[RISCV] Add tune info for postra scheduling direction (#115864)

The results differ on different platforms so it is really hard to
determine a common default value.
    
Tune info for postra scheduling direction is added and CPUs can
set their own preferable postra scheduling direction.

Author: wangpc-pp

llvm/lib/Target/RISCV/RISCVProcessors.td

@@ -10,6 +10,11 @@
 // RISC-V processors supported.
 //===----------------------------------------------------------------------===//
 
+// Predefined scheduling direction.
+defvar TopDown       = [{ MISched::TopDown }];
+defvar BottomUp      = [{ MISched::BottomUp }];
+defvar Bidirectional = [{ MISched::Bidirectional }];
+
 class RISCVTuneInfo {
   bits<8> PrefFunctionAlignment = 1;
   bits<8> PrefLoopAlignment = 1;
@@ -37,6 +42,9 @@ class RISCVTuneInfo {
 
   bits<32> MaxLoadsPerMemcmpOptSize = 4;
   bits<32> MaxLoadsPerMemcmp = 8;
+
+  // The direction of PostRA scheduling.
+  code PostRASchedDirection = TopDown;
 }
 
 def RISCVTuneInfoTable : GenericTable {
@@ -49,7 +57,8 @@ def RISCVTuneInfoTable : GenericTable {
                 "MaxStoresPerMemset", "MaxGluedStoresPerMemcpy",
                 "MaxStoresPerMemcpyOptSize", "MaxStoresPerMemcpy",
                 "MaxStoresPerMemmoveOptSize", "MaxStoresPerMemmove",
-                "MaxLoadsPerMemcmpOptSize", "MaxLoadsPerMemcmp"];
+                "MaxLoadsPerMemcmpOptSize", "MaxLoadsPerMemcmp",
+                "PostRASchedDirection"];
 }
 
 def getRISCVTuneInfo : SearchIndex {

llvm/lib/Target/RISCV/RISCVSubtarget.cpp

@@ -16,7 +16,6 @@
 #include "RISCV.h"
 #include "RISCVFrameLowering.h"
 #include "RISCVTargetMachine.h"
-#include "llvm/CodeGen/MachineScheduler.h"
 #include "llvm/CodeGen/MacroFusion.h"
 #include "llvm/CodeGen/ScheduleDAGMutation.h"
 #include "llvm/MC/TargetRegistry.h"
@@ -211,3 +210,18 @@ void RISCVSubtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
   // register-pressure tracking. This will increase compile time.
   Policy.ShouldTrackPressure = true;
 }
+
+void RISCVSubtarget::overridePostRASchedPolicy(MachineSchedPolicy &Policy,
+                                               unsigned NumRegionInstrs) const {
+  MISched::Direction PostRASchedDirection = getPostRASchedDirection();
+  if (PostRASchedDirection == MISched::TopDown) {
+    Policy.OnlyTopDown = true;
+    Policy.OnlyBottomUp = false;
+  } else if (PostRASchedDirection == MISched::BottomUp) {
+    Policy.OnlyTopDown = false;
+    Policy.OnlyBottomUp = true;
+  } else if (PostRASchedDirection == MISched::Bidirectional) {
+    Policy.OnlyTopDown = false;
+    Policy.OnlyBottomUp = false;
+  }
+}

llvm/lib/Target/RISCV/RISCVSubtarget.h

@@ -21,6 +21,7 @@
 #include "llvm/CodeGen/GlobalISel/CallLowering.h"
 #include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
 #include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
+#include "llvm/CodeGen/MachineScheduler.h"
 #include "llvm/CodeGen/SelectionDAGTargetInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/IR/DataLayout.h"
@@ -66,6 +67,9 @@ struct RISCVTuneInfo {
 
   unsigned MaxLoadsPerMemcmpOptSize;
   unsigned MaxLoadsPerMemcmp;
+
+  // The direction of PostRA scheduling.
+  MISched::Direction PostRASchedDirection;
 };
 
 #define GET_RISCVTuneInfoTable_DECL
@@ -365,8 +369,15 @@ class RISCVSubtarget : public RISCVGenSubtargetInfo {
                    : TuneInfo->MaxLoadsPerMemcmp;
   }
 
+  MISched::Direction getPostRASchedDirection() const {
+    return TuneInfo->PostRASchedDirection;
+  }
+
   void overrideSchedPolicy(MachineSchedPolicy &Policy,
                            unsigned NumRegionInstrs) const override;
+
+  void overridePostRASchedPolicy(MachineSchedPolicy &Policy,
+                                 unsigned NumRegionInstrs) const override;
 };
 } // End llvm namespace