SplitKit.cpp

//===---------- SplitKit.cpp - Toolkit for splitting live ranges ----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the SplitAnalysis class as well as mutator functions for
// live range splitting.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "regalloc"
#include "SplitKit.h"
#include "LiveRangeEdit.h"
#include "VirtRegMap.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GraphWriter.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"

using namespace llvm;

static cl::opt<bool>
AllowSplit("spiller-splits-edges",
           cl::desc("Allow critical edge splitting during spilling"));

//===----------------------------------------------------------------------===//
//                                 Edge Bundles
//===----------------------------------------------------------------------===//

/// compute - Compute the edge bundles for MF. Bundles depend only on the CFG.
void EdgeBundles::compute(const MachineFunction *mf) {
  MF = mf;
  EC.clear();
  EC.grow(2 * MF->size());

  for (MachineFunction::const_iterator I = MF->begin(), E = MF->end(); I != E;
       ++I) {
    const MachineBasicBlock &MBB = *I;
    unsigned OutE = 2 * MBB.getNumber() + 1;
    // Join the outgoing bundle with the ingoing bundles of all successors.
    for (MachineBasicBlock::const_succ_iterator SI = MBB.succ_begin(),
           SE = MBB.succ_end(); SI != SE; ++SI)
      EC.join(OutE, 2 * (*SI)->getNumber());
  }
  EC.compress();
}

/// view - Visualize the annotated bipartite CFG with Graphviz.
void EdgeBundles::view() const {
  ViewGraph(*this, "EdgeBundles");
}

/// Specialize WriteGraph, the standard implementation won't work.
raw_ostream &llvm::WriteGraph(raw_ostream &O, const EdgeBundles &G,
                              bool ShortNames,
                              const std::string &Title) {
  const MachineFunction *MF = G.getMachineFunction();

  O << "digraph {\n";
  for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
       I != E; ++I) {
    unsigned BB = I->getNumber();
    O << "\t\"BB#" << BB << "\" [ shape=box ]\n"
      << '\t' << G.getBundle(BB, false) << " -> \"BB#" << BB << "\"\n"
      << "\t\"BB#" << BB << "\" -> " << G.getBundle(BB, true) << '\n';
    for (MachineBasicBlock::const_succ_iterator SI = I->succ_begin(),
           SE = I->succ_end(); SI != SE; ++SI)
      O << "\t\"BB#" << BB << "\" -> \"BB#" << (*SI)->getNumber()
        << "\" [ color=lightgray ]\n";
  }
  O << "}\n";
  return O;
}


//===----------------------------------------------------------------------===//
//                                 Split Analysis
//===----------------------------------------------------------------------===//

SplitAnalysis::SplitAnalysis(const MachineFunction &mf,
                             const LiveIntervals &lis,
                             const MachineLoopInfo &mli)
  : mf_(mf),
    lis_(lis),
    loops_(mli),
    tii_(*mf.getTarget().getInstrInfo()),
    curli_(0) {}

void SplitAnalysis::clear() {
  usingInstrs_.clear();
  usingBlocks_.clear();
  usingLoops_.clear();
  curli_ = 0;
}

bool SplitAnalysis::canAnalyzeBranch(const MachineBasicBlock *MBB) {
  MachineBasicBlock *T, *F;
  SmallVector<MachineOperand, 4> Cond;
  return !tii_.AnalyzeBranch(const_cast<MachineBasicBlock&>(*MBB), T, F, Cond);
}

/// analyzeUses - Count instructions, basic blocks, and loops using curli.
void SplitAnalysis::analyzeUses() {
  const MachineRegisterInfo &MRI = mf_.getRegInfo();
  for (MachineRegisterInfo::reg_iterator I = MRI.reg_begin(curli_->reg);
       MachineInstr *MI = I.skipInstruction();) {
    if (MI->isDebugValue() || !usingInstrs_.insert(MI))
      continue;
    MachineBasicBlock *MBB = MI->getParent();
    if (usingBlocks_[MBB]++)
      continue;
    for (MachineLoop *Loop = loops_.getLoopFor(MBB); Loop;
         Loop = Loop->getParentLoop())
      usingLoops_[Loop]++;
  }
  DEBUG(dbgs() << "  counted "
               << usingInstrs_.size() << " instrs, "
               << usingBlocks_.size() << " blocks, "
               << usingLoops_.size()  << " loops.\n");
}

void SplitAnalysis::print(const BlockPtrSet &B, raw_ostream &OS) const {
  for (BlockPtrSet::const_iterator I = B.begin(), E = B.end(); I != E; ++I) {
    unsigned count = usingBlocks_.lookup(*I);
    OS << " BB#" << (*I)->getNumber();
    if (count)
      OS << '(' << count << ')';
  }
}

// Get three sets of basic blocks surrounding a loop: Blocks inside the loop,
// predecessor blocks, and exit blocks.
void SplitAnalysis::getLoopBlocks(const MachineLoop *Loop, LoopBlocks &Blocks) {
  Blocks.clear();

  // Blocks in the loop.
  Blocks.Loop.insert(Loop->block_begin(), Loop->block_end());

  // Predecessor blocks.
  const MachineBasicBlock *Header = Loop->getHeader();
  for (MachineBasicBlock::const_pred_iterator I = Header->pred_begin(),
       E = Header->pred_end(); I != E; ++I)
    if (!Blocks.Loop.count(*I))
      Blocks.Preds.insert(*I);

  // Exit blocks.
  for (MachineLoop::block_iterator I = Loop->block_begin(),
       E = Loop->block_end(); I != E; ++I) {
    const MachineBasicBlock *MBB = *I;
    for (MachineBasicBlock::const_succ_iterator SI = MBB->succ_begin(),
       SE = MBB->succ_end(); SI != SE; ++SI)
      if (!Blocks.Loop.count(*SI))
        Blocks.Exits.insert(*SI);
  }
}

void SplitAnalysis::print(const LoopBlocks &B, raw_ostream &OS) const {
  OS << "Loop:";
  print(B.Loop, OS);
  OS << ", preds:";
  print(B.Preds, OS);
  OS << ", exits:";
  print(B.Exits, OS);
}

/// analyzeLoopPeripheralUse - Return an enum describing how curli_ is used in
/// and around the Loop.
SplitAnalysis::LoopPeripheralUse SplitAnalysis::
analyzeLoopPeripheralUse(const SplitAnalysis::LoopBlocks &Blocks) {
  LoopPeripheralUse use = ContainedInLoop;
  for (BlockCountMap::iterator I = usingBlocks_.begin(), E = usingBlocks_.end();
       I != E; ++I) {
    const MachineBasicBlock *MBB = I->first;
    // Is this a peripheral block?
    if (use < MultiPeripheral &&
        (Blocks.Preds.count(MBB) || Blocks.Exits.count(MBB))) {
      if (I->second > 1) use = MultiPeripheral;
      else               use = SinglePeripheral;
      continue;
    }
    // Is it a loop block?
    if (Blocks.Loop.count(MBB))
      continue;
    // It must be an unrelated block.
    DEBUG(dbgs() << ", outside: BB#" << MBB->getNumber());
    return OutsideLoop;
  }
  return use;