StackSlotColoring.cpp revision 26367472a204219b67ba7686f39f91470b6d2c24 
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      AU.addPreservedID(MachineLoopInfoID);
70      AU.addPreservedID(MachineDominatorsID);
71      MachineFunctionPass::getAnalysisUsage(AU);
72    }
73
74    virtual bool runOnMachineFunction(MachineFunction &MF);
75    virtual const char* getPassName() const {
76      return "Stack Slot Coloring";
77    }
78
79  private:
80    bool InitializeSlots();
81    bool OverlapWithAssignments(LiveInterval *li, int Color) const;
82    int ColorSlot(LiveInterval *li);
83    bool ColorSlots(MachineFunction &MF);
84  };
85} // end anonymous namespace
86
87char StackSlotColoring::ID = 0;
88
89static RegisterPass<StackSlotColoring>
90X("stack-slot-coloring", "Stack Slot Coloring");
91
92FunctionPass *llvm::createStackSlotColoringPass() {
93  return new StackSlotColoring();
94}
95
96namespace {
97  // IntervalSorter - Comparison predicate that sort live intervals by
98  // their weight.
99  struct IntervalSorter {
100    bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
101      return LHS->weight > RHS->weight;
102    }
103  };
104}
105
106/// InitializeSlots - Process all spill stack slot liveintervals and add them
107/// to a sorted (by weight) list.
108bool StackSlotColoring::InitializeSlots() {
109  if (LS->getNumIntervals() < 2)
110    return false;
111
112  int LastFI = MFI->getObjectIndexEnd();
113  OrigAlignments.resize(LastFI);
114  OrigSizes.resize(LastFI);
115  AllColors.resize(LastFI);
116  UsedColors.resize(LastFI);
117  Assignments.resize(LastFI);
118
119  // Gather all spill slots into a list.
120  for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
121    LiveInterval &li = i->second;
122    int FI = li.getStackSlotIndex();
123    if (MFI->isDeadObjectIndex(FI))
124      continue;
125    SSIntervals.push_back(&li);
126    OrigAlignments[FI] = MFI->getObjectAlignment(FI);
127    OrigSizes[FI]      = MFI->getObjectSize(FI);
128    AllColors.set(FI);
129  }
130
131  // Sort them by weight.
132  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
133
134  // Get first "color".
135  NextColor = AllColors.find_first();
136  return true;
137}
138
139/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
140/// LiveIntervals that have already been assigned to the specified color.
141bool
142StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
143  const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
144  for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
145    LiveInterval *OtherLI = OtherLIs[i];
146    if (OtherLI->overlaps(*li))
147      return true;
148  }
149  return false;
150}
151
152/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
153///
154int StackSlotColoring::ColorSlot(LiveInterval *li) {
155  int Color = -1;
156  bool Share = false;
157  if (!DisableSharing) {
158    // Check if it's possible to reuse any of the used colors.
159    Color = UsedColors.find_first();
160    while (Color != -1) {
161      if (!OverlapWithAssignments(li, Color)) {
162        Share = true;
163        ++NumEliminated;
164        break;
165      }
166      Color = UsedColors.find_next(Color);
167    }
168  }
169
170  // Assign it to the first available color (assumed to be the best) if it's
171  // not possible to share a used color with other objects.
172  if (!Share) {
173    assert(NextColor != -1 && "No more spill slots?");
174    Color = NextColor;
175    UsedColors.set(Color);
176    NextColor = AllColors.find_next(NextColor);
177  }
178
179  // Record the assignment.
180  Assignments[Color].push_back(li);
181  int FI = li->getStackSlotIndex();
182  DOUT << "Assigning fi#" << FI << " to fi#" << Color << "\n";
183
184  // Change size and alignment of the allocated slot. If there are multiple
185  // objects sharing the same slot, then make sure the size and alignment
186  // are large enough for all.
187  unsigned Align = OrigAlignments[FI];
188  if (!Share || Align > MFI->getObjectAlignment(Color))
189    MFI->setObjectAlignment(Color, Align);
190  int64_t Size = OrigSizes[FI];
191  if (!Share || Size > MFI->getObjectSize(Color))
192    MFI->setObjectSize(Color, Size);
193  return Color;
194}
195
196/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
197/// operands in the function.
198bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
199  unsigned NumObjs = MFI->getObjectIndexEnd();
200  std::vector<int> SlotMapping(NumObjs, -1);
201
202  bool Changed = false;
203  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
204    LiveInterval *li = SSIntervals[i];
205    int SS = li->getStackSlotIndex();
206    int NewSS = ColorSlot(li);
207    SlotMapping[SS] = NewSS;
208    Changed |= (SS != NewSS);
209  }
210
211  if (!Changed)
212    return false;
213
214  // Rewrite all MO_FrameIndex operands.
215  // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
216  for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
217       MBB != E; ++MBB) {
218    for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
219         MII != EE; ++MII) {
220      MachineInstr &MI = *MII;
221      for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
222        MachineOperand &MO = MI.getOperand(i);
223        if (!MO.isFI())
224          continue;
225        int FI = MO.getIndex();
226        if (FI < 0)
227          continue;
228        FI = SlotMapping[FI];
229        if (FI == -1)
230          continue;
231        MO.setIndex(FI);
232      }
233    }
234  }
235
236  // Delete unused stack slots.
237  while (NextColor != -1) {
238    DOUT << "Removing unused stack object fi#" << NextColor << "\n";
239    MFI->RemoveStackObject(NextColor);
240    NextColor = AllColors.find_next(NextColor);
241  }
242
243  return true;
244}
245
246bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
247  DOUT << "********** Stack Slot Coloring **********\n";
248
249  MFI = MF.getFrameInfo();
250  LS = &getAnalysis<LiveStacks>();
251
252  bool Changed = false;
253  if (InitializeSlots())
254    Changed = ColorSlots(MF);
255
256  NextColor = -1;
257  SSIntervals.clear();
258  OrigAlignments.clear();
259  OrigSizes.clear();
260  AllColors.clear();
261  UsedColors.clear();
262  for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
263    Assignments[i].clear();
264  Assignments.clear();
265
266  return Changed;
267}
268