[PATCH] D14806: MachineScheduler: Add a target hook for deciding which RegPressure sets to increase

[Tom Stellard via llvm-commits]

tstellarAMD created this revision.
tstellarAMD added reviewers: MatzeB, qcolombet, escha, arsenm.
tstellarAMD added a subscriber: llvm-commits.

This patch adds a function called getRegPressureSetScore() to
TargetRegisterInfo.  The MachineScheduler uses this when comparing
instruction that increase the register pressure of different sets
to determine which set is safer to increase.

This hook is useful for GPU targets where the number of registers in the
class is not the best metric for determing which presser set is safer to
increase.

Future work may include adding more parameters to this function, like
for example, the current pressure level of the set or the amount that
the pressure will be increased/decreased.

http://reviews.llvm.org/D14806

Files:
  include/llvm/Target/TargetRegisterInfo.h
  lib/CodeGen/MachineScheduler.cpp

Index: lib/CodeGen/MachineScheduler.cpp
===================================================================
--- lib/CodeGen/MachineScheduler.cpp
+++ lib/CodeGen/MachineScheduler.cpp
@@ -2579,7 +2579,9 @@
                         const PressureChange &CandP,
                         GenericSchedulerBase::SchedCandidate &TryCand,
                         GenericSchedulerBase::SchedCandidate &Cand,
-                        GenericSchedulerBase::CandReason Reason) {
+                        GenericSchedulerBase::CandReason Reason,
+                        const TargetRegisterInfo *TRI,
+                        const MachineFunction &MF) {
   int TryRank = TryP.getPSetOrMax();
   int CandRank = CandP.getPSetOrMax();
   // If both candidates affect the same set, go with the smallest increase.
@@ -2593,6 +2595,12 @@
                  Reason)) {
     return true;
   }
+
+  if (TryP.isValid())
+    TryRank = TRI->getRegPressureSetScore(MF, TryRank);
+  if (CandP.isValid())
+    CandRank =TRI->getRegPressureSetScore(MF, CandRank);
+
   // If the candidates are decreasing pressure, reverse priority.
   if (TryP.getUnitInc() < 0)
     std::swap(TryRank, CandRank);
@@ -2695,13 +2703,15 @@
   // Avoid exceeding the target's limit.
   if (DAG->isTrackingPressure() && tryPressure(TryCand.RPDelta.Excess,
                                                Cand.RPDelta.Excess,
-                                               TryCand, Cand, RegExcess))
+                                               TryCand, Cand, RegExcess, TRI,
+                                               DAG->MF))
     return;
 
   // Avoid increasing the max critical pressure in the scheduled region.
   if (DAG->isTrackingPressure() && tryPressure(TryCand.RPDelta.CriticalMax,
                                                Cand.RPDelta.CriticalMax,
-                                               TryCand, Cand, RegCritical))
+                                               TryCand, Cand, RegCritical, TRI,
+                                               DAG->MF))
     return;
 
   // For loops that are acyclic path limited, aggressively schedule for latency.
@@ -2737,7 +2747,8 @@
   // Avoid increasing the max pressure of the entire region.
   if (DAG->isTrackingPressure() && tryPressure(TryCand.RPDelta.CurrentMax,
                                                Cand.RPDelta.CurrentMax,
-                                               TryCand, Cand, RegMax))
+                                               TryCand, Cand, RegMax, TRI,
+                                               DAG->MF))
     return;
 
   // Avoid critical resource consumption and balance the schedule.
Index: include/llvm/Target/TargetRegisterInfo.h
===================================================================
--- include/llvm/Target/TargetRegisterInfo.h
+++ include/llvm/Target/TargetRegisterInfo.h
@@ -674,6 +674,15 @@
     return 0;
   }
 
+  /// Return a heuristic for the machine scheduler to compare the profitability
+  /// of increasing one register pressure set versus another.  The scheduler
+  /// will prefer increasing the register pressure of the set which returns
+  /// the largest value for this function.
+  virtual unsigned getRegPressureSetScore(const MachineFunction &MF,
+                                          unsigned PSetID) const {
+    return PSetID;
+  }
+
   /// Get the weight in units of pressure for this register class.
   virtual const RegClassWeight &getRegClassWeight(
     const TargetRegisterClass *RC) const = 0;


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