[PowerPC][NFC] refactor eligible check for tail call optimization

[tingwang]

Summary

The check logic for TCO is scattered in two functions: IsEligibleForTailCallOptimization_64SVR4() IsEligibleForTailCallOptimization(), and serves instruction selection phase only at this moment.

There is one scenario (D131953) during transformation, we would like to determine if tailcall can be guaranteed or not. Existing logic cannot be directly reused due to dependency on DAG and SDValue etc.

This patch aims to refactor existing logic to export an API for TCO eligible query before instruction selection phase.

[shchenz]

LGTM. Please wait for some days for other reviewers.

nit: I think this patch should be NFC, right? If so please update the patch title.

[nemanjai]

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

5650–5660

This seems like a strange structure. You have 3 disjoint conditions that each simply set a Boolean variable that is then returned. Why not:

if (...)
  return false;
else if (...)
  return IsEligibleForTailCallOptimization_64SVR4(...);
else
  return IsEligibleForTailCallOptimization(...);

[tingwang]

Address comments.

[shchenz]

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

5651

nit: no need for the two else.

[tingwang]

Address comment and removed the second else.

[tingwang]

Continue NIT: maybe remove the first else makes more sense...

[nemanjai]

LGTM. Thanks.

llvm/lib/Target/PowerPC/PPCISelLowering.h

private:
     SDValue LowerINT_TO_FPVector(SDValue Op, SelectionDAG &DAG,
                                  const SDLoc &dl) const;
 
     SDValue LowerTRUNCATEVector(SDValue Op, SelectionDAG &DAG) const;
 
     SDValue getFramePointerFrameIndex(SelectionDAG & DAG) const;
     SDValue getReturnAddrFrameIndex(SelectionDAG & DAG) const;
 
-    bool
-    IsEligibleForTailCallOptimization(SDValue Callee,
-                                      CallingConv::ID CalleeCC,
-                                      bool isVarArg,
-                                      const SmallVectorImpl<ISD::InputArg> &Ins,
-                                      SelectionDAG& DAG) const;
+    bool IsEligibleForTailCallOptimization(
+        const GlobalValue *CalleeGV, CallingConv::ID CalleeCC,
+        CallingConv::ID CallerCC, bool isVarArg,
+        const SmallVectorImpl<ISD::InputArg> &Ins, bool isByValArg) const;
 
     bool IsEligibleForTailCallOptimization_64SVR4(
-        SDValue Callee, CallingConv::ID CalleeCC, const CallBase *CB,
-        bool isVarArg, const SmallVectorImpl<ISD::OutputArg> &Outs,
-        const SmallVectorImpl<ISD::InputArg> &Ins, SelectionDAG &DAG) const;
+        const GlobalValue *CalleeGV, CallingConv::ID CalleeCC,
+        CallingConv::ID CallerCC, const CallBase *CB, bool isVarArg,
+        const SmallVectorImpl<ISD::OutputArg> &Outs,
+        const SmallVectorImpl<ISD::InputArg> &Ins, bool isByValArg,
+        const Function *CallerFunc, bool isCalleeExternalSymbol) const;
+
+    bool isEligibleForTCO(const GlobalValue *CalleeGV, CallingConv::ID CalleeCC,
+                          CallingConv::ID CallerCC, const CallBase *CB,
+                          bool isVarArg,
+                          const SmallVectorImpl<ISD::OutputArg> &Outs,
+                          const SmallVectorImpl<ISD::InputArg> &Ins,
+                          bool isByValArg, const Function *CallerFunc,
+                          bool isCalleeExternalSymbol) const;
 
     SDValue EmitTailCallLoadFPAndRetAddr(SelectionDAG &DAG, int SPDiff,
                                          SDValue Chain, SDValue &LROpOut,
                                          SDValue &FPOpOut,
                                          const SDLoc &dl) const;
 
     SDValue getTOCEntry(SelectionDAG &DAG, const SDLoc &dl, SDValue GA) const;
 

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

static int CalculateTailCallSPDiff(SelectionDAG& DAG, bool isTailCall,
   int SPDiff = (int)CallerMinReservedArea - (int)ParamSize;
   // Remember only if the new adjustment is bigger.
   if (SPDiff < FI->getTailCallSPDelta())
     FI->setTailCallSPDelta(SPDiff);
 
   return SPDiff;
 }
 
-static bool isFunctionGlobalAddress(SDValue Callee);
+static bool isFunctionGlobalAddress(const GlobalValue *CalleeGV);
 
-static bool callsShareTOCBase(const Function *Caller, SDValue Callee,
+static bool callsShareTOCBase(const Function *Caller,
+                              const GlobalValue *CalleeGV,
                               const TargetMachine &TM) {
   // It does not make sense to call callsShareTOCBase() with a caller that
   // is PC Relative since PC Relative callers do not have a TOC.
 #ifndef NDEBUG
   const PPCSubtarget *STICaller = &TM.getSubtarget<PPCSubtarget>(*Caller);
   assert(!STICaller->isUsingPCRelativeCalls() &&
          "PC Relative callers do not have a TOC and cannot share a TOC Base");
 #endif
 
   // Callee is either a GlobalAddress or an ExternalSymbol. ExternalSymbols
   // don't have enough information to determine if the caller and callee share
   // the same  TOC base, so we have to pessimistically assume they don't for
   // correctness.
-  GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee);
-  if (!G)
+  if (!CalleeGV)
     return false;
 
-  const GlobalValue *GV = G->getGlobal();
-
   // If the callee is preemptable, then the static linker will use a plt-stub
   // which saves the toc to the stack, and needs a nop after the call
   // instruction to convert to a toc-restore.
-  if (!TM.shouldAssumeDSOLocal(*Caller->getParent(), GV))
+  if (!TM.shouldAssumeDSOLocal(*Caller->getParent(), CalleeGV))
     return false;
 
   // Functions with PC Relative enabled may clobber the TOC in the same DSO.
   // We may need a TOC restore in the situation where the caller requires a
   // valid TOC but the callee is PC Relative and does not.
-  const Function *F = dyn_cast<Function>(GV);
-  const GlobalAlias *Alias = dyn_cast<GlobalAlias>(GV);
+  const Function *F = dyn_cast<Function>(CalleeGV);
+  const GlobalAlias *Alias = dyn_cast<GlobalAlias>(CalleeGV);
 
   // If we have an Alias we can try to get the function from there.
   if (Alias) {
     const GlobalObject *GlobalObj = Alias->getAliaseeObject();
     F = dyn_cast<Function>(GlobalObj);
   }
 
   // If we still have no valid function pointer we do not have enough
   // information to determine if the callee uses PC Relative calls so we must
   // assume that it does.
   if (!F)
     return false;
 
   // If the callee uses PC Relative we cannot guarantee that the callee won't
   // clobber the TOC of the caller and so we must assume that the two
   // functions do not share a TOC base.
   const PPCSubtarget *STICallee = &TM.getSubtarget<PPCSubtarget>(*F);
   if (STICallee->isUsingPCRelativeCalls())
     return false;
 
   // If the GV is not a strong definition then we need to assume it can be
   // replaced by another function at link time. The function that replaces
   // it may not share the same TOC as the caller since the callee may be
   // replaced by a PC Relative version of the same function.
-  if (!GV->isStrongDefinitionForLinker())
+  if (!CalleeGV->isStrongDefinitionForLinker())
     return false;
 
   // The medium and large code models are expected to provide a sufficiently
   // large TOC to provide all data addressing needs of a module with a
   // single TOC.
   if (CodeModel::Medium == TM.getCodeModel() ||
       CodeModel::Large == TM.getCodeModel())
     return true;
 
   // Any explicitly-specified sections and section prefixes must also match.
   // Also, if we're using -ffunction-sections, then each function is always in
   // a different section (the same is true for COMDAT functions).
-  if (TM.getFunctionSections() || GV->hasComdat() || Caller->hasComdat() ||
-      GV->getSection() != Caller->getSection())
+  if (TM.getFunctionSections() || CalleeGV->hasComdat() ||
+      Caller->hasComdat() || CalleeGV->getSection() != Caller->getSection())
     return false;
-  if (const auto *F = dyn_cast<Function>(GV)) {
+  if (const auto *F = dyn_cast<Function>(CalleeGV)) {
     if (F->getSectionPrefix() != Caller->getSectionPrefix())
       return false;
   }
 
   return true;
 }
 
 static bool
areCallingConvEligibleForTCO_64SVR4(CallingConv::ID CallerCC,
   // We can safely tail call both fastcc and ccc callees from a c calling
   // convention caller. If the caller is fastcc, we may have less stack space
   // than a non-fastcc caller with the same signature so disable tail-calls in
   // that case.
   return CallerCC == CallingConv::C || CallerCC == CalleeCC;
 }
 
 bool PPCTargetLowering::IsEligibleForTailCallOptimization_64SVR4(
-    SDValue Callee, CallingConv::ID CalleeCC, const CallBase *CB, bool isVarArg,
+    const GlobalValue *CalleeGV, CallingConv::ID CalleeCC,
+    CallingConv::ID CallerCC, const CallBase *CB, bool isVarArg,
     const SmallVectorImpl<ISD::OutputArg> &Outs,
-    const SmallVectorImpl<ISD::InputArg> &Ins, SelectionDAG &DAG) const {
+    const SmallVectorImpl<ISD::InputArg> &Ins, bool isByValArg,
+    const Function *CallerFunc, bool isCalleeExternalSymbol) const {
   bool TailCallOpt = getTargetMachine().Options.GuaranteedTailCallOpt;
 
   if (DisableSCO && !TailCallOpt) return false;
 
   // Variadic argument functions are not supported.
   if (isVarArg) return false;
 
-  auto &Caller = DAG.getMachineFunction().getFunction();
   // Check that the calling conventions are compatible for tco.
-  if (!areCallingConvEligibleForTCO_64SVR4(Caller.getCallingConv(), CalleeCC))
+  if (!areCallingConvEligibleForTCO_64SVR4(CallerCC, CalleeCC))
     return false;
 
   // Caller contains any byval parameter is not supported.
-  if (any_of(Ins, [](const ISD::InputArg &IA) { return IA.Flags.isByVal(); }))
+  if (isByValArg ||
+      any_of(Ins, [](const ISD::InputArg &IA) { return IA.Flags.isByVal(); }))
     return false;
 
   // Callee contains any byval parameter is not supported, too.
   // Note: This is a quick work around, because in some cases, e.g.
   // caller's stack size > callee's stack size, we are still able to apply
   // sibling call optimization. For example, gcc is able to do SCO for caller1
   // in the following example, but not for caller2.
   //   struct test {
   //     long int a;
   //     char ary[56];
   //   } gTest;
   //   __attribute__((noinline)) int callee(struct test v, struct test *b) {
   //     b->a = v.a;
   //     return 0;
   //   }
   //   void caller1(struct test a, struct test c, struct test *b) {
   //     callee(gTest, b); }
   //   void caller2(struct test *b) { callee(gTest, b); }
   if (any_of(Outs, [](const ISD::OutputArg& OA) { return OA.Flags.isByVal(); }))
     return false;
 
   // If callee and caller use different calling conventions, we cannot pass
   // parameters on stack since offsets for the parameter area may be different.
-  if (Caller.getCallingConv() != CalleeCC &&
-      needStackSlotPassParameters(Subtarget, Outs))
+  if (CallerCC != CalleeCC && needStackSlotPassParameters(Subtarget, Outs))
     return false;
 
   // All variants of 64-bit ELF ABIs without PC-Relative addressing require that
   // the caller and callee share the same TOC for TCO/SCO. If the caller and
   // callee potentially have different TOC bases then we cannot tail call since
   // we need to restore the TOC pointer after the call.
   // ref: https://bugzilla.mozilla.org/show_bug.cgi?id=973977
   // We cannot guarantee this for indirect calls or calls to external functions.
   // When PC-Relative addressing is used, the concept of the TOC is no longer
   // applicable so this check is not required.
   // Check first for indirect calls.
   if (!Subtarget.isUsingPCRelativeCalls() &&
-      !isFunctionGlobalAddress(Callee) && !isa<ExternalSymbolSDNode>(Callee))
+      !isFunctionGlobalAddress(CalleeGV) && !isCalleeExternalSymbol)
     return false;
 
   // Check if we share the TOC base.
   if (!Subtarget.isUsingPCRelativeCalls() &&
-      !callsShareTOCBase(&Caller, Callee, getTargetMachine()))
+      !callsShareTOCBase(CallerFunc, CalleeGV, getTargetMachine()))
     return false;
 
   // TCO allows altering callee ABI, so we don't have to check further.
   if (CalleeCC == CallingConv::Fast && TailCallOpt)
     return true;
 
   if (DisableSCO) return false;
 
   // If callee use the same argument list that caller is using, then we can
   // apply SCO on this case. If it is not, then we need to check if callee needs
   // stack for passing arguments.
   // PC Relative tail calls may not have a CallBase.
   // If there is no CallBase we cannot verify if we have the same argument
   // list so assume that we don't have the same argument list.
-  if (CB && !hasSameArgumentList(&Caller, *CB) &&
+  if (CB && !hasSameArgumentList(CallerFunc, *CB) &&
       needStackSlotPassParameters(Subtarget, Outs))
     return false;
   else if (!CB && needStackSlotPassParameters(Subtarget, Outs))
     return false;
 
   return true;
 }
 
 /// IsEligibleForTailCallOptimization - Check whether the call is eligible
 /// for tail call optimization. Targets which want to do tail call
 /// optimization should implement this function.
-bool
-PPCTargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
-                                                     CallingConv::ID CalleeCC,
-                                                     bool isVarArg,
-                                      const SmallVectorImpl<ISD::InputArg> &Ins,
-                                                     SelectionDAG& DAG) const {
+bool PPCTargetLowering::IsEligibleForTailCallOptimization(
+    const GlobalValue *CalleeGV, CallingConv::ID CalleeCC,
+    CallingConv::ID CallerCC, bool isVarArg,
+    const SmallVectorImpl<ISD::InputArg> &Ins, bool isByValArg) const {
   if (!getTargetMachine().Options.GuaranteedTailCallOpt)
     return false;
 
   // Variable argument functions are not supported.
   if (isVarArg)
     return false;
 
-  MachineFunction &MF = DAG.getMachineFunction();
-  CallingConv::ID CallerCC = MF.getFunction().getCallingConv();
   if (CalleeCC == CallingConv::Fast && CallerCC == CalleeCC) {
     // Functions containing by val parameters are not supported.
-    for (unsigned i = 0; i != Ins.size(); i++) {
-       ISD::ArgFlagsTy Flags = Ins[i].Flags;
-       if (Flags.isByVal()) return false;
-    }
+    if (isByValArg ||
+        any_of(Ins, [](const ISD::InputArg &IA) { return IA.Flags.isByVal(); }))
+      return false;
 
     // Non-PIC/GOT tail calls are supported.
     if (getTargetMachine().getRelocationModel() != Reloc::PIC_)
       return true;
 
     // At the moment we can only do local tail calls (in same module, hidden
     // or protected) if we are generating PIC.
-    if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee))
-      return G->getGlobal()->hasHiddenVisibility()
-          || G->getGlobal()->hasProtectedVisibility();
+    if (CalleeGV)
+      return CalleeGV->hasHiddenVisibility() ||
+             CalleeGV->hasProtectedVisibility();
   }
 
   return false;
 }
 
 /// isCallCompatibleAddress - Return the immediate to use if the specified
 /// 32-bit value is representable in the immediate field of a BxA instruction.
 static SDNode *isBLACompatibleAddress(SDValue Op, SelectionDAG &DAG) {
PrepareTailCall(SelectionDAG &DAG, SDValue &InFlag, SDValue &Chain,
 
   // Emit callseq_end just before tailcall node.
   Chain = DAG.getCALLSEQ_END(Chain, NumBytes, 0, InFlag, dl);
   InFlag = Chain.getValue(1);
 }
 
 // Is this global address that of a function that can be called by name? (as
 // opposed to something that must hold a descriptor for an indirect call).
-static bool isFunctionGlobalAddress(SDValue Callee) {
-  if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
-    if (Callee.getOpcode() == ISD::GlobalTLSAddress ||
-        Callee.getOpcode() == ISD::TargetGlobalTLSAddress)
+static bool isFunctionGlobalAddress(const GlobalValue *GV) {
+  if (GV) {
+    if (GV->isThreadLocal())
       return false;
 
-    return G->getGlobal()->getValueType()->isFunctionTy();
+    return GV->getValueType()->isFunctionTy();
   }
 
   return false;
 }
 
 SDValue PPCTargetLowering::LowerCallResult(
     SDValue Chain, SDValue InFlag, CallingConv::ID CallConv, bool isVarArg,
     const SmallVectorImpl<ISD::InputArg> &Ins, const SDLoc &dl,
for (unsigned i = 0, e = RVLocs.size(); i != e; ++i) {
     InVals.push_back(Val);
   }
 
   return Chain;
 }
 
 static bool isIndirectCall(const SDValue &Callee, SelectionDAG &DAG,
                            const PPCSubtarget &Subtarget, bool isPatchPoint) {
+  auto *G = dyn_cast<GlobalAddressSDNode>(Callee);
+  const GlobalValue *GV = G ? G->getGlobal() : nullptr;
+
   // PatchPoint calls are not indirect.
   if (isPatchPoint)
     return false;
 
-  if (isFunctionGlobalAddress(Callee) || isa<ExternalSymbolSDNode>(Callee))
+  if (isFunctionGlobalAddress(GV) || isa<ExternalSymbolSDNode>(Callee))
     return false;
 
   // Darwin, and 32-bit ELF can use a BLA. The descriptor based ABIs can not
   // becuase the immediate function pointer points to a descriptor instead of
   // a function entry point. The ELFv2 ABI cannot use a BLA because the function
   // pointer immediate points to the global entry point, while the BLA would
   // need to jump to the local entry point (see rL211174).
   if (!Subtarget.usesFunctionDescriptors() && !Subtarget.isELFv2ABI() &&
if (CFlags.IsIndirect) {
     // immediately followed by a load of the TOC pointer from the the stack save
     // slot into gpr2. For 64-bit ELFv2 ABI with PCRel, do not restore the TOC
     // as it is not saved or used.
     RetOpc = isTOCSaveRestoreRequired(Subtarget) ? PPCISD::BCTRL_LOAD_TOC
                                                  : PPCISD::BCTRL;
   } else if (Subtarget.isUsingPCRelativeCalls()) {
     assert(Subtarget.is64BitELFABI() && "PC Relative is only on ELF ABI.");
     RetOpc = PPCISD::CALL_NOTOC;
-  } else if (Subtarget.isAIXABI() || Subtarget.is64BitELFABI())
+  } else if (Subtarget.isAIXABI() || Subtarget.is64BitELFABI()) {
     // The ABIs that maintain a TOC pointer accross calls need to have a nop
     // immediately following the call instruction if the caller and callee may
     // have different TOC bases. At link time if the linker determines the calls
     // may not share a TOC base, the call is redirected to a trampoline inserted
     // by the linker. The trampoline will (among other things) save the callers
     // TOC pointer at an ABI designated offset in the linkage area and the
     // linker will rewrite the nop to be a load of the TOC pointer from the
     // linkage area into gpr2.
-    RetOpc = callsShareTOCBase(&Caller, Callee, TM) ? PPCISD::CALL
-                                                    : PPCISD::CALL_NOP;
-  else
+    auto *G = dyn_cast<GlobalAddressSDNode>(Callee);
+    const GlobalValue *GV = G ? G->getGlobal() : nullptr;
+    RetOpc =
+        callsShareTOCBase(&Caller, GV, TM) ? PPCISD::CALL : PPCISD::CALL_NOP;
+  } else
     RetOpc = PPCISD::CALL;
   if (IsStrictFPCall) {
     switch (RetOpc) {
     default:
       llvm_unreachable("Unknown call opcode");
     case PPCISD::BCTRL_LOAD_TOC:
       RetOpc = PPCISD::BCTRL_LOAD_TOC_RM;
       break;
const auto getAIXFuncEntryPointSymbolSDNode = [&](const GlobalValue *GV) {
     const TargetLoweringObjectFile *TLOF = TM.getObjFileLowering();
     MCSymbolXCOFF *S =
         cast<MCSymbolXCOFF>(TLOF->getFunctionEntryPointSymbol(GV, TM));
 
     MVT PtrVT = DAG.getTargetLoweringInfo().getPointerTy(DAG.getDataLayout());
     return DAG.getMCSymbol(S, PtrVT);
   };
 
-  if (isFunctionGlobalAddress(Callee)) {
+  auto *G = dyn_cast<GlobalAddressSDNode>(Callee);
+  const GlobalValue *GV = G ? G->getGlobal() : nullptr;
+  if (isFunctionGlobalAddress(GV)) {
     const GlobalValue *GV = cast<GlobalAddressSDNode>(Callee)->getGlobal();
 
     if (Subtarget.isAIXABI()) {
       assert(!isa<GlobalIFunc>(GV) && "IFunc is not supported on AIX.");
       return getAIXFuncEntryPointSymbolSDNode(GV);
     }
     return DAG.getTargetGlobalAddress(GV, dl, Callee.getValueType(), 0,
                                       UsePlt ? PPCII::MO_PLT : 0);
SDValue PPCTargetLowering::FinishCall(
 
   Chain = DAG.getCALLSEQ_END(Chain, NumBytes, BytesCalleePops, Glue, dl);
   Glue = Chain.getValue(1);
 
   return LowerCallResult(Chain, Glue, CFlags.CallConv, CFlags.IsVarArg, Ins, dl,
                          DAG, InVals);
 }
 
+bool PPCTargetLowering::isEligibleForTCO(
+    const GlobalValue *CalleeGV, CallingConv::ID CalleeCC,
+    CallingConv::ID CallerCC, const CallBase *CB, bool isVarArg,
+    const SmallVectorImpl<ISD::OutputArg> &Outs,
+    const SmallVectorImpl<ISD::InputArg> &Ins, bool isByValArg,
+    const Function *CallerFunc, bool isCalleeExternalSymbol) const {
+  bool IsTailCall;
+  if (Subtarget.useLongCalls() && !(CB && CB->isMustTailCall()))
+    IsTailCall = false;
+  else if (Subtarget.isSVR4ABI() && Subtarget.isPPC64())
+    IsTailCall = IsEligibleForTailCallOptimization_64SVR4(
+        CalleeGV, CalleeCC, CallerCC, CB, isVarArg, Outs, Ins, isByValArg,
+        CallerFunc, isCalleeExternalSymbol);
+  else
+    IsTailCall = IsEligibleForTailCallOptimization(CalleeGV, CalleeCC, CallerCC,
+                                                   isVarArg, Ins, isByValArg);
+
+  return IsTailCall;
+}
+
 SDValue
 PPCTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
                              SmallVectorImpl<SDValue> &InVals) const {
   SelectionDAG &DAG                     = CLI.DAG;
   SDLoc &dl                             = CLI.DL;
   SmallVectorImpl<ISD::OutputArg> &Outs = CLI.Outs;
   SmallVectorImpl<SDValue> &OutVals     = CLI.OutVals;
   SmallVectorImpl<ISD::InputArg> &Ins   = CLI.Ins;
   SDValue Chain                         = CLI.Chain;
   SDValue Callee                        = CLI.Callee;
   bool &isTailCall                      = CLI.IsTailCall;
   CallingConv::ID CallConv              = CLI.CallConv;
   bool isVarArg                         = CLI.IsVarArg;
   bool isPatchPoint                     = CLI.IsPatchPoint;
   const CallBase *CB                    = CLI.CB;
 
   if (isTailCall) {
-    if (Subtarget.useLongCalls() && !(CB && CB->isMustTailCall()))
-      isTailCall = false;
-    else if (Subtarget.isSVR4ABI() && Subtarget.isPPC64())
-      isTailCall = IsEligibleForTailCallOptimization_64SVR4(
-          Callee, CallConv, CB, isVarArg, Outs, Ins, DAG);
-    else
-      isTailCall = IsEligibleForTailCallOptimization(Callee, CallConv, isVarArg,
-                                                     Ins, DAG);
+    MachineFunction &MF = DAG.getMachineFunction();
+    CallingConv::ID CallerCC = MF.getFunction().getCallingConv();
+    auto *G = dyn_cast<GlobalAddressSDNode>(Callee);
+    const GlobalValue *GV = G ? G->getGlobal() : nullptr;
+    bool IsCalleeExternalSymbol = isa<ExternalSymbolSDNode>(Callee);
+
+    isTailCall = isEligibleForTCO(GV, CallConv, CallerCC, CB, isVarArg, Outs,
+                                  Ins, false /*isByValArg*/,
+                                  &(MF.getFunction()), IsCalleeExternalSymbol);
     if (isTailCall) {
       ++NumTailCalls;
       if (!getTargetMachine().Options.GuaranteedTailCallOpt)
         ++NumSiblingCalls;
 
       // PC Relative calls no longer guarantee that the callee is a Global
       // Address Node. The callee could be an indirect tail call in which
       // case the SDValue for the callee could be a load (to load the address