misched: Added CanHandleTerminators.

This is a special flag for targets that really want their block
terminators in the DAG. The default scheduler cannot handle this
correctly, so it becomes the specialized scheduler's responsibility to
schedule terminators.

llvm-svn: 154712

llvm/include/llvm/CodeGen/ScheduleDAGInstrs.h

@@ -181,6 +181,13 @@ namespace llvm {
     /// the def-side latency only.
     bool UnitLatencies;
 
+    /// The standard DAG builder does not normally include terminators as DAG
+    /// nodes because it does not create the necessary dependencies to prevent
+    /// reordering. A specialized scheduler can overide
+    /// TargetInstrInfo::isSchedulingBoundary then enable this flag to indicate
+    /// it has taken responsibility for scheduling the terminator correctly.
+    bool CanHandleTerminators;
+
     /// State specific to the current scheduling region.
     /// ------------------------------------------------
 

llvm/lib/CodeGen/ScheduleDAGInstrs.cpp

@@ -39,8 +39,8 @@ ScheduleDAGInstrs::ScheduleDAGInstrs(MachineFunction &mf,
                                      LiveIntervals *lis)
   : ScheduleDAG(mf), MLI(mli), MDT(mdt), MFI(mf.getFrameInfo()),
     InstrItins(mf.getTarget().getInstrItineraryData()), LIS(lis),
-    IsPostRA(IsPostRAFlag), UnitLatencies(false), LoopRegs(MLI, MDT),
-    FirstDbgValue(0) {
+    IsPostRA(IsPostRAFlag), UnitLatencies(false), CanHandleTerminators(false),
+    LoopRegs(MLI, MDT), FirstDbgValue(0) {
   assert((IsPostRA || LIS) && "PreRA scheduling requires LiveIntervals");
   DbgValues.clear();
   assert(!(IsPostRA && MRI.getNumVirtRegs()) &&
@@ -554,7 +554,7 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA) {
       continue;
     }
 
-    assert(!MI->isTerminator() && !MI->isLabel() &&
+    assert((!MI->isTerminator() || CanHandleTerminators) && !MI->isLabel() &&
            "Cannot schedule terminators or labels!");
 
     SUnit *SU = MISUnitMap[MI];