[MISched] Use SchedRegion in overrideSchedPolicy and overridePostRASchedPolicy (#149297)

This patch updates `overrideSchedPolicy` and `overridePostRASchedPolicy`
to take a
`SchedRegion` parameter instead of just `NumRegionInstrs`. This provides
access to both the
instruction range and the parent `MachineBasicBlock`, which enables
looking up function-level
attributes.

With this change, targets can select post-RA scheduling direction per
function using a function
attribute. For example:

```cpp
void overridePostRASchedPolicy(MachineSchedPolicy &Policy,
                               const SchedRegion &Region) const {
  const Function &F = Region.RegionBegin->getMF()->getFunction();
  Attribute Attr = F.getFnAttribute("amdgpu-post-ra-direction");
  ...
}

Author: harrisonGPU

llvm/include/llvm/CodeGen/MachineScheduler.h

@@ -65,7 +65,7 @@
 //
 // void <SubTarget>Subtarget::
 // overrideSchedPolicy(MachineSchedPolicy &Policy,
-//                     unsigned NumRegionInstrs) const {
+//                     const SchedRegion &Region) const {
 //   Policy.<Flag> = true;
 // }
 //
@@ -218,6 +218,22 @@ struct MachineSchedPolicy {
   MachineSchedPolicy() = default;
 };
 
+/// A region of an MBB for scheduling.
+struct SchedRegion {
+  /// RegionBegin is the first instruction in the scheduling region, and
+  /// RegionEnd is either MBB->end() or the scheduling boundary after the
+  /// last instruction in the scheduling region. These iterators cannot refer
+  /// to instructions outside of the identified scheduling region because
+  /// those may be reordered before scheduling this region.
+  MachineBasicBlock::iterator RegionBegin;
+  MachineBasicBlock::iterator RegionEnd;
+  unsigned NumRegionInstrs;
+
+  SchedRegion(MachineBasicBlock::iterator B, MachineBasicBlock::iterator E,
+              unsigned N)
+      : RegionBegin(B), RegionEnd(E), NumRegionInstrs(N) {}
+};
+
 /// MachineSchedStrategy - Interface to the scheduling algorithm used by
 /// ScheduleDAGMI.
 ///

llvm/include/llvm/CodeGen/TargetSubtargetInfo.h

@@ -54,6 +54,7 @@ class TargetRegisterClass;
 class TargetRegisterInfo;
 class TargetSchedModel;
 class Triple;
+struct SchedRegion;
 
 //===----------------------------------------------------------------------===//
 ///
@@ -231,7 +232,7 @@ class LLVM_ABI TargetSubtargetInfo : public MCSubtargetInfo {
   /// scheduling heuristics (no custom MachineSchedStrategy) to make
   /// changes to the generic scheduling policy.
   virtual void overrideSchedPolicy(MachineSchedPolicy &Policy,
-                                   unsigned NumRegionInstrs) const {}
+                                   const SchedRegion &Region) const {}
 
   /// Override generic post-ra scheduling policy within a region.
   ///
@@ -241,7 +242,7 @@ class LLVM_ABI TargetSubtargetInfo : public MCSubtargetInfo {
   /// Note that some options like tracking register pressure won't take effect
   /// in post-ra scheduling.
   virtual void overridePostRASchedPolicy(MachineSchedPolicy &Policy,
-                                         unsigned NumRegionInstrs) const {}
+                                         const SchedRegion &Region) const {}
 
   // Perform target-specific adjustments to the latency of a schedule
   // dependency.

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -771,24 +771,6 @@ static bool isSchedBoundary(MachineBasicBlock::iterator MI,
          MI->isFakeUse();
 }
 
-/// A region of an MBB for scheduling.
-namespace {
-struct SchedRegion {
-  /// RegionBegin is the first instruction in the scheduling region, and
-  /// RegionEnd is either MBB->end() or the scheduling boundary after the
-  /// last instruction in the scheduling region. These iterators cannot refer
-  /// to instructions outside of the identified scheduling region because
-  /// those may be reordered before scheduling this region.
-  MachineBasicBlock::iterator RegionBegin;
-  MachineBasicBlock::iterator RegionEnd;
-  unsigned NumRegionInstrs;
-
-  SchedRegion(MachineBasicBlock::iterator B, MachineBasicBlock::iterator E,
-              unsigned N) :
-    RegionBegin(B), RegionEnd(E), NumRegionInstrs(N) {}
-};
-} // end anonymous namespace
-
 using MBBRegionsVector = SmallVector<SchedRegion, 16>;
 
 static void
@@ -3725,7 +3707,8 @@ void GenericScheduler::initPolicy(MachineBasicBlock::iterator Begin,
   RegionPolicy.OnlyBottomUp = true;
 
   // Allow the subtarget to override default policy.
-  MF.getSubtarget().overrideSchedPolicy(RegionPolicy, NumRegionInstrs);
+  SchedRegion Region(Begin, End, NumRegionInstrs);
+  MF.getSubtarget().overrideSchedPolicy(RegionPolicy, Region);
 
   // After subtarget overrides, apply command line options.
   if (!EnableRegPressure) {
@@ -4338,7 +4321,8 @@ void PostGenericScheduler::initPolicy(MachineBasicBlock::iterator Begin,
   RegionPolicy.OnlyBottomUp = false;
 
   // Allow the subtarget to override default policy.
-  MF.getSubtarget().overridePostRASchedPolicy(RegionPolicy, NumRegionInstrs);
+  SchedRegion Region(Begin, End, NumRegionInstrs);
+  MF.getSubtarget().overridePostRASchedPolicy(RegionPolicy, Region);
 
   // After subtarget overrides, apply command line options.
   if (PostRADirection == MISched::TopDown) {

llvm/lib/Target/AArch64/AArch64Subtarget.cpp

@@ -534,7 +534,7 @@ unsigned AArch64Subtarget::classifyGlobalFunctionReference(
 }
 
 void AArch64Subtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
-                                           unsigned NumRegionInstrs) const {
+                                           const SchedRegion &Region) const {
   // LNT run (at least on Cyclone) showed reasonably significant gains for
   // bi-directional scheduling. 253.perlbmk.
   Policy.OnlyTopDown = false;

llvm/lib/Target/AArch64/AArch64Subtarget.h

@@ -343,7 +343,8 @@ class AArch64Subtarget final : public AArch64GenSubtargetInfo {
   }
 
   void overrideSchedPolicy(MachineSchedPolicy &Policy,
-                           unsigned NumRegionInstrs) const override;
+                           const SchedRegion &Region) const override;
+
   void adjustSchedDependency(SUnit *Def, int DefOpIdx, SUnit *Use, int UseOpIdx,
                              SDep &Dep,
                              const TargetSchedModel *SchedModel) const override;

llvm/lib/Target/AMDGPU/GCNSubtarget.cpp

@@ -324,7 +324,7 @@ bool GCNSubtarget::zeroesHigh16BitsOfDest(unsigned Opcode) const {
 }
 
 void GCNSubtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
-                                       unsigned NumRegionInstrs) const {
+                                       const SchedRegion &Region) const {
   // Track register pressure so the scheduler can try to decrease
   // pressure once register usage is above the threshold defined by
   // SIRegisterInfo::getRegPressureSetLimit()

llvm/lib/Target/AMDGPU/GCNSubtarget.h

@@ -1022,7 +1022,7 @@ class GCNSubtarget final : public AMDGPUGenSubtargetInfo,
   }
 
   void overrideSchedPolicy(MachineSchedPolicy &Policy,
-                           unsigned NumRegionInstrs) const override;
+                           const SchedRegion &Region) const override;
 
   void mirFileLoaded(MachineFunction &MF) const override;
 

llvm/lib/Target/PowerPC/PPCSubtarget.cpp

@@ -171,7 +171,7 @@ void PPCSubtarget::getCriticalPathRCs(RegClassVector &CriticalPathRCs) const {
 }
 
 void PPCSubtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
-                                       unsigned NumRegionInstrs) const {
+                                       const SchedRegion &Region) const {
   // The GenericScheduler that we use defaults to scheduling bottom up only.
   // We want to schedule from both the top and the bottom and so we set
   // OnlyBottomUp to false.

llvm/lib/Target/PowerPC/PPCSubtarget.h

@@ -240,7 +240,8 @@ class PPCSubtarget : public PPCGenSubtargetInfo {
   void getCriticalPathRCs(RegClassVector &CriticalPathRCs) const override;
 
   void overrideSchedPolicy(MachineSchedPolicy &Policy,
-                           unsigned NumRegionInstrs) const override;
+                           const SchedRegion &Region) const override;
+
   bool useAA() const override;
 
   bool enableSubRegLiveness() const override;

llvm/lib/Target/RISCV/RISCVSubtarget.cpp

@@ -216,7 +216,7 @@ unsigned RISCVSubtarget::getMinimumJumpTableEntries() const {
 }
 
 void RISCVSubtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
-                                         unsigned NumRegionInstrs) const {
+                                         const SchedRegion &Region) const {
   // Do bidirectional scheduling since it provides a more balanced scheduling
   // leading to better performance. This will increase compile time.
   Policy.OnlyTopDown = false;
@@ -231,8 +231,8 @@ void RISCVSubtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
   Policy.ShouldTrackPressure = true;
 }
 
-void RISCVSubtarget::overridePostRASchedPolicy(MachineSchedPolicy &Policy,
-                                               unsigned NumRegionInstrs) const {
+void RISCVSubtarget::overridePostRASchedPolicy(
+    MachineSchedPolicy &Policy, const SchedRegion &Region) const {
   MISched::Direction PostRASchedDirection = getPostRASchedDirection();
   if (PostRASchedDirection == MISched::TopDown) {
     Policy.OnlyTopDown = true;