[AMDGPU] gfx908 scheduling

Differential Revision: https://reviews.llvm.org/D64590

llvm-svn: 365826

llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp

@@ -40,6 +40,11 @@ using namespace llvm;
 #undef AMDGPUSubtarget
 #include "R600GenSubtargetInfo.inc"
 
+static cl::opt<bool> DisablePowerSched(
+  "amdgpu-disable-power-sched",
+  cl::desc("Disable scheduling to minimize mAI power bursts"),
+  cl::init(false));
+
 GCNSubtarget::~GCNSubtarget() = default;
 
 R600Subtarget &
@@ -751,11 +756,130 @@ struct MemOpClusterMutation : ScheduleDAGMutation {
     }
   }
 };
+
+struct FillMFMAShadowMutation : ScheduleDAGMutation {
+  const SIInstrInfo *TII;
+
+  ScheduleDAGMI *DAG;
+
+  FillMFMAShadowMutation(const SIInstrInfo *tii) : TII(tii) {}
+
+  bool isSALU(const SUnit *SU) const {
+    const MachineInstr &MI = *SU->getInstr();
+    return TII->isSALU(MI) && !MI.isTerminator();
+  }
+
+  bool canAddEdge(const SUnit *Succ, const SUnit *Pred) const {
+    if (Pred->NodeNum < Succ->NodeNum)
+      return true;
+
+    SmallVector<const SUnit*, 64> Succs({Succ}), Preds({Pred});
+
+    for (unsigned I = 0; I < Succs.size(); ++I) {
+      for (const SDep &SI : Succs[I]->Succs) {
+        const SUnit *SU = SI.getSUnit();
+        if (SU != Succs[I] && llvm::find(Succs, SU) == Succs.end())
+          Succs.push_back(SU);
+      }
+    }
+
+    SmallPtrSet<const SUnit*, 32> Visited;
+    while (!Preds.empty()) {
+      const SUnit *SU = Preds.pop_back_val();
+      if (llvm::find(Succs, SU) != Succs.end())
+        return false;
+      Visited.insert(SU);
+      for (const SDep &SI : SU->Preds)
+        if (SI.getSUnit() != SU && !Visited.count(SI.getSUnit()))
+          Preds.push_back(SI.getSUnit());
+    }
+
+    return true;
+  }
+
+  // Link as much SALU intructions in chain as possible. Return the size
+  // of the chain. Links up to MaxChain instructions.
+  unsigned linkSALUChain(SUnit *From, SUnit *To, unsigned MaxChain,
+                         SmallPtrSetImpl<SUnit *> &Visited) const {
+    SmallVector<SUnit *, 8> Worklist({To});
+    unsigned Linked = 0;
+
+    while (!Worklist.empty() && MaxChain-- > 0) {
+      SUnit *SU = Worklist.pop_back_val();
+      if (!Visited.insert(SU).second)
+        continue;
+
+      LLVM_DEBUG(dbgs() << "Inserting edge from\n" ; DAG->dumpNode(*From);
+                 dbgs() << "to\n"; DAG->dumpNode(*SU); dbgs() << '\n');
+
+      if (SU->addPred(SDep(From, SDep::Artificial), false))
+        ++Linked;
+
+      for (SDep &SI : From->Succs) {
+        SUnit *SUv = SI.getSUnit();
+        if (SUv != From && TII->isVALU(*SUv->getInstr()) && canAddEdge(SUv, SU))
+          SUv->addPred(SDep(SU, SDep::Artificial), false);
+      }
+
+      for (SDep &SI : SU->Succs) {
+        SUnit *Succ = SI.getSUnit();
+        if (Succ != SU && isSALU(Succ) && canAddEdge(From, Succ))
+          Worklist.push_back(Succ);
+      }
+    }
+
+    return Linked;
+  }
+
+  void apply(ScheduleDAGInstrs *DAGInstrs) override {
+    const GCNSubtarget &ST = DAGInstrs->MF.getSubtarget<GCNSubtarget>();
+    if (!ST.hasMAIInsts() || DisablePowerSched)
+      return;
+    DAG = static_cast<ScheduleDAGMI*>(DAGInstrs);
+    const TargetSchedModel *TSchedModel = DAGInstrs->getSchedModel();
+    if (!TSchedModel || DAG->SUnits.empty())
+      return;
+
+    // Scan for MFMA long latency instructions and try to add a dependency
+    // of available SALU instructions to give them a chance to fill MFMA
+    // shadow. That is desirable to fill MFMA shadow with SALU instructions
+    // rather than VALU to prevent power consumption bursts and throttle.
+    auto LastSALU = DAG->SUnits.begin();
+    auto E = DAG->SUnits.end();
+    SmallPtrSet<SUnit*, 32> Visited;
+    for (SUnit &SU : DAG->SUnits) {
+      MachineInstr &MAI = *SU.getInstr();
+      if (!TII->isMAI(MAI) ||
+           MAI.getOpcode() == AMDGPU::V_ACCVGPR_WRITE_B32 ||
+           MAI.getOpcode() == AMDGPU::V_ACCVGPR_READ_B32)
+        continue;
+
+      unsigned Lat = TSchedModel->computeInstrLatency(&MAI) - 1;
+
+      LLVM_DEBUG(dbgs() << "Found MFMA: "; DAG->dumpNode(SU);
+                 dbgs() << "Need " << Lat
+                        << " instructions to cover latency.\n");
+
+      // Find up to Lat independent scalar instructions as early as
+      // possible such that they can be scheduled after this MFMA.
+      for ( ; Lat && LastSALU != E; ++LastSALU) {
+        if (Visited.count(&*LastSALU))
+          continue;
+
+        if (!isSALU(&*LastSALU) || !canAddEdge(&*LastSALU, &SU))
+          continue;
+
+        Lat -= linkSALUChain(&SU, &*LastSALU, Lat, Visited);
+      }
+    }
+  }
+};
 } // namespace
 
 void GCNSubtarget::getPostRAMutations(
     std::vector<std::unique_ptr<ScheduleDAGMutation>> &Mutations) const {
   Mutations.push_back(llvm::make_unique<MemOpClusterMutation>(&InstrInfo));
+  Mutations.push_back(llvm::make_unique<FillMFMAShadowMutation>(&InstrInfo));
 }
 
 const AMDGPUSubtarget &AMDGPUSubtarget::get(const MachineFunction &MF) {

llvm/lib/Target/AMDGPU/SIInstrInfo.h

@@ -660,6 +660,14 @@ public:
     return !RI.isSGPRReg(MRI, Dest);
   }
 
+  bool hasVGPRUses(const MachineInstr &MI) const {
+    const MachineFunction &MF = *MI.getParent()->getParent();
+    const MachineRegisterInfo &MRI = MF.getRegInfo();
+    return llvm::any_of(MI.explicit_uses(),
+                        [&MRI, this](const MachineOperand &MO) {
+      return MO.isReg() && RI.isVGPR(MRI, MO.getReg());});
+  }
+
   /// Whether we must prevent this instruction from executing with EXEC = 0.
   bool hasUnwantedEffectsWhenEXECEmpty(const MachineInstr &MI) const;
 

llvm/lib/Target/AMDGPU/SISchedule.td

@@ -24,6 +24,9 @@ def WriteSMEM   : SchedWrite;
 def WriteVMEM   : SchedWrite;
 def WriteBarrier : SchedWrite;
 
+def MIVGPRRead  : SchedRead;
+def MIMFMARead  : SchedRead;
+
 // Vector ALU instructions
 def Write32Bit         : SchedWrite;
 def WriteQuarterRate32 : SchedWrite;
@@ -43,6 +46,11 @@ def WriteDoubleCvt  : SchedWrite;
 // Half rate 64-bit instructions.
 def Write64Bit : SchedWrite;
 
+// mAI multipass instructions.
+def Write2PassMAI  : SchedWrite;
+def Write8PassMAI  : SchedWrite;
+def Write16PassMAI : SchedWrite;
+
 // FIXME: Should there be a class for instructions which are VALU
 // instructions and have VALU rates, but write to the SALU (i.e. VOPC
 // instructions)
@@ -97,6 +105,11 @@ class HWWriteRes<SchedWrite write, list<ProcResourceKind> resources,
 class HWVALUWriteRes<SchedWrite write, int latency> :
   HWWriteRes<write, [HWVALU], latency>;
 
+def PredMIReadVGPR : SchedPredicate<[{TII->hasVGPRUses(*MI)}]>;
+
+def MIReadVGPR : SchedReadVariant<[
+      SchedVar<PredMIReadVGPR, [MIVGPRRead]>,
+      SchedVar<NoSchedPred, [ReadDefault]>]>;
 
 // The latency numbers are taken from AMD Accelerated Parallel Processing
 // guide. They may not be accurate.
@@ -115,6 +128,24 @@ multiclass SICommonWriteRes {
   def : HWVALUWriteRes<Write32Bit,         1>;
   def : HWVALUWriteRes<Write64Bit,         2>;
   def : HWVALUWriteRes<WriteQuarterRate32, 4>;
+  def : HWVALUWriteRes<Write2PassMAI,      2>;
+  def : HWVALUWriteRes<Write8PassMAI,      8>;
+  def : HWVALUWriteRes<Write16PassMAI,    16>;
+
+  def : ReadAdvance<MIVGPRRead, -2>;
+  def : InstRW<[Write64Bit, MIReadVGPR], (instregex "^V_ACCVGPR_WRITE_B32$")>;
+
+  // Technicaly mfma reads can be from 0 to 4 cycles but that does not make
+  // sense to model because its register setup is huge. In particular if we
+  // properly model read advanice as -2 for a vgpr read it will result in a
+  // bad scheduling of acc writes before that mfma. To avoid it we would
+  // need to consume 2 or 4 more vgprs to be initialized before the acc
+  // write sequence. Just assume worst case here.
+  def : ReadAdvance<MIMFMARead, -4>;
+
+  def : InstRW<[Write2PassMAI,  MIMFMARead], (instregex "^V_MFMA_..._4X4X")>;
+  def : InstRW<[Write8PassMAI,  MIMFMARead], (instregex "^V_MFMA_..._16X16X")>;
+  def : InstRW<[Write16PassMAI, MIMFMARead], (instregex "^V_MFMA_..._32X32X")>;
 }
 
 def PredIsVGPR32Copy : SchedPredicate<[{TII->isVGPRCopy(*MI) && TII->getOpSize(*MI, 0) <= 32}]>;