Fix jit _ReuseLoc

Author: ShortDevelopment

lib/Runtime/ByteCode/ByteCodeEmitter.cpp

@@ -39,7 +39,7 @@ static void EmitNullPropagation(Js::RegSlot targetObjectSlot, ByteCodeGenerator
     // if (targetObject == null) goto skipLabel;
     byteCodeGenerator->Writer()->BrReg2(
         Js::OpCode::BrEq_A, funcInfo->currentOptionalChainSkipLabel,
-        targetObjectSlot, funcInfo->nullConstantRegister
+        targetObjectSlot, funcInfo->undefinedConstantRegister
     );
 }
 
@@ -57,22 +57,30 @@ static void EmitOptionalChainWrapper(ParseNodeUni *pnodeOptChain, ByteCodeGenera
     Js::ByteCodeLabel skipLabel = byteCodeGenerator->Writer()->DefineLabel();
     funcInfo->currentOptionalChainSkipLabel = skipLabel;
 
-    // Acquire slot for the result value
-    // Prefill it with `undefined` (Fallback for short-circuiting)
-    Js::RegSlot resultSlot = funcInfo->AcquireLoc(pnodeOptChain);
-    byteCodeGenerator->Writer()->Reg1(Js::OpCode::LdUndef, resultSlot);
-
     // Copy values from wrapper to inner expression
     ParseNodePtr innerNode = pnodeOptChain->pnode1;
     innerNode->isUsed = pnodeOptChain->isUsed;
-    innerNode->location = pnodeOptChain->location;
 
     // emit chain expression
     // Every `?.` node will call `EmitNullPropagation`
     // `EmitNullPropagation` short-circuits to `skipLabel` in case of a nullish value
     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_ReuseLoc, resultSlot, innerNode->location);
+
+    // Skip short-circuiting logic
+    Js::ByteCodeLabel doneLabel = byteCodeGenerator->Writer()->DefineLabel();
+    byteCodeGenerator->Writer()->Br(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);
     funcInfo->currentOptionalChainSkipLabel = previousSkipLabel;
 }
 

lib/Runtime/ByteCode/ByteCodeGenerator.cpp

@@ -4962,10 +4962,12 @@ void AssignRegisters(ParseNode *pnode, ByteCodeGenerator *byteCodeGenerator)
         CheckMaybeEscapedUse(pnode->AsParseNodeUni()->pnode1, byteCodeGenerator);
         break;
     case knopCoalesce:
-    case knopOptChain:
     case knopObject:
         byteCodeGenerator->AssignNullConstRegister();
         break;
+    case knopOptChain:
+        byteCodeGenerator->AssignUndefinedConstRegister();
+        break;
     case knopClassDecl:
         {
             FuncInfo * topFunc = byteCodeGenerator->TopFuncInfo();