ARMHazardRecognizer.cpp

Go to the documentation of this file.

//===-- ARMHazardRecognizer.cpp - ARM postra hazard recognizer ------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
#include "ARMHazardRecognizer.h"
#include "ARMBaseInstrInfo.h"
#include "ARMBaseRegisterInfo.h"
#include "ARMSubtarget.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
 
using namespace llvm;
 
static cl::opt<int> DataBankMask("arm-data-bank-mask", cl::init(-1),
                                 cl::Hidden);
static cl::opt<bool> AssumeITCMConflict("arm-assume-itcm-bankconflict",
                                        cl::init(false), cl::Hidden);
 
static bool hasRAWHazard(MachineInstr *DefMI, MachineInstr *MI,
                         const TargetRegisterInfo &TRI) {
  // FIXME: Detect integer instructions properly.
  const MCInstrDesc &MCID = MI->getDesc();
  unsigned Domain = MCID.TSFlags & ARMII::DomainMask;
  if (MI->mayStore())
    return false;
  unsigned Opcode = MCID.getOpcode();
  if (Opcode == ARM::VMOVRS || Opcode == ARM::VMOVRRD)
    return false;
  if ((Domain & ARMII::DomainVFP) || (Domain & ARMII::DomainNEON))
    return MI->readsRegister(DefMI->getOperand(0).getReg(), &TRI);
  return false;
}
 
ScheduleHazardRecognizer::HazardType
ARMHazardRecognizerFPMLx::getHazardType(SUnit *SU, int Stalls) {
  assert(Stalls == 0 && "ARM hazards don't support scoreboard lookahead");
 
  MachineInstr *MI = SU->getInstr();
 
  if (!MI->isDebugInstr()) {
    // Look for special VMLA / VMLS hazards. A VMUL / VADD / VSUB following
    // a VMLA / VMLS will cause 4 cycle stall.
    const MCInstrDesc &MCID = MI->getDesc();
    if (LastMI && (MCID.TSFlags & ARMII::DomainMask) != ARMII::DomainGeneral) {
      MachineInstr *DefMI = LastMI;
      const MCInstrDesc &LastMCID = LastMI->getDesc();
      const MachineFunction *MF = MI->getParent()->getParent();
      const ARMBaseInstrInfo &TII = *static_cast<const ARMBaseInstrInfo *>(
                                        MF->getSubtarget().getInstrInfo());
 
      // Skip over one non-VFP / NEON instruction.
      if (!LastMI->isBarrier() &&
          !(TII.getSubtarget().hasMuxedUnits() && LastMI->mayLoadOrStore()) &&
          (LastMCID.TSFlags & ARMII::DomainMask) == ARMII::DomainGeneral) {
        MachineBasicBlock::iterator I = LastMI;
        if (I != LastMI->getParent()->begin()) {
          I = std::prev(I);
          DefMI = &*I;
        }
      }
 
      if (TII.isFpMLxInstruction(DefMI->getOpcode()) &&
          (TII.canCauseFpMLxStall(MI->getOpcode()) ||
           hasRAWHazard(DefMI, MI, TII.getRegisterInfo()))) {
        // Try to schedule another instruction for the next 4 cycles.
        if (FpMLxStalls == 0)
          FpMLxStalls = 4;
        return Hazard;
      }
    }
  }
  return NoHazard;
}
 
void ARMHazardRecognizerFPMLx::Reset() {
  LastMI = nullptr;
  FpMLxStalls = 0;
}
 
void ARMHazardRecognizerFPMLx::EmitInstruction(SUnit *SU) {
  MachineInstr *MI = SU->getInstr();
  if (!MI->isDebugInstr()) {
    LastMI = MI;
    FpMLxStalls = 0;
  }
}
 
void ARMHazardRecognizerFPMLx::AdvanceCycle() {
  if (FpMLxStalls && --FpMLxStalls == 0)
    // Stalled for 4 cycles but still can't schedule any other instructions.
    LastMI = nullptr;
}
 
void ARMHazardRecognizerFPMLx::RecedeCycle() {
  llvm_unreachable("reverse ARM hazard checking unsupported");
}
 
///////// Bank conflicts handled as hazards //////////////
 
static bool getBaseOffset(const MachineInstr &MI, const MachineOperand *&BaseOp,
                          int64_t &Offset) {
 
  uint64_t TSFlags = MI.getDesc().TSFlags;
  unsigned AddrMode = (TSFlags & ARMII::AddrModeMask);
  unsigned IndexMode =
      (TSFlags & ARMII::IndexModeMask) >> ARMII::IndexModeShift;
 
  // Address mode tells us what we want to know about operands for T2
  // instructions (but not size).  It tells us size (but not about operands)
  // for T1 instructions.
  switch (AddrMode) {
  default:
    return false;
  case ARMII::AddrModeT2_i8:
    // t2LDRBT, t2LDRB_POST, t2LDRB_PRE, t2LDRBi8,
    // t2LDRHT, t2LDRH_POST, t2LDRH_PRE, t2LDRHi8,
    // t2LDRSBT, t2LDRSB_POST, t2LDRSB_PRE, t2LDRSBi8,
    // t2LDRSHT, t2LDRSH_POST, t2LDRSH_PRE, t2LDRSHi8,
    // t2LDRT, t2LDR_POST, t2LDR_PRE, t2LDRi8
    BaseOp = &MI.getOperand(1);
    Offset = (IndexMode == ARMII::IndexModePost)
                 ? 0
                 : (IndexMode == ARMII::IndexModePre ||
                    IndexMode == ARMII::IndexModeUpd)
                       ? MI.getOperand(3).getImm()
                       : MI.getOperand(2).getImm();
    return true;
  case ARMII::AddrModeT2_i12:
    // t2LDRBi12, t2LDRHi12
    // t2LDRSBi12, t2LDRSHi12
    // t2LDRi12
    BaseOp = &MI.getOperand(1);
    Offset = MI.getOperand(2).getImm();
    return true;
  case ARMII::AddrModeT2_i8s4:
    // t2LDRD_POST, t2LDRD_PRE, t2LDRDi8
    BaseOp = &MI.getOperand(2);
    Offset = (IndexMode == ARMII::IndexModePost)
                 ? 0
                 : (IndexMode == ARMII::IndexModePre ||
                    IndexMode == ARMII::IndexModeUpd)
                       ? MI.getOperand(4).getImm()
                       : MI.getOperand(3).getImm();
    return true;
  case ARMII::AddrModeT1_1:
    // tLDRBi, tLDRBr (watch out!), TLDRSB
  case ARMII::AddrModeT1_2:
    // tLDRHi, tLDRHr (watch out!), TLDRSH
  case ARMII::AddrModeT1_4:
    // tLDRi, tLDRr (watch out!)
    BaseOp = &MI.getOperand(1);
    Offset = MI.getOperand(2).isImm() ? MI.getOperand(2).getImm() : 0;
    return MI.getOperand(2).isImm();
  }
  return false;
}
 
ARMBankConflictHazardRecognizer::ARMBankConflictHazardRecognizer(
    const ScheduleDAG *DAG, int64_t CPUBankMask, bool CPUAssumeITCMConflict)
    : MF(DAG->MF), DL(DAG->MF.getDataLayout()),
      DataMask(DataBankMask.getNumOccurrences() ? int64_t(DataBankMask)
                                                : CPUBankMask),
      AssumeITCMBankConflict(AssumeITCMConflict.getNumOccurrences()
                                 ? AssumeITCMConflict
                                 : CPUAssumeITCMConflict) {
  MaxLookAhead = 1;
}
 
ScheduleHazardRecognizer::HazardType
ARMBankConflictHazardRecognizer::CheckOffsets(unsigned O0, unsigned O1) {
  return (((O0 ^ O1) & DataMask) != 0) ? NoHazard : Hazard;
}
 
ScheduleHazardRecognizer::HazardType
ARMBankConflictHazardRecognizer::getHazardType(SUnit *SU, int Stalls) {
  MachineInstr &L0 = *SU->getInstr();
  if (!L0.mayLoad() || L0.mayStore() || L0.getNumMemOperands() != 1)
    return NoHazard;
 
  auto MO0 = *L0.memoperands().begin();
  auto BaseVal0 = MO0->getValue();
  auto BasePseudoVal0 = MO0->getPseudoValue();
  int64_t Offset0 = 0;
 
  if (MO0->getSize() > 4)
    return NoHazard;
 
  bool SPvalid = false;
  const MachineOperand *SP = nullptr;
  int64_t SPOffset0 = 0;
 
  for (auto L1 : Accesses) {
    auto MO1 = *L1->memoperands().begin();
    auto BaseVal1 = MO1->getValue();
    auto BasePseudoVal1 = MO1->getPseudoValue();
    int64_t Offset1 = 0;
 
    // Pointers to the same object
    if (BaseVal0 && BaseVal1) {
      const Value *Ptr0, *Ptr1;
      Ptr0 = GetPointerBaseWithConstantOffset(BaseVal0, Offset0, DL, true);
      Ptr1 = GetPointerBaseWithConstantOffset(BaseVal1, Offset1, DL, true);
      if (Ptr0 == Ptr1 && Ptr0)
        return CheckOffsets(Offset0, Offset1);
    }
 
    if (BasePseudoVal0 && BasePseudoVal1 &&
        BasePseudoVal0->kind() == BasePseudoVal1->kind() &&
        BasePseudoVal0->kind() == PseudoSourceValue::FixedStack) {
      // Spills/fills
      auto FS0 = cast<FixedStackPseudoSourceValue>(BasePseudoVal0);
      auto FS1 = cast<FixedStackPseudoSourceValue>(BasePseudoVal1);
      Offset0 = MF.getFrameInfo().getObjectOffset(FS0->getFrameIndex());
      Offset1 = MF.getFrameInfo().getObjectOffset(FS1->getFrameIndex());
      return CheckOffsets(Offset0, Offset1);
    }
 
    // Constant pools (likely in ITCM)
    if (BasePseudoVal0 && BasePseudoVal1 &&
        BasePseudoVal0->kind() == BasePseudoVal1->kind() &&
        BasePseudoVal0->isConstantPool() && AssumeITCMBankConflict)
      return Hazard;
 
    // Is this a stack pointer-relative access?  We could in general try to
    // use "is this the same register and is it unchanged?", but the
    // memory operand tracking is highly likely to have already found that.
    // What we're after here is bank conflicts between different objects in
    // the stack frame.
    if (!SPvalid) { // set up SP
      if (!getBaseOffset(L0, SP, SPOffset0) || SP->getReg().id() != ARM::SP)
        SP = nullptr;
      SPvalid = true;
    }
    if (SP) {
      int64_t SPOffset1;
      const MachineOperand *SP1;
      if (getBaseOffset(*L1, SP1, SPOffset1) && SP1->getReg().id() == ARM::SP)
        return CheckOffsets(SPOffset0, SPOffset1);
    }
  }
 
  return NoHazard;
}
 
void ARMBankConflictHazardRecognizer::Reset() { Accesses.clear(); }
 
void ARMBankConflictHazardRecognizer::EmitInstruction(SUnit *SU) {
  MachineInstr &MI = *SU->getInstr();
  if (!MI.mayLoad() || MI.mayStore() || MI.getNumMemOperands() != 1)
    return;
 
  auto MO = *MI.memoperands().begin();
  uint64_t Size1 = MO->getSize();
  if (Size1 > 4)
    return;
  Accesses.push_back(&MI);
}
 
void ARMBankConflictHazardRecognizer::AdvanceCycle() { Accesses.clear(); }
 
void ARMBankConflictHazardRecognizer::RecedeCycle() { Accesses.clear(); }