Optimizations to the generated byte code

Cut the size of the generated byte code in half, by storing
parameters in a more compact form and always storing the
instruction type in the instruction.

We can still used computed goto's for a fast interpreter, by
looking up the jump point for the next instruction in the jump
table.

Another advantage is that the byte code is now platform independent
(modulo endianness).

The change comes with a 3% performance impact on x86_64, which
is acceptable considering the size savings on the bytecode.

Change-Id: I37de3e1f94611987a85e65ea86536583aa965d6d
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

2 files changed, 7 insertions, 35 deletions

diff --git a/src/qml/jsruntime/qv4vme_moth.cpp b/src/qml/jsruntime/qv4vme_moth.cpp
index a74016ab0c..2288d9ef0a 100644
--- a/src/qml/jsruntime/qv4vme_moth.cpp
+++ b/src/qml/jsruntime/qv4vme_moth.cpp
@@ -304,7 +304,7 @@ using namespace QV4::Moth;
 
 #  define MOTH_END_INSTR(I) } \
     genericInstr = reinterpret_cast<const Instr *>(code); \
-    goto *genericInstr->common.code; \
+    goto *jumpTable[genericInstr->common.instructionType]; \
 
 #else
 
@@ -356,11 +356,7 @@ Param traceParam(const Param &param)
     if (engine->hasException) \
         goto catchException
 
-QV4::ReturnedValue VME::run(ExecutionEngine *engine, const uchar *code
-#ifdef MOTH_THREADED_INTERPRETER
-        , void ***storeJumpTable
-#endif
-        )
+QV4::ReturnedValue VME::run(ExecutionEngine *engine, const uchar *code)
 {
 #ifdef DO_TRACE_INSTR
     qDebug("Starting VME with context=%p and code=%p", context, code);
@@ -369,15 +365,11 @@ QV4::ReturnedValue VME::run(ExecutionEngine *engine, const uchar *code
     qt_v4ResolvePendingBreakpointsHook();
 
 #ifdef MOTH_THREADED_INTERPRETER
-    if (storeJumpTable) {
 #define MOTH_INSTR_ADDR(I, FMT) &&op_##I,
-        static void *jumpTable[] = {
-            FOR_EACH_MOTH_INSTR(MOTH_INSTR_ADDR)
-        };
+    static void *jumpTable[] = {
+        FOR_EACH_MOTH_INSTR(MOTH_INSTR_ADDR)
+    };
 #undef MOTH_INSTR_ADDR
-        *storeJumpTable = jumpTable;
-        return QV4::Primitive::undefinedValue().asReturnedValue();
-    }
 #endif
 
     QV4::Value *stack = 0;
@@ -428,7 +420,7 @@ QV4::ReturnedValue VME::run(ExecutionEngine *engine, const uchar *code
     for (;;) {
         const Instr *genericInstr = reinterpret_cast<const Instr *>(code);
 #ifdef MOTH_THREADED_INTERPRETER
-        goto *genericInstr->common.code;
+        goto *jumpTable[genericInstr->common.instructionType];
 #else
         switch (genericInstr->common.instructionType) {
 #endif
@@ -960,18 +952,6 @@ QV4::ReturnedValue VME::run(ExecutionEngine *engine, const uchar *code
     }
 }
 
-#ifdef MOTH_THREADED_INTERPRETER
-void **VME::instructionJumpTable()
-{
-    static void **jumpTable = 0;
-    if (!jumpTable) {
-        const uchar *code = 0;
-        VME().run(0, code, &jumpTable);
-    }
-    return jumpTable;
-}
-#endif
-
 QV4::ReturnedValue VME::exec(ExecutionEngine *engine, const uchar *code)
 {
     VME vme;
diff --git a/src/qml/jsruntime/qv4vme_moth_p.h b/src/qml/jsruntime/qv4vme_moth_p.h
index f8893509d9..8d46207f2b 100644
--- a/src/qml/jsruntime/qv4vme_moth_p.h
+++ b/src/qml/jsruntime/qv4vme_moth_p.h
@@ -67,16 +67,8 @@ class VME
 public:
     static QV4::ReturnedValue exec(QV4::ExecutionEngine *, const uchar *);
 
-#ifdef MOTH_THREADED_INTERPRETER
-    static void **instructionJumpTable();
-#endif
-
 private:
-    QV4::ReturnedValue run(QV4::ExecutionEngine *, const uchar *code
-#ifdef MOTH_THREADED_INTERPRETER
-            , void ***storeJumpTable = 0
-#endif
-            );
+    QV4::ReturnedValue run(QV4::ExecutionEngine *, const uchar *code);
 };
 
 } // namespace Moth