lib/Target/ARM/ARMHazardRecognizer.cpp

//===-- ARMHazardRecognizer.cpp - ARM postra hazard recognizer ------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "ARMHazardRecognizer.h"
#include "ARMBaseInstrInfo.h"
#include "ARMSubtarget.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/Target/TargetRegisterInfo.h"
using namespace llvm;

static bool hasRAWHazard(MachineInstr *DefMI, MachineInstr *MI,
                         const TargetRegisterInfo &TRI) {
  // FIXME: Detect integer instructions properly.
  const TargetInstrDesc &TID = MI->getDesc();
  unsigned Domain = TID.TSFlags & ARMII::DomainMask;
  if (Domain == ARMII::DomainVFP) {
    unsigned Opcode = MI->getOpcode();
    if (Opcode == ARM::VSTRS || Opcode == ARM::VSTRD ||
        Opcode == ARM::VMOVRS || Opcode == ARM::VMOVRRD)
      return false;
  } else if (Domain == ARMII::DomainNEON) {
    if (MI->getDesc().mayStore() || MI->getDesc().mayLoad())
      return false;
  } else
    return false;
  return MI->readsRegister(DefMI->getOperand(0).getReg(), &TRI);
}

ScheduleHazardRecognizer::HazardType
ARMHazardRecognizer::getHazardType(SUnit *SU, int Stalls) {
  assert(Stalls == 0 && "ARM hazards don't support scoreboard lookahead");

  MachineInstr *MI = SU->getInstr();

  if (!MI->isDebugValue()) {
    if (ITBlockSize && MI != ITBlockMIs[ITBlockSize-1])
      return Hazard;

    // Look for special VMLA / VMLS hazards. A VMUL / VADD / VSUB following
    // a VMLA / VMLS will cause 4 cycle stall.
    const TargetInstrDesc &TID = MI->getDesc();
    if (LastMI && (TID.TSFlags & ARMII::DomainMask) != ARMII::DomainGeneral) {
      MachineInstr *DefMI = LastMI;
      const TargetInstrDesc &LastTID = LastMI->getDesc();
      // Skip over one non-VFP / NEON instruction.
      if (!LastTID.isBarrier() &&
          (LastTID.TSFlags & ARMII::DomainMask) == ARMII::DomainGeneral) {
        MachineBasicBlock::iterator I = LastMI;
        if (I != LastMI->getParent()->begin()) {
          I = llvm::prior(I);
          DefMI = &*I;
        }
      }

      if (TII.isFpMLxInstruction(DefMI->getOpcode()) &&
          (TII.canCauseFpMLxStall(MI->getOpcode()) ||
           hasRAWHazard(DefMI, MI, TRI))) {
        // Try to schedule another instruction for the next 4 cycles.
        if (FpMLxStalls == 0)
          FpMLxStalls = 4;
        return Hazard;
      }
    }
  }

  return ScoreboardHazardRecognizer::getHazardType(SU, Stalls);
}

void ARMHazardRecognizer::Reset() {
  LastMI = 0;
  FpMLxStalls = 0;
  ITBlockSize = 0;
  ScoreboardHazardRecognizer::Reset();
}

void ARMHazardRecognizer::EmitInstruction(SUnit *SU) {
  MachineInstr *MI = SU->getInstr();
  unsigned Opcode = MI->getOpcode();
  if (ITBlockSize) {
    --ITBlockSize;
  } else if (Opcode == ARM::t2IT) {
    unsigned Mask = MI->getOperand(1).getImm();
    unsigned NumTZ = CountTrailingZeros_32(Mask);
    assert(NumTZ <= 3 && "Invalid IT mask!");
    ITBlockSize = 4 - NumTZ;
    MachineBasicBlock::iterator I = MI;
    for (unsigned i = 0; i < ITBlockSize; ++i) {
      // Advance to the next instruction, skipping any dbg_value instructions.
      do {
        ++I;
      } while (I->isDebugValue());
      ITBlockMIs[ITBlockSize-1-i] = &*I;
    }
  }

  if (!MI->isDebugValue()) {
    LastMI = MI;
    FpMLxStalls = 0;
  }

  ScoreboardHazardRecognizer::EmitInstruction(SU);
}

void ARMHazardRecognizer::AdvanceCycle() {
  if (FpMLxStalls && --FpMLxStalls == 0)
    // Stalled for 4 cycles but still can't schedule any other instructions.
    LastMI = 0;
  ScoreboardHazardRecognizer::AdvanceCycle();
}

void ARMHazardRecognizer::RecedeCycle() {
  llvm_unreachable("reverse ARM hazard checking unsupported");
}