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This is slightly more interesting than the previous batch of changes. Specifically: 1. We refactor getSpillWeight to take a MachineBlockFrequencyInfo (MBFI) object. This enables us to completely encapsulate the actual manner we use the MachineBlockFrequencyInfo to get our spill weights. This yields cleaner code since one does not need to fetch the actual block frequency before getting the spill weight if all one wants it the spill weight. It also gives us access to entry frequency which we need for our computation. 2. Instead of having getSpillWeight take a MachineBasicBlock (as one might think) to look up the block frequency via the MBFI object, we instead take in a MachineInstr object. The reason for this is that the method is supposed to return the spill weight for an instruction according to the comments around the function. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197296 91177308-0d34-0410-b5e6-96231b3b80d8
463 lines
15 KiB
C++
463 lines
15 KiB
C++
//===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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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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//===----------------------------------------------------------------------===//
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//
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// This file implements the stack slot coloring pass.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "stackslotcoloring"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/ADT/BitVector.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/LiveIntervalAnalysis.h"
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#include "llvm/CodeGen/LiveStackAnalysis.h"
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#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineInstrBuilder.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/IR/Module.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include <vector>
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using namespace llvm;
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static cl::opt<bool>
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DisableSharing("no-stack-slot-sharing",
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cl::init(false), cl::Hidden,
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cl::desc("Suppress slot sharing during stack coloring"));
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static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
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STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
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STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated");
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namespace {
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class StackSlotColoring : public MachineFunctionPass {
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LiveStacks* LS;
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MachineFrameInfo *MFI;
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const TargetInstrInfo *TII;
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const MachineBlockFrequencyInfo *MBFI;
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// SSIntervals - Spill slot intervals.
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std::vector<LiveInterval*> SSIntervals;
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// SSRefs - Keep a list of MachineMemOperands for each spill slot.
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// MachineMemOperands can be shared between instructions, so we need
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// to be careful that renames like [FI0, FI1] -> [FI1, FI2] do not
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// become FI0 -> FI1 -> FI2.
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SmallVector<SmallVector<MachineMemOperand *, 8>, 16> SSRefs;
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// OrigAlignments - Alignments of stack objects before coloring.
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SmallVector<unsigned, 16> OrigAlignments;
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// OrigSizes - Sizess of stack objects before coloring.
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SmallVector<unsigned, 16> OrigSizes;
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// AllColors - If index is set, it's a spill slot, i.e. color.
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// FIXME: This assumes PEI locate spill slot with smaller indices
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// closest to stack pointer / frame pointer. Therefore, smaller
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// index == better color.
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BitVector AllColors;
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// NextColor - Next "color" that's not yet used.
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int NextColor;
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// UsedColors - "Colors" that have been assigned.
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BitVector UsedColors;
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// Assignments - Color to intervals mapping.
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SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
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public:
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static char ID; // Pass identification
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StackSlotColoring() :
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MachineFunctionPass(ID), NextColor(-1) {
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initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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AU.addRequired<SlotIndexes>();
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AU.addPreserved<SlotIndexes>();
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AU.addRequired<LiveStacks>();
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AU.addRequired<MachineBlockFrequencyInfo>();
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AU.addPreserved<MachineBlockFrequencyInfo>();
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AU.addPreservedID(MachineDominatorsID);
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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virtual bool runOnMachineFunction(MachineFunction &MF);
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private:
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void InitializeSlots();
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void ScanForSpillSlotRefs(MachineFunction &MF);
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bool OverlapWithAssignments(LiveInterval *li, int Color) const;
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int ColorSlot(LiveInterval *li);
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bool ColorSlots(MachineFunction &MF);
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void RewriteInstruction(MachineInstr *MI, SmallVectorImpl<int> &SlotMapping,
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MachineFunction &MF);
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bool RemoveDeadStores(MachineBasicBlock* MBB);
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};
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} // end anonymous namespace
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char StackSlotColoring::ID = 0;
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char &llvm::StackSlotColoringID = StackSlotColoring::ID;
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INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
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"Stack Slot Coloring", false, false)
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INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
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INITIALIZE_PASS_DEPENDENCY(LiveStacks)
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INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
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INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
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"Stack Slot Coloring", false, false)
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namespace {
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// IntervalSorter - Comparison predicate that sort live intervals by
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// their weight.
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struct IntervalSorter {
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bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
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return LHS->weight > RHS->weight;
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}
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};
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}
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/// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
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/// references and update spill slot weights.
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void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
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SSRefs.resize(MFI->getObjectIndexEnd());
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// FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
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for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
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MBBI != E; ++MBBI) {
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MachineBasicBlock *MBB = &*MBBI;
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for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
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MII != EE; ++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.isFI())
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continue;
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int FI = MO.getIndex();
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if (FI < 0)
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continue;
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if (!LS->hasInterval(FI))
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continue;
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LiveInterval &li = LS->getInterval(FI);
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if (!MI->isDebugValue())
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li.weight += LiveIntervals::getSpillWeight(false, true, MBFI, MI);
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}
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for (MachineInstr::mmo_iterator MMOI = MI->memoperands_begin(),
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EE = MI->memoperands_end(); MMOI != EE; ++MMOI) {
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MachineMemOperand *MMO = *MMOI;
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if (const Value *V = MMO->getValue()) {
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if (const FixedStackPseudoSourceValue *FSV =
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dyn_cast<FixedStackPseudoSourceValue>(V)) {
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int FI = FSV->getFrameIndex();
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if (FI >= 0)
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SSRefs[FI].push_back(MMO);
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}
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}
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}
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}
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}
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}
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/// InitializeSlots - Process all spill stack slot liveintervals and add them
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/// to a sorted (by weight) list.
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void StackSlotColoring::InitializeSlots() {
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int LastFI = MFI->getObjectIndexEnd();
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OrigAlignments.resize(LastFI);
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OrigSizes.resize(LastFI);
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AllColors.resize(LastFI);
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UsedColors.resize(LastFI);
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Assignments.resize(LastFI);
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// Gather all spill slots into a list.
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DEBUG(dbgs() << "Spill slot intervals:\n");
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for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
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LiveInterval &li = i->second;
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DEBUG(li.dump());
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int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
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if (MFI->isDeadObjectIndex(FI))
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continue;
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SSIntervals.push_back(&li);
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OrigAlignments[FI] = MFI->getObjectAlignment(FI);
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OrigSizes[FI] = MFI->getObjectSize(FI);
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AllColors.set(FI);
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}
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DEBUG(dbgs() << '\n');
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// Sort them by weight.
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std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
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// Get first "color".
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NextColor = AllColors.find_first();
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}
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/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
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/// LiveIntervals that have already been assigned to the specified color.
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bool
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StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
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const SmallVectorImpl<LiveInterval *> &OtherLIs = Assignments[Color];
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for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
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LiveInterval *OtherLI = OtherLIs[i];
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if (OtherLI->overlaps(*li))
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return true;
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}
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return false;
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}
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/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
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///
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int StackSlotColoring::ColorSlot(LiveInterval *li) {
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int Color = -1;
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bool Share = false;
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if (!DisableSharing) {
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// Check if it's possible to reuse any of the used colors.
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Color = UsedColors.find_first();
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while (Color != -1) {
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if (!OverlapWithAssignments(li, Color)) {
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Share = true;
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++NumEliminated;
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break;
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}
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Color = UsedColors.find_next(Color);
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}
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}
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// Assign it to the first available color (assumed to be the best) if it's
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// not possible to share a used color with other objects.
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if (!Share) {
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assert(NextColor != -1 && "No more spill slots?");
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Color = NextColor;
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UsedColors.set(Color);
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NextColor = AllColors.find_next(NextColor);
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}
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// Record the assignment.
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Assignments[Color].push_back(li);
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int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
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DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
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// Change size and alignment of the allocated slot. If there are multiple
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// objects sharing the same slot, then make sure the size and alignment
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// are large enough for all.
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unsigned Align = OrigAlignments[FI];
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if (!Share || Align > MFI->getObjectAlignment(Color))
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MFI->setObjectAlignment(Color, Align);
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int64_t Size = OrigSizes[FI];
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if (!Share || Size > MFI->getObjectSize(Color))
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MFI->setObjectSize(Color, Size);
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return Color;
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}
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/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
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/// operands in the function.
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bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
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unsigned NumObjs = MFI->getObjectIndexEnd();
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SmallVector<int, 16> SlotMapping(NumObjs, -1);
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SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
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SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
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BitVector UsedColors(NumObjs);
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DEBUG(dbgs() << "Color spill slot intervals:\n");
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bool Changed = false;
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for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
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LiveInterval *li = SSIntervals[i];
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int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
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int NewSS = ColorSlot(li);
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assert(NewSS >= 0 && "Stack coloring failed?");
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SlotMapping[SS] = NewSS;
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RevMap[NewSS].push_back(SS);
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SlotWeights[NewSS] += li->weight;
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UsedColors.set(NewSS);
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Changed |= (SS != NewSS);
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}
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DEBUG(dbgs() << "\nSpill slots after coloring:\n");
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for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
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LiveInterval *li = SSIntervals[i];
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int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
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li->weight = SlotWeights[SS];
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}
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// Sort them by new weight.
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std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
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#ifndef NDEBUG
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for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
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DEBUG(SSIntervals[i]->dump());
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DEBUG(dbgs() << '\n');
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#endif
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if (!Changed)
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return false;
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// Rewrite all MachineMemOperands.
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for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
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int NewFI = SlotMapping[SS];
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if (NewFI == -1 || (NewFI == (int)SS))
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continue;
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const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
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SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS];
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for (unsigned i = 0, e = RefMMOs.size(); i != e; ++i)
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RefMMOs[i]->setValue(NewSV);
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}
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// Rewrite all MO_FrameIndex operands. Look for dead stores.
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for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
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MBBI != E; ++MBBI) {
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MachineBasicBlock *MBB = &*MBBI;
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for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
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MII != EE; ++MII)
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RewriteInstruction(MII, SlotMapping, MF);
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RemoveDeadStores(MBB);
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}
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// Delete unused stack slots.
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while (NextColor != -1) {
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DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
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MFI->RemoveStackObject(NextColor);
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NextColor = AllColors.find_next(NextColor);
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}
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return true;
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}
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/// RewriteInstruction - Rewrite specified instruction by replacing references
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/// to old frame index with new one.
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void StackSlotColoring::RewriteInstruction(MachineInstr *MI,
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SmallVectorImpl<int> &SlotMapping,
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MachineFunction &MF) {
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// Update the operands.
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for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (!MO.isFI())
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continue;
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int OldFI = MO.getIndex();
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if (OldFI < 0)
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continue;
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int NewFI = SlotMapping[OldFI];
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if (NewFI == -1 || NewFI == OldFI)
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continue;
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MO.setIndex(NewFI);
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}
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// The MachineMemOperands have already been updated.
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}
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/// RemoveDeadStores - Scan through a basic block and look for loads followed
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/// by stores. If they're both using the same stack slot, then the store is
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/// definitely dead. This could obviously be much more aggressive (consider
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/// pairs with instructions between them), but such extensions might have a
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/// considerable compile time impact.
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bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
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// FIXME: This could be much more aggressive, but we need to investigate
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// the compile time impact of doing so.
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bool changed = false;
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SmallVector<MachineInstr*, 4> toErase;
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for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
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I != E; ++I) {
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if (DCELimit != -1 && (int)NumDead >= DCELimit)
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break;
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int FirstSS, SecondSS;
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if (TII->isStackSlotCopy(I, FirstSS, SecondSS) &&
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FirstSS == SecondSS &&
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FirstSS != -1) {
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++NumDead;
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changed = true;
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toErase.push_back(I);
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continue;
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}
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MachineBasicBlock::iterator NextMI = llvm::next(I);
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if (NextMI == MBB->end()) continue;
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unsigned LoadReg = 0;
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unsigned StoreReg = 0;
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if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
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if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
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if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
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++NumDead;
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changed = true;
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if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
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++NumDead;
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toErase.push_back(I);
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}
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toErase.push_back(NextMI);
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++I;
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}
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for (SmallVectorImpl<MachineInstr *>::iterator I = toErase.begin(),
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E = toErase.end(); I != E; ++I)
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(*I)->eraseFromParent();
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return changed;
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}
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bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
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DEBUG({
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dbgs() << "********** Stack Slot Coloring **********\n"
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<< "********** Function: " << MF.getName() << '\n';
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});
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MFI = MF.getFrameInfo();
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TII = MF.getTarget().getInstrInfo();
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LS = &getAnalysis<LiveStacks>();
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MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
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bool Changed = false;
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unsigned NumSlots = LS->getNumIntervals();
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if (NumSlots == 0)
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// Nothing to do!
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return false;
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// If there are calls to setjmp or sigsetjmp, don't perform stack slot
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// coloring. The stack could be modified before the longjmp is executed,
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// resulting in the wrong value being used afterwards. (See
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// <rdar://problem/8007500>.)
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if (MF.exposesReturnsTwice())
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return false;
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// Gather spill slot references
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ScanForSpillSlotRefs(MF);
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InitializeSlots();
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Changed = ColorSlots(MF);
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NextColor = -1;
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SSIntervals.clear();
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for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
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SSRefs[i].clear();
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SSRefs.clear();
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OrigAlignments.clear();
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OrigSizes.clear();
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AllColors.clear();
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UsedColors.clear();
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for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
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Assignments[i].clear();
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Assignments.clear();
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return Changed;
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}
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