Start compressing the byte code

As a first step, use only one byte for the instruction type.

Change-Id: I762a05233c277a7144472793bc71e41d9e8e82cb
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/qml/compiler/qv4bytecodegenerator.cpp

@@ -67,10 +67,24 @@ int BytecodeGenerator::newRegisterArray(int n)
     return t;
 }
 
+void BytecodeGenerator::compressInstructions()
+{
+    for (auto &i : instructions) {
+        Instr instr = i.instr;
+        i.packed[0] = static_cast<char>(i.type);
+        memcpy(i.packed + 1, reinterpret_cast<char *>(&instr), i.size);
+        ++i.size;
+        if (i.offsetForJump != -1)
+            ++i.offsetForJump;
+    }
+}
+
 void BytecodeGenerator::finalize(Compiler::Context *context)
 {
     QByteArray code;
 
+    compressInstructions();
+
     // content
     QVector<int> instructionOffsets;
     QVector<int> lineNumbers;
@@ -85,7 +99,7 @@ void BytecodeGenerator::finalize(Compiler::Context *context)
             }
         }
         instructionOffsets.append(code.size());
-        code.append(reinterpret_cast<const char *>(&i.instr), i.size);
+        code.append(i.packed, i.size);
     }
 
     // resolve jumps

src/qml/compiler/qv4bytecodegenerator_p.h

@@ -148,9 +148,8 @@ public:
     void addInstruction(const InstrData<InstrT> &data)
     {
         Instr genericInstr;
-        genericInstr.Nop.instructionType = InstrT;
-        InstrMeta<InstrT>::setDataNoCommon(genericInstr, data);
-        addInstructionHelper(InstrMeta<InstrT>::Size, genericInstr);
+        InstrMeta<InstrT>::setData(genericInstr, data);
+        addInstructionHelper(Moth::Instr::Type(InstrT), InstrMeta<InstrT>::Size, genericInstr);
     }
 
     Q_REQUIRED_RESULT Jump jump()
@@ -228,9 +227,8 @@ public:
     Jump addJumpInstruction(const InstrData<InstrT> &data)
     {
         Instr genericInstr;
-        genericInstr.Nop.instructionType = InstrT;
-        InstrMeta<InstrT>::setDataNoCommon(genericInstr, data);
-        return Jump(this, addInstructionHelper(InstrMeta<InstrT>::Size, genericInstr, offsetof(InstrData<InstrT>, offset)));
+        InstrMeta<InstrT>::setData(genericInstr, data);
+        return Jump(this, addInstructionHelper(Moth::Instr::Type(InstrT), InstrMeta<InstrT>::Size, genericInstr, offsetof(InstrData<InstrT>, offset)));
     }
 
 private:
@@ -238,18 +236,24 @@ private:
     friend struct Label;
     friend struct ExceptionHandler;
 
-    int addInstructionHelper(uint size, const Instr &i, int offsetOfOffset = -1) {
+    int addInstructionHelper(Moth::Instr::Type type, uint size, const Instr &i, int offsetOfOffset = -1) {
         int pos = instructions.size();
-        instructions.append({size, currentLine, offsetOfOffset, -1, i});
+        instructions.append({type, size, 0, currentLine, offsetOfOffset, -1, { i } });
         return pos;
     }
+    void compressInstructions();
 
     struct I {
+        Moth::Instr::Type type;
         uint size;
+        uint position;
         int line;
         int offsetForJump;
         int linkedLabel;
-        Instr instr;
+        union {
+            Instr instr;
+            char packed[sizeof(Instr) + 2]; // 2 for instruction and prefix
+        };
     };
 
     QVector<I> instructions;

src/qml/compiler/qv4instr_moth_p.h

@@ -302,8 +302,6 @@ QT_BEGIN_NAMESPACE
 
 #define MOTH_INSTR_ALIGN_MASK (Q_ALIGNOF(QV4::Moth::Instr) - 1)
 
-#define MOTH_INSTR_HEADER int instructionType;
-
 #define MOTH_INSTR_ENUM(I)  I,
 #define MOTH_INSTR_SIZE(I) ((sizeof(QV4::Moth::Instr::instr_##I) + MOTH_INSTR_ALIGN_MASK) & ~MOTH_INSTR_ALIGN_MASK)
 
@@ -335,7 +333,6 @@ QT_BEGIN_NAMESPACE
     INSTR_##instr(MOTH_EMIT_STRUCT)
 #define MOTH_EMIT_STRUCT_INSTRUCTION(name, nargs, ...) \
     struct instr_##name { \
-        MOTH_INSTR_HEADER \
         MOTH_DEFINE_ARGS(nargs, __VA_ARGS__) \
     };
 
@@ -373,8 +370,8 @@ QT_BEGIN_NAMESPACE
         MOTH_DECODE_ARG(arg4, type, 3);
 
 #define MOTH_DISPATCH() \
-    int instr = *reinterpret_cast<const int *>(code); \
-    code += 4; \
+    int instr = *code; \
+    ++code; \
     goto *jumpTable[instr];
 
 namespace QV4 {
@@ -455,11 +452,10 @@ QT_WARNING_DISABLE_GCC("-Wuninitialized")
         enum { Size = MOTH_INSTR_SIZE(I) }; \
         typedef Instr::instr_##I DataType; \
         static const DataType &data(const Instr &instr) { return instr.I; } \
-        static void setData(Instr &instr, const DataType &v) { instr.I = v; } \
-        static void setDataNoCommon(Instr &instr, const DataType &v) \
-        { memcpy(reinterpret_cast<char *>(&instr.I) + sizeof(Instr::instr_Nop), \
-                 reinterpret_cast<const char *>(&v) + sizeof(Instr::instr_Nop), \
-                 Size - sizeof(Instr::instr_Nop)); } \
+        static void setData(Instr &instr, const DataType &v) \
+        { memcpy(reinterpret_cast<char *>(&instr.I), \
+                 reinterpret_cast<const char *>(&v), \
+                 Size); } \
     };
 FOR_EACH_MOTH_INSTR(MOTH_INSTR_META_TEMPLATE);
 #undef MOTH_INSTR_META_TEMPLATE