Simplify CompiledData::Unit serialization

There are currently two places where we calculate the total size of a
CompiledData::Unit including all of its data, once in its calculateSize()
function and then when constructing the Unit itself. This is error prone when
trying to do changes to the layout, as two places need to be adjusted.  Instead
we can centralize the populating of the entire CompiledData::Unit header, the
calculation of the various offsets as well as the entire size in one shot in a
new generateHeader function. Afterwards we can allocate the final amount of
memory and copy the remaining bytes across and assemble the final data
structure.

Change-Id: Ic26d7812e59d2bee2f45cd72742e3195a56950df
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 83 insertions, 73 deletions

diff --git a/src/qml/compiler/qv4compileddata_p.h b/src/qml/compiler/qv4compileddata_p.h
index b6c0e6e704..a1d0a6d732 100644
--- a/src/qml/compiler/qv4compileddata_p.h
+++ b/src/qml/compiler/qv4compileddata_p.h
@@ -146,8 +146,6 @@ struct RegExp
         QJsonPrivate::qle_bitfield<0, 4> flags;
         QJsonPrivate::qle_bitfield<4, 28> stringIndex;
     };
-
-    static int calculateSize() { return sizeof(RegExp); }
 };
 
 struct Lookup
@@ -166,8 +164,6 @@ struct Lookup
     };
 
     Lookup() { type_and_flags = 0; nameIndex = 0; }
-
-    static int calculateSize() { return sizeof(Lookup); }
 };
 
 struct JSClassMember
@@ -687,15 +683,6 @@ struct Unit
         *nMembers = klass->nMembers;
         return reinterpret_cast<const JSClassMember*>(ptr + sizeof(JSClass));
     }
-
-    static int calculateSize(uint nFunctions, uint nRegExps, uint nConstants,
-                             uint nLookups, uint nClasses) {
-        return (sizeof(Unit)
-                + (nFunctions + nClasses) * sizeof(uint)
-                + nRegExps * RegExp::calculateSize()
-                + nConstants * sizeof(QV4::ReturnedValue)
-                + nLookups * Lookup::calculateSize()
-                + 7) & ~7; }
 };
 
 #if defined(Q_CC_MSVC) || defined(Q_CC_GNU)
diff --git a/src/qml/compiler/qv4compiler.cpp b/src/qml/compiler/qv4compiler.cpp
index 4651bc2c8f..fc462bb1c6 100644
--- a/src/qml/compiler/qv4compiler.cpp
+++ b/src/qml/compiler/qv4compiler.cpp
@@ -218,85 +218,45 @@ QV4::CompiledData::Unit *QV4::Compiler::JSUnitGenerator::generateUnit(GeneratorO
             registerString(*f->locals.at(i));
     }
 
-    int unitSize = QV4::CompiledData::Unit::calculateSize(irModule->functions.size(), regexps.size(),
-                                                          constants.size(), lookups.size(), jsClassOffsets.count());
-
     CompiledData::LEUInt32 *functionOffsets = reinterpret_cast<CompiledData::LEUInt32*>(alloca(irModule->functions.size() * sizeof(CompiledData::LEUInt32)));
-    uint functionDataSize = 0;
-    for (int i = 0; i < irModule->functions.size(); ++i) {
-        QV4::IR::Function *f = irModule->functions.at(i);
-        functionOffsets[i] = functionDataSize + unitSize;
+    uint jsClassDataOffset = 0;
 
-        const int qmlIdDepsCount = f->idObjectDependencies.count();
-        const int qmlPropertyDepsCount = f->scopeObjectPropertyDependencies.count() + f->contextObjectPropertyDependencies.count();
-        functionDataSize += QV4::CompiledData::Function::calculateSize(f->formals.size(), f->locals.size(), f->nestedFunctions.size(), qmlIdDepsCount, qmlPropertyDepsCount);
-    }
-
-    const int totalSize = unitSize + functionDataSize + jsClassData.size() + (option == GenerateWithStringTable ? stringTable.sizeOfTableAndData() : 0);
-    char *data = (char *)malloc(totalSize);
-    memset(data, 0, totalSize);
-    QV4::CompiledData::Unit *unit = (QV4::CompiledData::Unit*)data;
-
-    memcpy(unit->magic, QV4::CompiledData::magic_str, sizeof(unit->magic));
-    unit->architecture = 0; // ###
-    unit->flags = QV4::CompiledData::Unit::IsJavascript;
-    unit->version = 1;
-    unit->unitSize = totalSize;
-    unit->functionTableSize = irModule->functions.size();
-    unit->offsetToFunctionTable = sizeof(*unit);
-    unit->lookupTableSize = lookups.count();
-    unit->offsetToLookupTable = unit->offsetToFunctionTable + unit->functionTableSize * sizeof(uint);
-    unit->regexpTableSize = regexps.size();
-    unit->offsetToRegexpTable = unit->offsetToLookupTable + unit->lookupTableSize * CompiledData::Lookup::calculateSize();
-    unit->constantTableSize = constants.size();
-    unit->offsetToConstantTable = unit->offsetToRegexpTable + unit->regexpTableSize * CompiledData::RegExp::calculateSize();
-    unit->jsClassTableSize = jsClassOffsets.count();
-    unit->offsetToJSClassTable = unit->offsetToConstantTable + unit->constantTableSize * sizeof(ReturnedValue);
-    if (option == GenerateWithStringTable) {
-        unit->stringTableSize = stringTable.stringCount();
-        unit->offsetToStringTable = unitSize + functionDataSize + jsClassData.size();
-    } else {
-        unit->stringTableSize = 0;
-        unit->offsetToStringTable = 0;
+    char *dataPtr;
+    CompiledData::Unit *unit;
+    {
+        QV4::CompiledData::Unit tempHeader = generateHeader(option, functionOffsets, &jsClassDataOffset);
+        dataPtr = reinterpret_cast<char *>(malloc(tempHeader.unitSize));
+        memcpy(&unit, &dataPtr, sizeof(CompiledData::Unit*));
+        memcpy(unit, &tempHeader, sizeof(tempHeader));
     }
-    unit->indexOfRootFunction = -1;
-    unit->sourceFileIndex = getStringId(irModule->fileName);
-    unit->nImports = 0;
-    unit->offsetToImports = 0;
-    unit->nObjects = 0;
-    unit->offsetToObjects = 0;
-    unit->indexOfRootObject = 0;
 
-    memcpy(data + unit->offsetToFunctionTable, functionOffsets, unit->functionTableSize * sizeof(CompiledData::LEUInt32));
+    memcpy(dataPtr + unit->offsetToFunctionTable, functionOffsets, unit->functionTableSize * sizeof(CompiledData::LEUInt32));
 
-    char *f = data + unitSize;
     for (int i = 0; i < irModule->functions.size(); ++i) {
         QV4::IR::Function *function = irModule->functions.at(i);
         if (function == irModule->rootFunction)
             unit->indexOfRootFunction = i;
 
-        const int bytes = writeFunction(f, function);
-        f += bytes;
+        writeFunction(dataPtr + functionOffsets[i], function);
     }
 
-    CompiledData::Lookup *lookupsToWrite = (CompiledData::Lookup*)(data + unit->offsetToLookupTable);
+    CompiledData::Lookup *lookupsToWrite = reinterpret_cast<CompiledData::Lookup*>(dataPtr + unit->offsetToLookupTable);
     foreach (const CompiledData::Lookup &l, lookups)
         *lookupsToWrite++ = l;
 
-    CompiledData::RegExp *regexpTable = (CompiledData::RegExp *)(data + unit->offsetToRegexpTable);
+    CompiledData::RegExp *regexpTable = reinterpret_cast<CompiledData::RegExp *>(dataPtr + unit->offsetToRegexpTable);
     memcpy(regexpTable, regexps.constData(), regexps.size() * sizeof(*regexpTable));
 
-    ReturnedValue *constantTable = (ReturnedValue *)(data + unit->offsetToConstantTable);
+    ReturnedValue *constantTable = reinterpret_cast<ReturnedValue *>(dataPtr + unit->offsetToConstantTable);
     memcpy(constantTable, constants.constData(), constants.size() * sizeof(ReturnedValue));
 
     {
-        char *jsClassDataPtrToWrite = data + unitSize + functionDataSize;
-        memcpy(jsClassDataPtrToWrite, jsClassData.constData(), jsClassData.size());
+        memcpy(dataPtr + jsClassDataOffset, jsClassData.constData(), jsClassData.size());
 
         // write js classes and js class lookup table
-        CompiledData::LEUInt32 *jsClassOffsetTable = reinterpret_cast<CompiledData::LEUInt32 *>(data + unit->offsetToJSClassTable);
+        CompiledData::LEUInt32 *jsClassOffsetTable = reinterpret_cast<CompiledData::LEUInt32 *>(dataPtr + unit->offsetToJSClassTable);
         for (int i = 0; i < jsClassOffsets.count(); ++i)
-            jsClassOffsetTable[i] = jsClassDataPtrToWrite - data + jsClassOffsets.at(i);
+            jsClassOffsetTable[i] = jsClassDataOffset + jsClassOffsets.at(i);
     }
 
     // write strings and string table
@@ -306,7 +266,7 @@ QV4::CompiledData::Unit *QV4::Compiler::JSUnitGenerator::generateUnit(GeneratorO
     return unit;
 }
 
-int QV4::Compiler::JSUnitGenerator::writeFunction(char *f, QV4::IR::Function *irFunction) const
+void QV4::Compiler::JSUnitGenerator::writeFunction(char *f, QV4::IR::Function *irFunction) const
 {
     QV4::CompiledData::Function *function = (QV4::CompiledData::Function *)f;
 
@@ -390,7 +350,67 @@ int QV4::Compiler::JSUnitGenerator::writeFunction(char *f, QV4::IR::Function *ir
         *writtenDeps++ = property.key(); // property index
         *writtenDeps++ = property.value(); // notify index
     }
+}
+
+QV4::CompiledData::Unit QV4::Compiler::JSUnitGenerator::generateHeader(QV4::Compiler::JSUnitGenerator::GeneratorOption option, QJsonPrivate::q_littleendian<quint32> *functionOffsets, uint *jsClassDataOffset) const
+{
+    CompiledData::Unit unit;
+    memcpy(unit.magic, CompiledData::magic_str, sizeof(unit.magic));
+    unit.architecture = 0; // ###
+    unit.flags = QV4::CompiledData::Unit::IsJavascript;
+    unit.version = 1;
+    unit.functionTableSize = irModule->functions.size();
+
+    quint32 nextOffset = sizeof(CompiledData::Unit);
+
+    unit.offsetToFunctionTable = nextOffset;
+    nextOffset += unit.functionTableSize * sizeof(uint);
+
+    unit.lookupTableSize = lookups.count();
+    unit.offsetToLookupTable = nextOffset;
+    nextOffset += unit.lookupTableSize * sizeof(CompiledData::Lookup);
+
+    unit.regexpTableSize = regexps.size();
+    unit.offsetToRegexpTable = nextOffset;
+    nextOffset += unit.regexpTableSize * sizeof(CompiledData::RegExp);
 
-    return CompiledData::Function::calculateSize(function->nFormals, function->nLocals, function->nInnerFunctions,
-                                                 function->nDependingIdObjects, function->nDependingContextProperties + function->nDependingScopeProperties);
+    unit.constantTableSize = constants.size();
+    unit.offsetToConstantTable = nextOffset;
+    nextOffset += unit.constantTableSize * sizeof(ReturnedValue);
+
+    unit.jsClassTableSize = jsClassOffsets.count();
+    unit.offsetToJSClassTable = nextOffset;
+    nextOffset += unit.jsClassTableSize * sizeof(uint);
+
+    *jsClassDataOffset = nextOffset;
+    nextOffset += jsClassData.size();
+
+    for (int i = 0; i < irModule->functions.size(); ++i) {
+        QV4::IR::Function *f = irModule->functions.at(i);
+        functionOffsets[i] = nextOffset;
+
+        const int qmlIdDepsCount = f->idObjectDependencies.count();
+        const int qmlPropertyDepsCount = f->scopeObjectPropertyDependencies.count() + f->contextObjectPropertyDependencies.count();
+        nextOffset += QV4::CompiledData::Function::calculateSize(f->formals.size(), f->locals.size(), f->nestedFunctions.size(), qmlIdDepsCount, qmlPropertyDepsCount);
+    }
+
+    if (option == GenerateWithStringTable) {
+        unit.stringTableSize = stringTable.stringCount();
+        unit.offsetToStringTable = nextOffset;
+        nextOffset += stringTable.sizeOfTableAndData();
+    } else {
+        unit.stringTableSize = 0;
+        unit.offsetToStringTable = 0;
+    }
+    unit.indexOfRootFunction = -1;
+    unit.sourceFileIndex = getStringId(irModule->fileName);
+    unit.nImports = 0;
+    unit.offsetToImports = 0;
+    unit.nObjects = 0;
+    unit.offsetToObjects = 0;
+    unit.indexOfRootObject = 0;
+
+    unit.unitSize = nextOffset;
+
+    return unit;
 }
diff --git a/src/qml/compiler/qv4compiler_p.h b/src/qml/compiler/qv4compiler_p.h
index 2ff08d76dd..4b67fe8600 100644
--- a/src/qml/compiler/qv4compiler_p.h
+++ b/src/qml/compiler/qv4compiler_p.h
@@ -52,6 +52,7 @@
 
 #include <QtCore/qstring.h>
 #include "qv4jsir_p.h"
+#include <private/qjson_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -114,10 +115,12 @@ struct Q_QML_PRIVATE_EXPORT JSUnitGenerator {
 
     QV4::CompiledData::Unit *generateUnit(GeneratorOption option = GenerateWithStringTable);
     // Returns bytes written
-    int writeFunction(char *f, IR::Function *irFunction) const;
+    void writeFunction(char *f, IR::Function *irFunction) const;
 
     StringTableGenerator stringTable;
 private:
+    CompiledData::Unit generateHeader(GeneratorOption option, QJsonPrivate::q_littleendian<quint32> *functionOffsets, uint *jsClassDataOffset) const;
+
     IR::Module *irModule;
 
     QList<CompiledData::Lookup> lookups;