make sure ScheduleDAGInstrs::EmitSchedule does not crash when the first instruction in Sequence is a Noop
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145677 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/ScheduleDAGInstrs.cpp b/lib/CodeGen/ScheduleDAGInstrs.cpp
index 34b8ab0..5408cdf 100644
--- a/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -677,12 +677,12 @@
else
// Null SUnit* is a noop.
EmitNoop();
- }
- // Update the Begin iterator, as the first instruction in the block
- // may have been scheduled later.
- if (!Sequence.empty())
- Begin = Sequence[0]->getInstr();
+ // Update the Begin iterator, as the first instruction in the block
+ // may have been scheduled later.
+ if (i == 0)
+ Begin = prior(InsertPos);
+ }
// Reinsert any remaining debug_values.
for (std::vector<std::pair<MachineInstr *, MachineInstr *> >::iterator