[MachineOutliner][AArch64][NFC] Add early exit to candidate discarding logic

If we dropped too many candidates to be beneficial when dropping candidates
that modify the stack, there's no reason to check for other cost model
qualities.

llvm-svn: 348219

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

@@ -5214,6 +5214,12 @@ AArch64InstrInfo::getOutliningCandidateInfo(
     } else {
       SetCandidateCallInfo(MachineOutlinerDefault, 12);
     }
+
+    // If we dropped all of the candidates, bail out here.
+    if (RepeatedSequenceLocs.size() < 2) {
+      RepeatedSequenceLocs.clear();
+      return outliner::OutlinedFunction();
+    }
   }
 
   // Does every candidate's MBB contain a call? If so, then we might have a call