static cl::opt<bool>
AvoidSpeculation("avoid-speculation",
cl::desc("MachineLICM should avoid speculation"),
- cl::init(false), cl::Hidden);
+ cl::init(true), cl::Hidden);
STATISTIC(NumHoisted,
"Number of machine instructions hoisted out of loops");
namespace {
class MachineLICM : public MachineFunctionPass {
- bool PreRegAlloc;
-
const TargetMachine *TM;
const TargetInstrInfo *TII;
const TargetLowering *TLI;
const MachineFrameInfo *MFI;
MachineRegisterInfo *MRI;
const InstrItineraryData *InstrItins;
+ bool PreRegAlloc;
// Various analyses that we use...
AliasAnalysis *AA; // Alias analysis info.
MachineLoop *CurLoop; // The current loop we are working on.
MachineBasicBlock *CurPreheader; // The preheader for CurLoop.
- BitVector AllocatableSet;
+ // Exit blocks for CurLoop.
+ SmallVector<MachineBasicBlock*, 8> ExitBlocks;
+
+ bool isExitBlock(const MachineBasicBlock *MBB) const {
+ return std::find(ExitBlocks.begin(), ExitBlocks.end(), MBB) !=
+ ExitBlocks.end();
+ }
// Track 'estimated' register pressure.
SmallSet<unsigned, 32> RegSeen;
virtual bool runOnMachineFunction(MachineFunction &MF);
- const char *getPassName() const { return "Machine Instruction LICM"; }
-
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<MachineLoopInfo>();
AU.addRequired<MachineDominatorTree>();
/// ProcessMI - Examine the instruction for potentai LICM candidate. Also
/// gather register def and frame object update information.
- void ProcessMI(MachineInstr *MI, unsigned *PhysRegDefs,
+ void ProcessMI(MachineInstr *MI,
+ BitVector &PhysRegDefs,
+ BitVector &PhysRegClobbers,
SmallSet<int, 32> &StoredFIs,
SmallVector<CandidateInfo, 32> &Candidates);
/// 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);
- /// HasAnyPHIUse - Return true if the specified register is used by any
- /// phi node.
- bool HasAnyPHIUse(unsigned Reg) const;
+ /// HasLoopPHIUse - Return true if the specified instruction is used by any
+ /// phi node in the current loop.
+ bool HasLoopPHIUse(const MachineInstr *MI) const;
/// HasHighOperandLatency - Compute operand latency between a def of 'Reg'
/// and an use in the current loop, return true if the target considered
/// CanCauseHighRegPressure - Visit BBs from header to current BB,
/// check if hoisting an instruction of the given cost matrix can cause high
/// register pressure.
- bool CanCauseHighRegPressure(DenseMap<unsigned, int> &Cost);
+ bool CanCauseHighRegPressure(DenseMap<unsigned, int> &Cost, bool Cheap);
/// UpdateBackTraceRegPressure - Traverse the back trace from header to
/// the current block and update their register pressures to reflect the
/// If not then a load from this mbb may not be safe to hoist.
bool IsGuaranteedToExecute(MachineBasicBlock *BB);
- /// 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 EnterScope(MachineBasicBlock *MBB);
+
+ void ExitScope(MachineBasicBlock *MBB);
+
+ /// ExitScopeIfDone - Destroy scope for the MBB that corresponds to given
+ /// dominator tree node if its a leaf or all of its children are done. Walk
+ /// up the dominator tree to destroy ancestors which are now done.
+ void ExitScopeIfDone(MachineDomTreeNode *Node,
+ DenseMap<MachineDomTreeNode*, unsigned> &OpenChildren,
+ DenseMap<MachineDomTreeNode*, MachineDomTreeNode*> &ParentMap);
+
+ /// HoistOutOfLoop - Walk the specified loop in the CFG (defined by all
+ /// blocks dominated by the specified header 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, bool IsHeader = false);
+ void HoistOutOfLoop(MachineDomTreeNode *LoopHeaderNode);
+ void HoistRegion(MachineDomTreeNode *N, bool IsHeader);
/// getRegisterClassIDAndCost - For a given MI, register, and the operand
/// index, return the ID and cost of its representative register class by
} // end anonymous namespace
char MachineLICM::ID = 0;
+char &llvm::MachineLICMID = MachineLICM::ID;
INITIALIZE_PASS_BEGIN(MachineLICM, "machinelicm",
"Machine Loop Invariant Code Motion", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
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) {
}
bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
- if (PreRegAlloc)
- DEBUG(dbgs() << "******** Pre-regalloc Machine LICM: ");
- else
- DEBUG(dbgs() << "******** Post-regalloc Machine LICM: ");
- DEBUG(dbgs() << MF.getFunction()->getName() << " ********\n");
-
Changed = FirstInLoop = false;
TM = &MF.getTarget();
TII = TM->getInstrInfo();
MFI = MF.getFrameInfo();
MRI = &MF.getRegInfo();
InstrItins = TM->getInstrItineraryData();
- AllocatableSet = TRI->getAllocatableSet(MF);
+
+ PreRegAlloc = MRI->isSSA();
+
+ if (PreRegAlloc)
+ DEBUG(dbgs() << "******** Pre-regalloc Machine LICM: ");
+ else
+ DEBUG(dbgs() << "******** Post-regalloc Machine LICM: ");
+ DEBUG(dbgs() << MF.getName() << " ********\n");
if (PreRegAlloc) {
// Estimate register pressure during pre-regalloc pass.
while (!Worklist.empty()) {
CurLoop = Worklist.pop_back_val();
CurPreheader = 0;
+ ExitBlocks.clear();
// If this is done before regalloc, only visit outer-most preheader-sporting
// loops.
continue;
}
+ CurLoop->getExitBlocks(ExitBlocks);
+
if (!PreRegAlloc)
HoistRegionPostRA();
else {
// being hoisted.
MachineDomTreeNode *N = DT->getNode(CurLoop->getHeader());
FirstInLoop = true;
- HoistRegion(N, true);
+ HoistOutOfLoop(N);
CSEMap.clear();
}
}
/// ProcessMI - Examine the instruction for potentai LICM candidate. Also
/// gather register def and frame object update information.
void MachineLICM::ProcessMI(MachineInstr *MI,
- unsigned *PhysRegDefs,
+ BitVector &PhysRegDefs,
+ BitVector &PhysRegClobbers,
SmallSet<int, 32> &StoredFIs,
SmallVector<CandidateInfo, 32> &Candidates) {
bool RuledOut = false;
continue;
}
+ // We can't hoist an instruction defining a physreg that is clobbered in
+ // the loop.
+ if (MO.isRegMask()) {
+ PhysRegClobbers.setBitsNotInMask(MO.getRegMask());
+ continue;
+ }
+
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
"Not expecting virtual register!");
if (!MO.isDef()) {
- if (Reg && PhysRegDefs[Reg])
+ if (Reg && (PhysRegDefs.test(Reg) || PhysRegClobbers.test(Reg)))
// If it's using a non-loop-invariant register, then it's obviously not
// safe to hoist.
HasNonInvariantUse = true;
}
if (MO.isImplicit()) {
- ++PhysRegDefs[Reg];
- for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
- ++PhysRegDefs[*AS];
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+ PhysRegClobbers.set(*AI);
if (!MO.isDead())
// Non-dead implicit def? This cannot be hoisted.
RuledOut = true;
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)
+ // register, then this is not safe. Two defs is indicated by setting a
+ // PhysRegClobbers bit.
+ for (MCRegAliasIterator AS(Reg, TRI, true); AS.isValid(); ++AS) {
+ if (PhysRegDefs.test(*AS))
+ PhysRegClobbers.set(*AS);
+ if (PhysRegClobbers.test(*AS))
+ // MI defined register is seen defined by another instruction in
+ // the loop, it cannot be a LICM candidate.
RuledOut = true;
+ PhysRegDefs.set(*AS);
+ }
}
// Only consider reloads for now and remats which do not have register
/// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
/// invariants out to the preheader.
void MachineLICM::HoistRegionPostRA() {
+ MachineBasicBlock *Preheader = getCurPreheader();
+ if (!Preheader)
+ return;
+
unsigned NumRegs = TRI->getNumRegs();
- unsigned *PhysRegDefs = new unsigned[NumRegs];
- std::fill(PhysRegDefs, PhysRegDefs + NumRegs, 0);
+ BitVector PhysRegDefs(NumRegs); // Regs defined once in the loop.
+ BitVector PhysRegClobbers(NumRegs); // Regs defined more than once.
SmallVector<CandidateInfo, 32> Candidates;
SmallSet<int, 32> StoredFIs;
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 (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+ PhysRegDefs.set(*AI);
}
SpeculationState = SpeculateUnknown;
for (MachineBasicBlock::iterator
MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
MachineInstr *MI = &*MII;
- ProcessMI(MI, PhysRegDefs, StoredFIs, Candidates);
+ ProcessMI(MI, PhysRegDefs, PhysRegClobbers, StoredFIs, Candidates);
+ }
+ }
+
+ // Gather the registers read / clobbered by the terminator.
+ BitVector TermRegs(NumRegs);
+ MachineBasicBlock::iterator TI = Preheader->getFirstTerminator();
+ if (TI != Preheader->end()) {
+ for (unsigned i = 0, e = TI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = TI->getOperand(i);
+ if (!MO.isReg())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!Reg)
+ continue;
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+ TermRegs.set(*AI);
}
}
// 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.
+ // 3. Make sure candidate def should not clobber
+ // registers read by the terminator. Similarly its def should not be
+ // clobbered by the terminator.
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) {
+ unsigned Def = Candidates[i].Def;
+ if (!PhysRegClobbers.test(Def) && !TermRegs.test(Def)) {
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()]) {
+ unsigned Reg = MO.getReg();
+ if (PhysRegDefs.test(Reg) ||
+ PhysRegClobbers.test(Reg)) {
// If it's using a non-loop-invariant register, then it's obviously
// not safe to hoist.
Safe = false;
HoistPostRA(MI, Candidates[i].Def);
}
}
-
- delete[] PhysRegDefs;
}
/// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the current
/// 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";
- });
+ DEBUG(dbgs() << "Hoisting to BB#" << Preheader->getNumber() << " from BB#"
+ << MI->getParent()->getNumber() << ": " << *MI);
// 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
+ // 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);
bool MachineLICM::IsGuaranteedToExecute(MachineBasicBlock *BB) {
if (SpeculationState != SpeculateUnknown)
return SpeculationState == SpeculateFalse;
-
+
if (BB != CurLoop->getHeader()) {
// Check loop exiting blocks.
SmallVector<MachineBasicBlock*, 8> CurrentLoopExitingBlocks;
return 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, bool IsHeader) {
- assert(N != 0 && "Null dominator tree node?");
- MachineBasicBlock *BB = N->getBlock();
+void MachineLICM::EnterScope(MachineBasicBlock *MBB) {
+ DEBUG(dbgs() << "Entering: " << MBB->getName() << '\n');
- // If the header of the loop containing this basic block is a landing pad,
- // then don't try to hoist instructions out of this loop.
- const MachineLoop *ML = MLI->getLoopFor(BB);
- if (ML && ML->getHeader()->isLandingPad()) return;
+ // Remember livein register pressure.
+ BackTrace.push_back(RegPressure);
+}
- // If this subregion is not in the top level loop at all, exit.
- if (!CurLoop->contains(BB)) return;
+void MachineLICM::ExitScope(MachineBasicBlock *MBB) {
+ DEBUG(dbgs() << "Exiting: " << MBB->getName() << '\n');
+ BackTrace.pop_back();
+}
- MachineBasicBlock *Preheader = getCurPreheader();
- if (!Preheader)
+/// ExitScopeIfDone - Destroy scope for the MBB that corresponds to the given
+/// dominator tree node if its a leaf or all of its children are done. Walk
+/// up the dominator tree to destroy ancestors which are now done.
+void MachineLICM::ExitScopeIfDone(MachineDomTreeNode *Node,
+ DenseMap<MachineDomTreeNode*, unsigned> &OpenChildren,
+ DenseMap<MachineDomTreeNode*, MachineDomTreeNode*> &ParentMap) {
+ if (OpenChildren[Node])
return;
- if (IsHeader) {
+ // Pop scope.
+ ExitScope(Node->getBlock());
+
+ // Now traverse upwards to pop ancestors whose offsprings are all done.
+ while (MachineDomTreeNode *Parent = ParentMap[Node]) {
+ unsigned Left = --OpenChildren[Parent];
+ if (Left != 0)
+ break;
+ ExitScope(Parent->getBlock());
+ Node = Parent;
+ }
+}
+
+/// HoistOutOfLoop - Walk the specified loop in the CFG (defined by all
+/// blocks dominated by the specified header 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::HoistOutOfLoop(MachineDomTreeNode *HeaderN) {
+ SmallVector<MachineDomTreeNode*, 32> Scopes;
+ SmallVector<MachineDomTreeNode*, 8> WorkList;
+ DenseMap<MachineDomTreeNode*, MachineDomTreeNode*> ParentMap;
+ DenseMap<MachineDomTreeNode*, unsigned> OpenChildren;
+
+ // Perform a DFS walk to determine the order of visit.
+ WorkList.push_back(HeaderN);
+ do {
+ MachineDomTreeNode *Node = WorkList.pop_back_val();
+ assert(Node != 0 && "Null dominator tree node?");
+ MachineBasicBlock *BB = Node->getBlock();
+
+ // If the header of the loop containing this basic block is a landing pad,
+ // then don't try to hoist instructions out of this loop.
+ const MachineLoop *ML = MLI->getLoopFor(BB);
+ if (ML && ML->getHeader()->isLandingPad())
+ continue;
+
+ // If this subregion is not in the top level loop at all, exit.
+ if (!CurLoop->contains(BB))
+ continue;
+
+ Scopes.push_back(Node);
+ const std::vector<MachineDomTreeNode*> &Children = Node->getChildren();
+ unsigned NumChildren = Children.size();
+
+ // 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)
+ NumChildren = 0;
+
+ OpenChildren[Node] = NumChildren;
+ // Add children in reverse order as then the next popped worklist node is
+ // the first child of this node. This means we ultimately traverse the
+ // DOM tree in exactly the same order as if we'd recursed.
+ for (int i = (int)NumChildren-1; i >= 0; --i) {
+ MachineDomTreeNode *Child = Children[i];
+ ParentMap[Child] = Node;
+ WorkList.push_back(Child);
+ }
+ } while (!WorkList.empty());
+
+ if (Scopes.size() != 0) {
+ MachineBasicBlock *Preheader = getCurPreheader();
+ if (!Preheader)
+ return;
+
// Compute registers which are livein into the loop headers.
RegSeen.clear();
BackTrace.clear();
InitRegPressure(Preheader);
}
- // Remember livein register pressure.
- BackTrace.push_back(RegPressure);
+ // Now perform LICM.
+ for (unsigned i = 0, e = Scopes.size(); i != e; ++i) {
+ MachineDomTreeNode *Node = Scopes[i];
+ MachineBasicBlock *MBB = Node->getBlock();
- SpeculationState = SpeculateUnknown;
- for (MachineBasicBlock::iterator
- MII = BB->begin(), E = BB->end(); MII != E; ) {
- MachineBasicBlock::iterator NextMII = MII; ++NextMII;
- MachineInstr *MI = &*MII;
- if (!Hoist(MI, Preheader))
- UpdateRegPressure(MI);
- MII = NextMII;
- }
+ MachineBasicBlock *Preheader = getCurPreheader();
+ if (!Preheader)
+ continue;
- // 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]);
- }
+ EnterScope(MBB);
- BackTrace.pop_back();
+ // Process the block
+ SpeculationState = SpeculateUnknown;
+ for (MachineBasicBlock::iterator
+ MII = MBB->begin(), E = MBB->end(); MII != E; ) {
+ MachineBasicBlock::iterator NextMII = MII; ++NextMII;
+ MachineInstr *MI = &*MII;
+ if (!Hoist(MI, Preheader))
+ UpdateRegPressure(MI);
+ MII = NextMII;
+ }
+
+ // If it's a leaf node, it's done. Traverse upwards to pop ancestors.
+ ExitScopeIfDone(Node, OpenChildren, ParentMap);
+ }
}
static bool isOperandKill(const MachineOperand &MO, MachineRegisterInfo *MRI) {
unsigned &RCId, unsigned &RCCost) const {
const TargetRegisterClass *RC = MRI->getRegClass(Reg);
EVT VT = *RC->vt_begin();
- if (VT == MVT::untyped) {
+ if (VT == MVT::Untyped) {
RCId = RC->getID();
RCCost = 1;
} else {
RCCost = TLI->getRepRegClassCostFor(VT);
}
}
-
+
/// InitRegPressure - Find all virtual register references that are liveout of
/// the preheader to initialize the starting "register pressure". Note this
/// does not count live through (livein but not used) registers.
}
}
-/// isLoadFromGOT - Return true if this machine instruction loads from
-/// global offset table.
-static bool isLoadFromGOT(MachineInstr &MI) {
- assert (MI.getDesc().mayLoad() && "Expected MI that loads!");
+/// isLoadFromGOTOrConstantPool - Return true if this machine instruction
+/// loads from global offset table or constant pool.
+static bool isLoadFromGOTOrConstantPool(MachineInstr &MI) {
+ assert (MI.mayLoad() && "Expected MI that loads!");
for (MachineInstr::mmo_iterator I = MI.memoperands_begin(),
- E = MI.memoperands_end(); I != E; ++I) {
+ E = MI.memoperands_end(); I != E; ++I) {
if (const Value *V = (*I)->getValue()) {
if (const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(V))
- if (PSV == PSV->getGOT())
- return true;
+ if (PSV == PSV->getGOT() || PSV == PSV->getConstantPool())
+ return true;
}
}
return false;
// from constant memory are not safe to speculate all the time, for example
// indexed load from a jump table.
// Stores and side effects are already checked by isSafeToMove.
- if (I.getDesc().mayLoad() && !isLoadFromGOT(I) &&
+ if (I.mayLoad() && !isLoadFromGOTOrConstantPool(I) &&
!IsGuaranteedToExecute(I.getParent()))
return false;
/// 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;
// 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 (!MRI->def_empty(Reg))
- return false;
- if (AllocatableSet.test(Reg))
+ if (!MRI->isConstantPhysReg(Reg, *I.getParent()->getParent()))
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 (!MRI->def_empty(AliasReg))
- return false;
- if (AllocatableSet.test(AliasReg))
- return false;
- }
// Otherwise it's safe to move.
continue;
} else if (!MO.isDead()) {
}
-/// HasAnyPHIUse - Return true if the specified register is used by any
-/// phi node.
-bool MachineLICM::HasAnyPHIUse(unsigned Reg) const {
- for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
- UE = MRI->use_end(); UI != UE; ++UI) {
- MachineInstr *UseMI = &*UI;
- if (UseMI->isPHI())
- return true;
- // Look pass copies as well.
- if (UseMI->isCopy()) {
- unsigned Def = UseMI->getOperand(0).getReg();
- if (TargetRegisterInfo::isVirtualRegister(Def) &&
- HasAnyPHIUse(Def))
- return true;
+/// HasLoopPHIUse - Return true if the specified instruction is used by a
+/// phi node and hoisting it could cause a copy to be inserted.
+bool MachineLICM::HasLoopPHIUse(const MachineInstr *MI) const {
+ SmallVector<const MachineInstr*, 8> Work(1, MI);
+ do {
+ MI = Work.pop_back_val();
+ for (ConstMIOperands MO(MI); MO.isValid(); ++MO) {
+ if (!MO->isReg() || !MO->isDef())
+ continue;
+ unsigned Reg = MO->getReg();
+ if (!TargetRegisterInfo::isVirtualRegister(Reg))
+ continue;
+ for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
+ UE = MRI->use_end(); UI != UE; ++UI) {
+ MachineInstr *UseMI = &*UI;
+ // A PHI may cause a copy to be inserted.
+ if (UseMI->isPHI()) {
+ // A PHI inside the loop causes a copy because the live range of Reg is
+ // extended across the PHI.
+ if (CurLoop->contains(UseMI))
+ return true;
+ // A PHI in an exit block can cause a copy to be inserted if the PHI
+ // has multiple predecessors in the loop with different values.
+ // For now, approximate by rejecting all exit blocks.
+ if (isExitBlock(UseMI->getParent()))
+ return true;
+ continue;
+ }
+ // Look past copies as well.
+ if (UseMI->isCopy() && CurLoop->contains(UseMI))
+ Work.push_back(UseMI);
+ }
}
- }
+ } while (!Work.empty());
return false;
}
/// IsCheapInstruction - Return true if the instruction is marked "cheap" or
/// the operand latency between its def and a use is one or less.
bool MachineLICM::IsCheapInstruction(MachineInstr &MI) const {
- if (MI.getDesc().isAsCheapAsAMove() || MI.isCopyLike())
+ if (MI.isAsCheapAsAMove() || MI.isCopyLike())
return true;
if (!InstrItins || InstrItins->isEmpty())
return false;
/// CanCauseHighRegPressure - Visit BBs from header to current BB, check
/// if hoisting an instruction of the given cost matrix can cause high
/// register pressure.
-bool MachineLICM::CanCauseHighRegPressure(DenseMap<unsigned, int> &Cost) {
+bool MachineLICM::CanCauseHighRegPressure(DenseMap<unsigned, int> &Cost,
+ bool CheapInstr) {
for (DenseMap<unsigned, int>::iterator CI = Cost.begin(), CE = Cost.end();
CI != CE; ++CI) {
- if (CI->second <= 0)
+ if (CI->second <= 0)
continue;
unsigned RCId = CI->first;
+ unsigned Limit = RegLimit[RCId];
+ int Cost = CI->second;
+
+ // Don't hoist cheap instructions if they would increase register pressure,
+ // even if we're under the limit.
+ if (CheapInstr)
+ return true;
+
for (unsigned i = BackTrace.size(); i != 0; --i) {
SmallVector<unsigned, 8> &RP = BackTrace[i-1];
- if (RP[RCId] + CI->second >= RegLimit[RCId])
+ if (RP[RCId] + Cost >= Limit)
return true;
}
}
if (MI.isImplicitDef())
return true;
- // If the instruction is cheap, only hoist if it is re-materilizable. LICM
- // will increase register pressure. It's probably not worth it if the
- // instruction is cheap.
- // 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 (IsCheapInstruction(MI)) {
- if (!TII->isTriviallyReMaterializable(&MI, AA))
- return false;
- } else {
- // Estimate register pressure to determine whether to LICM the instruction.
- // In low register pressure situation, we can be more aggressive about
- // hoisting. Also, favors hoisting long latency instructions even in
- // moderately high pressure situation.
- // FIXME: If there are long latency loop-invariant instructions inside the
- // loop at this point, why didn't the optimizer's LICM hoist them?
- DenseMap<unsigned, int> Cost;
- for (unsigned i = 0, e = MI.getDesc().getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = MI.getOperand(i);
- if (!MO.isReg() || MO.isImplicit())
- continue;
- unsigned Reg = MO.getReg();
- if (!TargetRegisterInfo::isVirtualRegister(Reg))
- continue;
+ // Besides removing computation from the loop, hoisting an instruction has
+ // these effects:
+ //
+ // - The value defined by the instruction becomes live across the entire
+ // loop. This increases register pressure in the loop.
+ //
+ // - If the value is used by a PHI in the loop, a copy will be required for
+ // lowering the PHI after extending the live range.
+ //
+ // - When hoisting the last use of a value in the loop, that value no longer
+ // needs to be live in the loop. This lowers register pressure in the loop.
+
+ bool CheapInstr = IsCheapInstruction(MI);
+ bool CreatesCopy = HasLoopPHIUse(&MI);
+
+ // Don't hoist a cheap instruction if it would create a copy in the loop.
+ if (CheapInstr && CreatesCopy) {
+ DEBUG(dbgs() << "Won't hoist cheap instr with loop PHI use: " << MI);
+ return false;
+ }
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(&MI, Reg, i, RCId, RCCost);
- if (MO.isDef()) {
- if (HasHighOperandLatency(MI, i, Reg)) {
- ++NumHighLatency;
- return true;
- }
+ // Rematerializable instructions should always be hoisted since the register
+ // allocator can just pull them down again when needed.
+ if (TII->isTriviallyReMaterializable(&MI, AA))
+ return true;
+
+ // Estimate register pressure to determine whether to LICM the instruction.
+ // In low register pressure situation, we can be more aggressive about
+ // hoisting. Also, favors hoisting long latency instructions even in
+ // moderately high pressure situation.
+ // Cheap instructions will only be hoisted if they don't increase register
+ // pressure at all.
+ // FIXME: If there are long latency loop-invariant instructions inside the
+ // loop at this point, why didn't the optimizer's LICM hoist them?
+ DenseMap<unsigned, int> Cost;
+ for (unsigned i = 0, e = MI.getDesc().getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI.getOperand(i);
+ if (!MO.isReg() || MO.isImplicit())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!TargetRegisterInfo::isVirtualRegister(Reg))
+ continue;
- DenseMap<unsigned, int>::iterator CI = Cost.find(RCId);
- if (CI != Cost.end())
- CI->second += RCCost;
- else
- Cost.insert(std::make_pair(RCId, RCCost));
- } else if (isOperandKill(MO, MRI)) {
- // Is a virtual register use is a kill, hoisting it out of the loop
- // may actually reduce register pressure or be register pressure
- // neutral.
- DenseMap<unsigned, int>::iterator CI = Cost.find(RCId);
- if (CI != Cost.end())
- CI->second -= RCCost;
- else
- Cost.insert(std::make_pair(RCId, -RCCost));
+ unsigned RCId, RCCost;
+ getRegisterClassIDAndCost(&MI, Reg, i, RCId, RCCost);
+ if (MO.isDef()) {
+ if (HasHighOperandLatency(MI, i, Reg)) {
+ DEBUG(dbgs() << "Hoist High Latency: " << MI);
+ ++NumHighLatency;
+ return true;
}
+ Cost[RCId] += RCCost;
+ } else if (isOperandKill(MO, MRI)) {
+ // Is a virtual register use is a kill, hoisting it out of the loop
+ // may actually reduce register pressure or be register pressure
+ // neutral.
+ Cost[RCId] -= RCCost;
}
+ }
- // Visit BBs from header to current BB, if hoisting this doesn't cause
- // high register pressure, then it's safe to proceed.
- if (!CanCauseHighRegPressure(Cost)) {
- ++NumLowRP;
- return true;
- }
+ // Visit BBs from header to current BB, if hoisting this doesn't cause
+ // high register pressure, then it's safe to proceed.
+ if (!CanCauseHighRegPressure(Cost, CheapInstr)) {
+ DEBUG(dbgs() << "Hoist non-reg-pressure: " << MI);
+ ++NumLowRP;
+ return true;
+ }
- // Do not "speculate" in high register pressure situation. If an
- // instruction is not guaranteed to be executed in the loop, it's best to be
- // conservative.
- if (AvoidSpeculation &&
- (!IsGuaranteedToExecute(MI.getParent()) && !MayCSE(&MI)))
- return false;
+ // Don't risk increasing register pressure if it would create copies.
+ if (CreatesCopy) {
+ DEBUG(dbgs() << "Won't hoist instr with loop PHI use: " << MI);
+ return false;
+ }
- // High register pressure situation, only hoist if the instruction is going to
- // be remat'ed.
- if (!TII->isTriviallyReMaterializable(&MI, AA) &&
- !MI.isInvariantLoad(AA))
- return false;
+ // Do not "speculate" in high register pressure situation. If an
+ // instruction is not guaranteed to be executed in the loop, it's best to be
+ // conservative.
+ if (AvoidSpeculation &&
+ (!IsGuaranteedToExecute(MI.getParent()) && !MayCSE(&MI))) {
+ DEBUG(dbgs() << "Won't speculate: " << MI);
+ return false;
}
- // If result(s) of this instruction is used by PHIs outside of the loop, then
- // don't hoist it if the instruction because it will introduce an extra copy.
- for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = MI.getOperand(i);
- if (!MO.isReg() || !MO.isDef())
- continue;
- if (HasAnyPHIUse(MO.getReg()))
- return false;
+ // High register pressure situation, only hoist if the instruction is going
+ // to be remat'ed.
+ if (!TII->isTriviallyReMaterializable(&MI, AA) &&
+ !MI.isInvariantLoad(AA)) {
+ DEBUG(dbgs() << "Can't remat / high reg-pressure: " << MI);
+ return false;
}
return true;
MachineInstr *MachineLICM::ExtractHoistableLoad(MachineInstr *MI) {
// Don't unfold simple loads.
- if (MI->getDesc().canFoldAsLoad())
+ if (MI->canFoldAsLoad())
return 0;
// If not, we may be able to unfold a load and hoist that.
if (NewOpc == 0) return 0;
const MCInstrDesc &MID = TII->get(NewOpc);
if (MID.getNumDefs() != 1) return 0;
- const TargetRegisterClass *RC = TII->getRegClass(MID, LoadRegIndex, TRI);
+ MachineFunction &MF = *MI->getParent()->getParent();
+ const TargetRegisterClass *RC = TII->getRegClass(MID, LoadRegIndex, TRI, MF);
// Ok, we're unfolding. Create a temporary register and do the unfold.
unsigned Reg = MRI->createVirtualRegister(RC);
- MachineFunction &MF = *MI->getParent()->getParent();
SmallVector<MachineInstr *, 2> NewMIs;
bool Success =
TII->unfoldMemoryOperand(MF, MI, Reg,
assert(NewMIs.size() == 2 &&
"Unfolded a load into multiple instructions!");
MachineBasicBlock *MBB = MI->getParent();
- MBB->insert(MI, NewMIs[0]);
- MBB->insert(MI, NewMIs[1]);
+ MachineBasicBlock::iterator Pos = MI;
+ MBB->insert(Pos, NewMIs[0]);
+ MBB->insert(Pos, 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])) {
projects / oota-llvm.git / blobdiff