MachineScheduler/ScheduleDAG: Add support to skipping a node.

The DAG mutators in the scheduler cannot really remove DAG nodes as
additional anlysis information such as ScheduleDAGToplogicalSort are
already computed at this point and rely on a fixed number of DAG nodes.

Alleviate the missing removal with a new flag: Setting the new skip
flag on a node ignores it during scheduling.

llvm-svn: 286655

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineScheduler.cpp b/llvm/lib/CodeGen/MachineScheduler.cpp
index 3984a15861d..f7dd53b9b9b 100644
--- a/llvm/lib/CodeGen/MachineScheduler.cpp
+++ b/llvm/lib/CodeGen/MachineScheduler.cpp
@@ -707,6 +707,7 @@ void ScheduleDAGMI::schedule() {
     DEBUG(dbgs() << "** ScheduleDAGMI::schedule picking next node\n");
     SUnit *SU = SchedImpl->pickNode(IsTopNode);
     if (!SU) break;
+    assert(!SU->skip);
 
     assert(!SU->isScheduled && "Node already scheduled");
     if (!checkSchedLimit())
@@ -764,6 +765,8 @@ findRootsAndBiasEdges(SmallVectorImpl<SUnit*> &TopRoots,
                       SmallVectorImpl<SUnit*> &BotRoots) {
   for (std::vector<SUnit>::iterator
          I = SUnits.begin(), E = SUnits.end(); I != E; ++I) {
+    if (I->skip)
+      continue;
     SUnit *SU = &(*I);
     assert(!SU->isBoundaryNode() && "Boundary node should not be in SUnits");
 
@@ -1518,6 +1521,8 @@ void BaseMemOpClusterMutation::apply(ScheduleDAGInstrs *DAGInstrs) {
   SmallVector<SmallVector<SUnit*,4>, 32> StoreChainDependents;
   for (unsigned Idx = 0, End = DAG->SUnits.size(); Idx != End; ++Idx) {
     SUnit *SU = &DAG->SUnits[Idx];
+    if (SU->skip)
+      continue;
     if ((IsLoad && !SU->getInstr()->mayLoad()) ||
         (!IsLoad && !SU->getInstr()->mayStore()))
       continue;
@@ -1810,6 +1815,8 @@ void CopyConstrain::apply(ScheduleDAGInstrs *DAGInstrs) {
 
   for (unsigned Idx = 0, End = DAG->SUnits.size(); Idx != End; ++Idx) {
     SUnit *SU = &DAG->SUnits[Idx];
+    if (SU->skip)
+      continue;
     if (!SU->getInstr()->isCopy())
       continue;