+static bool InstructionWillNotHaveChain(const Instruction *I) {
+ return !I->mayHaveSideEffects() && !I->mayReadFromMemory() &&
+ isSafeToSpeculativelyExecute(I);
+}
+
+/// Identify if RI has a previous instruction in the "Tail Position" and return
+/// it. Otherwise return 0.
+///
+/// This is based off of the code in llvm::isInTailCallPosition
+static CallInst *FindPotentialTailCall(BasicBlock *BB, ReturnInst *RI,
+ const TargetLoweringBase *TLI) {
+ // Establish a reasonable upper bound on the maximum amount of instructions we
+ // will look through to find a tail call.
+ unsigned SearchCounter = 0;
+ const unsigned MaxSearch = 4;
+ bool NoInterposingChain = true;
+
+ for (BasicBlock::reverse_iterator I = llvm::next(BB->rbegin()), E = BB->rend();
+ I != E && SearchCounter < MaxSearch; ++I) {
+ Instruction *Inst = &*I;
+
+ // Skip over debug intrinsics and do not allow them to affect our MaxSearch
+ // counter.
+ if (isa<DbgInfoIntrinsic>(Inst))
+ continue;
+
+ // If we find a call and the following conditions are satisifed, then we
+ // have found a tail call that satisfies at least the target independent
+ // requirements of a tail call:
+ //
+ // 1. The call site has the tail marker.
+ //
+ // 2. The call site either will not cause the creation of a chain or if a
+ // chain is necessary there are no instructions in between the callsite and
+ // the call which would create an interposing chain.
+ //
+ // 3. The return type of the function does not impede tail call
+ // optimization.
+ if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
+ if (CI->isTailCall() &&
+ (InstructionWillNotHaveChain(CI) || NoInterposingChain) &&
+ returnTypeIsEligibleForTailCall(BB->getParent(), CI, RI, *TLI))
+ return CI;
+ }
+
+ // If we did not find a call see if we have an instruction that may create
+ // an interposing chain.
+ NoInterposingChain = NoInterposingChain && InstructionWillNotHaveChain(Inst);
+
+ // Increment max search.
+ SearchCounter++;
+ }
+
+ return 0;
+}
+
+/// Insert code into the entry block that stores the __stack_chk_guard
+/// variable onto the stack:
+///
+/// entry:
+/// StackGuardSlot = alloca i8*
+/// StackGuard = load __stack_chk_guard
+/// call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
+///
+/// Returns true if the platform/triple supports the stackprotectorcreate pseudo
+/// node.
+static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
+ const TargetLoweringBase *TLI, const Triple &Trip,
+ AllocaInst *&AI, Value *&StackGuardVar) {
+ bool SupportsSelectionDAGSP = false;
+ PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
+ unsigned AddressSpace, Offset;
+ if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
+ Constant *OffsetVal =
+ ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);
+
+ StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
+ PointerType::get(PtrTy,
+ AddressSpace));
+ } else if (Trip.getOS() == llvm::Triple::OpenBSD) {
+ StackGuardVar = M->getOrInsertGlobal("__guard_local", PtrTy);
+ cast<GlobalValue>(StackGuardVar)
+ ->setVisibility(GlobalValue::HiddenVisibility);
+ } else {
+ SupportsSelectionDAGSP = true;
+ StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
+ }
+
+ BasicBlock &Entry = F->getEntryBlock();
+ Instruction *InsPt = &Entry.front();
+
+ AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
+ LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
+
+ Value *Args[] = { LI, AI };
+ CallInst::
+ Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
+ Args, "", InsPt);
+
+ return SupportsSelectionDAGSP;
+}
+