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223e47cc LB |
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 | ||
223e47cc LB |
10 | #include "llvm/CodeGen/CalcSpillWeights.h" |
11 | #include "llvm/CodeGen/LiveIntervalAnalysis.h" | |
1a4d82fc | 12 | #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" |
223e47cc LB |
13 | #include "llvm/CodeGen/MachineFunction.h" |
14 | #include "llvm/CodeGen/MachineLoopInfo.h" | |
15 | #include "llvm/CodeGen/MachineRegisterInfo.h" | |
223e47cc LB |
16 | #include "llvm/Support/Debug.h" |
17 | #include "llvm/Support/raw_ostream.h" | |
18 | #include "llvm/Target/TargetInstrInfo.h" | |
223e47cc | 19 | #include "llvm/Target/TargetRegisterInfo.h" |
1a4d82fc | 20 | #include "llvm/Target/TargetSubtargetInfo.h" |
223e47cc LB |
21 | using namespace llvm; |
22 | ||
1a4d82fc | 23 | #define DEBUG_TYPE "calcspillweights" |
223e47cc | 24 | |
1a4d82fc JJ |
25 | void llvm::calculateSpillWeightsAndHints(LiveIntervals &LIS, |
26 | MachineFunction &MF, | |
27 | const MachineLoopInfo &MLI, | |
28 | const MachineBlockFrequencyInfo &MBFI, | |
29 | VirtRegAuxInfo::NormalizingFn norm) { | |
223e47cc LB |
30 | DEBUG(dbgs() << "********** Compute Spill Weights **********\n" |
31 | << "********** Function: " << MF.getName() << '\n'); | |
32 | ||
223e47cc | 33 | MachineRegisterInfo &MRI = MF.getRegInfo(); |
1a4d82fc | 34 | VirtRegAuxInfo VRAI(MF, LIS, MLI, MBFI, norm); |
223e47cc LB |
35 | for (unsigned i = 0, e = MRI.getNumVirtRegs(); i != e; ++i) { |
36 | unsigned Reg = TargetRegisterInfo::index2VirtReg(i); | |
37 | if (MRI.reg_nodbg_empty(Reg)) | |
38 | continue; | |
1a4d82fc | 39 | VRAI.calculateSpillWeightAndHint(LIS.getInterval(Reg)); |
223e47cc | 40 | } |
223e47cc LB |
41 | } |
42 | ||
43 | // Return the preferred allocation register for reg, given a COPY instruction. | |
44 | static unsigned copyHint(const MachineInstr *mi, unsigned reg, | |
45 | const TargetRegisterInfo &tri, | |
46 | const MachineRegisterInfo &mri) { | |
47 | unsigned sub, hreg, hsub; | |
48 | if (mi->getOperand(0).getReg() == reg) { | |
49 | sub = mi->getOperand(0).getSubReg(); | |
50 | hreg = mi->getOperand(1).getReg(); | |
51 | hsub = mi->getOperand(1).getSubReg(); | |
52 | } else { | |
53 | sub = mi->getOperand(1).getSubReg(); | |
54 | hreg = mi->getOperand(0).getReg(); | |
55 | hsub = mi->getOperand(0).getSubReg(); | |
56 | } | |
57 | ||
58 | if (!hreg) | |
59 | return 0; | |
60 | ||
61 | if (TargetRegisterInfo::isVirtualRegister(hreg)) | |
62 | return sub == hsub ? hreg : 0; | |
63 | ||
64 | const TargetRegisterClass *rc = mri.getRegClass(reg); | |
65 | ||
66 | // Only allow physreg hints in rc. | |
67 | if (sub == 0) | |
68 | return rc->contains(hreg) ? hreg : 0; | |
69 | ||
70 | // reg:sub should match the physreg hreg. | |
71 | return tri.getMatchingSuperReg(hreg, sub, rc); | |
72 | } | |
73 | ||
74 | // Check if all values in LI are rematerializable | |
75 | static bool isRematerializable(const LiveInterval &LI, | |
76 | const LiveIntervals &LIS, | |
77 | const TargetInstrInfo &TII) { | |
78 | for (LiveInterval::const_vni_iterator I = LI.vni_begin(), E = LI.vni_end(); | |
79 | I != E; ++I) { | |
80 | const VNInfo *VNI = *I; | |
81 | if (VNI->isUnused()) | |
82 | continue; | |
83 | if (VNI->isPHIDef()) | |
84 | return false; | |
85 | ||
86 | MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def); | |
87 | assert(MI && "Dead valno in interval"); | |
88 | ||
89 | if (!TII.isTriviallyReMaterializable(MI, LIS.getAliasAnalysis())) | |
90 | return false; | |
91 | } | |
92 | return true; | |
93 | } | |
94 | ||
1a4d82fc JJ |
95 | void |
96 | VirtRegAuxInfo::calculateSpillWeightAndHint(LiveInterval &li) { | |
223e47cc | 97 | MachineRegisterInfo &mri = MF.getRegInfo(); |
1a4d82fc JJ |
98 | const TargetRegisterInfo &tri = *MF.getSubtarget().getRegisterInfo(); |
99 | MachineBasicBlock *mbb = nullptr; | |
100 | MachineLoop *loop = nullptr; | |
223e47cc LB |
101 | bool isExiting = false; |
102 | float totalWeight = 0; | |
85aaf69f | 103 | unsigned numInstr = 0; // Number of instructions using li |
223e47cc LB |
104 | SmallPtrSet<MachineInstr*, 8> visited; |
105 | ||
1a4d82fc | 106 | // Find the best physreg hint and the best virtreg hint. |
223e47cc LB |
107 | float bestPhys = 0, bestVirt = 0; |
108 | unsigned hintPhys = 0, hintVirt = 0; | |
109 | ||
110 | // Don't recompute a target specific hint. | |
111 | bool noHint = mri.getRegAllocationHint(li.reg).first != 0; | |
112 | ||
113 | // Don't recompute spill weight for an unspillable register. | |
114 | bool Spillable = li.isSpillable(); | |
115 | ||
1a4d82fc JJ |
116 | for (MachineRegisterInfo::reg_instr_iterator |
117 | I = mri.reg_instr_begin(li.reg), E = mri.reg_instr_end(); | |
118 | I != E; ) { | |
119 | MachineInstr *mi = &*(I++); | |
85aaf69f | 120 | numInstr++; |
970d7e83 | 121 | if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugValue()) |
223e47cc | 122 | continue; |
85aaf69f | 123 | if (!visited.insert(mi).second) |
223e47cc LB |
124 | continue; |
125 | ||
126 | float weight = 1.0f; | |
127 | if (Spillable) { | |
128 | // Get loop info for mi. | |
129 | if (mi->getParent() != mbb) { | |
130 | mbb = mi->getParent(); | |
131 | loop = Loops.getLoopFor(mbb); | |
223e47cc LB |
132 | isExiting = loop ? loop->isLoopExiting(mbb) : false; |
133 | } | |
134 | ||
135 | // Calculate instr weight. | |
136 | bool reads, writes; | |
1a4d82fc JJ |
137 | std::tie(reads, writes) = mi->readsWritesVirtualRegister(li.reg); |
138 | weight = LiveIntervals::getSpillWeight( | |
139 | writes, reads, &MBFI, mi); | |
223e47cc LB |
140 | |
141 | // Give extra weight to what looks like a loop induction variable update. | |
142 | if (writes && isExiting && LIS.isLiveOutOfMBB(li, mbb)) | |
143 | weight *= 3; | |
144 | ||
145 | totalWeight += weight; | |
146 | } | |
147 | ||
148 | // Get allocation hints from copies. | |
149 | if (noHint || !mi->isCopy()) | |
150 | continue; | |
151 | unsigned hint = copyHint(mi, li.reg, tri, mri); | |
152 | if (!hint) | |
153 | continue; | |
1a4d82fc JJ |
154 | // Force hweight onto the stack so that x86 doesn't add hidden precision, |
155 | // making the comparison incorrectly pass (i.e., 1 > 1 == true??). | |
156 | // | |
157 | // FIXME: we probably shouldn't use floats at all. | |
158 | volatile float hweight = Hint[hint] += weight; | |
223e47cc | 159 | if (TargetRegisterInfo::isPhysicalRegister(hint)) { |
970d7e83 | 160 | if (hweight > bestPhys && mri.isAllocatable(hint)) |
223e47cc LB |
161 | bestPhys = hweight, hintPhys = hint; |
162 | } else { | |
163 | if (hweight > bestVirt) | |
164 | bestVirt = hweight, hintVirt = hint; | |
165 | } | |
166 | } | |
167 | ||
168 | Hint.clear(); | |
169 | ||
170 | // Always prefer the physreg hint. | |
171 | if (unsigned hint = hintPhys ? hintPhys : hintVirt) { | |
172 | mri.setRegAllocationHint(li.reg, 0, hint); | |
173 | // Weakly boost the spill weight of hinted registers. | |
174 | totalWeight *= 1.01F; | |
175 | } | |
176 | ||
177 | // If the live interval was already unspillable, leave it that way. | |
178 | if (!Spillable) | |
179 | return; | |
180 | ||
181 | // Mark li as unspillable if all live ranges are tiny. | |
182 | if (li.isZeroLength(LIS.getSlotIndexes())) { | |
183 | li.markNotSpillable(); | |
184 | return; | |
185 | } | |
186 | ||
187 | // If all of the definitions of the interval are re-materializable, | |
188 | // it is a preferred candidate for spilling. | |
189 | // FIXME: this gets much more complicated once we support non-trivial | |
190 | // re-materialization. | |
1a4d82fc | 191 | if (isRematerializable(li, LIS, *MF.getSubtarget().getInstrInfo())) |
223e47cc LB |
192 | totalWeight *= 0.5F; |
193 | ||
85aaf69f | 194 | li.weight = normalize(totalWeight, li.getSize(), numInstr); |
223e47cc | 195 | } |