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>

1 files changed, 18 insertions, 7 deletions

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 *);