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//===-- MachineLICM.cpp - Machine Loop Invariant Code Motion Pass ---------===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This pass performs loop invariant code motion on machine instructions. We
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// attempt to remove as much code from the body of a loop as possible.
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// This pass does not attempt to throttle itself to limit register pressure.
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// The register allocation phases are expected to perform rematerialization
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// to recover when register pressure is high.
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// This pass is not intended to be a replacement or a complete alternative
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// for the LLVM-IR-level LICM pass. It is only designed to hoist simple
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// constructs that are not exposed before lowering and instruction selection.
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "machine-licm"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/MachineDominators.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineLoopInfo.h"
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#include "llvm/CodeGen/MachineMemOperand.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/PseudoSourceValue.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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STATISTIC(NumHoisted, "Number of machine instructions hoisted out of loops");
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STATISTIC(NumCSEed, "Number of hoisted machine instructions CSEed");
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STATISTIC(NumPostRAHoisted,
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"Number of machine instructions hoisted out of loops post regalloc");
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class MachineLICM : public MachineFunctionPass {
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const TargetMachine *TM;
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const TargetInstrInfo *TII;
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const TargetRegisterInfo *TRI;
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const MachineFrameInfo *MFI;
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MachineRegisterInfo *RegInfo;
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// Various analyses that we use...
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AliasAnalysis *AA; // Alias analysis info.
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MachineLoopInfo *MLI; // Current MachineLoopInfo
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MachineDominatorTree *DT; // Machine dominator tree for the cur loop
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// State that is updated as we process loops
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bool Changed; // True if a loop is changed.
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bool FirstInLoop; // True if it's the first LICM in the loop.
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MachineLoop *CurLoop; // The current loop we are working on.
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MachineBasicBlock *CurPreheader; // The preheader for CurLoop.
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BitVector AllocatableSet;
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// For each opcode, keep a list of potential CSE instructions.
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DenseMap<unsigned, std::vector<const MachineInstr*> > CSEMap;
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static char ID; // Pass identification, replacement for typeid
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MachineFunctionPass(ID), PreRegAlloc(true) {}
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explicit MachineLICM(bool PreRA) :
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MachineFunctionPass(ID), PreRegAlloc(PreRA) {}
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virtual bool runOnMachineFunction(MachineFunction &MF);
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const char *getPassName() const { return "Machine Instruction LICM"; }
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<MachineLoopInfo>();
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AU.addRequired<MachineDominatorTree>();
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AU.addRequired<AliasAnalysis>();
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AU.addPreserved<MachineLoopInfo>();
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AU.addPreserved<MachineDominatorTree>();
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MachineFunctionPass::getAnalysisUsage(AU);
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virtual void releaseMemory() {
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/// CandidateInfo - Keep track of information about hoisting candidates.
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struct CandidateInfo {
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CandidateInfo(MachineInstr *mi, unsigned def, int fi)
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: MI(mi), Def(def), FI(fi) {}
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/// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
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/// invariants out to the preheader.
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void HoistRegionPostRA();
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/// HoistPostRA - When an instruction is found to only use loop invariant
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/// operands that is safe to hoist, this instruction is called to do the
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void HoistPostRA(MachineInstr *MI, unsigned Def);
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/// ProcessMI - Examine the instruction for potentai LICM candidate. Also
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/// gather register def and frame object update information.
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void ProcessMI(MachineInstr *MI, unsigned *PhysRegDefs,
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SmallSet<int, 32> &StoredFIs,
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SmallVector<CandidateInfo, 32> &Candidates);
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/// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the
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void AddToLiveIns(unsigned Reg);
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/// IsLICMCandidate - Returns true if the instruction may be a suitable
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/// candidate for LICM. e.g. If the instruction is a call, then it's
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/// obviously not safe to hoist it.
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bool IsLICMCandidate(MachineInstr &I);
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/// IsLoopInvariantInst - Returns true if the instruction is loop
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/// invariant. I.e., all virtual register operands are defined outside of
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/// the loop, physical registers aren't accessed (explicitly or implicitly),
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/// and the instruction is hoistable.
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bool IsLoopInvariantInst(MachineInstr &I);
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/// IsProfitableToHoist - Return true if it is potentially profitable to
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/// hoist the given loop invariant.
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bool IsProfitableToHoist(MachineInstr &MI);
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/// HoistRegion - Walk the specified region of the CFG (defined by all
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/// blocks dominated by the specified block, and that are in the current
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/// loop) in depth first order w.r.t the DominatorTree. This allows us to
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/// visit definitions before uses, allowing us to hoist a loop body in one
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/// pass without iteration.
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void HoistRegion(MachineDomTreeNode *N);
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/// isLoadFromConstantMemory - Return true if the given instruction is a
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/// load from constant memory.
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bool isLoadFromConstantMemory(MachineInstr *MI);
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/// ExtractHoistableLoad - Unfold a load from the given machineinstr if
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/// the load itself could be hoisted. Return the unfolded and hoistable
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/// load, or null if the load couldn't be unfolded or if it wouldn't
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MachineInstr *ExtractHoistableLoad(MachineInstr *MI);
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/// LookForDuplicate - Find an instruction amount PrevMIs that is a
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/// duplicate of MI. Return this instruction if it's found.
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const MachineInstr *LookForDuplicate(const MachineInstr *MI,
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std::vector<const MachineInstr*> &PrevMIs);
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/// EliminateCSE - Given a LICM'ed instruction, look for an instruction on
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/// the preheader that compute the same value. If it's found, do a RAU on
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/// with the definition of the existing instruction rather than hoisting
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/// the instruction to the preheader.
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bool EliminateCSE(MachineInstr *MI,
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DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator &CI);
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/// Hoist - When an instruction is found to only use loop invariant operands
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/// that is safe to hoist, this instruction is called to do the dirty work.
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void Hoist(MachineInstr *MI);
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/// InitCSEMap - Initialize the CSE map with instructions that are in the
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/// current loop preheader that may become duplicates of instructions that
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/// are hoisted out of the loop.
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void InitCSEMap(MachineBasicBlock *BB);
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/// getCurPreheader - Get the preheader for the current loop, splitting
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/// a critical edge if needed.
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MachineBasicBlock *getCurPreheader();
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} // end anonymous namespace
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char MachineLICM::ID = 0;
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INITIALIZE_PASS(MachineLICM, "machinelicm",
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"Machine Loop Invariant Code Motion", false, false);
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FunctionPass *llvm::createMachineLICMPass(bool PreRegAlloc) {
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return new MachineLICM(PreRegAlloc);
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/// LoopIsOuterMostWithPredecessor - Test if the given loop is the outer-most
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/// loop that has a unique predecessor.
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static bool LoopIsOuterMostWithPredecessor(MachineLoop *CurLoop) {
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// Check whether this loop even has a unique predecessor.
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if (!CurLoop->getLoopPredecessor())
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// Ok, now check to see if any of its outer loops do.
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for (MachineLoop *L = CurLoop->getParentLoop(); L; L = L->getParentLoop())
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if (L->getLoopPredecessor())
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// None of them did, so this is the outermost with a unique predecessor.
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bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
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DEBUG(dbgs() << "******** Pre-regalloc Machine LICM ********\n");
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DEBUG(dbgs() << "******** Post-regalloc Machine LICM ********\n");
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Changed = FirstInLoop = false;
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TM = &MF.getTarget();
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TII = TM->getInstrInfo();
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TRI = TM->getRegisterInfo();
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MFI = MF.getFrameInfo();
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RegInfo = &MF.getRegInfo();
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AllocatableSet = TRI->getAllocatableSet(MF);
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// Get our Loop information...
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MLI = &getAnalysis<MachineLoopInfo>();
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DT = &getAnalysis<MachineDominatorTree>();
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AA = &getAnalysis<AliasAnalysis>();
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SmallVector<MachineLoop *, 8> Worklist(MLI->begin(), MLI->end());
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while (!Worklist.empty()) {
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CurLoop = Worklist.pop_back_val();
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// If this is done before regalloc, only visit outer-most preheader-sporting
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if (PreRegAlloc && !LoopIsOuterMostWithPredecessor(CurLoop)) {
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Worklist.append(CurLoop->begin(), CurLoop->end());
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// CSEMap is initialized for loop header when the first instruction is
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MachineDomTreeNode *N = DT->getNode(CurLoop->getHeader());
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/// InstructionStoresToFI - Return true if instruction stores to the
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static bool InstructionStoresToFI(const MachineInstr *MI, int FI) {
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for (MachineInstr::mmo_iterator o = MI->memoperands_begin(),
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oe = MI->memoperands_end(); o != oe; ++o) {
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if (!(*o)->isStore() || !(*o)->getValue())
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if (const FixedStackPseudoSourceValue *Value =
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dyn_cast<const FixedStackPseudoSourceValue>((*o)->getValue())) {
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if (Value->getFrameIndex() == FI)
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/// ProcessMI - Examine the instruction for potentai LICM candidate. Also
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/// gather register def and frame object update information.
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void MachineLICM::ProcessMI(MachineInstr *MI,
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unsigned *PhysRegDefs,
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SmallSet<int, 32> &StoredFIs,
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SmallVector<CandidateInfo, 32> &Candidates) {
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bool RuledOut = false;
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bool HasNonInvariantUse = false;
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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const MachineOperand &MO = MI->getOperand(i);
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// Remember if the instruction stores to the frame index.
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int FI = MO.getIndex();
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if (!StoredFIs.count(FI) &&
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MFI->isSpillSlotObjectIndex(FI) &&
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InstructionStoresToFI(MI, FI))
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StoredFIs.insert(FI);
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HasNonInvariantUse = true;
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unsigned Reg = MO.getReg();
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assert(TargetRegisterInfo::isPhysicalRegister(Reg) &&
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"Not expecting virtual register!");
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if (Reg && PhysRegDefs[Reg])
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// If it's using a non-loop-invariant register, then it's obviously not
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HasNonInvariantUse = true;
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if (MO.isImplicit()) {
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for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
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// Non-dead implicit def? This cannot be hoisted.
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// No need to check if a dead implicit def is also defined by
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// another instruction.
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// FIXME: For now, avoid instructions with multiple defs, unless
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// it's a dead implicit def.
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// If we have already seen another instruction that defines the same
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// register, then this is not safe.
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if (++PhysRegDefs[Reg] > 1)
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// MI defined register is seen defined by another instruction in
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// the loop, it cannot be a LICM candidate.
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for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
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if (++PhysRegDefs[*AS] > 1)
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// Only consider reloads for now and remats which do not have register
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// operands. FIXME: Consider unfold load folding instructions.
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if (Def && !RuledOut) {
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if ((!HasNonInvariantUse && IsLICMCandidate(*MI)) ||
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(TII->isLoadFromStackSlot(MI, FI) && MFI->isSpillSlotObjectIndex(FI)))
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Candidates.push_back(CandidateInfo(MI, Def, FI));
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/// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
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/// invariants out to the preheader.
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void MachineLICM::HoistRegionPostRA() {
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unsigned NumRegs = TRI->getNumRegs();
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unsigned *PhysRegDefs = new unsigned[NumRegs];
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std::fill(PhysRegDefs, PhysRegDefs + NumRegs, 0);
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SmallVector<CandidateInfo, 32> Candidates;
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SmallSet<int, 32> StoredFIs;
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// Walk the entire region, count number of defs for each register, and
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// collect potential LICM candidates.
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const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
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for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
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MachineBasicBlock *BB = Blocks[i];
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// Conservatively treat live-in's as an external def.
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// FIXME: That means a reload that're reused in successor block(s) will not
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for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
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E = BB->livein_end(); I != E; ++I) {
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for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
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for (MachineBasicBlock::iterator
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MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
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MachineInstr *MI = &*MII;
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ProcessMI(MI, PhysRegDefs, StoredFIs, Candidates);
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// Now evaluate whether the potential candidates qualify.
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// 1. Check if the candidate defined register is defined by another
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// instruction in the loop.
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// 2. If the candidate is a load from stack slot (always true for now),
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// check if the slot is stored anywhere in the loop.
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for (unsigned i = 0, e = Candidates.size(); i != e; ++i) {
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if (Candidates[i].FI != INT_MIN &&
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StoredFIs.count(Candidates[i].FI))
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if (PhysRegDefs[Candidates[i].Def] == 1) {
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MachineInstr *MI = Candidates[i].MI;
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for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
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const MachineOperand &MO = MI->getOperand(j);
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if (!MO.isReg() || MO.isDef() || !MO.getReg())
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if (PhysRegDefs[MO.getReg()]) {
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// If it's using a non-loop-invariant register, then it's obviously
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// not safe to hoist.
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HoistPostRA(MI, Candidates[i].Def);
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delete[] PhysRegDefs;
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/// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the current
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/// loop, and make sure it is not killed by any instructions in the loop.
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void MachineLICM::AddToLiveIns(unsigned Reg) {
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const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
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for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
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MachineBasicBlock *BB = Blocks[i];
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if (!BB->isLiveIn(Reg))
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for (MachineBasicBlock::iterator
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MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
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MachineInstr *MI = &*MII;
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (!MO.isReg() || !MO.getReg() || MO.isDef()) continue;
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if (MO.getReg() == Reg || TRI->isSuperRegister(Reg, MO.getReg()))
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/// HoistPostRA - When an instruction is found to only use loop invariant
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/// operands that is safe to hoist, this instruction is called to do the
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void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
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MachineBasicBlock *Preheader = getCurPreheader();
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if (!Preheader) return;
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// Now move the instructions to the predecessor, inserting it before any
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// terminator instructions.
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dbgs() << "Hoisting " << *MI;
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if (Preheader->getBasicBlock())
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dbgs() << " to MachineBasicBlock "
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<< Preheader->getName();
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if (MI->getParent()->getBasicBlock())
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dbgs() << " from MachineBasicBlock "
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<< MI->getParent()->getName();
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// Splice the instruction to the preheader.
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MachineBasicBlock *MBB = MI->getParent();
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Preheader->splice(Preheader->getFirstTerminator(), MBB, MI);
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// Add register to livein list to all the BBs in the current loop since a
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// loop invariant must be kept live throughout the whole loop. This is
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// important to ensure later passes do not scavenge the def register.
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/// HoistRegion - Walk the specified region of the CFG (defined by all blocks
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/// dominated by the specified block, and that are in the current loop) in depth
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/// first order w.r.t the DominatorTree. This allows us to visit definitions
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/// before uses, allowing us to hoist a loop body in one pass without iteration.
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void MachineLICM::HoistRegion(MachineDomTreeNode *N) {
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assert(N != 0 && "Null dominator tree node?");
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MachineBasicBlock *BB = N->getBlock();
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// If this subregion is not in the top level loop at all, exit.
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if (!CurLoop->contains(BB)) return;
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for (MachineBasicBlock::iterator
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MII = BB->begin(), E = BB->end(); MII != E; ) {
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MachineBasicBlock::iterator NextMII = MII; ++NextMII;
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// Don't hoist things out of a large switch statement. This often causes
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// code to be hoisted that wasn't going to be executed, and increases
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// register pressure in a situation where it's likely to matter.
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if (BB->succ_size() < 25) {
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const std::vector<MachineDomTreeNode*> &Children = N->getChildren();
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for (unsigned I = 0, E = Children.size(); I != E; ++I)
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HoistRegion(Children[I]);
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/// IsLICMCandidate - Returns true if the instruction may be a suitable
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/// candidate for LICM. e.g. If the instruction is a call, then it's obviously
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/// not safe to hoist it.
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bool MachineLICM::IsLICMCandidate(MachineInstr &I) {
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// Check if it's safe to move the instruction.
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bool DontMoveAcrossStore = true;
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if (!I.isSafeToMove(TII, AA, DontMoveAcrossStore))
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/// IsLoopInvariantInst - Returns true if the instruction is loop
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/// invariant. I.e., all virtual register operands are defined outside of the
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/// loop, physical registers aren't accessed explicitly, and there are no side
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/// effects that aren't captured by the operands or other flags.
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bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
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if (!IsLICMCandidate(I))
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// The instruction is loop invariant if all of its operands are.
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for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
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const MachineOperand &MO = I.getOperand(i);
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unsigned Reg = MO.getReg();
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if (Reg == 0) continue;
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// Don't hoist an instruction that uses or defines a physical register.
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if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
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// If the physreg has no defs anywhere, it's just an ambient register
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// and we can freely move its uses. Alternatively, if it's allocatable,
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// it could get allocated to something with a def during allocation.
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if (!RegInfo->def_empty(Reg))
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if (AllocatableSet.test(Reg))
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// Check for a def among the register's aliases too.
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for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
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unsigned AliasReg = *Alias;
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if (!RegInfo->def_empty(AliasReg))
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if (AllocatableSet.test(AliasReg))
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// Otherwise it's safe to move.
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} else if (!MO.isDead()) {
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// A def that isn't dead. We can't move it.
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} else if (CurLoop->getHeader()->isLiveIn(Reg)) {
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// If the reg is live into the loop, we can't hoist an instruction
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// which would clobber it.
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assert(RegInfo->getVRegDef(Reg) &&
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"Machine instr not mapped for this vreg?!");
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// If the loop contains the definition of an operand, then the instruction
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// isn't loop invariant.
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if (CurLoop->contains(RegInfo->getVRegDef(Reg)))
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// If we got this far, the instruction is loop invariant!
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/// HasPHIUses - Return true if the specified register has any PHI use.
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static bool HasPHIUses(unsigned Reg, MachineRegisterInfo *RegInfo) {
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for (MachineRegisterInfo::use_iterator UI = RegInfo->use_begin(Reg),
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UE = RegInfo->use_end(); UI != UE; ++UI) {
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MachineInstr *UseMI = &*UI;
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/// isLoadFromConstantMemory - Return true if the given instruction is a
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/// load from constant memory. Machine LICM will hoist these even if they are
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/// not re-materializable.
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bool MachineLICM::isLoadFromConstantMemory(MachineInstr *MI) {
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if (!MI->getDesc().mayLoad()) return false;
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if (!MI->hasOneMemOperand()) return false;
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MachineMemOperand *MMO = *MI->memoperands_begin();
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if (MMO->isVolatile()) return false;
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if (!MMO->getValue()) return false;
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const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(MMO->getValue());
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MachineFunction &MF = *MI->getParent()->getParent();
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return PSV->isConstant(MF.getFrameInfo());
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return AA->pointsToConstantMemory(MMO->getValue());
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/// IsProfitableToHoist - Return true if it is potentially profitable to hoist
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/// the given loop invariant.
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bool MachineLICM::IsProfitableToHoist(MachineInstr &MI) {
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// FIXME: For now, only hoist re-materilizable instructions. LICM will
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// increase register pressure. We want to make sure it doesn't increase
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// Also hoist loads from constant memory, e.g. load from stubs, GOT. Hoisting
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// these tend to help performance in low register pressure situation. The
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// trade off is it may cause spill in high pressure situation. It will end up
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// adding a store in the loop preheader. But the reload is no more expensive.
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// The side benefit is these loads are frequently CSE'ed.
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if (!TII->isTriviallyReMaterializable(&MI, AA)) {
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if (!isLoadFromConstantMemory(&MI))
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// If result(s) of this instruction is used by PHIs, then don't hoist it.
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// The presence of joins makes it difficult for current register allocator
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// implementation to perform remat.
627
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
628
const MachineOperand &MO = MI.getOperand(i);
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if (!MO.isReg() || !MO.isDef())
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if (HasPHIUses(MO.getReg(), RegInfo))
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MachineInstr *MachineLICM::ExtractHoistableLoad(MachineInstr *MI) {
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// If not, we may be able to unfold a load and hoist that.
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// First test whether the instruction is loading from an amenable
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if (!isLoadFromConstantMemory(MI))
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// Next determine the register class for a temporary register.
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unsigned LoadRegIndex;
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TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(),
650
/*UnfoldStore=*/false,
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if (NewOpc == 0) return 0;
653
const TargetInstrDesc &TID = TII->get(NewOpc);
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if (TID.getNumDefs() != 1) return 0;
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const TargetRegisterClass *RC = TID.OpInfo[LoadRegIndex].getRegClass(TRI);
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// Ok, we're unfolding. Create a temporary register and do the unfold.
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unsigned Reg = RegInfo->createVirtualRegister(RC);
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MachineFunction &MF = *MI->getParent()->getParent();
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SmallVector<MachineInstr *, 2> NewMIs;
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TII->unfoldMemoryOperand(MF, MI, Reg,
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/*UnfoldLoad=*/true, /*UnfoldStore=*/false,
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"unfoldMemoryOperand failed when getOpcodeAfterMemoryUnfold "
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assert(NewMIs.size() == 2 &&
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"Unfolded a load into multiple instructions!");
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MachineBasicBlock *MBB = MI->getParent();
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MBB->insert(MI, NewMIs[0]);
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MBB->insert(MI, NewMIs[1]);
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// If unfolding produced a load that wasn't loop-invariant or profitable to
675
// hoist, discard the new instructions and bail.
676
if (!IsLoopInvariantInst(*NewMIs[0]) || !IsProfitableToHoist(*NewMIs[0])) {
677
NewMIs[0]->eraseFromParent();
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NewMIs[1]->eraseFromParent();
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// Otherwise we successfully unfolded a load that we can hoist.
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MI->eraseFromParent();
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void MachineLICM::InitCSEMap(MachineBasicBlock *BB) {
687
for (MachineBasicBlock::iterator I = BB->begin(),E = BB->end(); I != E; ++I) {
688
const MachineInstr *MI = &*I;
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// FIXME: For now, only hoist re-materilizable instructions. LICM will
690
// increase register pressure. We want to make sure it doesn't increase
692
if (TII->isTriviallyReMaterializable(MI, AA)) {
693
unsigned Opcode = MI->getOpcode();
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DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator
695
CI = CSEMap.find(Opcode);
696
if (CI != CSEMap.end())
697
CI->second.push_back(MI);
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std::vector<const MachineInstr*> CSEMIs;
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CSEMIs.push_back(MI);
701
CSEMap.insert(std::make_pair(Opcode, CSEMIs));
708
MachineLICM::LookForDuplicate(const MachineInstr *MI,
709
std::vector<const MachineInstr*> &PrevMIs) {
710
for (unsigned i = 0, e = PrevMIs.size(); i != e; ++i) {
711
const MachineInstr *PrevMI = PrevMIs[i];
712
if (TII->produceSameValue(MI, PrevMI))
718
bool MachineLICM::EliminateCSE(MachineInstr *MI,
719
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator &CI) {
720
// Do not CSE implicit_def so ProcessImplicitDefs can properly propagate
721
// the undef property onto uses.
722
if (CI == CSEMap.end() || MI->isImplicitDef())
725
if (const MachineInstr *Dup = LookForDuplicate(MI, CI->second)) {
726
DEBUG(dbgs() << "CSEing " << *MI << " with " << *Dup);
728
// Replace virtual registers defined by MI by their counterparts defined
730
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
731
const MachineOperand &MO = MI->getOperand(i);
733
// Physical registers may not differ here.
734
assert((!MO.isReg() || MO.getReg() == 0 ||
735
!TargetRegisterInfo::isPhysicalRegister(MO.getReg()) ||
736
MO.getReg() == Dup->getOperand(i).getReg()) &&
737
"Instructions with different phys regs are not identical!");
739
if (MO.isReg() && MO.isDef() &&
740
!TargetRegisterInfo::isPhysicalRegister(MO.getReg())) {
741
RegInfo->replaceRegWith(MO.getReg(), Dup->getOperand(i).getReg());
742
RegInfo->clearKillFlags(Dup->getOperand(i).getReg());
745
MI->eraseFromParent();
752
/// Hoist - When an instruction is found to use only loop invariant operands
753
/// that are safe to hoist, this instruction is called to do the dirty work.
755
void MachineLICM::Hoist(MachineInstr *MI) {
756
MachineBasicBlock *Preheader = getCurPreheader();
757
if (!Preheader) return;
759
// First check whether we should hoist this instruction.
760
if (!IsLoopInvariantInst(*MI) || !IsProfitableToHoist(*MI)) {
761
// If not, try unfolding a hoistable load.
762
MI = ExtractHoistableLoad(MI);
766
// Now move the instructions to the predecessor, inserting it before any
767
// terminator instructions.
769
dbgs() << "Hoisting " << *MI;
770
if (Preheader->getBasicBlock())
771
dbgs() << " to MachineBasicBlock "
772
<< Preheader->getName();
773
if (MI->getParent()->getBasicBlock())
774
dbgs() << " from MachineBasicBlock "
775
<< MI->getParent()->getName();
779
// If this is the first instruction being hoisted to the preheader,
780
// initialize the CSE map with potential common expressions.
782
InitCSEMap(Preheader);
786
// Look for opportunity to CSE the hoisted instruction.
787
unsigned Opcode = MI->getOpcode();
788
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator
789
CI = CSEMap.find(Opcode);
790
if (!EliminateCSE(MI, CI)) {
791
// Otherwise, splice the instruction to the preheader.
792
Preheader->splice(Preheader->getFirstTerminator(),MI->getParent(),MI);
794
// Clear the kill flags of any register this instruction defines,
795
// since they may need to be live throughout the entire loop
796
// rather than just live for part of it.
797
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
798
MachineOperand &MO = MI->getOperand(i);
799
if (MO.isReg() && MO.isDef() && !MO.isDead())
800
RegInfo->clearKillFlags(MO.getReg());
803
// Add to the CSE map.
804
if (CI != CSEMap.end())
805
CI->second.push_back(MI);
807
std::vector<const MachineInstr*> CSEMIs;
808
CSEMIs.push_back(MI);
809
CSEMap.insert(std::make_pair(Opcode, CSEMIs));
817
MachineBasicBlock *MachineLICM::getCurPreheader() {
818
// Determine the block to which to hoist instructions. If we can't find a
819
// suitable loop predecessor, we can't do any hoisting.
821
// If we've tried to get a preheader and failed, don't try again.
822
if (CurPreheader == reinterpret_cast<MachineBasicBlock *>(-1))
826
CurPreheader = CurLoop->getLoopPreheader();
828
MachineBasicBlock *Pred = CurLoop->getLoopPredecessor();
830
CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
834
CurPreheader = Pred->SplitCriticalEdge(CurLoop->getHeader(), this);
836
CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);