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63f757463c
llvm-mirror/lib/CodeGen/MachineLICM.cpp
Owen Anderson 63f757463c Begin adding static dependence information to passes, which will allow us to 
perform initialization without static constructors AND without explicit initialization
by the client.  For the moment, passes are required to initialize both their
(potential) dependencies and any passes they preserve.  I hope to be able to relax
the latter requirement in the future.

llvm-svn: 116334
2010-10-12 19:48:12 +00:00

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//===-- MachineLICM.cpp - Machine Loop Invariant Code Motion Pass ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs loop invariant code motion on machine instructions. We
// attempt to remove as much code from the body of a loop as possible.
//
// This pass does not attempt to throttle itself to limit register pressure.
// The register allocation phases are expected to perform rematerialization
// to recover when register pressure is high.
//
// This pass is not intended to be a replacement or a complete alternative
// for the LLVM-IR-level LICM pass. It is only designed to hoist simple
// constructs that are not exposed before lowering and instruction selection.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "machine-licm"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
STATISTIC(NumHoisted, "Number of machine instructions hoisted out of loops");
STATISTIC(NumCSEed, "Number of hoisted machine instructions CSEed");
STATISTIC(NumPostRAHoisted,
"Number of machine instructions hoisted out of loops post regalloc");
namespace {
class MachineLICM : public MachineFunctionPass {
bool PreRegAlloc;
const TargetMachine *TM;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
const MachineFrameInfo *MFI;
MachineRegisterInfo *RegInfo;
// Various analyses that we use...
AliasAnalysis *AA; // Alias analysis info.
MachineLoopInfo *MLI; // Current MachineLoopInfo
MachineDominatorTree *DT; // Machine dominator tree for the cur loop
// State that is updated as we process loops
bool Changed; // True if a loop is changed.
bool FirstInLoop; // True if it's the first LICM in the loop.
MachineLoop *CurLoop; // The current loop we are working on.
MachineBasicBlock *CurPreheader; // The preheader for CurLoop.
BitVector AllocatableSet;
// For each opcode, keep a list of potential CSE instructions.
DenseMap<unsigned, std::vector<const MachineInstr*> > CSEMap;
public:
static char ID; // Pass identification, replacement for typeid
MachineLICM() :
MachineFunctionPass(ID), PreRegAlloc(true) {}
explicit MachineLICM(bool PreRA) :
MachineFunctionPass(ID), PreRegAlloc(PreRA) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
const char *getPassName() const { return "Machine Instruction LICM"; }
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<MachineLoopInfo>();
AU.addRequired<MachineDominatorTree>();
AU.addRequired<AliasAnalysis>();
AU.addPreserved<MachineLoopInfo>();
AU.addPreserved<MachineDominatorTree>();
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual void releaseMemory() {
CSEMap.clear();
}
private:
/// CandidateInfo - Keep track of information about hoisting candidates.
struct CandidateInfo {
MachineInstr *MI;
unsigned Def;
int FI;
CandidateInfo(MachineInstr *mi, unsigned def, int fi)
: MI(mi), Def(def), FI(fi) {}
};
/// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
/// invariants out to the preheader.
void HoistRegionPostRA();
/// HoistPostRA - When an instruction is found to only use loop invariant
/// operands that is safe to hoist, this instruction is called to do the
/// dirty work.
void HoistPostRA(MachineInstr *MI, unsigned Def);
/// ProcessMI - Examine the instruction for potentai LICM candidate. Also
/// gather register def and frame object update information.
void ProcessMI(MachineInstr *MI, unsigned *PhysRegDefs,
SmallSet<int, 32> &StoredFIs,
SmallVector<CandidateInfo, 32> &Candidates);
/// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the
/// current loop.
void AddToLiveIns(unsigned Reg);
/// IsLICMCandidate - Returns true if the instruction may be a suitable
/// candidate for LICM. e.g. If the instruction is a call, then it's
/// obviously not safe to hoist it.
bool IsLICMCandidate(MachineInstr &I);
/// IsLoopInvariantInst - Returns true if the instruction is loop
/// invariant. I.e., all virtual register operands are defined outside of
/// the loop, physical registers aren't accessed (explicitly or implicitly),
/// and the instruction is hoistable.
///
bool IsLoopInvariantInst(MachineInstr &I);
/// IsProfitableToHoist - Return true if it is potentially profitable to
/// hoist the given loop invariant.
bool IsProfitableToHoist(MachineInstr &MI);
/// HoistRegion - Walk the specified region of the CFG (defined by all
/// blocks dominated by the specified block, and that are in the current
/// loop) in depth first order w.r.t the DominatorTree. This allows us to
/// visit definitions before uses, allowing us to hoist a loop body in one
/// pass without iteration.
///
void HoistRegion(MachineDomTreeNode *N);
/// isLoadFromConstantMemory - Return true if the given instruction is a
/// load from constant memory.
bool isLoadFromConstantMemory(MachineInstr *MI);
/// ExtractHoistableLoad - Unfold a load from the given machineinstr if
/// the load itself could be hoisted. Return the unfolded and hoistable
/// load, or null if the load couldn't be unfolded or if it wouldn't
/// be hoistable.
MachineInstr *ExtractHoistableLoad(MachineInstr *MI);
/// LookForDuplicate - Find an instruction amount PrevMIs that is a
/// duplicate of MI. Return this instruction if it's found.
const MachineInstr *LookForDuplicate(const MachineInstr *MI,
std::vector<const MachineInstr*> &PrevMIs);
/// EliminateCSE - Given a LICM'ed instruction, look for an instruction on
/// the preheader that compute the same value. If it's found, do a RAU on
/// with the definition of the existing instruction rather than hoisting
/// the instruction to the preheader.
bool EliminateCSE(MachineInstr *MI,
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator &CI);
/// Hoist - When an instruction is found to only use loop invariant operands
/// that is safe to hoist, this instruction is called to do the dirty work.
///
void Hoist(MachineInstr *MI);
/// InitCSEMap - Initialize the CSE map with instructions that are in the
/// current loop preheader that may become duplicates of instructions that
/// are hoisted out of the loop.
void InitCSEMap(MachineBasicBlock *BB);
/// getCurPreheader - Get the preheader for the current loop, splitting
/// a critical edge if needed.
MachineBasicBlock *getCurPreheader();
};
} // end anonymous namespace
char MachineLICM::ID = 0;
INITIALIZE_PASS_BEGIN(MachineLICM, "machinelicm",
"Machine Loop Invariant Code Motion", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(MachineLICM, "machinelicm",
"Machine Loop Invariant Code Motion", false, false)
FunctionPass *llvm::createMachineLICMPass(bool PreRegAlloc) {
return new MachineLICM(PreRegAlloc);
}
/// LoopIsOuterMostWithPredecessor - Test if the given loop is the outer-most
/// loop that has a unique predecessor.
static bool LoopIsOuterMostWithPredecessor(MachineLoop *CurLoop) {
// Check whether this loop even has a unique predecessor.
if (!CurLoop->getLoopPredecessor())
return false;
// Ok, now check to see if any of its outer loops do.
for (MachineLoop *L = CurLoop->getParentLoop(); L; L = L->getParentLoop())
if (L->getLoopPredecessor())
return false;
// None of them did, so this is the outermost with a unique predecessor.
return true;
}
bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
if (PreRegAlloc)
DEBUG(dbgs() << "******** Pre-regalloc Machine LICM ********\n");
else
DEBUG(dbgs() << "******** Post-regalloc Machine LICM ********\n");
Changed = FirstInLoop = false;
TM = &MF.getTarget();
TII = TM->getInstrInfo();
TRI = TM->getRegisterInfo();
MFI = MF.getFrameInfo();
RegInfo = &MF.getRegInfo();
AllocatableSet = TRI->getAllocatableSet(MF);
// Get our Loop information...
MLI = &getAnalysis<MachineLoopInfo>();
DT = &getAnalysis<MachineDominatorTree>();
AA = &getAnalysis<AliasAnalysis>();
SmallVector<MachineLoop *, 8> Worklist(MLI->begin(), MLI->end());
while (!Worklist.empty()) {
CurLoop = Worklist.pop_back_val();
CurPreheader = 0;
// If this is done before regalloc, only visit outer-most preheader-sporting
// loops.
if (PreRegAlloc && !LoopIsOuterMostWithPredecessor(CurLoop)) {
Worklist.append(CurLoop->begin(), CurLoop->end());
continue;
}
if (!PreRegAlloc)
HoistRegionPostRA();
else {
// CSEMap is initialized for loop header when the first instruction is
// being hoisted.
MachineDomTreeNode *N = DT->getNode(CurLoop->getHeader());
FirstInLoop = true;
HoistRegion(N);
CSEMap.clear();
}
}
return Changed;
}
/// InstructionStoresToFI - Return true if instruction stores to the
/// specified frame.
static bool InstructionStoresToFI(const MachineInstr *MI, int FI) {
for (MachineInstr::mmo_iterator o = MI->memoperands_begin(),
oe = MI->memoperands_end(); o != oe; ++o) {
if (!(*o)->isStore() || !(*o)->getValue())
continue;
if (const FixedStackPseudoSourceValue *Value =
dyn_cast<const FixedStackPseudoSourceValue>((*o)->getValue())) {
if (Value->getFrameIndex() == FI)
return true;
}
}
return false;
}
/// ProcessMI - Examine the instruction for potentai LICM candidate. Also
/// gather register def and frame object update information.
void MachineLICM::ProcessMI(MachineInstr *MI,
unsigned *PhysRegDefs,
SmallSet<int, 32> &StoredFIs,
SmallVector<CandidateInfo, 32> &Candidates) {
bool RuledOut = false;
bool HasNonInvariantUse = false;
unsigned Def = 0;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (MO.isFI()) {
// Remember if the instruction stores to the frame index.
int FI = MO.getIndex();
if (!StoredFIs.count(FI) &&
MFI->isSpillSlotObjectIndex(FI) &&
InstructionStoresToFI(MI, FI))
StoredFIs.insert(FI);
HasNonInvariantUse = true;
continue;
}
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
assert(TargetRegisterInfo::isPhysicalRegister(Reg) &&
"Not expecting virtual register!");
if (!MO.isDef()) {
if (Reg && PhysRegDefs[Reg])
// If it's using a non-loop-invariant register, then it's obviously not
// safe to hoist.
HasNonInvariantUse = true;
continue;
}
if (MO.isImplicit()) {
++PhysRegDefs[Reg];
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
++PhysRegDefs[*AS];
if (!MO.isDead())
// Non-dead implicit def? This cannot be hoisted.
RuledOut = true;
// No need to check if a dead implicit def is also defined by
// another instruction.
continue;
}
// FIXME: For now, avoid instructions with multiple defs, unless
// it's a dead implicit def.
if (Def)
RuledOut = true;
else
Def = Reg;
// If we have already seen another instruction that defines the same
// register, then this is not safe.
if (++PhysRegDefs[Reg] > 1)
// MI defined register is seen defined by another instruction in
// the loop, it cannot be a LICM candidate.
RuledOut = true;
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
if (++PhysRegDefs[*AS] > 1)
RuledOut = true;
}
// Only consider reloads for now and remats which do not have register
// operands. FIXME: Consider unfold load folding instructions.
if (Def && !RuledOut) {
int FI = INT_MIN;
if ((!HasNonInvariantUse && IsLICMCandidate(*MI)) ||
(TII->isLoadFromStackSlot(MI, FI) && MFI->isSpillSlotObjectIndex(FI)))
Candidates.push_back(CandidateInfo(MI, Def, FI));
}
}
/// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
/// invariants out to the preheader.
void MachineLICM::HoistRegionPostRA() {
unsigned NumRegs = TRI->getNumRegs();
unsigned *PhysRegDefs = new unsigned[NumRegs];
std::fill(PhysRegDefs, PhysRegDefs + NumRegs, 0);
SmallVector<CandidateInfo, 32> Candidates;
SmallSet<int, 32> StoredFIs;
// Walk the entire region, count number of defs for each register, and
// collect potential LICM candidates.
const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
MachineBasicBlock *BB = Blocks[i];
// Conservatively treat live-in's as an external def.
// FIXME: That means a reload that're reused in successor block(s) will not
// be LICM'ed.
for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
E = BB->livein_end(); I != E; ++I) {
unsigned Reg = *I;
++PhysRegDefs[Reg];
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
++PhysRegDefs[*AS];
}
for (MachineBasicBlock::iterator
MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
MachineInstr *MI = &*MII;
ProcessMI(MI, PhysRegDefs, StoredFIs, Candidates);
}
}
// Now evaluate whether the potential candidates qualify.
// 1. Check if the candidate defined register is defined by another
// instruction in the loop.
// 2. If the candidate is a load from stack slot (always true for now),
// check if the slot is stored anywhere in the loop.
for (unsigned i = 0, e = Candidates.size(); i != e; ++i) {
if (Candidates[i].FI != INT_MIN &&
StoredFIs.count(Candidates[i].FI))
continue;
if (PhysRegDefs[Candidates[i].Def] == 1) {
bool Safe = true;
MachineInstr *MI = Candidates[i].MI;
for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
const MachineOperand &MO = MI->getOperand(j);
if (!MO.isReg() || MO.isDef() || !MO.getReg())
continue;
if (PhysRegDefs[MO.getReg()]) {
// If it's using a non-loop-invariant register, then it's obviously
// not safe to hoist.
Safe = false;
break;
}
}
if (Safe)
HoistPostRA(MI, Candidates[i].Def);
}
}
delete[] PhysRegDefs;
}
/// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the current
/// loop, and make sure it is not killed by any instructions in the loop.
void MachineLICM::AddToLiveIns(unsigned Reg) {
const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
MachineBasicBlock *BB = Blocks[i];
if (!BB->isLiveIn(Reg))
BB->addLiveIn(Reg);
for (MachineBasicBlock::iterator
MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
MachineInstr *MI = &*MII;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.getReg() || MO.isDef()) continue;
if (MO.getReg() == Reg || TRI->isSuperRegister(Reg, MO.getReg()))
MO.setIsKill(false);
}
}
}
}
/// HoistPostRA - When an instruction is found to only use loop invariant
/// operands that is safe to hoist, this instruction is called to do the
/// dirty work.
void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
MachineBasicBlock *Preheader = getCurPreheader();
if (!Preheader) return;
// Now move the instructions to the predecessor, inserting it before any
// terminator instructions.
DEBUG({
dbgs() << "Hoisting " << *MI;
if (Preheader->getBasicBlock())
dbgs() << " to MachineBasicBlock "
<< Preheader->getName();
if (MI->getParent()->getBasicBlock())
dbgs() << " from MachineBasicBlock "
<< MI->getParent()->getName();
dbgs() << "\n";
});
// Splice the instruction to the preheader.
MachineBasicBlock *MBB = MI->getParent();
Preheader->splice(Preheader->getFirstTerminator(), MBB, MI);
// Add register to livein list to all the BBs in the current loop since a
// loop invariant must be kept live throughout the whole loop. This is
// important to ensure later passes do not scavenge the def register.
AddToLiveIns(Def);
++NumPostRAHoisted;
Changed = true;
}
/// HoistRegion - Walk the specified region of the CFG (defined by all blocks
/// dominated by the specified block, and that are in the current loop) in depth
/// first order w.r.t the DominatorTree. This allows us to visit definitions
/// before uses, allowing us to hoist a loop body in one pass without iteration.
///
void MachineLICM::HoistRegion(MachineDomTreeNode *N) {
assert(N != 0 && "Null dominator tree node?");
MachineBasicBlock *BB = N->getBlock();
// If this subregion is not in the top level loop at all, exit.
if (!CurLoop->contains(BB)) return;
for (MachineBasicBlock::iterator
MII = BB->begin(), E = BB->end(); MII != E; ) {
MachineBasicBlock::iterator NextMII = MII; ++NextMII;
Hoist(&*MII);
MII = NextMII;
}
// Don't hoist things out of a large switch statement. This often causes
// code to be hoisted that wasn't going to be executed, and increases
// register pressure in a situation where it's likely to matter.
if (BB->succ_size() < 25) {
const std::vector<MachineDomTreeNode*> &Children = N->getChildren();
for (unsigned I = 0, E = Children.size(); I != E; ++I)
HoistRegion(Children[I]);
}
}
/// IsLICMCandidate - Returns true if the instruction may be a suitable
/// candidate for LICM. e.g. If the instruction is a call, then it's obviously
/// not safe to hoist it.
bool MachineLICM::IsLICMCandidate(MachineInstr &I) {
// Check if it's safe to move the instruction.
bool DontMoveAcrossStore = true;
if (!I.isSafeToMove(TII, AA, DontMoveAcrossStore))
return false;
return true;
}
/// IsLoopInvariantInst - Returns true if the instruction is loop
/// invariant. I.e., all virtual register operands are defined outside of the
/// loop, physical registers aren't accessed explicitly, and there are no side
/// effects that aren't captured by the operands or other flags.
///
bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
if (!IsLICMCandidate(I))
return false;
// The instruction is loop invariant if all of its operands are.
for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
const MachineOperand &MO = I.getOperand(i);
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (Reg == 0) continue;
// Don't hoist an instruction that uses or defines a physical register.
if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
if (MO.isUse()) {
// If the physreg has no defs anywhere, it's just an ambient register
// and we can freely move its uses. Alternatively, if it's allocatable,
// it could get allocated to something with a def during allocation.
if (!RegInfo->def_empty(Reg))
return false;
if (AllocatableSet.test(Reg))
return false;
// Check for a def among the register's aliases too.
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
unsigned AliasReg = *Alias;
if (!RegInfo->def_empty(AliasReg))
return false;
if (AllocatableSet.test(AliasReg))
return false;
}
// Otherwise it's safe to move.
continue;
} else if (!MO.isDead()) {
// A def that isn't dead. We can't move it.
return false;
} else if (CurLoop->getHeader()->isLiveIn(Reg)) {
// If the reg is live into the loop, we can't hoist an instruction
// which would clobber it.
return false;
}
}
if (!MO.isUse())
continue;
assert(RegInfo->getVRegDef(Reg) &&
"Machine instr not mapped for this vreg?!");
// If the loop contains the definition of an operand, then the instruction
// isn't loop invariant.
if (CurLoop->contains(RegInfo->getVRegDef(Reg)))
return false;
}
// If we got this far, the instruction is loop invariant!
return true;
}
/// HasPHIUses - Return true if the specified register has any PHI use.
static bool HasPHIUses(unsigned Reg, MachineRegisterInfo *RegInfo) {
for (MachineRegisterInfo::use_iterator UI = RegInfo->use_begin(Reg),
UE = RegInfo->use_end(); UI != UE; ++UI) {
MachineInstr *UseMI = &*UI;
if (UseMI->isPHI())
return true;
}
return false;
}
/// isLoadFromConstantMemory - Return true if the given instruction is a
/// load from constant memory. Machine LICM will hoist these even if they are
/// not re-materializable.
bool MachineLICM::isLoadFromConstantMemory(MachineInstr *MI) {
if (!MI->getDesc().mayLoad()) return false;
if (!MI->hasOneMemOperand()) return false;
MachineMemOperand *MMO = *MI->memoperands_begin();
if (MMO->isVolatile()) return false;
if (!MMO->getValue()) return false;
const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(MMO->getValue());
if (PSV) {
MachineFunction &MF = *MI->getParent()->getParent();
return PSV->isConstant(MF.getFrameInfo());
} else {
return AA->pointsToConstantMemory(MMO->getValue());
}
}
/// IsProfitableToHoist - Return true if it is potentially profitable to hoist
/// the given loop invariant.
bool MachineLICM::IsProfitableToHoist(MachineInstr &MI) {
// FIXME: For now, only hoist re-materilizable instructions. LICM will
// increase register pressure. We want to make sure it doesn't increase
// spilling.
// Also hoist loads from constant memory, e.g. load from stubs, GOT. Hoisting
// these tend to help performance in low register pressure situation. The
// trade off is it may cause spill in high pressure situation. It will end up
// adding a store in the loop preheader. But the reload is no more expensive.
// The side benefit is these loads are frequently CSE'ed.
if (!TII->isTriviallyReMaterializable(&MI, AA)) {
if (!isLoadFromConstantMemory(&MI))
return false;
}
// If result(s) of this instruction is used by PHIs, then don't hoist it.
// The presence of joins makes it difficult for current register allocator
// implementation to perform remat.
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
if (HasPHIUses(MO.getReg(), RegInfo))
return false;
}
return true;
}
MachineInstr *MachineLICM::ExtractHoistableLoad(MachineInstr *MI) {
// Don't unfold simple loads.
if (MI->getDesc().canFoldAsLoad())
return 0;
// If not, we may be able to unfold a load and hoist that.
// First test whether the instruction is loading from an amenable
// memory location.
if (!isLoadFromConstantMemory(MI))
return 0;
// Next determine the register class for a temporary register.
unsigned LoadRegIndex;
unsigned NewOpc =
TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(),
/*UnfoldLoad=*/true,
/*UnfoldStore=*/false,
&LoadRegIndex);
if (NewOpc == 0) return 0;
const TargetInstrDesc &TID = TII->get(NewOpc);
if (TID.getNumDefs() != 1) return 0;
const TargetRegisterClass *RC = TID.OpInfo[LoadRegIndex].getRegClass(TRI);
// Ok, we're unfolding. Create a temporary register and do the unfold.
unsigned Reg = RegInfo->createVirtualRegister(RC);
MachineFunction &MF = *MI->getParent()->getParent();
SmallVector<MachineInstr *, 2> NewMIs;
bool Success =
TII->unfoldMemoryOperand(MF, MI, Reg,
/*UnfoldLoad=*/true, /*UnfoldStore=*/false,
NewMIs);
(void)Success;
assert(Success &&
"unfoldMemoryOperand failed when getOpcodeAfterMemoryUnfold "
"succeeded!");
assert(NewMIs.size() == 2 &&
"Unfolded a load into multiple instructions!");
MachineBasicBlock *MBB = MI->getParent();
MBB->insert(MI, NewMIs[0]);
MBB->insert(MI, NewMIs[1]);
// If unfolding produced a load that wasn't loop-invariant or profitable to
// hoist, discard the new instructions and bail.
if (!IsLoopInvariantInst(*NewMIs[0]) || !IsProfitableToHoist(*NewMIs[0])) {
NewMIs[0]->eraseFromParent();
NewMIs[1]->eraseFromParent();
return 0;
}
// Otherwise we successfully unfolded a load that we can hoist.
MI->eraseFromParent();
return NewMIs[0];
}
void MachineLICM::InitCSEMap(MachineBasicBlock *BB) {
for (MachineBasicBlock::iterator I = BB->begin(),E = BB->end(); I != E; ++I) {
const MachineInstr *MI = &*I;
// FIXME: For now, only hoist re-materilizable instructions. LICM will
// increase register pressure. We want to make sure it doesn't increase
// spilling.
if (TII->isTriviallyReMaterializable(MI, AA)) {
unsigned Opcode = MI->getOpcode();
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator
CI = CSEMap.find(Opcode);
if (CI != CSEMap.end())
CI->second.push_back(MI);
else {
std::vector<const MachineInstr*> CSEMIs;
CSEMIs.push_back(MI);
CSEMap.insert(std::make_pair(Opcode, CSEMIs));
}
}
}
}
const MachineInstr*
MachineLICM::LookForDuplicate(const MachineInstr *MI,
std::vector<const MachineInstr*> &PrevMIs) {
for (unsigned i = 0, e = PrevMIs.size(); i != e; ++i) {
const MachineInstr *PrevMI = PrevMIs[i];
if (TII->produceSameValue(MI, PrevMI))
return PrevMI;
}
return 0;
}
bool MachineLICM::EliminateCSE(MachineInstr *MI,
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator &CI) {
// Do not CSE implicit_def so ProcessImplicitDefs can properly propagate
// the undef property onto uses.
if (CI == CSEMap.end() || MI->isImplicitDef())
return false;
if (const MachineInstr *Dup = LookForDuplicate(MI, CI->second)) {
DEBUG(dbgs() << "CSEing " << *MI << " with " << *Dup);
// Replace virtual registers defined by MI by their counterparts defined
// by Dup.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
// Physical registers may not differ here.
assert((!MO.isReg() || MO.getReg() == 0 ||
!TargetRegisterInfo::isPhysicalRegister(MO.getReg()) ||
MO.getReg() == Dup->getOperand(i).getReg()) &&
"Instructions with different phys regs are not identical!");
if (MO.isReg() && MO.isDef() &&
!TargetRegisterInfo::isPhysicalRegister(MO.getReg())) {
RegInfo->replaceRegWith(MO.getReg(), Dup->getOperand(i).getReg());
RegInfo->clearKillFlags(Dup->getOperand(i).getReg());
}
}
MI->eraseFromParent();
++NumCSEed;
return true;
}
return false;
}
/// Hoist - When an instruction is found to use only loop invariant operands
/// that are safe to hoist, this instruction is called to do the dirty work.
///
void MachineLICM::Hoist(MachineInstr *MI) {
MachineBasicBlock *Preheader = getCurPreheader();
if (!Preheader) return;
// First check whether we should hoist this instruction.
if (!IsLoopInvariantInst(*MI) || !IsProfitableToHoist(*MI)) {
// If not, try unfolding a hoistable load.
MI = ExtractHoistableLoad(MI);
if (!MI) return;
}
// Now move the instructions to the predecessor, inserting it before any
// terminator instructions.
DEBUG({
dbgs() << "Hoisting " << *MI;
if (Preheader->getBasicBlock())
dbgs() << " to MachineBasicBlock "
<< Preheader->getName();
if (MI->getParent()->getBasicBlock())
dbgs() << " from MachineBasicBlock "
<< MI->getParent()->getName();
dbgs() << "\n";
});
// If this is the first instruction being hoisted to the preheader,
// initialize the CSE map with potential common expressions.
if (FirstInLoop) {
InitCSEMap(Preheader);
FirstInLoop = false;
}
// Look for opportunity to CSE the hoisted instruction.
unsigned Opcode = MI->getOpcode();
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator
CI = CSEMap.find(Opcode);
if (!EliminateCSE(MI, CI)) {
// Otherwise, splice the instruction to the preheader.
Preheader->splice(Preheader->getFirstTerminator(),MI->getParent(),MI);
// Clear the kill flags of any register this instruction defines,
// since they may need to be live throughout the entire loop
// rather than just live for part of it.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDef() && !MO.isDead())
RegInfo->clearKillFlags(MO.getReg());
}
// Add to the CSE map.
if (CI != CSEMap.end())
CI->second.push_back(MI);
else {
std::vector<const MachineInstr*> CSEMIs;
CSEMIs.push_back(MI);
CSEMap.insert(std::make_pair(Opcode, CSEMIs));
}
}
++NumHoisted;
Changed = true;
}
MachineBasicBlock *MachineLICM::getCurPreheader() {
// Determine the block to which to hoist instructions. If we can't find a
// suitable loop predecessor, we can't do any hoisting.
// If we've tried to get a preheader and failed, don't try again.
if (CurPreheader == reinterpret_cast<MachineBasicBlock *>(-1))
return 0;
if (!CurPreheader) {
CurPreheader = CurLoop->getLoopPreheader();
if (!CurPreheader) {
MachineBasicBlock *Pred = CurLoop->getLoopPredecessor();
if (!Pred) {
CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
return 0;
}
CurPreheader = Pred->SplitCriticalEdge(CurLoop->getHeader(), this);
if (!CurPreheader) {
CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
return 0;
}
}
}
return CurPreheader;
}
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