1//===-- RegisterPressure.h - Dynamic Register Pressure -*- C++ -*-------===//
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 defines the RegisterPressure class which can be used to track
11// MachineInstr level register pressure.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_CODEGEN_REGISTERPRESSURE_H
16#define LLVM_CODEGEN_REGISTERPRESSURE_H
17
18#include "llvm/CodeGen/SlotIndexes.h"
19#include "llvm/Target/TargetRegisterInfo.h"
20#include "llvm/ADT/SparseSet.h"
21
22namespace llvm {
23
24class LiveIntervals;
25class RegisterClassInfo;
26class MachineInstr;
27
28/// Base class for register pressure results.
29struct RegisterPressure {
30  /// Map of max reg pressure indexed by pressure set ID, not class ID.
31  std::vector<unsigned> MaxSetPressure;
32
33  /// List of live in registers.
34  SmallVector<unsigned,8> LiveInRegs;
35  SmallVector<unsigned,8> LiveOutRegs;
36
37  /// Increase register pressure for each pressure set impacted by this register
38  /// class. Normally called by RegPressureTracker, but may be called manually
39  /// to account for live through (global liveness).
40  void increase(const TargetRegisterClass *RC, const TargetRegisterInfo *TRI);
41
42  /// Decrease register pressure for each pressure set impacted by this register
43  /// class. This is only useful to account for spilling or rematerialization.
44  void decrease(const TargetRegisterClass *RC, const TargetRegisterInfo *TRI);
45
46  void dump(const TargetRegisterInfo *TRI);
47};
48
49/// RegisterPressure computed within a region of instructions delimited by
50/// TopIdx and BottomIdx.  During pressure computation, the maximum pressure per
51/// register pressure set is increased. Once pressure within a region is fully
52/// computed, the live-in and live-out sets are recorded.
53///
54/// This is preferable to RegionPressure when LiveIntervals are available,
55/// because delimiting regions by SlotIndex is more robust and convenient than
56/// holding block iterators. The block contents can change without invalidating
57/// the pressure result.
58struct IntervalPressure : RegisterPressure {
59  /// Record the boundary of the region being tracked.
60  SlotIndex TopIdx;
61  SlotIndex BottomIdx;
62
63  void reset();
64
65  void openTop(SlotIndex NextTop);
66
67  void openBottom(SlotIndex PrevBottom);
68};
69
70/// RegisterPressure computed within a region of instructions delimited by
71/// TopPos and BottomPos. This is a less precise version of IntervalPressure for
72/// use when LiveIntervals are unavailable.
73struct RegionPressure : RegisterPressure {
74  /// Record the boundary of the region being tracked.
75  MachineBasicBlock::const_iterator TopPos;
76  MachineBasicBlock::const_iterator BottomPos;
77
78  void reset();
79
80  void openTop(MachineBasicBlock::const_iterator PrevTop);
81
82  void openBottom(MachineBasicBlock::const_iterator PrevBottom);
83};
84
85/// An element of pressure difference that identifies the pressure set and
86/// amount of increase or decrease in units of pressure.
87struct PressureElement {
88  unsigned PSetID;
89  int UnitIncrease;
90
91  PressureElement(): PSetID(~0U), UnitIncrease(0) {}
92  PressureElement(unsigned id, int inc): PSetID(id), UnitIncrease(inc) {}
93
94  bool isValid() const { return PSetID != ~0U; }
95};
96
97/// Store the effects of a change in pressure on things that MI scheduler cares
98/// about.
99///
100/// Excess records the value of the largest difference in register units beyond
101/// the target's pressure limits across the affected pressure sets, where
102/// largest is defined as the absolute value of the difference. Negative
103/// ExcessUnits indicates a reduction in pressure that had already exceeded the
104/// target's limits.
105///
106/// CriticalMax records the largest increase in the tracker's max pressure that
107/// exceeds the critical limit for some pressure set determined by the client.
108///
109/// CurrentMax records the largest increase in the tracker's max pressure that
110/// exceeds the current limit for some pressure set determined by the client.
111struct RegPressureDelta {
112  PressureElement Excess;
113  PressureElement CriticalMax;
114  PressureElement CurrentMax;
115
116  RegPressureDelta() {}
117};
118
119/// Track the current register pressure at some position in the instruction
120/// stream, and remember the high water mark within the region traversed. This
121/// does not automatically consider live-through ranges. The client may
122/// independently adjust for global liveness.
123///
124/// Each RegPressureTracker only works within a MachineBasicBlock. Pressure can
125/// be tracked across a larger region by storing a RegisterPressure result at
126/// each block boundary and explicitly adjusting pressure to account for block
127/// live-in and live-out register sets.
128///
129/// RegPressureTracker holds a reference to a RegisterPressure result that it
130/// computes incrementally. During downward tracking, P.BottomIdx or P.BottomPos
131/// is invalid until it reaches the end of the block or closeRegion() is
132/// explicitly called. Similarly, P.TopIdx is invalid during upward
133/// tracking. Changing direction has the side effect of closing region, and
134/// traversing past TopIdx or BottomIdx reopens it.
135class RegPressureTracker {
136  const MachineFunction     *MF;
137  const TargetRegisterInfo  *TRI;
138  const RegisterClassInfo   *RCI;
139  const MachineRegisterInfo *MRI;
140  const LiveIntervals       *LIS;
141
142  /// We currently only allow pressure tracking within a block.
143  const MachineBasicBlock *MBB;
144
145  /// Track the max pressure within the region traversed so far.
146  RegisterPressure &P;
147
148  /// Run in two modes dependending on whether constructed with IntervalPressure
149  /// or RegisterPressure. If requireIntervals is false, LIS are ignored.
150  bool RequireIntervals;
151
152  /// Register pressure corresponds to liveness before this instruction
153  /// iterator. It may point to the end of the block rather than an instruction.
154  MachineBasicBlock::const_iterator CurrPos;
155
156  /// Pressure map indexed by pressure set ID, not class ID.
157  std::vector<unsigned> CurrSetPressure;
158
159  /// List of live registers.
160  SparseSet<unsigned> LivePhysRegs;
161  SparseSet<unsigned, VirtReg2IndexFunctor> LiveVirtRegs;
162
163public:
164  RegPressureTracker(IntervalPressure &rp) :
165    MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(true) {}
166
167  RegPressureTracker(RegionPressure &rp) :
168    MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(false) {}
169
170  void init(const MachineFunction *mf, const RegisterClassInfo *rci,
171            const LiveIntervals *lis, const MachineBasicBlock *mbb,
172            MachineBasicBlock::const_iterator pos);
173
174  /// Force liveness of registers. Particularly useful to initialize the
175  /// livein/out state of the tracker before the first call to advance/recede.
176  void addLiveRegs(ArrayRef<unsigned> Regs);
177
178  /// Get the MI position corresponding to this register pressure.
179  MachineBasicBlock::const_iterator getPos() const { return CurrPos; }
180
181  // Reset the MI position corresponding to the register pressure. This allows
182  // schedulers to move instructions above the RegPressureTracker's
183  // CurrPos. Since the pressure is computed before CurrPos, the iterator
184  // position changes while pressure does not.
185  void setPos(MachineBasicBlock::const_iterator Pos) { CurrPos = Pos; }
186
187  /// Recede across the previous instruction.
188  bool recede();
189
190  /// Advance across the current instruction.
191  bool advance();
192
193  /// Finalize the region boundaries and recored live ins and live outs.
194  void closeRegion();
195
196  /// Get the resulting register pressure over the traversed region.
197  /// This result is complete if either advance() or recede() has returned true,
198  /// or if closeRegion() was explicitly invoked.
199  RegisterPressure &getPressure() { return P; }
200
201  /// Get the register set pressure at the current position, which may be less
202  /// than the pressure across the traversed region.
203  std::vector<unsigned> &getRegSetPressureAtPos() { return CurrSetPressure; }
204
205  void discoverPhysLiveIn(unsigned Reg);
206  void discoverPhysLiveOut(unsigned Reg);
207
208  void discoverVirtLiveIn(unsigned Reg);
209  void discoverVirtLiveOut(unsigned Reg);
210
211  bool isTopClosed() const;
212  bool isBottomClosed() const;
213
214  void closeTop();
215  void closeBottom();
216
217  /// Consider the pressure increase caused by traversing this instruction
218  /// bottom-up. Find the pressure set with the most change beyond its pressure
219  /// limit based on the tracker's current pressure, and record the number of
220  /// excess register units of that pressure set introduced by this instruction.
221  void getMaxUpwardPressureDelta(const MachineInstr *MI,
222                                 RegPressureDelta &Delta,
223                                 ArrayRef<PressureElement> CriticalPSets,
224                                 ArrayRef<unsigned> MaxPressureLimit);
225
226  /// Consider the pressure increase caused by traversing this instruction
227  /// top-down. Find the pressure set with the most change beyond its pressure
228  /// limit based on the tracker's current pressure, and record the number of
229  /// excess register units of that pressure set introduced by this instruction.
230  void getMaxDownwardPressureDelta(const MachineInstr *MI,
231                                   RegPressureDelta &Delta,
232                                   ArrayRef<PressureElement> CriticalPSets,
233                                   ArrayRef<unsigned> MaxPressureLimit);
234
235  /// Find the pressure set with the most change beyond its pressure limit after
236  /// traversing this instruction either upward or downward depending on the
237  /// closed end of the current region.
238  void getMaxPressureDelta(const MachineInstr *MI, RegPressureDelta &Delta,
239                           ArrayRef<PressureElement> CriticalPSets,
240                           ArrayRef<unsigned> MaxPressureLimit) {
241    if (isTopClosed())
242      return getMaxDownwardPressureDelta(MI, Delta, CriticalPSets,
243                                         MaxPressureLimit);
244
245    assert(isBottomClosed() && "Uninitialized pressure tracker");
246    return getMaxUpwardPressureDelta(MI, Delta, CriticalPSets,
247                                     MaxPressureLimit);
248  }
249
250  /// Get the pressure of each PSet after traversing this instruction bottom-up.
251  void getUpwardPressure(const MachineInstr *MI,
252                         std::vector<unsigned> &PressureResult,
253                         std::vector<unsigned> &MaxPressureResult);
254
255  /// Get the pressure of each PSet after traversing this instruction top-down.
256  void getDownwardPressure(const MachineInstr *MI,
257                           std::vector<unsigned> &PressureResult,
258                           std::vector<unsigned> &MaxPressureResult);
259
260  void getPressureAfterInst(const MachineInstr *MI,
261                            std::vector<unsigned> &PressureResult,
262                            std::vector<unsigned> &MaxPressureResult) {
263    if (isTopClosed())
264      return getUpwardPressure(MI, PressureResult, MaxPressureResult);
265
266    assert(isBottomClosed() && "Uninitialized pressure tracker");
267    return getDownwardPressure(MI, PressureResult, MaxPressureResult);
268  }
269
270protected:
271  void increasePhysRegPressure(ArrayRef<unsigned> Regs);
272  void decreasePhysRegPressure(ArrayRef<unsigned> Regs);
273
274  void increaseVirtRegPressure(ArrayRef<unsigned> Regs);
275  void decreaseVirtRegPressure(ArrayRef<unsigned> Regs);
276
277  void bumpUpwardPressure(const MachineInstr *MI);
278  void bumpDownwardPressure(const MachineInstr *MI);
279};
280} // end namespace llvm
281
282#endif
283