1 //===------------------------ CalcSpillWeights.cpp ------------------------===//
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 #define DEBUG_TYPE "calcspillweights"
11
12 #include "llvm/Function.h"
13 #include "llvm/ADT/SmallSet.h"
14 #include "llvm/CodeGen/CalcSpillWeights.h"
15 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
16 #include "llvm/CodeGen/MachineFunction.h"
17 #include "llvm/CodeGen/MachineLoopInfo.h"
18 #include "llvm/CodeGen/MachineRegisterInfo.h"
19 #include "llvm/CodeGen/SlotIndexes.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Support/raw_ostream.h"
22 #include "llvm/Target/TargetInstrInfo.h"
23 #include "llvm/Target/TargetMachine.h"
24 #include "llvm/Target/TargetRegisterInfo.h"
25 using namespace llvm;
26
27 char CalculateSpillWeights::ID = 0;
28 INITIALIZE_PASS_BEGIN(CalculateSpillWeights, "calcspillweights",
29 "Calculate spill weights", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)30 INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
31 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
32 INITIALIZE_PASS_END(CalculateSpillWeights, "calcspillweights",
33 "Calculate spill weights", false, false)
34
35 void CalculateSpillWeights::getAnalysisUsage(AnalysisUsage &au) const {
36 au.addRequired<LiveIntervals>();
37 au.addRequired<MachineLoopInfo>();
38 au.setPreservesAll();
39 MachineFunctionPass::getAnalysisUsage(au);
40 }
41
runOnMachineFunction(MachineFunction & fn)42 bool CalculateSpillWeights::runOnMachineFunction(MachineFunction &fn) {
43
44 DEBUG(dbgs() << "********** Compute Spill Weights **********\n"
45 << "********** Function: "
46 << fn.getFunction()->getName() << '\n');
47
48 LiveIntervals &lis = getAnalysis<LiveIntervals>();
49 VirtRegAuxInfo vrai(fn, lis, getAnalysis<MachineLoopInfo>());
50 for (LiveIntervals::iterator I = lis.begin(), E = lis.end(); I != E; ++I) {
51 LiveInterval &li = *I->second;
52 if (TargetRegisterInfo::isVirtualRegister(li.reg))
53 vrai.CalculateWeightAndHint(li);
54 }
55 return false;
56 }
57
58 // Return the preferred allocation register for reg, given a COPY instruction.
copyHint(const MachineInstr * mi,unsigned reg,const TargetRegisterInfo & tri,const MachineRegisterInfo & mri)59 static unsigned copyHint(const MachineInstr *mi, unsigned reg,
60 const TargetRegisterInfo &tri,
61 const MachineRegisterInfo &mri) {
62 unsigned sub, hreg, hsub;
63 if (mi->getOperand(0).getReg() == reg) {
64 sub = mi->getOperand(0).getSubReg();
65 hreg = mi->getOperand(1).getReg();
66 hsub = mi->getOperand(1).getSubReg();
67 } else {
68 sub = mi->getOperand(1).getSubReg();
69 hreg = mi->getOperand(0).getReg();
70 hsub = mi->getOperand(0).getSubReg();
71 }
72
73 if (!hreg)
74 return 0;
75
76 if (TargetRegisterInfo::isVirtualRegister(hreg))
77 return sub == hsub ? hreg : 0;
78
79 const TargetRegisterClass *rc = mri.getRegClass(reg);
80
81 // Only allow physreg hints in rc.
82 if (sub == 0)
83 return rc->contains(hreg) ? hreg : 0;
84
85 // reg:sub should match the physreg hreg.
86 return tri.getMatchingSuperReg(hreg, sub, rc);
87 }
88
CalculateWeightAndHint(LiveInterval & li)89 void VirtRegAuxInfo::CalculateWeightAndHint(LiveInterval &li) {
90 MachineRegisterInfo &mri = MF.getRegInfo();
91 const TargetRegisterInfo &tri = *MF.getTarget().getRegisterInfo();
92 MachineBasicBlock *mbb = 0;
93 MachineLoop *loop = 0;
94 unsigned loopDepth = 0;
95 bool isExiting = false;
96 float totalWeight = 0;
97 SmallPtrSet<MachineInstr*, 8> visited;
98
99 // Find the best physreg hist and the best virtreg hint.
100 float bestPhys = 0, bestVirt = 0;
101 unsigned hintPhys = 0, hintVirt = 0;
102
103 // Don't recompute a target specific hint.
104 bool noHint = mri.getRegAllocationHint(li.reg).first != 0;
105
106 // Don't recompute spill weight for an unspillable register.
107 bool Spillable = li.isSpillable();
108
109 for (MachineRegisterInfo::reg_iterator I = mri.reg_begin(li.reg);
110 MachineInstr *mi = I.skipInstruction();) {
111 if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugValue())
112 continue;
113 if (!visited.insert(mi))
114 continue;
115
116 float weight = 1.0f;
117 if (Spillable) {
118 // Get loop info for mi.
119 if (mi->getParent() != mbb) {
120 mbb = mi->getParent();
121 loop = Loops.getLoopFor(mbb);
122 loopDepth = loop ? loop->getLoopDepth() : 0;
123 isExiting = loop ? loop->isLoopExiting(mbb) : false;
124 }
125
126 // Calculate instr weight.
127 bool reads, writes;
128 tie(reads, writes) = mi->readsWritesVirtualRegister(li.reg);
129 weight = LiveIntervals::getSpillWeight(writes, reads, loopDepth);
130
131 // Give extra weight to what looks like a loop induction variable update.
132 if (writes && isExiting && LIS.isLiveOutOfMBB(li, mbb))
133 weight *= 3;
134
135 totalWeight += weight;
136 }
137
138 // Get allocation hints from copies.
139 if (noHint || !mi->isCopy())
140 continue;
141 unsigned hint = copyHint(mi, li.reg, tri, mri);
142 if (!hint)
143 continue;
144 float hweight = Hint[hint] += weight;
145 if (TargetRegisterInfo::isPhysicalRegister(hint)) {
146 if (hweight > bestPhys && LIS.isAllocatable(hint))
147 bestPhys = hweight, hintPhys = hint;
148 } else {
149 if (hweight > bestVirt)
150 bestVirt = hweight, hintVirt = hint;
151 }
152 }
153
154 Hint.clear();
155
156 // Always prefer the physreg hint.
157 if (unsigned hint = hintPhys ? hintPhys : hintVirt) {
158 mri.setRegAllocationHint(li.reg, 0, hint);
159 // Weakly boost the spill weight of hinted registers.
160 totalWeight *= 1.01F;
161 }
162
163 // If the live interval was already unspillable, leave it that way.
164 if (!Spillable)
165 return;
166
167 // Mark li as unspillable if all live ranges are tiny.
168 if (li.isZeroLength(LIS.getSlotIndexes())) {
169 li.markNotSpillable();
170 return;
171 }
172
173 // If all of the definitions of the interval are re-materializable,
174 // it is a preferred candidate for spilling. If none of the defs are
175 // loads, then it's potentially very cheap to re-materialize.
176 // FIXME: this gets much more complicated once we support non-trivial
177 // re-materialization.
178 bool isLoad = false;
179 if (LIS.isReMaterializable(li, 0, isLoad)) {
180 if (isLoad)
181 totalWeight *= 0.9F;
182 else
183 totalWeight *= 0.5F;
184 }
185
186 li.weight = normalizeSpillWeight(totalWeight, li.getSize());
187 }
188