Fix small bug

Author: ShortDevelopment

lib/Runtime/ByteCode/ByteCodeEmitter.cpp

@@ -67,20 +67,29 @@ static void EmitOptionalChainWrapper(ParseNodeUni *pnodeOptChain, ByteCodeGenera
     emitChainContent(innerNode);
     funcInfo->ReleaseLoc(innerNode);
 
-    // Acquire slot for the result value    
-    Js::RegSlot resultSlot = funcInfo->AcquireLoc(pnodeOptChain);
-    // Copy chain result
-    byteCodeGenerator->Writer()->Reg2(Js::OpCode::Ld_A, resultSlot, innerNode->location);
+    if (innerNode->isUsed)
+    {
+        Assert(Js::Constants::NoRegister != innerNode->location);
 
-    // Skip short-circuiting logic
-    Js::ByteCodeLabel doneLabel = byteCodeGenerator->Writer()->DefineLabel();
-    byteCodeGenerator->Writer()->Br(doneLabel);
+        // Acquire slot for the result value
+        Js::RegSlot resultSlot = funcInfo->AcquireLoc(pnodeOptChain);
+        // Copy chain result
+        byteCodeGenerator->Writer()->Reg2(Js::OpCode::Ld_A, resultSlot, innerNode->location);
 
-    // Set `undefined` on short-circuiting
-    byteCodeGenerator->Writer()->MarkLabel(skipLabel);
-    byteCodeGenerator->Writer()->Reg2(Js::OpCode::Ld_A_ReuseLoc, resultSlot, funcInfo->undefinedConstantRegister);
+        // Skip short-circuiting logic
+        Js::ByteCodeLabel doneLabel = byteCodeGenerator->Writer()->DefineLabel();
+        byteCodeGenerator->Writer()->Br(doneLabel);
 
-    byteCodeGenerator->Writer()->MarkLabel(doneLabel);
+        // Set `undefined` on short-circuiting
+        byteCodeGenerator->Writer()->MarkLabel(skipLabel);
+        byteCodeGenerator->Writer()->Reg2(Js::OpCode::Ld_A_ReuseLoc, resultSlot, funcInfo->undefinedConstantRegister);
+
+        byteCodeGenerator->Writer()->MarkLabel(doneLabel);
+    }
+    else
+    {
+        byteCodeGenerator->Writer()->MarkLabel(skipLabel);
+    }
     funcInfo->currentOptionalChainSkipLabel = previousSkipLabel;
 }