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//===---------- 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 "splitter"
#include "SplitKit.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
//===----------------------------------------------------------------------===//
// Split Analysis
//===----------------------------------------------------------------------===//
SplitAnalysis::SplitAnalysis(const MachineFunction *mf,
const LiveIntervals *lis,
const MachineLoopInfo *mli)
: mf_(*mf),
lis_(*lis),
loops_(*mli),
curli_(0) {}
void SplitAnalysis::clear() {
usingInstrs_.clear();
usingBlocks_.clear();
usingLoops_.clear();
}
/// analyseUses - Count instructions, basic blocks, and loops using curli.
void SplitAnalysis::analyseUses() {
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;
if (MachineLoop *Loop = loops_.getLoopFor(MBB))
usingLoops_.insert(Loop);
}
DEBUG(dbgs() << "Counted "
<< usingInstrs_.size() << " instrs, "
<< usingBlocks_.size() << " blocks, "
<< usingLoops_.size() << " loops in "
<< *curli_ << "\n");
}
SplitAnalysis::LoopPeripheralUse
SplitAnalysis::analyzeLoopPeripheralUse(const MachineLoop *Loop) {
// Peripheral blocks.
SmallVector<MachineBasicBlock*, 16> Peri;
Loop->getExitBlocks(Peri);
if (MachineBasicBlock *PredBB = Loop->getLoopPredecessor())
Peri.push_back(PredBB);
array_pod_sort(Peri.begin(), Peri.end());
Peri.erase(std::unique(Peri.begin(), Peri.end()), Peri.end());
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 &&
std::binary_search(Peri.begin(), Peri.end(), MBB)) {
if (I->second > 1) use = MultiPeripheral;
else use = SinglePeripheral;
continue;
}
// Is it a loop block?
if (Loop->contains(MBB))
continue;
// It must be an unrelated block.
return OutsideLoop;
}
return use;
}
void SplitAnalysis::analyze(const LiveInterval *li) {
clear();
curli_ = li;
analyseUses();
}
const MachineLoop *SplitAnalysis::getBestSplitLoop() {
LoopPtrSet Loops, SecondLoops;
// Find first-class and second class candidate loops.
// We prefer to split around loops where curli is used outside the periphery.
for (LoopPtrSet::const_iterator I = usingLoops_.begin(),
E = usingLoops_.end(); I != E; ++I)
switch(analyzeLoopPeripheralUse(*I)) {
case OutsideLoop:
Loops.insert(*I);
break;
case MultiPeripheral:
SecondLoops.insert(*I);
break;
default:
continue;
}
// If there are no first class loops available, look at second class loops.
if (Loops.empty())
Loops = SecondLoops;
if (Loops.empty())
return 0;
// Pick the earliest loop.
// FIXME: Are there other heuristics to consider?
// - avoid breaking critical edges.
// - avoid impossible loops.
const MachineLoop *Best = 0;
SlotIndex BestIdx;
for (LoopPtrSet::const_iterator I = Loops.begin(), E = Loops.end(); I != E;
++I) {
SlotIndex Idx = lis_.getMBBStartIdx((*I)->getHeader());
if (!Best || Idx < BestIdx)
Best = *I, BestIdx = Idx;
}
return Best;
}
//===----------------------------------------------------------------------===//
// Loop Splitting
//===----------------------------------------------------------------------===//
bool llvm::splitAroundLoop(SplitAnalysis &sa, const MachineLoop *loop) {
return false;
}