Implement the dead temporal zone

With const and let it is possible to access the declared member before
initialization. This is expected to throw a type reference error at
run-time.

We initialize such variables with the empty value when entering their
scope and check upon access for that. For locals we place the lexically
scoped variables at the end. For register allocated lexical variables we
group them into one batch and remember the index/size.

Change-Id: Icb493ee0de0525bb682e1bc58981a4dfd33f750e
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/qml/jit/qv4baselineassembler.cpp b/src/qml/jit/qv4baselineassembler.cpp
index c7d8f3c72c..5950901499 100644
--- a/src/qml/jit/qv4baselineassembler.cpp
+++ b/src/qml/jit/qv4baselineassembler.cpp
@@ -66,6 +66,7 @@ namespace JIT {
 #define callHelper(x) PlatformAssemblerCommon::callRuntimeUnchecked(#x, reinterpret_cast<void *>(&x))
 
 const QV4::Value::ValueTypeInternal IntegerTag = QV4::Value::ValueTypeInternal::Integer;
+const QV4::Value::ValueTypeInternal EmptyTag = QV4::Value::ValueTypeInternal::Empty;
 
 static ReturnedValue toNumberHelper(ReturnedValue v)
 {
@@ -172,6 +173,11 @@ public:
         return branch64(Equal, AccumulatorRegister, TrustedImm64(Primitive::emptyValue().asReturnedValue()));
     }
 
+    Jump jumpNotEmpty()
+    {
+        return branch64(NotEqual, AccumulatorRegister, TrustedImm64(Primitive::emptyValue().asReturnedValue()));
+    }
+
     void toBoolean(std::function<void(RegisterID)> continuation)
     {
         urshift64(AccumulatorRegister, TrustedImm32(Value::IsIntegerConvertible_Shift), ScratchRegister);
@@ -634,6 +640,11 @@ public:
         return branch32(Equal, AccumulatorRegisterTag, TrustedImm32(Primitive::emptyValue().asReturnedValue() >> 32));
     }
 
+    Jump jumpNotEmpty()
+    {
+        return branch32(NotEqual, AccumulatorRegisterTag, TrustedImm32(Primitive::emptyValue().asReturnedValue() >> 32));
+    }
+
     void toBoolean(std::function<void(RegisterID)> continuation)
     {
         urshift32(AccumulatorRegisterTag, TrustedImm32(Value::IsIntegerConvertible_Shift - 32),
@@ -1538,6 +1549,19 @@ void BaselineAssembler::popContext()
     pasm()->storeHeapObject(PlatformAssembler::ScratchRegister, regAddr(CallData::Context));
 }
 
+void BaselineAssembler::deadTemporalZoneCheck(int offsetForSavedIP, int variableName)
+{
+    auto valueIsAliveJump = pasm()->jumpNotEmpty();
+    storeInstructionPointer(offsetForSavedIP);
+    saveAccumulatorInFrame();
+    prepareCallWithArgCount(2);
+    passInt32AsArg(variableName, 1);
+    passEngineAsArg(0);
+    ASM_GENERATE_RUNTIME_CALL(Runtime::method_throwReferenceError, CallResultDestination::Ignore);
+    gotoCatchException();
+    valueIsAliveJump.link(pasm());
+}
+
 void BaselineAssembler::ret()
 {
     pasm()->generateFunctionExit();