1 //===-- RegisterPressure.h - Dynamic Register Pressure -*- C++ -*-------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the RegisterPressure class which can be used to track
11 // MachineInstr level register pressure.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_CODEGEN_REGISTERPRESSURE_H
16 #define LLVM_CODEGEN_REGISTERPRESSURE_H
18 #include "llvm/ADT/SparseSet.h"
19 #include "llvm/CodeGen/SlotIndexes.h"
20 #include "llvm/Target/TargetRegisterInfo.h"
26 class RegisterClassInfo;
29 /// Base class for register pressure results.
30 struct RegisterPressure {
31 /// Map of max reg pressure indexed by pressure set ID, not class ID.
32 std::vector<unsigned> MaxSetPressure;
34 /// List of live in virtual registers or physical register units.
35 SmallVector<unsigned,8> LiveInRegs;
36 SmallVector<unsigned,8> LiveOutRegs;
38 /// Increase register pressure for each pressure set impacted by this register
39 /// class. Normally called by RegPressureTracker, but may be called manually
40 /// to account for live through (global liveness).
42 /// \param Reg is either a virtual register number or register unit number.
43 void increase(unsigned Reg, const TargetRegisterInfo *TRI,
44 const MachineRegisterInfo *MRI);
46 /// Decrease register pressure for each pressure set impacted by this register
47 /// class. This is only useful to account for spilling or rematerialization.
49 /// \param Reg is either a virtual register number or register unit number.
50 void decrease(unsigned Reg, const TargetRegisterInfo *TRI,
51 const MachineRegisterInfo *MRI);
53 void dump(const TargetRegisterInfo *TRI) const;
56 /// RegisterPressure computed within a region of instructions delimited by
57 /// TopIdx and BottomIdx. During pressure computation, the maximum pressure per
58 /// register pressure set is increased. Once pressure within a region is fully
59 /// computed, the live-in and live-out sets are recorded.
61 /// This is preferable to RegionPressure when LiveIntervals are available,
62 /// because delimiting regions by SlotIndex is more robust and convenient than
63 /// holding block iterators. The block contents can change without invalidating
64 /// the pressure result.
65 struct IntervalPressure : RegisterPressure {
66 /// Record the boundary of the region being tracked.
72 void openTop(SlotIndex NextTop);
74 void openBottom(SlotIndex PrevBottom);
77 /// RegisterPressure computed within a region of instructions delimited by
78 /// TopPos and BottomPos. This is a less precise version of IntervalPressure for
79 /// use when LiveIntervals are unavailable.
80 struct RegionPressure : RegisterPressure {
81 /// Record the boundary of the region being tracked.
82 MachineBasicBlock::const_iterator TopPos;
83 MachineBasicBlock::const_iterator BottomPos;
87 void openTop(MachineBasicBlock::const_iterator PrevTop);
89 void openBottom(MachineBasicBlock::const_iterator PrevBottom);
92 /// An element of pressure difference that identifies the pressure set and
93 /// amount of increase or decrease in units of pressure.
94 struct PressureElement {
98 PressureElement(): PSetID(~0U), UnitIncrease(0) {}
99 PressureElement(unsigned id, int inc): PSetID(id), UnitIncrease(inc) {}
101 bool isValid() const { return PSetID != ~0U; }
104 /// Store the effects of a change in pressure on things that MI scheduler cares
107 /// Excess records the value of the largest difference in register units beyond
108 /// the target's pressure limits across the affected pressure sets, where
109 /// largest is defined as the absolute value of the difference. Negative
110 /// ExcessUnits indicates a reduction in pressure that had already exceeded the
113 /// CriticalMax records the largest increase in the tracker's max pressure that
114 /// exceeds the critical limit for some pressure set determined by the client.
116 /// CurrentMax records the largest increase in the tracker's max pressure that
117 /// exceeds the current limit for some pressure set determined by the client.
118 struct RegPressureDelta {
119 PressureElement Excess;
120 PressureElement CriticalMax;
121 PressureElement CurrentMax;
123 RegPressureDelta() {}
126 /// \brief A set of live virtual registers and physical register units.
128 /// Virtual and physical register numbers require separate sparse sets, but most
129 /// of the RegisterPressureTracker handles them uniformly.
131 SparseSet<unsigned> PhysRegs;
132 SparseSet<unsigned, VirtReg2IndexFunctor> VirtRegs;
134 bool contains(unsigned Reg) {
135 if (TargetRegisterInfo::isVirtualRegister(Reg))
136 return VirtRegs.count(Reg);
137 return PhysRegs.count(Reg);
140 bool insert(unsigned Reg) {
141 if (TargetRegisterInfo::isVirtualRegister(Reg))
142 return VirtRegs.insert(Reg).second;
143 return PhysRegs.insert(Reg).second;
146 bool erase(unsigned Reg) {
147 if (TargetRegisterInfo::isVirtualRegister(Reg))
148 return VirtRegs.erase(Reg);
149 return PhysRegs.erase(Reg);
153 /// Track the current register pressure at some position in the instruction
154 /// stream, and remember the high water mark within the region traversed. This
155 /// does not automatically consider live-through ranges. The client may
156 /// independently adjust for global liveness.
158 /// Each RegPressureTracker only works within a MachineBasicBlock. Pressure can
159 /// be tracked across a larger region by storing a RegisterPressure result at
160 /// each block boundary and explicitly adjusting pressure to account for block
161 /// live-in and live-out register sets.
163 /// RegPressureTracker holds a reference to a RegisterPressure result that it
164 /// computes incrementally. During downward tracking, P.BottomIdx or P.BottomPos
165 /// is invalid until it reaches the end of the block or closeRegion() is
166 /// explicitly called. Similarly, P.TopIdx is invalid during upward
167 /// tracking. Changing direction has the side effect of closing region, and
168 /// traversing past TopIdx or BottomIdx reopens it.
169 class RegPressureTracker {
170 const MachineFunction *MF;
171 const TargetRegisterInfo *TRI;
172 const RegisterClassInfo *RCI;
173 const MachineRegisterInfo *MRI;
174 const LiveIntervals *LIS;
176 /// We currently only allow pressure tracking within a block.
177 const MachineBasicBlock *MBB;
179 /// Track the max pressure within the region traversed so far.
182 /// Run in two modes dependending on whether constructed with IntervalPressure
183 /// or RegisterPressure. If requireIntervals is false, LIS are ignored.
184 bool RequireIntervals;
186 /// Register pressure corresponds to liveness before this instruction
187 /// iterator. It may point to the end of the block or a DebugValue rather than
189 MachineBasicBlock::const_iterator CurrPos;
191 /// Pressure map indexed by pressure set ID, not class ID.
192 std::vector<unsigned> CurrSetPressure;
194 /// Set of live registers.
198 RegPressureTracker(IntervalPressure &rp) :
199 MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(true) {}
201 RegPressureTracker(RegionPressure &rp) :
202 MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(false) {}
204 void init(const MachineFunction *mf, const RegisterClassInfo *rci,
205 const LiveIntervals *lis, const MachineBasicBlock *mbb,
206 MachineBasicBlock::const_iterator pos);
208 /// Force liveness of virtual registers or physical register
209 /// units. Particularly useful to initialize the livein/out state of the
210 /// tracker before the first call to advance/recede.
211 void addLiveRegs(ArrayRef<unsigned> Regs);
213 /// Get the MI position corresponding to this register pressure.
214 MachineBasicBlock::const_iterator getPos() const { return CurrPos; }
216 // Reset the MI position corresponding to the register pressure. This allows
217 // schedulers to move instructions above the RegPressureTracker's
218 // CurrPos. Since the pressure is computed before CurrPos, the iterator
219 // position changes while pressure does not.
220 void setPos(MachineBasicBlock::const_iterator Pos) { CurrPos = Pos; }
222 /// \brief Get the SlotIndex for the first nondebug instruction including or
223 /// after the current position.
224 SlotIndex getCurrSlot() const;
226 /// Recede across the previous instruction.
229 /// Advance across the current instruction.
232 /// Finalize the region boundaries and recored live ins and live outs.
235 /// Get the resulting register pressure over the traversed region.
236 /// This result is complete if either advance() or recede() has returned true,
237 /// or if closeRegion() was explicitly invoked.
238 RegisterPressure &getPressure() { return P; }
239 const RegisterPressure &getPressure() const { return P; }
241 /// Get the register set pressure at the current position, which may be less
242 /// than the pressure across the traversed region.
243 std::vector<unsigned> &getRegSetPressureAtPos() { return CurrSetPressure; }
245 void discoverLiveOut(unsigned Reg);
246 void discoverLiveIn(unsigned Reg);
248 bool isTopClosed() const;
249 bool isBottomClosed() const;
254 /// Consider the pressure increase caused by traversing this instruction
255 /// bottom-up. Find the pressure set with the most change beyond its pressure
256 /// limit based on the tracker's current pressure, and record the number of
257 /// excess register units of that pressure set introduced by this instruction.
258 void getMaxUpwardPressureDelta(const MachineInstr *MI,
259 RegPressureDelta &Delta,
260 ArrayRef<PressureElement> CriticalPSets,
261 ArrayRef<unsigned> MaxPressureLimit);
263 /// Consider the pressure increase caused by traversing this instruction
264 /// top-down. Find the pressure set with the most change beyond its pressure
265 /// limit based on the tracker's current pressure, and record the number of
266 /// excess register units of that pressure set introduced by this instruction.
267 void getMaxDownwardPressureDelta(const MachineInstr *MI,
268 RegPressureDelta &Delta,
269 ArrayRef<PressureElement> CriticalPSets,
270 ArrayRef<unsigned> MaxPressureLimit);
272 /// Find the pressure set with the most change beyond its pressure limit after
273 /// traversing this instruction either upward or downward depending on the
274 /// closed end of the current region.
275 void getMaxPressureDelta(const MachineInstr *MI, RegPressureDelta &Delta,
276 ArrayRef<PressureElement> CriticalPSets,
277 ArrayRef<unsigned> MaxPressureLimit) {
279 return getMaxDownwardPressureDelta(MI, Delta, CriticalPSets,
282 assert(isBottomClosed() && "Uninitialized pressure tracker");
283 return getMaxUpwardPressureDelta(MI, Delta, CriticalPSets,
287 /// Get the pressure of each PSet after traversing this instruction bottom-up.
288 void getUpwardPressure(const MachineInstr *MI,
289 std::vector<unsigned> &PressureResult,
290 std::vector<unsigned> &MaxPressureResult);
292 /// Get the pressure of each PSet after traversing this instruction top-down.
293 void getDownwardPressure(const MachineInstr *MI,
294 std::vector<unsigned> &PressureResult,
295 std::vector<unsigned> &MaxPressureResult);
297 void getPressureAfterInst(const MachineInstr *MI,
298 std::vector<unsigned> &PressureResult,
299 std::vector<unsigned> &MaxPressureResult) {
301 return getUpwardPressure(MI, PressureResult, MaxPressureResult);
303 assert(isBottomClosed() && "Uninitialized pressure tracker");
304 return getDownwardPressure(MI, PressureResult, MaxPressureResult);
310 const LiveInterval *getInterval(unsigned Reg) const;
312 void increaseRegPressure(ArrayRef<unsigned> Regs);
313 void decreaseRegPressure(ArrayRef<unsigned> Regs);
315 void bumpUpwardPressure(const MachineInstr *MI);
316 void bumpDownwardPressure(const MachineInstr *MI);
318 } // end namespace llvm