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//===------------------------ CalcSpillWeights.cpp ------------------------===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "calcspillweights"
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#include "llvm/Function.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/CodeGen/CalcSpillWeights.h"
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#include "llvm/CodeGen/LiveIntervalAnalysis.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineLoopInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/SlotIndexes.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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char CalculateSpillWeights::ID = 0;
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static RegisterPass<CalculateSpillWeights> X("calcspillweights",
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"Calculate spill weights");
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void CalculateSpillWeights::getAnalysisUsage(AnalysisUsage &au) const {
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au.addRequired<LiveIntervals>();
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au.addRequired<MachineLoopInfo>();
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MachineFunctionPass::getAnalysisUsage(au);
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bool CalculateSpillWeights::runOnMachineFunction(MachineFunction &fn) {
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DEBUG(dbgs() << "********** Compute Spill Weights **********\n"
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<< "********** Function: "
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<< fn.getFunction()->getName() << '\n');
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LiveIntervals *lis = &getAnalysis<LiveIntervals>();
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MachineLoopInfo *loopInfo = &getAnalysis<MachineLoopInfo>();
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const TargetInstrInfo *tii = fn.getTarget().getInstrInfo();
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MachineRegisterInfo *mri = &fn.getRegInfo();
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SmallSet<unsigned, 4> processed;
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for (MachineFunction::iterator mbbi = fn.begin(), mbbe = fn.end();
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mbbi != mbbe; ++mbbi) {
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MachineBasicBlock* mbb = mbbi;
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SlotIndex mbbEnd = lis->getMBBEndIdx(mbb);
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MachineLoop* loop = loopInfo->getLoopFor(mbb);
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unsigned loopDepth = loop ? loop->getLoopDepth() : 0;
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bool isExiting = loop ? loop->isLoopExiting(mbb) : false;
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for (MachineBasicBlock::const_iterator mii = mbb->begin(), mie = mbb->end();
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const MachineInstr *mi = mii;
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if (tii->isIdentityCopy(*mi) || mi->isImplicitDef() || mi->isDebugValue())
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for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) {
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const MachineOperand &mopi = mi->getOperand(i);
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if (!mopi.isReg() || mopi.getReg() == 0)
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unsigned reg = mopi.getReg();
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if (!TargetRegisterInfo::isVirtualRegister(mopi.getReg()))
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// Multiple uses of reg by the same instruction. It should not
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// contribute to spill weight again.
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if (!processed.insert(reg))
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bool hasDef = mopi.isDef();
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bool hasUse = !hasDef;
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for (unsigned j = i+1; j != e; ++j) {
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const MachineOperand &mopj = mi->getOperand(j);
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if (!mopj.isReg() || mopj.getReg() != reg)
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hasDef |= mopj.isDef();
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hasUse |= mopj.isUse();
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LiveInterval ®Int = lis->getInterval(reg);
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float weight = lis->getSpillWeight(hasDef, hasUse, loopDepth);
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if (hasDef && isExiting) {
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// Looks like this is a loop count variable update.
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SlotIndex defIdx = lis->getInstructionIndex(mi).getDefIndex();
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const LiveRange *dlr =
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lis->getInterval(reg).getLiveRangeContaining(defIdx);
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if (dlr->end >= mbbEnd)
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regInt.weight += weight;
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for (LiveIntervals::iterator I = lis->begin(), E = lis->end(); I != E; ++I) {
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LiveInterval &li = *I->second;
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if (TargetRegisterInfo::isVirtualRegister(li.reg)) {
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// If the live interval length is essentially zero, i.e. in every live
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// range the use follows def immediately, it doesn't make sense to spill
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// it and hope it will be easier to allocate for this li.
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if (isZeroLengthInterval(&li)) {
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li.weight = HUGE_VALF;
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SmallVector<LiveInterval*, 4> spillIs;
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if (lis->isReMaterializable(li, spillIs, isLoad)) {
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// If all of the definitions of the interval are re-materializable,
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// it is a preferred candidate for spilling. If non of the defs are
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// loads, then it's potentially very cheap to re-materialize.
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// FIXME: this gets much more complicated once we support non-trivial
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// re-materialization.
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// Slightly prefer live interval that has been assigned a preferred reg.
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std::pair<unsigned, unsigned> Hint = mri->getRegAllocationHint(li.reg);
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if (Hint.first || Hint.second)
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lis->normalizeSpillWeight(li);
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/// Returns true if the given live interval is zero length.
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bool CalculateSpillWeights::isZeroLengthInterval(LiveInterval *li) const {
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for (LiveInterval::Ranges::const_iterator
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i = li->ranges.begin(), e = li->ranges.end(); i != e; ++i)
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if (i->end.getPrevIndex() > i->start)