Added MachineSchedPolicy.

Allow subtargets to customize the generic scheduling strategy.
This is convenient for targets that don't need to add new heuristics
by specializing the strategy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190176 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 37 insertions, 2 deletions

diff --git a/include/llvm/CodeGen/MachineScheduler.h b/include/llvm/CodeGen/MachineScheduler.h
index e3768bc72b..18744e7132 100644
--- a/include/llvm/CodeGen/MachineScheduler.h
+++ b/include/llvm/CodeGen/MachineScheduler.h
@@ -101,15 +101,39 @@ public:
 
 class ScheduleDAGMI;
 
+/// Define a generic scheduling policy for targets that don't provide their own
+/// MachineSchedStrategy. This can be overriden for each scheduling region
+/// before building the DAG.
+struct MachineSchedPolicy {
+  // Allow the scheduler to disable register pressure tracking.
+  bool ShouldTrackPressure;
+
+  // Allow the scheduler to force top-down or bottom-up scheduling. If neither
+  // is true, the scheduler runs in both directions and converges.
+  bool OnlyTopDown;
+  bool OnlyBottomUp;
+
+  MachineSchedPolicy():
+    ShouldTrackPressure(false), OnlyTopDown(false), OnlyBottomUp(false) {}
+};
+
 /// MachineSchedStrategy - Interface to the scheduling algorithm used by
 /// ScheduleDAGMI.
+///
+/// Initialization sequence:
+///   initPolicy -> shouldTrackPressure -> initialize(DAG) -> registerRoots
 class MachineSchedStrategy {
 public:
   virtual ~MachineSchedStrategy() {}
 
+  /// Optionally override the per-region scheduling policy.
+  virtual void initPolicy(MachineBasicBlock::iterator Begin,
+                          MachineBasicBlock::iterator End,
+                          unsigned NumRegionInstrs) {}
+
   /// Check if pressure tracking is needed before building the DAG and
-  /// initializing this strategy.
-  virtual bool shouldTrackPressure(unsigned NumRegionInstrs) { return true; }
+  /// initializing this strategy. Called after initPolicy.
+  virtual bool shouldTrackPressure() const { return true; }
 
   /// Initialize the strategy after building the DAG for a new region.
   virtual void initialize(ScheduleDAGMI *DAG) = 0;
diff --git a/include/llvm/Target/TargetSubtargetInfo.h b/include/llvm/Target/TargetSubtargetInfo.h
index 2092aba8a2..37365b2a9c 100644
--- a/include/llvm/Target/TargetSubtargetInfo.h
+++ b/include/llvm/Target/TargetSubtargetInfo.h
@@ -25,6 +25,7 @@ class SDep;
 class SUnit;
 class TargetRegisterClass;
 class TargetSchedModel;
+struct MachineSchedPolicy;
 template <typename T> class SmallVectorImpl;
 
 //===----------------------------------------------------------------------===//
@@ -62,6 +63,16 @@ public:
   /// scheduler. It does not yet disable the postRA scheduler.
   virtual bool enableMachineScheduler() const;
 
+  /// \brief Override generic scheduling policy within a region.
+  ///
+  /// This is a convenient way for targets that don't provide any custom
+  /// scheduling heuristics (no custom MachineSchedStrategy) to make
+  /// changes to the generic scheduling policy.
+  virtual void overrideSchedPolicy(MachineSchedPolicy &Policy,
+                                   MachineInstr *begin,
+                                   MachineInstr *end,
+                                   unsigned NumRegionInstrs) const {}
+
   // enablePostRAScheduler - If the target can benefit from post-regalloc
   // scheduling and the specified optimization level meets the requirement
   // return true to enable post-register-allocation scheduling. In