Change the instruction encoding for the bytecode

Change the encoding, so that even instructions are short ones,
odd instructions long. This implies that the lowest bit encodes
whether an instruction is short or long (1 vs 4 byte encoded).

This prepares for allowing us to extend the totoal number of
instructions beyond 128.

Change-Id: I4732e7241d3593b24ad25cd69555edc25f38d2f6
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

4 files changed, 27 insertions, 22 deletions

diff --git a/src/qml/compiler/qv4bytecodegenerator.cpp b/src/qml/compiler/qv4bytecodegenerator.cpp
index 1d1e98ea58..6efeac2a31 100644
--- a/src/qml/compiler/qv4bytecodegenerator.cpp
+++ b/src/qml/compiler/qv4bytecodegenerator.cpp
@@ -70,10 +70,9 @@ int BytecodeGenerator::newRegisterArray(int n)
 
 void BytecodeGenerator::packInstruction(I &i)
 {
-    uchar type = *reinterpret_cast<uchar *>(i.packed);
-    Q_ASSERT(type >= MOTH_NUM_INSTRUCTIONS());
-    if (type >= MOTH_NUM_INSTRUCTIONS())
-        type -= MOTH_NUM_INSTRUCTIONS();
+    Instr::Type type = Instr::unpack(i.packed);
+    Q_ASSERT(int(type) < MOTH_NUM_INSTRUCTIONS());
+    type = Instr::narrowInstructionType(type);
     int instructionsAsInts[sizeof(Instr)/sizeof(int)] = {};
     int nMembers = Moth::InstrInfo::argumentCount[static_cast<int>(i.type)];
     for (int j = 0; j < nMembers; ++j) {
@@ -89,10 +88,10 @@ void BytecodeGenerator::packInstruction(I &i)
             break;
         }
     }
-    char *code = i.packed;
+    uchar *code = i.packed;
     switch (width) {
     case Normal:
-        *reinterpret_cast<uchar *>(code) = type;
+        Instr::pack(code, type);
         ++code;
         for (int n = 0; n < nMembers; ++n) {
             qint8 v = static_cast<qint8>(instructionsAsInts[n]);
@@ -122,7 +121,7 @@ void BytecodeGenerator::adjustJumpOffsets()
 //        qDebug() << "adjusting jump offset for instruction" << index << i.position << i.size << "offsetForJump" << i.offsetForJump << "target"
 //                 << labels.at(i.linkedLabel) << linkedInstruction.position << "jumpOffset" << jumpOffset;
         uchar type = *reinterpret_cast<const uchar *>(i.packed);
-        if (type >= MOTH_NUM_INSTRUCTIONS()) {
+        if (Instr::isWide(Instr::Type(type))) {
             Q_ASSERT(i.offsetForJump == i.size - 4);
             qToLittleEndian<qint32>(jumpOffset, c);
         } else {
@@ -177,7 +176,7 @@ void BytecodeGenerator::finalize(Compiler::Context *context)
             entry.line = currentLine;
             lineNumbers.append(entry);
         }
-        code.append(i.packed, i.size);
+        code.append(reinterpret_cast<const char *>(i.packed), i.size);
     }
 
     context->code = code;
@@ -228,10 +227,10 @@ QT_WARNING_POP
     if (offsetOfOffset != -1)
         offsetOfOffset += 1;
     I instr{type, static_cast<short>(s + 1), 0, currentLine, offsetOfOffset, -1, "\0\0" };
-    char *code = instr.packed;
-    *reinterpret_cast<uchar *>(code) = static_cast<uchar>(MOTH_NUM_INSTRUCTIONS() + static_cast<int>(type));
+    uchar *code = instr.packed;
+    Instr::pack(code, Instr::wideInstructionType(type));
     ++code;
-    Q_ASSERT(MOTH_NUM_INSTRUCTIONS() + static_cast<int>(type) < 256);
+    Q_ASSERT(static_cast<uint>(Instr::wideInstructionType(type)) < 256);
 
     for (int j = 0; j < argCount; ++j) {
         qToLittleEndian<qint32>(i.argumentsAsInts[j], code);
diff --git a/src/qml/compiler/qv4bytecodegenerator_p.h b/src/qml/compiler/qv4bytecodegenerator_p.h
index 78ce3624ea..dca5771356 100644
--- a/src/qml/compiler/qv4bytecodegenerator_p.h
+++ b/src/qml/compiler/qv4bytecodegenerator_p.h
@@ -279,7 +279,7 @@ private:
         int line;
         int offsetForJump;
         int linkedLabel;
-        char packed[sizeof(Instr) + 2]; // 2 for instruction and prefix
+        unsigned char packed[sizeof(Instr) + 2]; // 2 for instruction type
     };
 
     void compressInstructions();
diff --git a/src/qml/compiler/qv4instr_moth.cpp b/src/qml/compiler/qv4instr_moth.cpp
index 5621b456d5..6773f97c8b 100644
--- a/src/qml/compiler/qv4instr_moth.cpp
+++ b/src/qml/compiler/qv4instr_moth.cpp
@@ -46,7 +46,7 @@ using namespace QV4::Moth;
 
 int InstrInfo::size(Instr::Type type)
 {
-#define MOTH_RETURN_INSTR_SIZE(I) case Instr::Type::I: return InstrMeta<int(Instr::Type::I)>::Size;
+#define MOTH_RETURN_INSTR_SIZE(I) case Instr::Type::I: case Instr::Type::I##_Wide: return InstrMeta<int(Instr::Type::I)>::Size;
     switch (type) {
     FOR_EACH_MOTH_INSTR(MOTH_RETURN_INSTR_SIZE)
     }
diff --git a/src/qml/compiler/qv4instr_moth_p.h b/src/qml/compiler/qv4instr_moth_p.h
index 7c1d4db4ca..29fc28c128 100644
--- a/src/qml/compiler/qv4instr_moth_p.h
+++ b/src/qml/compiler/qv4instr_moth_p.h
@@ -321,7 +321,7 @@ QT_BEGIN_NAMESPACE
     F(Sub) \
     F(LoadQmlContext) \
     F(LoadQmlImportedScripts)
-#define MOTH_NUM_INSTRUCTIONS() (static_cast<int>(Moth::Instr::Type::LoadQmlImportedScripts) + 1)
+#define MOTH_NUM_INSTRUCTIONS() (static_cast<int>(Moth::Instr::Type::LoadQmlImportedScripts_Wide))
 
 #if defined(Q_CC_GNU) && !defined(Q_CC_INTEL)
 // icc before version 1200 doesn't support computed goto, and at least up to version 18.0.0 the
@@ -332,7 +332,7 @@ QT_BEGIN_NAMESPACE
 
 #define MOTH_INSTR_ALIGN_MASK (Q_ALIGNOF(QV4::Moth::Instr) - 1)
 
-#define MOTH_INSTR_ENUM(I)  I,
+#define MOTH_INSTR_ENUM(I)  I, I##_Wide,
 #define MOTH_INSTR_SIZE(I) (sizeof(QV4::Moth::Instr::instr_##I))
 
 #define MOTH_EXPAND_FOR_MSVC(x) x
@@ -375,7 +375,7 @@ QT_BEGIN_NAMESPACE
 #define MOTH_COLLECT_NARGS(instr) \
     INSTR_##instr(MOTH_COLLECT_ARG_COUNT)
 #define MOTH_COLLECT_ARG_COUNT_INSTRUCTION(name, nargs, ...) \
-    nargs,
+    nargs, nargs,
 
 #define MOTH_DECODE_ARG(arg, type, nargs, offset) \
     arg = qFromLittleEndian<type>( \
@@ -430,18 +430,16 @@ QT_BEGIN_NAMESPACE
 #ifdef MOTH_COMPUTED_GOTO
 /* collect jump labels */
 #define COLLECT_LABELS(instr) \
-    INSTR_##instr(GET_LABEL)
+    INSTR_##instr(GET_LABEL) \
+    INSTR_##instr(GET_LABEL_WIDE)
 #define GET_LABEL_INSTRUCTION(name, ...) \
     &&op_byte_##name,
-#define COLLECT_LABELS_WIDE(instr) \
-    INSTR_##instr(GET_LABEL_WIDE)
 #define GET_LABEL_WIDE_INSTRUCTION(name, ...) \
     &&op_int_##name,
 
 #define MOTH_JUMP_TABLE \
     static const void *jumpTable[] = { \
         FOR_EACH_MOTH_INSTR(COLLECT_LABELS) \
-        FOR_EACH_MOTH_INSTR(COLLECT_LABELS_WIDE) \
     };
 
 #define MOTH_DISPATCH() \
@@ -456,7 +454,7 @@ QT_BEGIN_NAMESPACE
 #define MOTH_INSTR_CASE_AND_JUMP_WIDE(instr) \
     INSTR_##instr(GET_CASE_AND_JUMP_WIDE)
 #define GET_CASE_AND_JUMP_WIDE_INSTRUCTION(name, ...) \
-    case (static_cast<uchar>(Instr::Type::name) + MOTH_NUM_INSTRUCTIONS()): goto op_int_##name;
+    case (static_cast<uchar>(Instr::Type::name##_Wide)): goto op_int_##name;
 
 #define MOTH_DISPATCH() \
     switch (static_cast<uchar>(*code)) { \
@@ -507,6 +505,14 @@ union Instr
         FOR_EACH_MOTH_INSTR(MOTH_INSTR_ENUM)
     };
 
+    static Type wideInstructionType(Type t) { return Type(int(t) | 1); }
+    static Type narrowInstructionType(Type t) { return Type(int(t) & ~1); }
+    static bool isWide(Type t) { return int(t) & 1; }
+    static bool isNarrow(Type t) { return !(int(t) & 1); }
+
+    static Type unpack(const uchar *c) { return Type(*c); }
+    static void pack(uchar *c, Type t) { *c = uchar(uint(t)); }
+
     FOR_EACH_MOTH_INSTR(MOTH_EMIT_STRUCTS)
 
     FOR_EACH_MOTH_INSTR(MOTH_EMIT_INSTR_MEMBERS)
@@ -520,7 +526,7 @@ struct InstrInfo
     static int size(Instr::Type type);
 };
 
-Q_STATIC_ASSERT(MOTH_NUM_INSTRUCTIONS() <= 128);
+Q_STATIC_ASSERT(MOTH_NUM_INSTRUCTIONS() <= 256);
 
 template<int N>
 struct InstrMeta {