Index: lib/CodeGen/SelectionDAG/FastISel.cpp =================================================================== --- lib/CodeGen/SelectionDAG/FastISel.cpp +++ lib/CodeGen/SelectionDAG/FastISel.cpp @@ -1035,8 +1035,10 @@ } case Instruction::Unreachable: - // Nothing to emit. - return true; + if (TM.Options.TrapUnreachable) + return FastEmit_(MVT::Other, MVT::Other, ISD::TRAP) != 0; + else + return true; case Instruction::Alloca: // FunctionLowering has the static-sized case covered. Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h =================================================================== --- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h +++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h @@ -642,7 +642,7 @@ void visitBr(const BranchInst &I); void visitSwitch(const SwitchInst &I); void visitIndirectBr(const IndirectBrInst &I); - void visitUnreachable(const UnreachableInst &I) { /* noop */ } + void visitUnreachable(const UnreachableInst &I); // Helpers for visitSwitch bool handleSmallSwitchRange(CaseRec& CR, Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp =================================================================== --- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp +++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp @@ -2765,6 +2765,11 @@ getValue(I.getAddress()))); } +void SelectionDAGBuilder::visitUnreachable(const UnreachableInst &I) { + if (DAG.getTarget().Options.TrapUnreachable) + DAG.setRoot(DAG.getNode(ISD::TRAP, getCurSDLoc(), MVT::Other, DAG.getRoot())); +} + void SelectionDAGBuilder::visitFSub(const User &I) { // -0.0 - X --> fneg Type *Ty = I.getType(); Index: lib/Target/X86/X86TargetMachine.cpp =================================================================== --- lib/Target/X86/X86TargetMachine.cpp +++ lib/Target/X86/X86TargetMachine.cpp @@ -108,6 +108,13 @@ if (Options.FloatABIType == FloatABI::Default) this->Options.FloatABIType = FloatABI::Hard; + // Windows stack unwinder gets confused when execution flow "falls through" + // after a call to 'noreturn' function. + // To prevent that, we emit a trap for 'unreachable' IR instructions. + // (which on X86, happens to be the 'ud2' instruction) + if (Subtarget.isTargetWin64()) + this->Options.TrapUnreachable = true; + initAsmInfo(); }