();
@@ -474,16 +466,8 @@ ReturnedValue ScriptFunction::call(Managed *that, CallData *callData)
         }
     }
 
-    ScopedValue result(scope);
-    SAVE_JS_STACK(f->scope);
-    try {
-        result = f->function->code(ctx, f->function->codeData);
-    } catch (...) {
-        context->rethrowException();
-    }
-    CHECK_JS_STACK(f->scope);
-    ctx->engine->popContext();
-    return result.asReturnedValue();
+    ExecutionContextSaver ctxSaver(context);
+    return f->function->code(ctx, f->function->codeData);
 }
 
 DEFINE_MANAGED_VTABLE(SimpleScriptFunction);
@@ -540,16 +524,12 @@ ReturnedValue SimpleScriptFunction::construct(Managed *that, CallData *callData)
     callData->thisObject = obj;
     ExecutionContext *ctx = context->newCallContext(stackSpace, scope.alloc(f->varCount), f.getPointer(), callData);
 
-    try {
-        Scoped<Object> result(scope, f->function->code(ctx, f->function->codeData));
-        ctx->engine->popContext();
+    ExecutionContextSaver ctxSaver(context);
+    Scoped<Object> result(scope, f->function->code(ctx, f->function->codeData));
 
-        if (!result)
-            return obj.asReturnedValue();
-        return result.asReturnedValue();
-    } catch (...) {
-        context->rethrowException();
-    }
+    if (!result)
+        return obj.asReturnedValue();
+    return result.asReturnedValue();
 }
 
 ReturnedValue SimpleScriptFunction::call(Managed *that, CallData *callData)
@@ -570,16 +550,8 @@ ReturnedValue SimpleScriptFunction::call(Managed *that, CallData *callData)
         }
     }
 
-    ScopedValue result(scope);
-    SAVE_JS_STACK(f->scope);
-    try {
-        result = f->function->code(ctx, f->function->codeData);
-    } catch (...) {
-        context->rethrowException();
-    }
-    CHECK_JS_STACK(f->scope);
-    ctx->engine->popContext();
-    return result.asReturnedValue();
+    ExecutionContextSaver ctxSaver(context);
+    return f->function->code(ctx, f->function->codeData);
 }
 
 
@@ -613,15 +585,8 @@ ReturnedValue BuiltinFunction::call(Managed *that, CallData *callData)
     ctx.callData = callData;
     v4->pushContext(&ctx);
 
-    ScopedValue result(scope);
-    try {
-        result = f->code(&ctx);
-    } catch (...) {
-        context->rethrowException();
-    }
-
-    context->engine->popContext();
-    return result.asReturnedValue();
+    ExecutionContextSaver ctxSaver(context);
+    return f->code(&ctx);
 }
 
 ReturnedValue IndexedBuiltinFunction::call(Managed *that, CallData *callData)
@@ -637,15 +602,8 @@ ReturnedValue IndexedBuiltinFunction::call(Managed *that, CallData *callData)
     ctx.callData = callData;
     v4->pushContext(&ctx);
 
-    ScopedValue result(scope);
-    try {
-        result = f->code(&ctx, f->index);
-    } catch (...) {
-        context->rethrowException();
-    }
-
-    context->engine->popContext();
-    return result.asReturnedValue();
+    ExecutionContextSaver ctxSaver(context);
+    return f->code(&ctx, f->index);
 }
 
 DEFINE_MANAGED_VTABLE(IndexedBuiltinFunction);
diff --git a/src/qml/jsruntime/qv4globalobject.cpp b/src/qml/jsruntime/qv4globalobject.cpp
index 3b1e0b1bae..4dcdb08415 100644
--- a/src/qml/jsruntime/qv4globalobject.cpp
+++ b/src/qml/jsruntime/qv4globalobject.cpp
@@ -355,6 +355,27 @@ EvalFunction::EvalFunction(ExecutionContext *scope)
 
 ReturnedValue EvalFunction::evalCall(CallData *callData, bool directCall)
 {
+    struct ContextStateSaver {
+        ExecutionContext *savedContext;
+        bool strictMode;
+        ExecutionContext::EvalCode *evalCode;
+        CompiledData::CompilationUnit *compilationUnit;
+
+        ContextStateSaver(ExecutionContext *context)
+            : savedContext(context)
+            , strictMode(context->strictMode)
+            , evalCode(context->currentEvalCode)
+            , compilationUnit(context->compilationUnit)
+        {}
+
+        ~ContextStateSaver()
+        {
+            savedContext->strictMode = strictMode;
+            savedContext->currentEvalCode = evalCode;
+            savedContext->compilationUnit = compilationUnit;
+        }
+    };
+
     if (callData->argc < 1)
         return Encode::undefined();
 
@@ -395,36 +416,19 @@ ReturnedValue EvalFunction::evalCall(CallData *callData, bool directCall)
         return e->call(callData);
     }
 
+    ExecutionContextSaver ctxSaver(parentContext);
+    ContextStateSaver stateSaver(ctx);
+
     ExecutionContext::EvalCode evalCode;
     evalCode.function = function;
     evalCode.next = ctx->currentEvalCode;
     ctx->currentEvalCode = &evalCode;
 
     // set the correct strict mode flag on the context
-    bool cstrict = ctx->strictMode;
     ctx->strictMode = strictMode;
-
-    CompiledData::CompilationUnit * const oldCompilationUnit = ctx->compilationUnit;
     ctx->compilationUnit = function->compilationUnit;
 
-    ScopedValue result(scope);
-    try {
-        result = function->code(ctx, function->codeData);
-    } catch (...) {
-        ctx->strictMode = cstrict;
-        ctx->currentEvalCode = evalCode.next;
-        ctx->compilationUnit = oldCompilationUnit;
-        ctx->rethrowException();
-    }
-
-    ctx->strictMode = cstrict;
-    ctx->currentEvalCode = evalCode.next;
-    ctx->compilationUnit = oldCompilationUnit;
-
-    while (engine->current != parentContext)
-        engine->popContext();
-
-    return result.asReturnedValue();
+    return function->code(ctx, function->codeData);
 }
 
 
diff --git a/src/qml/jsruntime/qv4script.cpp b/src/qml/jsruntime/qv4script.cpp
index 885ea8ea76..d30132140b 100644
--- a/src/qml/jsruntime/qv4script.cpp
+++ b/src/qml/jsruntime/qv4script.cpp
@@ -227,6 +227,27 @@ void Script::parse()
 
 ReturnedValue Script::run()
 {
+    struct ContextStateSaver {
+        ExecutionContext *savedContext;
+        bool strictMode;
+        Lookup *lookups;
+        CompiledData::CompilationUnit *compilationUnit;
+
+        ContextStateSaver(ExecutionContext *context)
+            : savedContext(context)
+            , strictMode(context->strictMode)
+            , lookups(context->lookups)
+            , compilationUnit(context->compilationUnit)
+        {}
+
+        ~ContextStateSaver()
+        {
+            savedContext->strictMode = strictMode;
+            savedContext->lookups = lookups;
+            savedContext->compilationUnit = compilationUnit;
+        }
+    };
+
     if (!parsed)
         parse();
     if (!vmFunction)
@@ -238,29 +259,13 @@ ReturnedValue Script::run()
     if (qml.isUndefined()) {
         TemporaryAssignment<Function*> savedGlobalCode(engine->globalCode, vmFunction);
 
-        bool strict = scope->strictMode;
-        Lookup *oldLookups = scope->lookups;
-        CompiledData::CompilationUnit * const oldCompilationUnit = scope->compilationUnit;
-
+        ExecutionContextSaver ctxSaver(scope);
+        ContextStateSaver stateSaver(scope);
         scope->strictMode = vmFunction->isStrict();
         scope->lookups = vmFunction->compilationUnit->runtimeLookups;
         scope->compilationUnit = vmFunction->compilationUnit;
 
-        QV4::ScopedValue result(valueScope);
-        try {
-            result = vmFunction->code(scope, vmFunction->codeData);
-        } catch (...) {
-            scope->strictMode = strict;
-            scope->lookups = oldLookups;
-            scope->compilationUnit = oldCompilationUnit;
-            scope->rethrowException();
-        }
-
-        scope->lookups = oldLookups;
-        scope->compilationUnit = oldCompilationUnit;
-
-        return result.asReturnedValue();
-
+        return vmFunction->code(scope, vmFunction->codeData);
     } else {
         ScopedObject qmlObj(valueScope, qml.value());
         FunctionObject *f = new (engine->memoryManager) QmlBindingWrapper(scope, vmFunction, qmlObj);