Implement output tracing for generator bail-in

Since bailing in happens in the jit'd code, we have to generate code to output the trace. If tracing is enabled, we will fill the array of bail-in symbols in the generator instance (`bailInSymbolsTraceArray`) with their ids and values and finally output them with a call to a runtime helper.

`-trace:bailin` together with `-trace:bailout -verbose` can help us easily debug jit'd generators by comparing the values when bailing out for `yield` and bailing in:

```
BailOut: function: func68 ( (chakra-core#1.1), chakra-core#2) offset: #003f Opcode: Yield Kind: BailOutForGeneratorYield
BailOut:   Register #  0: Not live
BailOut:   Register #  1: Constant table
BailOut:   Register #  2: Register r15     16, value: 0x0000023CE132EEA0 (Yield Return Value)
BailOut:   Register #  3: Register r12     13, value: 0x0001000000000004
BailOut:   Return Value: 0x0000023CE132EEA0

BailIn: function: func68 ( (chakra-core#1.1), chakra-core#2) offset: chakra-core#42
BailIn: Register #   3, value: 0x0001000000000004
```

```
BailOut: function: func68 ( (chakra-core#1.1), chakra-core#2) offset: #006b Opcode: Yield Kind: BailOutForGeneratorYield
BailOut:   Register #  0: Not live
BailOut:   Register #  1: Constant table
BailOut:   Register #  3: Register r15     16, value: 0x0000023CE133E060 (Yield Return Value)
BailOut:   Return Value: 0x0000023CE133E060

BailIn: function: func68 ( (chakra-core#1.1), chakra-core#2) offset: #006e
BailIn: No symbols reloaded
```

lib/Backend/IRBuilder.cpp

@@ -1891,6 +1891,20 @@ IRBuilder::BuildReg2(Js::OpCode newOpcode, uint32 offset, Js::RegSlot R0, Js::Re
         this->AddInstr(bailInLabel, offset);
         this->m_func->AddYieldOffsetResumeLabel(nextOffset, bailInLabel);
 
+
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+        if (PHASE_TRACE(Js::Phase::BailInPhase, this->m_func))
+        {
+            IR::LabelInstr* traceBailInLabel = IR::LabelInstr::New(Js::OpCode::GeneratorOutputBailInTraceLabel, m_func);
+            traceBailInLabel->m_hasNonBranchRef = true;     // set to true so that we don't move this label around
+            LABELNAMESET(traceBailInLabel, "OutputBailInTrace");
+            this->AddInstr(traceBailInLabel, offset);
+
+            IR::Instr* traceBailIn = IR::Instr::New(Js::OpCode::GeneratorOutputBailInTrace, m_func);
+            this->AddInstr(traceBailIn, offset);
+        }
+#endif
+
         // This label indicates the section where we start loading the ResumeYieldData on the stack
         // that comes from either .next(), .return(), or .throw() to the right symbol and finally
         // extract its data through Op_ResumeYield

lib/Backend/JnHelperMethodList.h

@@ -543,6 +543,10 @@ HELPERCALL(Await,                       Js::InterpreterStackFrame::OP_Await, Att
 
 HELPERCALL(CreateInterpreterStackFrameForGenerator, Js::InterpreterStackFrame::CreateInterpreterStackFrameForGenerator, AttrCanNotBeReentrant)
 
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+HELPERCALL(OutputGeneratorBailInTrace, Js::JavascriptGenerator::OutputBailInTrace, AttrCanNotBeReentrant)
+#endif
+
 #if DBG
 HELPERCALL(IntRangeCheckFailure, Js::JavascriptNativeOperators::IntRangeCheckFailure, AttrCanNotBeReentrant)
 #endif

lib/Backend/LinearScan.cpp

@@ -5039,6 +5039,15 @@ IR::Instr* LinearScan::GeneratorBailIn::GenerateBailIn(IR::Instr* resumeLabelIns
     this->InsertRestoreSymbols(bailOutInfo->byteCodeUpwardExposedUsed, insertionPoint);
     Assert(!this->func->IsStackArgsEnabled());
 
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+    if (PHASE_TRACE(Js::Phase::BailInPhase, this->func))
+    {
+        IR::Instr* insertBailInTraceBefore = instrAfter;
+        Assert(insertBailInTraceBefore->m_opcode == Js::OpCode::GeneratorOutputBailInTraceLabel);
+        this->InsertBailInTrace(bailOutInfo->byteCodeUpwardExposedUsed, insertBailInTraceBefore->m_next);
+    }
+#endif
+
     return instrAfter;
 }
 
@@ -5195,3 +5204,67 @@ uint32 LinearScan::GeneratorBailIn::GetOffsetFromInterpreterStackFrame(Js::RegSl
         return regSlot * sizeof(Js::Var) + Js::InterpreterStackFrame::GetOffsetOfLocals();
     }
 }
+
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+void LinearScan::GeneratorBailIn::InsertBailInTrace(BVSparse<JitArenaAllocator>* symbols, IR::Instr* insertBeforeInstr)
+{
+    IR::RegOpnd* traceBailInSymbolsArrayRegOpnd = this->interpreterFrameRegOpnd;
+
+    // Load JavascriptGenerator->bailInSymbolsTraceArray
+    {
+        LinearScan::InsertMove(traceBailInSymbolsArrayRegOpnd, this->CreateGeneratorObjectOpnd(), insertBeforeInstr);
+        IR::IndirOpnd* traceBailInSymbolsArrayIndirOpnd = IR::IndirOpnd::New(traceBailInSymbolsArrayRegOpnd, Js::JavascriptGenerator::GetBailInSymbolsTraceArrayOffset(), TyMachPtr, this->func);
+        LinearScan::InsertMove(traceBailInSymbolsArrayRegOpnd, traceBailInSymbolsArrayIndirOpnd, insertBeforeInstr);
+    }
+
+    int count = 0;
+    FOREACH_BITSET_IN_SPARSEBV(symId, symbols)
+    {
+        StackSym* stackSym = this->func->m_symTable->FindStackSym(symId);
+        Lifetime* lifetime = stackSym->scratch.linearScan.lifetime;
+
+        if (!this->NeedsReloadingValueWhenBailIn(stackSym, lifetime))
+        {
+            continue;
+        }
+
+        int offset = sizeof(Js::JavascriptGenerator::BailInSymbol) * count;
+
+        // Assign JavascriptGenerator->bailInSymbolsTraceArray[count]->id
+        {
+            IR::IndirOpnd* idIndirOpnd = IR::IndirOpnd::New(traceBailInSymbolsArrayRegOpnd, offset + Js::JavascriptGenerator::BailInSymbol::GetBailInSymbolIdOffset(), TyMachPtr, this->func);
+            IR::IntConstOpnd* idConstOpnd = IR::IntConstOpnd::New(stackSym->m_id, TyUint8, this->func);
+            LinearScan::InsertMove(idIndirOpnd, idConstOpnd, insertBeforeInstr);
+        }
+
+        // Assign JavascriptGenerator->bailInSymbolsTraceArray[count]->value
+        {
+            IR::IndirOpnd* valueIndirOpnd = IR::IndirOpnd::New(traceBailInSymbolsArrayRegOpnd, offset + Js::JavascriptGenerator::BailInSymbol::GetBailInSymbolValueOffset(), TyMachPtr, this->func);
+            IR::Opnd* srcOpnd;
+            if (lifetime->isSpilled)
+            {
+                IR::SymOpnd* stackSymOpnd = IR::SymOpnd::New(stackSym, stackSym->GetType(), this->func);
+                LinearScan::InsertMove(this->tempRegOpnd, stackSymOpnd, insertBeforeInstr);
+                srcOpnd = this->tempRegOpnd;
+            }
+            else
+            {
+                srcOpnd = IR::RegOpnd::New(stackSym, stackSym->GetType(), this->func);
+                srcOpnd->AsRegOpnd()->SetReg(lifetime->reg);
+            }
+            LinearScan::InsertMove(valueIndirOpnd, srcOpnd, insertBeforeInstr);
+        }
+
+        count++;
+    }
+    NEXT_BITSET_IN_SPARSEBV;
+
+    // Assign JavascriptGenerator->bailInSymbolsTraceArrayCount
+    {
+        LinearScan::InsertMove(this->tempRegOpnd, this->CreateGeneratorObjectOpnd(), insertBeforeInstr);
+        IR::IndirOpnd* traceBailInSymbolsArrayCountIndirOpnd = IR::IndirOpnd::New(this->tempRegOpnd, Js::JavascriptGenerator::GetBailInSymbolsTraceArrayCountOffset(), TyMachPtr, this->func);
+        IR::IntConstOpnd* countOpnd = IR::IntConstOpnd::New(count, TyInt32, this->func);
+        LinearScan::InsertMove(traceBailInSymbolsArrayCountIndirOpnd, countOpnd, insertBeforeInstr);
+    }
+}
+#endif

lib/Backend/LinearScan.h

@@ -272,6 +272,9 @@ class LinearScan
 
         void InsertRestoreSymbols(BVSparse<JitArenaAllocator>* symbols, BailInInsertionPoint& insertionPoint);
 
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+        void InsertBailInTrace(BVSparse<JitArenaAllocator>* symbols, IR::Instr* insertBeforeInstr);
+#endif
     public:
         GeneratorBailIn(Func* func, LinearScan* linearScan);
         IR::Instr* GenerateBailIn(IR::Instr* resumeLabelInstr, BailOutInfo* bailOutInfo);

lib/Backend/Lower.cpp

@@ -3031,6 +3031,14 @@ Lowerer::LowerRange(IR::Instr *instrStart, IR::Instr *instrEnd, bool defaultDoFa
             break;
         }
 
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+        case Js::OpCode::GeneratorOutputBailInTrace:
+        {
+            this->m_lowerGeneratorHelper.LowerGeneratorTraceBailIn(instr);
+            break;
+        }
+#endif
+
         case Js::OpCode::GeneratorResumeJumpTable:
         {
             this->m_lowerGeneratorHelper.InsertBailOutForElidedYield();
@@ -3140,6 +3148,9 @@ Lowerer::LowerRange(IR::Instr *instrStart, IR::Instr *instrEnd, bool defaultDoFa
             instrPrev = this->LowerStPropIdArrFromVar(instr);
             break;
 
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+        case Js::OpCode::GeneratorOutputBailInTraceLabel:
+#endif
         case Js::OpCode::GeneratorBailInLabel:
         case Js::OpCode::GeneratorResumeYieldLabel:
         case Js::OpCode::GeneratorEpilogueFrameNullOut:
@@ -26550,6 +26561,9 @@ Lowerer::ValidOpcodeAfterLower(IR::Instr* instr, Func * func)
         Assert(func->HasTry() && func->DoOptimizeTry());
         return func && !func->isPostFinalLower; //Lowered in FinalLower phase
 
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+    case Js::OpCode::GeneratorOutputBailInTraceLabel:
+#endif
     case Js::OpCode::GeneratorBailInLabel:
     case Js::OpCode::GeneratorResumeYieldLabel:
     case Js::OpCode::GeneratorEpilogueFrameNullOut:
@@ -29286,6 +29300,18 @@ Lowerer::LowerGeneratorHelper::LowerCreateInterpreterStackFrameForGenerator(IR::
     this->lowererMD.ChangeToHelperCall(instr, IR::HelperCreateInterpreterStackFrameForGenerator);
 }
 
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+void
+Lowerer::LowerGeneratorHelper::LowerGeneratorTraceBailIn(IR::Instr* instr)
+{
+    StackSym* genParamSym = StackSym::NewParamSlotSym(1, instr->m_func);
+    instr->m_func->SetArgOffset(genParamSym, LowererMD::GetFormalParamOffset() * MachPtr);
+    IR::SymOpnd* genParamOpnd = IR::SymOpnd::New(genParamSym, TyMachPtr, instr->m_func);
+    this->lowererMD.LoadHelperArgument(instr, genParamOpnd);
+    this->lowererMD.ChangeToHelperCall(instr, IR::HelperOutputGeneratorBailInTrace);
+}
+#endif
+
 IR::SymOpnd*
 Lowerer::LowerGeneratorHelper::CreateResumeYieldDataOpnd() const
 {

lib/Backend/Lower.h

@@ -893,6 +893,10 @@ class Lowerer
         void LowerResumeGenerator(IR::Instr* instr);
         void LowerYield(IR::Instr* instr);
         void LowerGeneratorLoadResumeYieldData(IR::Instr* instr);
+
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+        void LowerGeneratorTraceBailIn(IR::Instr* instr);
+#endif
     };
 
     LowerGeneratorHelper m_lowerGeneratorHelper;

lib/Common/ConfigFlagsList.h

@@ -324,6 +324,7 @@ PHASE(All)
                 PHASE(FinishPartial)
         PHASE(Host)
         PHASE(BailOut)
+        PHASE(BailIn)
         PHASE(RegexQc)
         PHASE(RegexOptBT)
         PHASE(InlineCache)

lib/Runtime/ByteCode/OpCodes.h

@@ -853,6 +853,8 @@ MACRO_BACKEND_ONLY(LazyBailOutThunkLabel, Empty, None)
 MACRO_BACKEND_ONLY(GeneratorResumeJumpTable,                Reg1,   OpSideEffect) // OpSideEffect because we don't want this to be deadstored
 MACRO_BACKEND_ONLY(GeneratorCreateInterpreterStackFrame,    Reg1,   OpSideEffect) // OpSideEffect because we don't want this to be deadstored
 MACRO_BACKEND_ONLY(GeneratorLoadResumeYieldData,            Reg1,   OpSideEffect) // OpSideEffect because we don't want this to be deadstored
+MACRO_BACKEND_ONLY(GeneratorOutputBailInTrace,              Empty,  OpSideEffect) // OpSideEffect because we don't want this to be deadstored
+MACRO_BACKEND_ONLY(GeneratorOutputBailInTraceLabel,         Empty,  None)         // OpSideEffect because we don't want this to be deadstored
 MACRO_BACKEND_ONLY(GeneratorBailInLabel,                    Empty,  None)
 MACRO_BACKEND_ONLY(GeneratorResumeYieldLabel,               Empty,  None)
 MACRO_BACKEND_ONLY(GeneratorEpilogueFrameNullOut,           Empty,  None)

lib/Runtime/Language/InterpreterStackFrame.cpp

@@ -1844,6 +1844,20 @@ namespace Js
         newInstance->m_reader.Create(executeFunction);
 
         generator->SetFrame(newInstance, varSizeInBytes);
+
+        // Moving this to when we create the generator instance in the first place would be nice.
+        // But at that point the function might not have been parsed yet, so we don't have the locals count.
+        // We are also allocating more space than we actually need because we shouldn't need to
+        // reload all the symbols when bailing in.
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+        if (PHASE_TRACE(Js::Phase::BailInPhase, function->GetFunctionBody()))
+        {
+            generator->bailInSymbolsTraceArray = (Js::JavascriptGenerator::BailInSymbol*) RecyclerNewArrayLeafZ(
+                functionScriptContext->GetRecycler(), Js::JavascriptGenerator::BailInSymbol, executeFunction->GetFunctionBody()->GetLocalsCount()
+            );
+        }
+#endif
+
         return newInstance;
     }
 

lib/Runtime/Library/JavascriptGenerator.cpp

@@ -672,6 +672,28 @@ namespace Js
         return  function->GetScriptContext()->GetLibrary()->GetUndefined();
     }
 
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+    void JavascriptGenerator::OutputBailInTrace(JavascriptGenerator* generator)
+    {
+        char16 debugStringBuffer[MAX_FUNCTION_BODY_DEBUG_STRING_SIZE];
+        FunctionBody *fnBody = generator->scriptFunction->GetFunctionBody();
+        Output::Print(_u("BailIn: function: %s (%s) offset: #%04x\n"), fnBody->GetDisplayName(), fnBody->GetDebugNumberSet(debugStringBuffer), generator->frame->m_reader.GetCurrentOffset());
+
+        if (generator->bailInSymbolsTraceArrayCount == 0)
+        {
+            Output::Print(_u("BailIn: No symbols reloaded\n"), fnBody->GetDisplayName(), fnBody->GetDebugNumberSet(debugStringBuffer));
+        }
+        else
+        {
+            for (int i = 0; i < generator->bailInSymbolsTraceArrayCount; i++)
+            {
+                const JavascriptGenerator::BailInSymbol& symbol = generator->bailInSymbolsTraceArray[i];
+                Output::Print(_u("BailIn: Register #%4d, value: 0x%p\n"), symbol.id, symbol.value);
+            }
+        }
+    }
+#endif
+
     template <> bool VarIsImpl<AsyncGeneratorNextProcessor>(RecyclableObject* obj)
     {
         if (VarIs<JavascriptFunction>(obj))

lib/Runtime/Library/JavascriptGenerator.h

@@ -163,6 +163,23 @@ namespace Js
         virtual void ExtractSnapObjectDataInto(TTD::NSSnapObjects::SnapObject* objData, TTD::SlabAllocator& alloc) override;
         //virtual void ProcessCorePaths() override;
 #endif
+
+#ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+    public:
+        struct BailInSymbol {
+            uint32 id;
+            Var value;
+            static uint32 GetBailInSymbolIdOffset() { return offsetof(BailInSymbol, id); }
+            static uint32 GetBailInSymbolValueOffset() { return offsetof(BailInSymbol, value); }
+        };
+
+        Field(BailInSymbol*) bailInSymbolsTraceArray = nullptr;
+        Field(int) bailInSymbolsTraceArrayCount = 0;
+
+        static uint32 GetBailInSymbolsTraceArrayOffset() { return offsetof(JavascriptGenerator, bailInSymbolsTraceArray); }
+        static uint32 GetBailInSymbolsTraceArrayCountOffset() { return offsetof(JavascriptGenerator, bailInSymbolsTraceArrayCount); }
+        static void OutputBailInTrace(JavascriptGenerator* generator);
+#endif
     };
 
     template <> bool VarIsImpl<JavascriptGenerator>(RecyclableObject* obj);