diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -3960,12 +3960,12 @@
     // the argument into a virtual register so that we can access it from the
     // return points.
     if (Ins[I].Flags.isSRet()) {
-      Register Reg = FuncInfo->getSRetReturnReg();
-      if (!Reg) {
-        MVT PtrTy = getPointerTy(DAG.getDataLayout());
-        Reg = MF.getRegInfo().createVirtualRegister(getRegClassFor(PtrTy));
-        FuncInfo->setSRetReturnReg(Reg);
-      }
+      assert(!FuncInfo->getSRetReturnReg() &&
+             "SRet return has already been set");
+      MVT PtrTy = getPointerTy(DAG.getDataLayout());
+      Register Reg =
+          MF.getRegInfo().createVirtualRegister(getRegClassFor(PtrTy));
+      FuncInfo->setSRetReturnReg(Reg);
       SDValue Copy = DAG.getCopyToReg(DAG.getEntryNode(), dl, Reg, InVals[I]);
       Chain = DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Copy, Chain);
       break;