llvm/lib/Target/R600/SIMachineFunctionInfo.cpp

//===-- SIMachineFunctionInfo.cpp - SI Machine Function Info -------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
/// \file
//===----------------------------------------------------------------------===//


#include "SIMachineFunctionInfo.h"
#include "SIInstrInfo.h"
#include "SIRegisterInfo.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/LLVMContext.h"

#define MAX_LANES 64

using namespace llvm;


// Pin the vtable to this file.
void SIMachineFunctionInfo::anchor() {}

SIMachineFunctionInfo::SIMachineFunctionInfo(const MachineFunction &MF)
  : AMDGPUMachineFunction(MF),
    PSInputAddr(0),
    SpillTracker(),
    NumUserSGPRs(0) { }

static unsigned createLaneVGPR(MachineRegisterInfo &MRI, MachineFunction *MF) {
  unsigned VGPR = MRI.createVirtualRegister(&AMDGPU::VReg_32RegClass);

  // We need to add this register as live out for the function, in order to
  // have the live range calculated directly.
  //
  // When register spilling begins, we have already calculated the live
  // live intervals for all the registers.  Since we are spilling SGPRs to
  // VGPRs, we need to update the Lane VGPR's live interval every time we
  // spill or restore a register.
  //
  // Unfortunately, there is no good way to update the live interval as
  // the TargetInstrInfo callbacks for spilling and restoring don't give
  // us access to the live interval information.
  //
  // We are lucky, though, because the InlineSpiller calls
  // LiveRangeEdit::calculateRegClassAndHint() which iterates through
  // all the new register that have been created when restoring a register
  // and calls LiveIntervals::getInterval(), which creates and computes
  // the live interval for the newly created register.  However, once this
  // live intervals is created, it doesn't change and since we usually reuse
  // the Lane VGPR multiple times, this means any uses after the first aren't
  // added to the live interval.
  //
  // To work around this, we add Lane VGPRs to the functions live out list,
  // so that we can guarantee its live range will cover all of its uses.

  for (MachineBasicBlock &MBB : *MF) {
    if (MBB.back().getOpcode() == AMDGPU::S_ENDPGM) {
      MBB.back().addOperand(*MF, MachineOperand::CreateReg(VGPR, false, true));
      return VGPR;
    }
  }

  LLVMContext &Ctx = MF->getFunction()->getContext();
  Ctx.emitError("Could not find S_ENDPGM instruction.");

  return VGPR;
}

unsigned SIMachineFunctionInfo::RegSpillTracker::reserveLanes(
    MachineRegisterInfo &MRI, MachineFunction *MF, unsigned NumRegs) {
  unsigned StartLane = CurrentLane;
  CurrentLane += NumRegs;
  if (!LaneVGPR) {
    LaneVGPR = createLaneVGPR(MRI, MF);
  } else {
    if (CurrentLane >= MAX_LANES) {
      StartLane = CurrentLane = 0;
      LaneVGPR = createLaneVGPR(MRI, MF);
    }
  }
  return StartLane;
}

void SIMachineFunctionInfo::RegSpillTracker::addSpilledReg(unsigned FrameIndex,
                                                           unsigned Reg,
                                                           int Lane) {
  SpilledRegisters[FrameIndex] = SpilledReg(Reg, Lane);
}
/// \brief Returns a register that is not used at any point in the function.
///        If all registers are used, then this function will return
//         AMDGPU::NoRegister.
static unsigned findUnusedVGPR(const MachineRegisterInfo &MRI) {

  const TargetRegisterClass *RC = &AMDGPU::VGPR_32RegClass;

  for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end();
       I != E; ++I) {
    if (!MRI.isPhysRegUsed(*I))
      return *I;
  }
  return AMDGPU::NoRegister;
}

SIMachineFunctionInfo::SpilledReg SIMachineFunctionInfo::getSpilledReg(
                                                       MachineFunction *MF,
                                                       unsigned FrameIndex,
                                                       unsigned SubIdx) {
  const MachineFrameInfo *FrameInfo = MF->getFrameInfo();
  MachineRegisterInfo &MRI = MF->getRegInfo();
  int64_t Offset = FrameInfo->getObjectOffset(FrameIndex);
  Offset += SubIdx * 4;

  unsigned LaneVGPRIdx = Offset / (64 * 4);
  unsigned Lane = (Offset / 4) % 64;

  struct SpilledReg Spill;

  if (!LaneVGPRs.count(LaneVGPRIdx)) {
    unsigned LaneVGPR = findUnusedVGPR(MRI);
    LaneVGPRs[LaneVGPRIdx] = LaneVGPR;
    MRI.setPhysRegUsed(LaneVGPR);

    // Add this register as live-in to all blocks to avoid machine verifer
    // complaining about use of an undefined physical register.
    for (MachineFunction::iterator BI = MF->begin(), BE = MF->end();
         BI != BE; ++BI) {
      BI->addLiveIn(LaneVGPR);
    }
  }

  Spill.VGPR = LaneVGPRs[LaneVGPRIdx];
  Spill.Lane = Lane;
  return Spill;
}