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; }
103 // If signed PSetID is negative, it is invalid; convert it to INT_MAX to give
104 // it lowest priority.
105 int PSetRank() const { return PSetID & INT_MAX; }
108 /// Store the effects of a change in pressure on things that MI scheduler cares
111 /// Excess records the value of the largest difference in register units beyond
112 /// the target's pressure limits across the affected pressure sets, where
113 /// largest is defined as the absolute value of the difference. Negative
114 /// ExcessUnits indicates a reduction in pressure that had already exceeded the
117 /// CriticalMax records the largest increase in the tracker's max pressure that
118 /// exceeds the critical limit for some pressure set determined by the client.
120 /// CurrentMax records the largest increase in the tracker's max pressure that
121 /// exceeds the current limit for some pressure set determined by the client.
122 struct RegPressureDelta {
123 PressureElement Excess;
124 PressureElement CriticalMax;
125 PressureElement CurrentMax;
127 RegPressureDelta() {}
130 /// \brief A set of live virtual registers and physical register units.
132 /// Virtual and physical register numbers require separate sparse sets, but most
133 /// of the RegisterPressureTracker handles them uniformly.
135 SparseSet<unsigned> PhysRegs;
136 SparseSet<unsigned, VirtReg2IndexFunctor> VirtRegs;
138 bool contains(unsigned Reg) {
139 if (TargetRegisterInfo::isVirtualRegister(Reg))
140 return VirtRegs.count(Reg);
141 return PhysRegs.count(Reg);
144 bool insert(unsigned Reg) {
145 if (TargetRegisterInfo::isVirtualRegister(Reg))
146 return VirtRegs.insert(Reg).second;
147 return PhysRegs.insert(Reg).second;
150 bool erase(unsigned Reg) {
151 if (TargetRegisterInfo::isVirtualRegister(Reg))
152 return VirtRegs.erase(Reg);
153 return PhysRegs.erase(Reg);
157 /// Track the current register pressure at some position in the instruction
158 /// stream, and remember the high water mark within the region traversed. This
159 /// does not automatically consider live-through ranges. The client may
160 /// independently adjust for global liveness.
162 /// Each RegPressureTracker only works within a MachineBasicBlock. Pressure can
163 /// be tracked across a larger region by storing a RegisterPressure result at
164 /// each block boundary and explicitly adjusting pressure to account for block
165 /// live-in and live-out register sets.
167 /// RegPressureTracker holds a reference to a RegisterPressure result that it
168 /// computes incrementally. During downward tracking, P.BottomIdx or P.BottomPos
169 /// is invalid until it reaches the end of the block or closeRegion() is
170 /// explicitly called. Similarly, P.TopIdx is invalid during upward
171 /// tracking. Changing direction has the side effect of closing region, and
172 /// traversing past TopIdx or BottomIdx reopens it.
173 class RegPressureTracker {
174 const MachineFunction *MF;
175 const TargetRegisterInfo *TRI;
176 const RegisterClassInfo *RCI;
177 const MachineRegisterInfo *MRI;
178 const LiveIntervals *LIS;
180 /// We currently only allow pressure tracking within a block.
181 const MachineBasicBlock *MBB;
183 /// Track the max pressure within the region traversed so far.
186 /// Run in two modes dependending on whether constructed with IntervalPressure
187 /// or RegisterPressure. If requireIntervals is false, LIS are ignored.
188 bool RequireIntervals;
190 /// Register pressure corresponds to liveness before this instruction
191 /// iterator. It may point to the end of the block or a DebugValue rather than
193 MachineBasicBlock::const_iterator CurrPos;
195 /// Pressure map indexed by pressure set ID, not class ID.
196 std::vector<unsigned> CurrSetPressure;
198 /// Set of live registers.
202 RegPressureTracker(IntervalPressure &rp) :
203 MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(true) {}
205 RegPressureTracker(RegionPressure &rp) :
206 MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(false) {}
208 void init(const MachineFunction *mf, const RegisterClassInfo *rci,
209 const LiveIntervals *lis, const MachineBasicBlock *mbb,
210 MachineBasicBlock::const_iterator pos);
212 /// Force liveness of virtual registers or physical register
213 /// units. Particularly useful to initialize the livein/out state of the
214 /// tracker before the first call to advance/recede.
215 void addLiveRegs(ArrayRef<unsigned> Regs);
217 /// Get the MI position corresponding to this register pressure.
218 MachineBasicBlock::const_iterator getPos() const { return CurrPos; }
220 // Reset the MI position corresponding to the register pressure. This allows
221 // schedulers to move instructions above the RegPressureTracker's
222 // CurrPos. Since the pressure is computed before CurrPos, the iterator
223 // position changes while pressure does not.
224 void setPos(MachineBasicBlock::const_iterator Pos) { CurrPos = Pos; }
226 /// \brief Get the SlotIndex for the first nondebug instruction including or
227 /// after the current position.
228 SlotIndex getCurrSlot() const;
230 /// Recede across the previous instruction.
233 /// Advance across the current instruction.
236 /// Finalize the region boundaries and recored live ins and live outs.
239 /// Get the resulting register pressure over the traversed region.
240 /// This result is complete if either advance() or recede() has returned true,
241 /// or if closeRegion() was explicitly invoked.
242 RegisterPressure &getPressure() { return P; }
243 const RegisterPressure &getPressure() const { return P; }
245 /// Get the register set pressure at the current position, which may be less
246 /// than the pressure across the traversed region.
247 std::vector<unsigned> &getRegSetPressureAtPos() { return CurrSetPressure; }
249 void discoverLiveOut(unsigned Reg);
250 void discoverLiveIn(unsigned Reg);
252 bool isTopClosed() const;
253 bool isBottomClosed() const;
258 /// Consider the pressure increase caused by traversing this instruction
259 /// bottom-up. Find the pressure set with the most change beyond its pressure
260 /// limit based on the tracker's current pressure, and record the number of
261 /// excess register units of that pressure set introduced by this instruction.
262 void getMaxUpwardPressureDelta(const MachineInstr *MI,
263 RegPressureDelta &Delta,
264 ArrayRef<PressureElement> CriticalPSets,
265 ArrayRef<unsigned> MaxPressureLimit);
267 /// Consider the pressure increase caused by traversing this instruction
268 /// top-down. Find the pressure set with the most change beyond its pressure
269 /// limit based on the tracker's current pressure, and record the number of
270 /// excess register units of that pressure set introduced by this instruction.
271 void getMaxDownwardPressureDelta(const MachineInstr *MI,
272 RegPressureDelta &Delta,
273 ArrayRef<PressureElement> CriticalPSets,
274 ArrayRef<unsigned> MaxPressureLimit);
276 /// Find the pressure set with the most change beyond its pressure limit after
277 /// traversing this instruction either upward or downward depending on the
278 /// closed end of the current region.
279 void getMaxPressureDelta(const MachineInstr *MI, RegPressureDelta &Delta,
280 ArrayRef<PressureElement> CriticalPSets,
281 ArrayRef<unsigned> MaxPressureLimit) {
283 return getMaxDownwardPressureDelta(MI, Delta, CriticalPSets,
286 assert(isBottomClosed() && "Uninitialized pressure tracker");
287 return getMaxUpwardPressureDelta(MI, Delta, CriticalPSets,
291 /// Get the pressure of each PSet after traversing this instruction bottom-up.
292 void getUpwardPressure(const MachineInstr *MI,
293 std::vector<unsigned> &PressureResult,
294 std::vector<unsigned> &MaxPressureResult);
296 /// Get the pressure of each PSet after traversing this instruction top-down.
297 void getDownwardPressure(const MachineInstr *MI,
298 std::vector<unsigned> &PressureResult,
299 std::vector<unsigned> &MaxPressureResult);
301 void getPressureAfterInst(const MachineInstr *MI,
302 std::vector<unsigned> &PressureResult,
303 std::vector<unsigned> &MaxPressureResult) {
305 return getUpwardPressure(MI, PressureResult, MaxPressureResult);
307 assert(isBottomClosed() && "Uninitialized pressure tracker");
308 return getDownwardPressure(MI, PressureResult, MaxPressureResult);
314 const LiveInterval *getInterval(unsigned Reg) const;
316 void increaseRegPressure(ArrayRef<unsigned> Regs);
317 void decreaseRegPressure(ArrayRef<unsigned> Regs);
319 void bumpUpwardPressure(const MachineInstr *MI);
320 void bumpDownwardPressure(const MachineInstr *MI);
322 } // end namespace llvm