diff --git a/lib/Target/X86/X86ISelPattern.cpp b/lib/Target/X86/X86ISelPattern.cpp index 5c4594aa9ec..28f799ee4a8 100644 --- a/lib/Target/X86/X86ISelPattern.cpp +++ b/lib/Target/X86/X86ISelPattern.cpp @@ -3067,6 +3067,20 @@ void ISel::EmitFastCCToFastCCTailCall(SDNode *TailCallNode) { // TODO: handle jmp [mem] if (!isDirect) { + // We do not want the register allocator to allocate CalleeReg to a callee + // saved register, as these will be restored before the JMP. To prevent + // this, emit explicit clobbers of callee saved regs here. A better way to + // solve this would be to specify that the register constraints of TAILJMPr + // only allow registers that are not callee saved, but we currently can't + // express that. This forces all four of these regs to be saved and + // reloaded for all functions with an indirect tail call. + // TODO: Improve this! + BuildMI(BB, X86::IMPLICIT_DEF, 4) + .addReg(X86::ESI, MachineOperand::Def) + .addReg(X86::EDI, MachineOperand::Def) + .addReg(X86::EBX, MachineOperand::Def) + .addReg(X86::EBP, MachineOperand::Def); + BuildMI(BB, X86::TAILJMPr, 1).addReg(CalleeReg); } else if (GlobalAddressSDNode *GASD = dyn_cast(Callee)){ BuildMI(BB, X86::TAILJMPd, 1).addGlobalAddress(GASD->getGlobal(), true);