// 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/ADT/DenseMap.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.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/MC/MCInstrItineraries.h"
-#include "llvm/Target/TargetLowering.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/CodeGen/TargetSchedule.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetLowering.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
+#define DEBUG_TYPE "machine-licm"
+
static cl::opt<bool>
AvoidSpeculation("avoid-speculation",
cl::desc("MachineLICM should avoid speculation"),
cl::init(true), cl::Hidden);
+static cl::opt<bool>
+HoistCheapInsts("hoist-cheap-insts",
+ cl::desc("MachineLICM should hoist even cheap instructions"),
+ cl::init(false), cl::Hidden);
+
+static cl::opt<bool>
+SinkInstsToAvoidSpills("sink-insts-to-avoid-spills",
+ cl::desc("MachineLICM should sink instructions into "
+ "loops to avoid register spills"),
+ cl::init(false), cl::Hidden);
+
STATISTIC(NumHoisted,
"Number of machine instructions hoisted out of loops");
STATISTIC(NumLowRP,
namespace {
class MachineLICM : public MachineFunctionPass {
- bool PreRegAlloc;
-
- const TargetMachine *TM;
const TargetInstrInfo *TII;
- const TargetLowering *TLI;
+ const TargetLoweringBase *TLI;
const TargetRegisterInfo *TRI;
const MachineFrameInfo *MFI;
MachineRegisterInfo *MRI;
- const InstrItineraryData *InstrItins;
+ TargetSchedModel SchedModel;
+ 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.
+ // 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;
SmallVector<unsigned, 8> RegPressure;
- // Register pressure "limit" per register class. If the pressure
+ // Register pressure "limit" per register pressure set. If the pressure
// is higher than the limit, then it's considered high.
SmallVector<unsigned, 8> RegLimit;
initializeMachineLICMPass(*PassRegistry::getPassRegistry());
}
- virtual bool runOnMachineFunction(MachineFunction &MF);
+ bool runOnMachineFunction(MachineFunction &MF) override;
- const char *getPassName() const { return "Machine Instruction LICM"; }
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineLoopInfo>();
AU.addRequired<MachineDominatorTree>();
- AU.addRequired<AliasAnalysis>();
+ AU.addRequired<AAResultsWrapperPass>();
AU.addPreserved<MachineLoopInfo>();
AU.addPreserved<MachineDominatorTree>();
MachineFunctionPass::getAnalysisUsage(AU);
}
- virtual void releaseMemory() {
+ void releaseMemory() override {
RegSeen.clear();
RegPressure.clear();
RegLimit.clear();
BackTrace.clear();
- for (DenseMap<unsigned,std::vector<const MachineInstr*> >::iterator
- CI = CSEMap.begin(), CE = CSEMap.end(); CI != CE; ++CI)
- CI->second.clear();
CSEMap.clear();
}
private:
- /// CandidateInfo - Keep track of information about hoisting candidates.
+ /// Keep track of information about hoisting candidates.
struct CandidateInfo {
MachineInstr *MI;
unsigned Def;
: 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,
- BitVector &PhysRegDefs,
- BitVector &PhysRegClobbers,
- SmallSet<int, 32> &StoredFIs,
- SmallVector<CandidateInfo, 32> &Candidates);
+ void ProcessMI(MachineInstr *MI, BitVector &PhysRegDefs,
+ BitVector &PhysRegClobbers, SmallSet<int, 32> &StoredFIs,
+ SmallVectorImpl<CandidateInfo> &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);
- /// HasAnyPHIUse - Return true if the specified register is used by any
- /// phi node.
- bool HasAnyPHIUse(unsigned Reg) const;
+ 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
- /// it 'high'.
bool HasHighOperandLatency(MachineInstr &MI, unsigned DefIdx,
unsigned Reg) const;
bool IsCheapInstruction(MachineInstr &MI) const;
- /// 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(const 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
- /// effect of hoisting MI from the current block to the preheader.
void UpdateBackTraceRegPressure(const MachineInstr *MI);
- /// IsProfitableToHoist - Return true if it is potentially profitable to
- /// hoist the given loop invariant.
bool IsProfitableToHoist(MachineInstr &MI);
- /// IsGuaranteedToExecute - Check if this mbb is guaranteed to execute.
- /// If not then a load from this mbb may not be safe to hoist.
bool IsGuaranteedToExecute(MachineBasicBlock *BB);
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 ExitScopeIfDone(
+ MachineDomTreeNode *Node,
+ DenseMap<MachineDomTreeNode *, unsigned> &OpenChildren,
+ DenseMap<MachineDomTreeNode *, MachineDomTreeNode *> &ParentMap);
+
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
- /// reference.
- void getRegisterClassIDAndCost(const MachineInstr *MI,
- unsigned Reg, unsigned OpIdx,
- unsigned &RCId, unsigned &RCCost) const;
+ void SinkIntoLoop();
- /// 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.
void InitRegPressure(MachineBasicBlock *BB);
- /// UpdateRegPressure - Update estimate of register pressure after the
- /// specified instruction.
- void UpdateRegPressure(const MachineInstr *MI);
+ DenseMap<unsigned, int> calcRegisterCost(const MachineInstr *MI,
+ bool ConsiderSeen,
+ bool ConsiderUnseenAsDef);
+
+ void UpdateRegPressure(const MachineInstr *MI,
+ bool ConsiderUnseenAsDef = false);
- /// 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);
+ 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);
+ bool EliminateCSE(
+ MachineInstr *MI,
+ DenseMap<unsigned, std::vector<const MachineInstr *>>::iterator &CI);
- /// MayCSE - Return true if the given instruction will be CSE'd if it's
- /// hoisted out of the loop.
bool MayCSE(MachineInstr *MI);
- /// 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.
- /// It returns true if the instruction is hoisted.
bool Hoist(MachineInstr *MI, MachineBasicBlock *Preheader);
- /// 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;
+char &llvm::MachineLICMID = MachineLICM::ID;
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_DEPENDENCY(AAResultsWrapperPass)
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.
+/// 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())
}
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");
+ if (skipOptnoneFunction(*MF.getFunction()))
+ return false;
Changed = FirstInLoop = false;
- TM = &MF.getTarget();
- TII = TM->getInstrInfo();
- TLI = TM->getTargetLowering();
- TRI = TM->getRegisterInfo();
+ const TargetSubtargetInfo &ST = MF.getSubtarget();
+ TII = ST.getInstrInfo();
+ TLI = ST.getTargetLowering();
+ TRI = ST.getRegisterInfo();
MFI = MF.getFrameInfo();
MRI = &MF.getRegInfo();
- InstrItins = TM->getInstrItineraryData();
+ SchedModel.init(ST.getSchedModel(), &ST, TII);
+
+ 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.
- unsigned NumRC = TRI->getNumRegClasses();
- RegPressure.resize(NumRC);
+ unsigned NumRPS = TRI->getNumRegPressureSets();
+ RegPressure.resize(NumRPS);
std::fill(RegPressure.begin(), RegPressure.end(), 0);
- RegLimit.resize(NumRC);
- for (TargetRegisterInfo::regclass_iterator I = TRI->regclass_begin(),
- E = TRI->regclass_end(); I != E; ++I)
- RegLimit[(*I)->getID()] = TRI->getRegPressureLimit(*I, MF);
+ RegLimit.resize(NumRPS);
+ for (unsigned i = 0, e = NumRPS; i != e; ++i)
+ RegLimit[i] = TRI->getRegPressureSetLimit(MF, i);
}
// Get our Loop information...
MLI = &getAnalysis<MachineLoopInfo>();
DT = &getAnalysis<MachineDominatorTree>();
- AA = &getAnalysis<AliasAnalysis>();
+ AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
SmallVector<MachineLoop *, 8> Worklist(MLI->begin(), MLI->end());
while (!Worklist.empty()) {
CurLoop = Worklist.pop_back_val();
- CurPreheader = 0;
+ CurPreheader = nullptr;
+ ExitBlocks.clear();
// If this is done before regalloc, only visit outer-most preheader-sporting
// loops.
continue;
}
+ CurLoop->getExitBlocks(ExitBlocks);
+
if (!PreRegAlloc)
HoistRegionPostRA();
else {
FirstInLoop = true;
HoistOutOfLoop(N);
CSEMap.clear();
+
+ if (SinkInstsToAvoidSpills)
+ SinkIntoLoop();
}
}
return Changed;
}
-/// InstructionStoresToFI - Return true if instruction stores to the
-/// specified frame.
+/// Return true if instruction stores to the specified frame.
static bool InstructionStoresToFI(const MachineInstr *MI, int FI) {
+ // If we lost memory operands, conservatively assume that the instruction
+ // writes to all slots.
+ if (MI->memoperands_empty())
+ return true;
for (MachineInstr::mmo_iterator o = MI->memoperands_begin(),
oe = MI->memoperands_end(); o != oe; ++o) {
- if (!(*o)->isStore() || !(*o)->getValue())
+ if (!(*o)->isStore() || !(*o)->getPseudoValue())
continue;
if (const FixedStackPseudoSourceValue *Value =
- dyn_cast<const FixedStackPseudoSourceValue>((*o)->getValue())) {
+ dyn_cast<FixedStackPseudoSourceValue>((*o)->getPseudoValue())) {
if (Value->getFrameIndex() == FI)
return true;
}
return false;
}
-/// ProcessMI - Examine the instruction for potentai LICM candidate. Also
+/// Examine the instruction for potentai LICM candidate. Also
/// gather register def and frame object update information.
void MachineLICM::ProcessMI(MachineInstr *MI,
BitVector &PhysRegDefs,
BitVector &PhysRegClobbers,
SmallSet<int, 32> &StoredFIs,
- SmallVector<CandidateInfo, 32> &Candidates) {
+ SmallVectorImpl<CandidateInfo> &Candidates) {
bool RuledOut = false;
bool HasNonInvariantUse = false;
unsigned Def = 0;
}
if (MO.isImplicit()) {
- for (const unsigned *AS = TRI->getOverlaps(Reg); *AS; ++AS)
- PhysRegClobbers.set(*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;
// If we have already seen another instruction that defines the same
// register, then this is not safe. Two defs is indicated by setting a
// PhysRegClobbers bit.
- for (const unsigned *AS = TRI->getOverlaps(Reg); *AS; ++AS) {
+ 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);
}
+ if (PhysRegClobbers.test(Reg))
+ // MI defined register is seen defined by another instruction in
+ // the loop, it cannot be a LICM candidate.
+ RuledOut = true;
}
// 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.
+/// 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();
BitVector PhysRegDefs(NumRegs); // Regs defined once in the loop.
BitVector PhysRegClobbers(NumRegs); // Regs defined more than once.
// Walk the entire region, count number of defs for each register, and
// collect potential LICM candidates.
- const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
+ const std::vector<MachineBasicBlock *> &Blocks = CurLoop->getBlocks();
for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
MachineBasicBlock *BB = Blocks[i];
// 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 (ML && ML->getHeader()->isEHPad()) continue;
// 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;
- for (const unsigned *AS = TRI->getOverlaps(Reg); *AS; ++AS)
- PhysRegDefs.set(*AS);
+ for (const auto &LI : BB->liveins()) {
+ for (MCRegAliasIterator AI(LI.PhysReg, TRI, true); AI.isValid(); ++AI)
+ PhysRegDefs.set(*AI);
}
SpeculationState = SpeculateUnknown;
}
}
+ // 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);
+ }
+ }
+
// 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.
+ // 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 (!PhysRegClobbers.test(Candidates[i].Def)) {
+ 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.test(MO.getReg()) ||
- PhysRegClobbers.test(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;
}
}
-/// 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.
+/// 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();
+ 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))
}
}
-/// 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.
+/// 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.
Changed = true;
}
-// IsGuaranteedToExecute - Check if this mbb is guaranteed to execute.
-// If not then a load from this mbb may not be safe to hoist.
+/// Check if this mbb is guaranteed to execute. If not then a load from this mbb
+/// may not be safe to hoist.
bool MachineLICM::IsGuaranteedToExecute(MachineBasicBlock *BB) {
if (SpeculationState != SpeculateUnknown)
return SpeculationState == SpeculateFalse;
BackTrace.pop_back();
}
-/// 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.
+/// 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) {
}
}
-/// 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.
+/// 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) {
+ MachineBasicBlock *Preheader = getCurPreheader();
+ if (!Preheader)
+ return;
+
SmallVector<MachineDomTreeNode*, 32> Scopes;
SmallVector<MachineDomTreeNode*, 8> WorkList;
DenseMap<MachineDomTreeNode*, MachineDomTreeNode*> ParentMap;
// Perform a DFS walk to determine the order of visit.
WorkList.push_back(HeaderN);
- do {
+ while (!WorkList.empty()) {
MachineDomTreeNode *Node = WorkList.pop_back_val();
- assert(Node != 0 && "Null dominator tree node?");
+ assert(Node && "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())
+ if (ML && ML->getHeader()->isEHPad())
continue;
// If this subregion is not in the top level loop at all, exit.
ParentMap[Child] = Node;
WorkList.push_back(Child);
}
- } while (!WorkList.empty());
+ }
- if (Scopes.size() != 0) {
- MachineBasicBlock *Preheader = getCurPreheader();
- if (!Preheader)
- return;
+ if (Scopes.size() == 0)
+ return;
- // Compute registers which are livein into the loop headers.
- RegSeen.clear();
- BackTrace.clear();
- InitRegPressure(Preheader);
- }
+ // Compute registers which are livein into the loop headers.
+ RegSeen.clear();
+ BackTrace.clear();
+ InitRegPressure(Preheader);
// Now perform LICM.
for (unsigned i = 0, e = Scopes.size(); i != e; ++i) {
MachineDomTreeNode *Node = Scopes[i];
MachineBasicBlock *MBB = Node->getBlock();
- MachineBasicBlock *Preheader = getCurPreheader();
- if (!Preheader)
- continue;
-
EnterScope(MBB);
// Process the block
}
}
-static bool isOperandKill(const MachineOperand &MO, MachineRegisterInfo *MRI) {
- return MO.isKill() || MRI->hasOneNonDBGUse(MO.getReg());
-}
+/// Sink instructions into loops if profitable. This especially tries to prevent
+/// register spills caused by register pressure if there is little to no
+/// overhead moving instructions into loops.
+void MachineLICM::SinkIntoLoop() {
+ MachineBasicBlock *Preheader = getCurPreheader();
+ if (!Preheader)
+ return;
-/// getRegisterClassIDAndCost - For a given MI, register, and the operand
-/// index, return the ID and cost of its representative register class.
-void
-MachineLICM::getRegisterClassIDAndCost(const MachineInstr *MI,
- unsigned Reg, unsigned OpIdx,
- unsigned &RCId, unsigned &RCCost) const {
- const TargetRegisterClass *RC = MRI->getRegClass(Reg);
- EVT VT = *RC->vt_begin();
- if (VT == MVT::Untyped) {
- RCId = RC->getID();
- RCCost = 1;
- } else {
- RCId = TLI->getRepRegClassFor(VT)->getID();
- RCCost = TLI->getRepRegClassCostFor(VT);
+ SmallVector<MachineInstr *, 8> Candidates;
+ for (MachineBasicBlock::instr_iterator I = Preheader->instr_begin();
+ I != Preheader->instr_end(); ++I) {
+ // We need to ensure that we can safely move this instruction into the loop.
+ // As such, it must not have side-effects, e.g. such as a call has.
+ if (IsLoopInvariantInst(*I) && !HasLoopPHIUse(&*I))
+ Candidates.push_back(&*I);
+ }
+
+ for (MachineInstr *I : Candidates) {
+ const MachineOperand &MO = I->getOperand(0);
+ if (!MO.isDef() || !MO.isReg() || !MO.getReg())
+ continue;
+ if (!MRI->hasOneDef(MO.getReg()))
+ continue;
+ bool CanSink = true;
+ MachineBasicBlock *B = nullptr;
+ for (MachineInstr &MI : MRI->use_instructions(MO.getReg())) {
+ // FIXME: Come up with a proper cost model that estimates whether sinking
+ // the instruction (and thus possibly executing it on every loop
+ // iteration) is more expensive than a register.
+ // For now assumes that copies are cheap and thus almost always worth it.
+ if (!MI.isCopy()) {
+ CanSink = false;
+ break;
+ }
+ if (!B) {
+ B = MI.getParent();
+ continue;
+ }
+ B = DT->findNearestCommonDominator(B, MI.getParent());
+ if (!B) {
+ CanSink = false;
+ break;
+ }
+ }
+ if (!CanSink || !B || B == Preheader)
+ continue;
+ B->splice(B->getFirstNonPHI(), Preheader, I);
}
}
-/// 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.
+static bool isOperandKill(const MachineOperand &MO, MachineRegisterInfo *MRI) {
+ return MO.isKill() || MRI->hasOneNonDBGUse(MO.getReg());
+}
+
+/// 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.
void MachineLICM::InitRegPressure(MachineBasicBlock *BB) {
std::fill(RegPressure.begin(), RegPressure.end(), 0);
// defs as well. This happens whenever the preheader is created by splitting
// the critical edge from the loop predecessor to the loop header.
if (BB->pred_size() == 1) {
- MachineBasicBlock *TBB = 0, *FBB = 0;
+ MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
if (!TII->AnalyzeBranch(*BB, TBB, FBB, Cond, false) && Cond.empty())
InitRegPressure(*BB->pred_begin());
}
- for (MachineBasicBlock::iterator MII = BB->begin(), E = BB->end();
- MII != E; ++MII) {
- MachineInstr *MI = &*MII;
- 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;
+ for (const MachineInstr &MI : *BB)
+ UpdateRegPressure(&MI, /*ConsiderUnseenAsDef=*/true);
+}
- bool isNew = RegSeen.insert(Reg);
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(MI, Reg, i, RCId, RCCost);
- if (MO.isDef())
- RegPressure[RCId] += RCCost;
- else {
- bool isKill = isOperandKill(MO, MRI);
- if (isNew && !isKill)
- // Haven't seen this, it must be a livein.
- RegPressure[RCId] += RCCost;
- else if (!isNew && isKill)
- RegPressure[RCId] -= RCCost;
- }
- }
+/// Update estimate of register pressure after the specified instruction.
+void MachineLICM::UpdateRegPressure(const MachineInstr *MI,
+ bool ConsiderUnseenAsDef) {
+ auto Cost = calcRegisterCost(MI, /*ConsiderSeen=*/true, ConsiderUnseenAsDef);
+ for (const auto &RPIdAndCost : Cost) {
+ unsigned Class = RPIdAndCost.first;
+ if (static_cast<int>(RegPressure[Class]) < -RPIdAndCost.second)
+ RegPressure[Class] = 0;
+ else
+ RegPressure[Class] += RPIdAndCost.second;
}
}
-/// UpdateRegPressure - Update estimate of register pressure after the
-/// specified instruction.
-void MachineLICM::UpdateRegPressure(const MachineInstr *MI) {
+/// Calculate the additional register pressure that the registers used in MI
+/// cause.
+///
+/// If 'ConsiderSeen' is true, updates 'RegSeen' and uses the information to
+/// figure out which usages are live-ins.
+/// FIXME: Figure out a way to consider 'RegSeen' from all code paths.
+DenseMap<unsigned, int>
+MachineLICM::calcRegisterCost(const MachineInstr *MI, bool ConsiderSeen,
+ bool ConsiderUnseenAsDef) {
+ DenseMap<unsigned, int> Cost;
if (MI->isImplicitDef())
- return;
-
- SmallVector<unsigned, 4> Defs;
+ return Cost;
for (unsigned i = 0, e = MI->getDesc().getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || MO.isImplicit())
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
- bool isNew = RegSeen.insert(Reg);
+ // FIXME: It seems bad to use RegSeen only for some of these calculations.
+ bool isNew = ConsiderSeen ? RegSeen.insert(Reg).second : false;
+ const TargetRegisterClass *RC = MRI->getRegClass(Reg);
+
+ RegClassWeight W = TRI->getRegClassWeight(RC);
+ int RCCost = 0;
if (MO.isDef())
- Defs.push_back(Reg);
- else if (!isNew && isOperandKill(MO, MRI)) {
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(MI, Reg, i, RCId, RCCost);
- if (RCCost > RegPressure[RCId])
- RegPressure[RCId] = 0;
+ RCCost = W.RegWeight;
+ else {
+ bool isKill = isOperandKill(MO, MRI);
+ if (isNew && !isKill && ConsiderUnseenAsDef)
+ // Haven't seen this, it must be a livein.
+ RCCost = W.RegWeight;
+ else if (!isNew && isKill)
+ RCCost = -W.RegWeight;
+ }
+ if (RCCost == 0)
+ continue;
+ const int *PS = TRI->getRegClassPressureSets(RC);
+ for (; *PS != -1; ++PS) {
+ if (Cost.find(*PS) == Cost.end())
+ Cost[*PS] = RCCost;
else
- RegPressure[RCId] -= RCCost;
+ Cost[*PS] += RCCost;
}
}
-
- unsigned Idx = 0;
- while (!Defs.empty()) {
- unsigned Reg = Defs.pop_back_val();
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(MI, Reg, Idx, RCId, RCCost);
- RegPressure[RCId] += RCCost;
- ++Idx;
- }
+ return Cost;
}
-/// isLoadFromGOTOrConstantPool - Return true if this machine instruction
-/// loads from global offset table or constant pool.
-static bool isLoadFromGOTOrConstantPool(MachineInstr &MI) {
+/// Return true if this machine instruction loads from global offset table or
+/// constant pool.
+static bool mayLoadFromGOTOrConstantPool(MachineInstr &MI) {
assert (MI.mayLoad() && "Expected MI that loads!");
+
+ // If we lost memory operands, conservatively assume that the instruction
+ // reads from everything..
+ if (MI.memoperands_empty())
+ return true;
+
for (MachineInstr::mmo_iterator I = MI.memoperands_begin(),
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() || PSV == PSV->getConstantPool())
- return true;
+ if (const PseudoSourceValue *PSV = (*I)->getPseudoValue()) {
+ if (PSV->isGOT() || PSV->isConstantPool())
+ return true;
}
}
return false;
}
-/// 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.
+/// 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))
+ if (!I.isSafeToMove(AA, DontMoveAcrossStore))
return false;
// If it is load then check if it is guaranteed to execute by making sure that
// 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.mayLoad() && !isLoadFromGOTOrConstantPool(I) &&
+ if (I.mayLoad() && !mayLoadFromGOTOrConstantPool(I) &&
!IsGuaranteedToExecute(I.getParent()))
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
+/// 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) {
}
-/// 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;
+/// 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 (const MachineOperand &MO : MI->operands()) {
+ if (!MO.isReg() || !MO.isDef())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!TargetRegisterInfo::isVirtualRegister(Reg))
+ continue;
+ for (MachineInstr &UseMI : MRI->use_instructions(Reg)) {
+ // 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;
}
-/// HasHighOperandLatency - Compute operand latency between a def of 'Reg'
-/// and an use in the current loop, return true if the target considered
-/// it 'high'.
+/// Compute operand latency between a def of 'Reg' and an use in the current
+/// loop, return true if the target considered it high.
bool MachineLICM::HasHighOperandLatency(MachineInstr &MI,
unsigned DefIdx, unsigned Reg) const {
- if (!InstrItins || InstrItins->isEmpty() || MRI->use_nodbg_empty(Reg))
+ if (MRI->use_nodbg_empty(Reg))
return false;
- for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(Reg),
- E = MRI->use_nodbg_end(); I != E; ++I) {
- MachineInstr *UseMI = &*I;
- if (UseMI->isCopyLike())
+ for (MachineInstr &UseMI : MRI->use_nodbg_instructions(Reg)) {
+ if (UseMI.isCopyLike())
continue;
- if (!CurLoop->contains(UseMI->getParent()))
+ if (!CurLoop->contains(UseMI.getParent()))
continue;
- for (unsigned i = 0, e = UseMI->getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = UseMI->getOperand(i);
+ for (unsigned i = 0, e = UseMI.getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = UseMI.getOperand(i);
if (!MO.isReg() || !MO.isUse())
continue;
unsigned MOReg = MO.getReg();
if (MOReg != Reg)
continue;
- if (TII->hasHighOperandLatency(InstrItins, MRI, &MI, DefIdx, UseMI, i))
+ if (TII->hasHighOperandLatency(SchedModel, MRI, &MI, DefIdx, &UseMI, i))
return true;
}
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.
+/// 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.isAsCheapAsAMove() || MI.isCopyLike())
+ if (TII->isAsCheapAsAMove(&MI) || MI.isCopyLike())
return true;
- if (!InstrItins || InstrItins->isEmpty())
- return false;
bool isCheap = false;
unsigned NumDefs = MI.getDesc().getNumDefs();
if (TargetRegisterInfo::isPhysicalRegister(Reg))
continue;
- if (!TII->hasLowDefLatency(InstrItins, &MI, i))
+ if (!TII->hasLowDefLatency(SchedModel, &MI, i))
return false;
isCheap = true;
}
return isCheap;
}
-/// 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) {
- for (DenseMap<unsigned, int>::iterator CI = Cost.begin(), CE = Cost.end();
- CI != CE; ++CI) {
- if (CI->second <= 0)
+/// 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(const DenseMap<unsigned, int>& Cost,
+ bool CheapInstr) {
+ for (const auto &RPIdAndCost : Cost) {
+ if (RPIdAndCost.second <= 0)
continue;
- unsigned RCId = CI->first;
- unsigned Limit = RegLimit[RCId];
- int Cost = CI->second;
- for (unsigned i = BackTrace.size(); i != 0; --i) {
- SmallVector<unsigned, 8> &RP = BackTrace[i-1];
- if (RP[RCId] + Cost >= Limit)
+ unsigned Class = RPIdAndCost.first;
+ int Limit = RegLimit[Class];
+
+ // Don't hoist cheap instructions if they would increase register pressure,
+ // even if we're under the limit.
+ if (CheapInstr && !HoistCheapInsts)
+ return true;
+
+ for (const auto &RP : BackTrace)
+ if (static_cast<int>(RP[Class]) + RPIdAndCost.second >= Limit)
return true;
- }
}
return false;
}
-/// UpdateBackTraceRegPressure - Traverse the back trace from header to the
-/// current block and update their register pressures to reflect the effect
-/// of hoisting MI from the current block to the preheader.
+/// Traverse the back trace from header to the current block and update their
+/// register pressures to reflect the effect of hoisting MI from the current
+/// block to the preheader.
void MachineLICM::UpdateBackTraceRegPressure(const MachineInstr *MI) {
- if (MI->isImplicitDef())
- return;
-
// First compute the 'cost' of the instruction, i.e. its contribution
// to register pressure.
- 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;
-
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(MI, Reg, i, RCId, RCCost);
- if (MO.isDef()) {
- 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)) {
- DenseMap<unsigned, int>::iterator CI = Cost.find(RCId);
- if (CI != Cost.end())
- CI->second -= RCCost;
- else
- Cost.insert(std::make_pair(RCId, -RCCost));
- }
- }
+ auto Cost = calcRegisterCost(MI, /*ConsiderSeen=*/false,
+ /*ConsiderUnseenAsDef=*/false);
// Update register pressure of blocks from loop header to current block.
- for (unsigned i = 0, e = BackTrace.size(); i != e; ++i) {
- SmallVector<unsigned, 8> &RP = BackTrace[i];
- for (DenseMap<unsigned, int>::iterator CI = Cost.begin(), CE = Cost.end();
- CI != CE; ++CI) {
- unsigned RCId = CI->first;
- RP[RCId] += CI->second;
- }
- }
+ for (auto &RP : BackTrace)
+ for (const auto &RPIdAndCost : Cost)
+ RP[RPIdAndCost.first] += RPIdAndCost.second;
}
-/// IsProfitableToHoist - Return true if it is potentially profitable to hoist
-/// the given loop invariant.
+/// Return true if it is potentially profitable to hoist the given loop
+/// invariant.
bool MachineLICM::IsProfitableToHoist(MachineInstr &MI) {
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;
-
- unsigned RCId, RCCost;
- getRegisterClassIDAndCost(&MI, Reg, i, RCId, RCCost);
- if (MO.isDef()) {
- if (HasHighOperandLatency(MI, i, Reg)) {
- ++NumHighLatency;
- return true;
- }
+ // 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;
+ }
- 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));
- }
- }
+ // 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;
- // 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;
+ // FIXME: If there are long latency loop-invariant instructions inside the
+ // loop at this point, why didn't the optimizer's LICM hoist them?
+ 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;
+ if (MO.isDef() && HasHighOperandLatency(MI, i, Reg)) {
+ DEBUG(dbgs() << "Hoist High Latency: " << MI);
+ ++NumHighLatency;
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;
+ // 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.
+ auto Cost = calcRegisterCost(&MI, /*ConsiderSeen=*/false,
+ /*ConsiderUnseenAsDef=*/false);
+
+ // 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;
+ }
- // 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;
+ // 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;
}
- // 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;
+ // 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;
+ }
+
+ // 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;
}
+/// 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 *MachineLICM::ExtractHoistableLoad(MachineInstr *MI) {
// Don't unfold simple loads.
if (MI->canFoldAsLoad())
- return 0;
+ return nullptr;
// 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 (!MI->isInvariantLoad(AA))
- return 0;
+ return nullptr;
// Next determine the register class for a temporary register.
unsigned LoadRegIndex;
/*UnfoldLoad=*/true,
/*UnfoldStore=*/false,
&LoadRegIndex);
- if (NewOpc == 0) return 0;
+ if (NewOpc == 0) return nullptr;
const MCInstrDesc &MID = TII->get(NewOpc);
- if (MID.getNumDefs() != 1) return 0;
- const TargetRegisterClass *RC = TII->getRegClass(MID, LoadRegIndex, TRI);
+ if (MID.getNumDefs() != 1) return nullptr;
+ 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,
if (!IsLoopInvariantInst(*NewMIs[0]) || !IsProfitableToHoist(*NewMIs[0])) {
NewMIs[0]->eraseFromParent();
NewMIs[1]->eraseFromParent();
- return 0;
+ return nullptr;
}
// Update register pressure for the unfolded instruction.
return NewMIs[0];
}
+/// 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 MachineLICM::InitCSEMap(MachineBasicBlock *BB) {
for (MachineBasicBlock::iterator I = BB->begin(),E = BB->end(); I != E; ++I) {
const MachineInstr *MI = &*I;
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));
- }
+ CSEMap[Opcode].push_back(MI);
}
}
+/// Find an instruction amount PrevMIs that is a duplicate of MI.
+/// Return this instruction if it's found.
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, (PreRegAlloc ? MRI : 0)))
+ if (TII->produceSameValue(MI, PrevMI, (PreRegAlloc ? MRI : nullptr)))
return PrevMI;
}
- return 0;
+ return nullptr;
}
+/// Given a LICM'ed instruction, look for an instruction on the preheader that
+/// computes 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 MachineLICM::EliminateCSE(MachineInstr *MI,
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator &CI) {
// Do not CSE implicit_def so ProcessImplicitDefs can properly propagate
return false;
}
-/// MayCSE - Return true if the given instruction will be CSE'd if it's
-/// hoisted out of the loop.
+/// Return true if the given instruction will be CSE'd if it's hoisted out of
+/// the loop.
bool MachineLICM::MayCSE(MachineInstr *MI) {
unsigned Opcode = MI->getOpcode();
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator
if (CI == CSEMap.end() || MI->isImplicitDef())
return false;
- return LookForDuplicate(MI, CI->second) != 0;
+ return LookForDuplicate(MI, CI->second) != nullptr;
}
-/// Hoist - When an instruction is found to use only loop invariant operands
+/// 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.
-///
+/// It returns true if the instruction is hoisted.
bool MachineLICM::Hoist(MachineInstr *MI, MachineBasicBlock *Preheader) {
// First check whether we should hoist this instruction.
if (!IsLoopInvariantInst(*MI) || !IsProfitableToHoist(*MI)) {
// 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));
- }
+ else
+ CSEMap[Opcode].push_back(MI);
}
++NumHoisted;
return true;
}
+/// Get the preheader for the current loop, splitting a critical edge if needed.
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;
+ return nullptr;
if (!CurPreheader) {
CurPreheader = CurLoop->getLoopPreheader();
MachineBasicBlock *Pred = CurLoop->getLoopPredecessor();
if (!Pred) {
CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
- return 0;
+ return nullptr;
}
CurPreheader = Pred->SplitCriticalEdge(CurLoop->getHeader(), this);
if (!CurPreheader) {
CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
- return 0;
+ return nullptr;
}
}
}
projects / oota-llvm.git / blobdiff