path: root/lib/CodeGen/MachineTraceMetrics.cpp

//===- lib/CodeGen/MachineTraceMetrics.cpp ----------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "early-ifcvt"
#include "MachineTraceMetrics.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/PostOrderIterator.h"

using namespace llvm;

char MachineTraceMetrics::ID = 0;
char &llvm::MachineTraceMetricsID = MachineTraceMetrics::ID;

INITIALIZE_PASS_BEGIN(MachineTraceMetrics,
                  "machine-trace-metrics", "Machine Trace Metrics", false, true)
INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_END(MachineTraceMetrics,
                  "machine-trace-metrics", "Machine Trace Metrics", false, true)

MachineTraceMetrics::MachineTraceMetrics()
  : MachineFunctionPass(ID), TII(0), TRI(0), MRI(0), Loops(0) {
  std::fill(Ensembles, array_endof(Ensembles), (Ensemble*)0);
}

void MachineTraceMetrics::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesAll();
  AU.addRequired<MachineBranchProbabilityInfo>();
  AU.addRequired<MachineLoopInfo>();
  MachineFunctionPass::getAnalysisUsage(AU);
}

bool MachineTraceMetrics::runOnMachineFunction(MachineFunction &Func) {
  MF = &Func;
  TII = MF->getTarget().getInstrInfo();
  TRI = MF->getTarget().getRegisterInfo();
  MRI = &MF->getRegInfo();
  Loops = &getAnalysis<MachineLoopInfo>();
  BlockInfo.resize(MF->getNumBlockIDs());
  return false;
}

void MachineTraceMetrics::releaseMemory() {
  BlockInfo.clear();
  for (unsigned i = 0; i != TS_NumStrategies; ++i) {
    delete Ensembles[i];
    Ensembles[i] = 0;
  }
}

//===----------------------------------------------------------------------===//
//                          Fixed block information
//===----------------------------------------------------------------------===//
//
// The number of instructions in a basic block and the CPU resources used by
// those instructions don't depend on any given trace strategy.

/// Is MI an instruction that should be considered free because it will likely
/// be eliminated by later passes?
static bool isFree(const MachineInstr *MI) {
  switch(MI->getOpcode()) {
  default: return false;
  case TargetOpcode::PHI:
  case TargetOpcode::PROLOG_LABEL:
  case TargetOpcode::EH_LABEL:
  case TargetOpcode::GC_LABEL:
  case TargetOpcode::KILL:
  case TargetOpcode::EXTRACT_SUBREG:
  case TargetOpcode::INSERT_SUBREG:
  case TargetOpcode::IMPLICIT_DEF:
  case TargetOpcode::SUBREG_TO_REG:
  case TargetOpcode::COPY_TO_REGCLASS:
  case TargetOpcode::DBG_VALUE:
  case TargetOpcode::REG_SEQUENCE:
  case TargetOpcode::COPY:
    return true;
  }
}

/// Compute the resource usage in basic block MBB.
const MachineTraceMetrics::FixedBlockInfo*
MachineTraceMetrics::getResources(const MachineBasicBlock *MBB) {
  assert(MBB && "No basic block");
  FixedBlockInfo *FBI = &BlockInfo[MBB->getNumber()];
  if (FBI->hasResources())
    return FBI;

  // Compute resource usage in the block.
  // FIXME: Compute per-functional unit counts.
  FBI->HasCalls = false;
  unsigned InstrCount = 0;
  for (MachineBasicBlock::const_iterator I = MBB->begin(), E = MBB->end();
       I != E; ++I) {
    const MachineInstr *MI = I;
    if (isFree(MI))
      continue;
    ++InstrCount;
    if (MI->isCall())
      FBI->HasCalls = true;
  }
  FBI->InstrCount = InstrCount;
  return FBI;
}

//===----------------------------------------------------------------------===//
//                         Ensemble utility functions
//===----------------------------------------------------------------------===//

MachineTraceMetrics::Ensemble::Ensemble(MachineTraceMetrics *ct)
  : CT(*ct) {
  BlockInfo.resize(CT.BlockInfo.size());
}

// Virtual destructor serves as an anchor.
MachineTraceMetrics::Ensemble::~Ensemble() {}

const MachineLoop*
MachineTraceMetrics::Ensemble::getLoopFor(const MachineBasicBlock *MBB) const {
  return CT.Loops->getLoopFor(MBB);
}

// Update resource-related information in the TraceBlockInfo for MBB.
// Only update resources related to the trace above MBB.
void MachineTraceMetrics::Ensemble::
computeDepthResources(const MachineBasicBlock *MBB) {
  TraceBlockInfo *TBI = &BlockInfo[MBB->getNumber()];

  // Compute resources from trace above. The top block is simple.
  if (!TBI->Pred) {
    TBI->InstrDepth = 0;
    TBI->Head = MBB->getNumber();
    return;
  }

  // Compute from the block above. A post-order traversal ensures the
  // predecessor is always computed first.
  TraceBlockInfo *PredTBI = &BlockInfo[TBI->Pred->getNumber()];
  assert(PredTBI->hasValidDepth() && "Trace above has not been computed yet");
  const FixedBlockInfo *PredFBI = CT.getResources(TBI->Pred);
  TBI->InstrDepth = PredTBI->InstrDepth + PredFBI->InstrCount;
  TBI->Head = PredTBI->Head;
}

// Update resource-related information in the TraceBlockInfo for MBB.
// Only update resources related to the trace below MBB.
void MachineTraceMetrics::Ensemble::
computeHeightResources(const MachineBasicBlock *MBB) {
  TraceBlockInfo *TBI = &BlockInfo[MBB->getNumber()];

  // Compute resources for the current block.
  TBI->InstrHeight = CT.getResources(MBB)->InstrCount;

  // The trace tail is done.
  if (!TBI->Succ) {
    TBI->Tail = MBB->getNumber();
    return;
  }

  // Compute from the block below. A post-order traversal ensures the
  // predecessor is always computed first.
  TraceBlockInfo *SuccTBI = &BlockInfo[TBI->Succ->getNumber()];
  assert(SuccTBI->hasValidHeight() && "Trace below has not been computed yet");
  TBI->InstrHeight += SuccTBI->InstrHeight;
  TBI->Tail = SuccTBI->Tail;
}

// Check if depth resources for MBB are valid and return the TBI.
// Return NULL if the resources have been invalidated.
const MachineTraceMetrics::TraceBlockInfo*
MachineTraceMetrics::Ensemble::
getDepthResources(const MachineBasicBlock *MBB) const {
  const TraceBlockInfo *TBI = &BlockInfo[MBB->getNumber()];
  return TBI->hasValidDepth() ? TBI : 0;
}

// Check if height resources for MBB are valid and return the TBI.
// Return NULL if the resources have been invalidated.
const MachineTraceMetrics::TraceBlockInfo*
MachineTraceMetrics::Ensemble::
getHeightResources(const MachineBasicBlock *MBB) const {
  const TraceBlockInfo *TBI = &BlockInfo[MBB->getNumber()];
  return TBI->hasValidHeight() ? TBI : 0;
}

//===----------------------------------------------------------------------===//
//                         Trace Selection Strategies
//===----------------------------------------------------------------------===//
//
// A trace selection strategy is implemented as a sub-class of Ensemble. The
// trace through a block B is computed by two DFS traversals of the CFG
// starting from B. One upwards, and one downwards. During the upwards DFS,
// pickTracePred() is called on the post-ordered blocks. During the downwards
// DFS, pickTraceSucc() is called in a post-order.
//

// MinInstrCountEnsemble - Pick the trace that executes the least number of
// instructions.
namespace {
class MinInstrCountEnsemble : public MachineTraceMetrics::Ensemble {
  const char *getName() const { return "MinInstr"; }
  const MachineBasicBlock *pickTracePred(const MachineBasicBlock*);
  const MachineBasicBlock *pickTraceSucc(const MachineBasicBlock*);

public:
  MinInstrCountEnsemble(MachineTraceMetrics