StackSlotColoring.cpp revision ae73dc1448d25b02cabc7c64c86c64371453dda8 
1//===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the stack slot coloring pass.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "stackcoloring"
15#include "llvm/CodeGen/Passes.h"
16#include "llvm/CodeGen/LiveStackAnalysis.h"
17#include "llvm/CodeGen/MachineFrameInfo.h"
18#include "llvm/Support/CommandLine.h"
19#include "llvm/Support/Compiler.h"
20#include "llvm/Support/Debug.h"
21#include "llvm/ADT/BitVector.h"
22#include "llvm/ADT/SmallVector.h"
23#include "llvm/ADT/Statistic.h"
24#include <vector>
25using namespace llvm;
26
27static cl::opt<bool>
28DisableSharing("no-stack-slot-sharing",
29             cl::init(false), cl::Hidden,
30             cl::desc("Surpress slot sharing during stack coloring"));
31
32STATISTIC(NumEliminated,   "Number of stack slots eliminated due to coloring");
33
34namespace {
35  class VISIBILITY_HIDDEN StackSlotColoring : public MachineFunctionPass {
36    LiveStacks* LS;
37    MachineFrameInfo *MFI;
38
39    // SSIntervals - Spill slot intervals.
40    std::vector<LiveInterval*> SSIntervals;
41
42    // OrigAlignments - Alignments of stack objects before coloring.
43    SmallVector<unsigned, 16> OrigAlignments;
44
45    // OrigSizes - Sizess of stack objects before coloring.
46    SmallVector<unsigned, 16> OrigSizes;
47
48    // AllColors - If index is set, it's a spill slot, i.e. color.
49    // FIXME: This assumes PEI locate spill slot with smaller indices
50    // closest to stack pointer / frame pointer. Therefore, smaller
51    // index == better color.
52    BitVector AllColors;
53
54    // NextColor - Next "color" that's not yet used.
55    int NextColor;
56
57    // UsedColors - "Colors" that have been assigned.
58    BitVector UsedColors;
59
60    // Assignments - Color to intervals mapping.
61    SmallVector<SmallVector<LiveInterval*,4>,16> Assignments;
62
63  public:
64    static char ID; // Pass identification
65    StackSlotColoring() : MachineFunctionPass(&ID), NextColor(-1) {}
66
67    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
68      AU.addRequired<LiveStacks>();
69      MachineFunctionPass::getAnalysisUsage(AU);
70    }
71
72    virtual bool runOnMachineFunction(MachineFunction &MF);
73    virtual const char* getPassName() const {
74      return "Stack Slot Coloring";
75    }
76
77  private:
78    bool InitializeSlots();
79    bool OverlapWithAssignments(LiveInterval *li, int Color) const;
80    int ColorSlot(LiveInterval *li);
81    bool ColorSlots(MachineFunction &MF);
82  };
83} // end anonymous namespace
84
85char StackSlotColoring::ID = 0;
86
87static RegisterPass<StackSlotColoring>
88X("stack-slot-coloring", "Stack Slot Coloring");
89
90FunctionPass *llvm::createStackSlotColoringPass() {
91  return new StackSlotColoring();
92}
93
94namespace {
95  // IntervalSorter - Comparison predicate that sort live intervals by
96  // their weight.
97  struct IntervalSorter {
98    bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
99      return LHS->weight > RHS->weight;
100    }
101  };
102}
103
104/// InitializeSlots - Process all spill stack slot liveintervals and add them
105/// to a sorted (by weight) list.
106bool StackSlotColoring::InitializeSlots() {
107  if (LS->getNumIntervals() < 2)
108    return false;
109
110  int LastFI = MFI->getObjectIndexEnd();
111  OrigAlignments.resize(LastFI);
112  OrigSizes.resize(LastFI);
113  AllColors.resize(LastFI);
114  UsedColors.resize(LastFI);
115  Assignments.resize(LastFI);
116
117  // Gather all spill slots into a list.
118  for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
119    LiveInterval &li = i->second;
120    int FI = li.getStackSlotIndex();
121    if (MFI->isDeadObjectIndex(FI))
122      continue;
123    SSIntervals.push_back(&li);
124    OrigAlignments[FI] = MFI->getObjectAlignment(FI);
125    OrigSizes[FI]      = MFI->getObjectSize(FI);
126    AllColors.set(FI);
127  }
128
129  // Sort them by weight.
130  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
131
132  // Get first "color".
133  NextColor = AllColors.find_first();
134  return true;
135}
136
137/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
138/// LiveIntervals that have already been assigned to the specified color.
139bool
140StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
141  const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
142  for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
143    LiveInterval *OtherLI = OtherLIs[i];
144    if (OtherLI->overlaps(*li))
145      return true;
146  }
147  return false;
148}
149
150/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
151///
152int StackSlotColoring::ColorSlot(LiveInterval *li) {
153  int Color = -1;
154  bool Share = false;
155  if (!DisableSharing) {
156    // Check if it's possible to reuse any of the used colors.
157    Color = UsedColors.find_first();
158    while (Color != -1) {
159      if (!OverlapWithAssignments(li, Color)) {
160        Share = true;
161        ++NumEliminated;
162        break;
163      }
164      Color = UsedColors.find_next(Color);
165    }
166  }
167
168  // Assign it to the first available color (assumed to be the best) if it's
169  // not possible to share a used color with other objects.
170  if (!Share) {
171    assert(NextColor != -1 && "No more spill slots?");
172    Color = NextColor;
173    UsedColors.set(Color);
174    NextColor = AllColors.find_next(NextColor);
175  }
176
177  // Record the assignment.
178  Assignments[Color].push_back(li);
179  int FI = li->getStackSlotIndex();
180  DOUT << "Assigning fi #" << FI << " to fi #" << Color << "\n";
181
182  // Change size and alignment of the allocated slot. If there are multiple
183  // objects sharing the same slot, then make sure the size and alignment
184  // are large enough for all.
185  unsigned Align = OrigAlignments[FI];
186  if (!Share || Align > MFI->getObjectAlignment(Color))
187    MFI->setObjectAlignment(Color, Align);
188  int64_t Size = OrigSizes[FI];
189  if (!Share || Size > MFI->getObjectSize(Color))
190    MFI->setObjectSize(Color, Size);
191  return Color;
192}
193
194/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
195/// operands in the function.
196bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
197  unsigned NumObjs = MFI->getObjectIndexEnd();
198  std::vector<int> SlotMapping(NumObjs, -1);
199
200  bool Changed = false;
201  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
202    LiveInterval *li = SSIntervals[i];
203    int SS = li->getStackSlotIndex();
204    int NewSS = ColorSlot(li);
205    SlotMapping[SS] = NewSS;
206    Changed |= (SS != NewSS);
207  }
208
209  if (!Changed)
210    return false;
211
212  // Rewrite all MO_FrameIndex operands.
213  // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
214  for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
215       MBB != E; ++MBB) {
216    for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
217         MII != EE; ++MII) {
218      MachineInstr &MI = *MII;
219      for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
220        MachineOperand &MO = MI.getOperand(i);
221        if (!MO.isFrameIndex())
222          continue;
223        int FI = MO.getIndex();
224        if (FI < 0)
225          continue;
226        FI = SlotMapping[FI];
227        if (FI == -1)
228          continue;
229        MO.setIndex(FI);
230      }
231    }
232  }
233
234  // Delete unused stack slots.
235  while (NextColor != -1) {
236    DOUT << "Removing unused stack object fi #" << NextColor << "\n";
237    MFI->RemoveStackObject(NextColor);
238    NextColor = AllColors.find_next(NextColor);
239  }
240
241  return true;
242}
243
244bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
245  DOUT << "********** Stack Slot Coloring **********\n";
246
247  MFI = MF.getFrameInfo();
248  LS = &getAnalysis<LiveStacks>();
249
250  bool Changed = false;
251  if (InitializeSlots())
252    Changed = ColorSlots(MF);
253
254  NextColor = -1;
255  SSIntervals.clear();
256  OrigAlignments.clear();
257  OrigSizes.clear();
258  AllColors.clear();
259  UsedColors.clear();
260  for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
261    Assignments[i].clear();
262  Assignments.clear();
263
264  return Changed;
265}
266