[CodeGen] Don't attempt a tail-call with implicit sret.

Tailcalls are only OK with forwarded sret pointers. With sret demotion,
they're not, as we'd have a pointer into a soon-to-be-dead stack frame.

Differential Revison: http://reviews.llvm.org/D8510


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233409 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -7193,6 +7193,10 @@ TargetLowering::LowerCallTo(TargetLowering::CallLoweringInfo &CLI) const {
     Entry.Alignment = Align;
     CLI.getArgs().insert(CLI.getArgs().begin(), Entry);
     CLI.RetTy = Type::getVoidTy(CLI.RetTy->getContext());
+
+    // sret demotion isn't compatible with tail-calls, since the sret argument
+    // points into the callers stack frame.
+    CLI.IsTailCall = false;
   } else {
     for (unsigned I = 0, E = RetTys.size(); I != E; ++I) {
       EVT VT = RetTys[I];