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

1 files changed, 5 insertions, 5 deletions

diff --git a/lib/CodeGen/ScheduleDAGInstrs.cpp b/lib/CodeGen/ScheduleDAGInstrs.cpp
index 34b8ab0b47..5408cdf1ad 100644
--- a/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -677,12 +677,12 @@ MachineBasicBlock *ScheduleDAGInstrs::EmitSchedule() {
     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