[MachineOutliner][AArch64] Save + restore LR in noreturn functions

Conservatively always save + restore LR in noreturn functions.

These functions do not end in a RET, and so they aren't guaranteed to have an
instruction which uses LR in any way. So, as a result, you can end up in
unfortunate situations where you can't backtrace out of these functions in a
debugger.

Remove the old noreturn test, and add a new one which is more descriptive.

Remove the restriction that we can't outline from noreturn functions as well
since we now do the right thing.

1 files changed, 0 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/MachineOutliner.cpp b/llvm/lib/CodeGen/MachineOutliner.cpp
index f742ac6b55c..d6ce08a0097 100644
--- a/llvm/lib/CodeGen/MachineOutliner.cpp
+++ b/llvm/lib/CodeGen/MachineOutliner.cpp
@@ -1306,12 +1306,6 @@ void MachineOutliner::populateMapper(InstructionMapper &Mapper, Module &M,
     if (F.empty())
       continue;
 
-    // Disable outlining from noreturn functions right now. Noreturn requires
-    // special handling for the case where what we are outlining could be a
-    // tail call.
-    if (F.hasFnAttribute(Attribute::NoReturn))
-      continue;
-
     // There's something in F. Check if it has a MachineFunction associated with
     // it.
     MachineFunction *MF = MMI.getMachineFunction(F);