1 //===- MachineLoopInfo.cpp - Natural Loop Calculator ----------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines the MachineLoopInfo class that is used to identify natural
10 // loops and determine the loop depth of various nodes of the CFG. Note that
11 // the loops identified may actually be several natural loops that share the
12 // same header node... not just a single natural loop.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "llvm/CodeGen/MachineLoopInfo.h"
17 #include "llvm/CodeGen/MachineDominators.h"
18 #include "llvm/CodeGen/MachineRegisterInfo.h"
19 #include "llvm/CodeGen/TargetInstrInfo.h"
20 #include "llvm/CodeGen/TargetSubtargetInfo.h"
21 #include "llvm/Config/llvm-config.h"
22 #include "llvm/InitializePasses.h"
23 #include "llvm/Pass.h"
24 #include "llvm/PassRegistry.h"
25 #include "llvm/Support/GenericLoopInfoImpl.h"
26
27 using namespace llvm;
28
29 // Explicitly instantiate methods in LoopInfoImpl.h for MI-level Loops.
30 template class llvm::LoopBase<MachineBasicBlock, MachineLoop>;
31 template class llvm::LoopInfoBase<MachineBasicBlock, MachineLoop>;
32
33 AnalysisKey MachineLoopAnalysis::Key;
34
35 MachineLoopAnalysis::Result
run(MachineFunction & MF,MachineFunctionAnalysisManager & MFAM)36 MachineLoopAnalysis::run(MachineFunction &MF,
37 MachineFunctionAnalysisManager &MFAM) {
38 return MachineLoopInfo(MFAM.getResult<MachineDominatorTreeAnalysis>(MF));
39 }
40
41 PreservedAnalyses
run(MachineFunction & MF,MachineFunctionAnalysisManager & MFAM)42 MachineLoopPrinterPass::run(MachineFunction &MF,
43 MachineFunctionAnalysisManager &MFAM) {
44 OS << "Machine loop info for machine function '" << MF.getName() << "':\n";
45 MFAM.getResult<MachineLoopAnalysis>(MF).print(OS);
46 return PreservedAnalyses::all();
47 }
48
49 char MachineLoopInfoWrapperPass::ID = 0;
MachineLoopInfoWrapperPass()50 MachineLoopInfoWrapperPass::MachineLoopInfoWrapperPass()
51 : MachineFunctionPass(ID) {
52 initializeMachineLoopInfoWrapperPassPass(*PassRegistry::getPassRegistry());
53 }
54 INITIALIZE_PASS_BEGIN(MachineLoopInfoWrapperPass, "machine-loops",
55 "Machine Natural Loop Construction", true, true)
56 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTreeWrapperPass)
57 INITIALIZE_PASS_END(MachineLoopInfoWrapperPass, "machine-loops",
58 "Machine Natural Loop Construction", true, true)
59
60 char &llvm::MachineLoopInfoID = MachineLoopInfoWrapperPass::ID;
61
runOnMachineFunction(MachineFunction &)62 bool MachineLoopInfoWrapperPass::runOnMachineFunction(MachineFunction &) {
63 LI.calculate(getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree());
64 return false;
65 }
66
invalidate(MachineFunction &,const PreservedAnalyses & PA,MachineFunctionAnalysisManager::Invalidator &)67 bool MachineLoopInfo::invalidate(
68 MachineFunction &, const PreservedAnalyses &PA,
69 MachineFunctionAnalysisManager::Invalidator &) {
70 // Check whether the analysis, all analyses on functions, or the function's
71 // CFG have been preserved.
72 auto PAC = PA.getChecker<MachineLoopAnalysis>();
73 return !PAC.preserved() &&
74 !PAC.preservedSet<AllAnalysesOn<MachineFunction>>() &&
75 !PAC.preservedSet<CFGAnalyses>();
76 }
77
calculate(MachineDominatorTree & MDT)78 void MachineLoopInfo::calculate(MachineDominatorTree &MDT) {
79 releaseMemory();
80 analyze(MDT.getBase());
81 }
82
getAnalysisUsage(AnalysisUsage & AU) const83 void MachineLoopInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
84 AU.setPreservesAll();
85 AU.addRequired<MachineDominatorTreeWrapperPass>();
86 MachineFunctionPass::getAnalysisUsage(AU);
87 }
88
getTopBlock()89 MachineBasicBlock *MachineLoop::getTopBlock() {
90 MachineBasicBlock *TopMBB = getHeader();
91 MachineFunction::iterator Begin = TopMBB->getParent()->begin();
92 if (TopMBB->getIterator() != Begin) {
93 MachineBasicBlock *PriorMBB = &*std::prev(TopMBB->getIterator());
94 while (contains(PriorMBB)) {
95 TopMBB = PriorMBB;
96 if (TopMBB->getIterator() == Begin)
97 break;
98 PriorMBB = &*std::prev(TopMBB->getIterator());
99 }
100 }
101 return TopMBB;
102 }
103
getBottomBlock()104 MachineBasicBlock *MachineLoop::getBottomBlock() {
105 MachineBasicBlock *BotMBB = getHeader();
106 MachineFunction::iterator End = BotMBB->getParent()->end();
107 if (BotMBB->getIterator() != std::prev(End)) {
108 MachineBasicBlock *NextMBB = &*std::next(BotMBB->getIterator());
109 while (contains(NextMBB)) {
110 BotMBB = NextMBB;
111 if (BotMBB == &*std::next(BotMBB->getIterator()))
112 break;
113 NextMBB = &*std::next(BotMBB->getIterator());
114 }
115 }
116 return BotMBB;
117 }
118
findLoopControlBlock() const119 MachineBasicBlock *MachineLoop::findLoopControlBlock() const {
120 if (MachineBasicBlock *Latch = getLoopLatch()) {
121 if (isLoopExiting(Latch))
122 return Latch;
123 else
124 return getExitingBlock();
125 }
126 return nullptr;
127 }
128
getStartLoc() const129 DebugLoc MachineLoop::getStartLoc() const {
130 // Try the pre-header first.
131 if (MachineBasicBlock *PHeadMBB = getLoopPreheader())
132 if (const BasicBlock *PHeadBB = PHeadMBB->getBasicBlock())
133 if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc())
134 return DL;
135
136 // If we have no pre-header or there are no instructions with debug
137 // info in it, try the header.
138 if (MachineBasicBlock *HeadMBB = getHeader())
139 if (const BasicBlock *HeadBB = HeadMBB->getBasicBlock())
140 return HeadBB->getTerminator()->getDebugLoc();
141
142 return DebugLoc();
143 }
144
145 MachineBasicBlock *
findLoopPreheader(MachineLoop * L,bool SpeculativePreheader,bool FindMultiLoopPreheader) const146 MachineLoopInfo::findLoopPreheader(MachineLoop *L, bool SpeculativePreheader,
147 bool FindMultiLoopPreheader) const {
148 if (MachineBasicBlock *PB = L->getLoopPreheader())
149 return PB;
150
151 if (!SpeculativePreheader)
152 return nullptr;
153
154 MachineBasicBlock *HB = L->getHeader(), *LB = L->getLoopLatch();
155 if (HB->pred_size() != 2 || HB->hasAddressTaken())
156 return nullptr;
157 // Find the predecessor of the header that is not the latch block.
158 MachineBasicBlock *Preheader = nullptr;
159 for (MachineBasicBlock *P : HB->predecessors()) {
160 if (P == LB)
161 continue;
162 // Sanity.
163 if (Preheader)
164 return nullptr;
165 Preheader = P;
166 }
167
168 // Check if the preheader candidate is a successor of any other loop
169 // headers. We want to avoid having two loop setups in the same block.
170 if (!FindMultiLoopPreheader) {
171 for (MachineBasicBlock *S : Preheader->successors()) {
172 if (S == HB)
173 continue;
174 MachineLoop *T = getLoopFor(S);
175 if (T && T->getHeader() == S)
176 return nullptr;
177 }
178 }
179 return Preheader;
180 }
181
getLoopID() const182 MDNode *MachineLoop::getLoopID() const {
183 MDNode *LoopID = nullptr;
184 if (const auto *MBB = findLoopControlBlock()) {
185 // If there is a single latch block, then the metadata
186 // node is attached to its terminating instruction.
187 const auto *BB = MBB->getBasicBlock();
188 if (!BB)
189 return nullptr;
190 if (const auto *TI = BB->getTerminator())
191 LoopID = TI->getMetadata(LLVMContext::MD_loop);
192 } else if (const auto *MBB = getHeader()) {
193 // There seem to be multiple latch blocks, so we have to
194 // visit all predecessors of the loop header and check
195 // their terminating instructions for the metadata.
196 if (const auto *Header = MBB->getBasicBlock()) {
197 // Walk over all blocks in the loop.
198 for (const auto *MBB : this->blocks()) {
199 const auto *BB = MBB->getBasicBlock();
200 if (!BB)
201 return nullptr;
202 const auto *TI = BB->getTerminator();
203 if (!TI)
204 return nullptr;
205 MDNode *MD = nullptr;
206 // Check if this terminating instruction jumps to the loop header.
207 for (const auto *Succ : successors(TI)) {
208 if (Succ == Header) {
209 // This is a jump to the header - gather the metadata from it.
210 MD = TI->getMetadata(LLVMContext::MD_loop);
211 break;
212 }
213 }
214 if (!MD)
215 return nullptr;
216 if (!LoopID)
217 LoopID = MD;
218 else if (MD != LoopID)
219 return nullptr;
220 }
221 }
222 }
223 if (LoopID &&
224 (LoopID->getNumOperands() == 0 || LoopID->getOperand(0) != LoopID))
225 LoopID = nullptr;
226 return LoopID;
227 }
228
isLoopInvariantImplicitPhysReg(Register Reg) const229 bool MachineLoop::isLoopInvariantImplicitPhysReg(Register Reg) const {
230 MachineFunction *MF = getHeader()->getParent();
231 MachineRegisterInfo *MRI = &MF->getRegInfo();
232
233 if (MRI->isConstantPhysReg(Reg))
234 return true;
235
236 if (!MF->getSubtarget()
237 .getRegisterInfo()
238 ->shouldAnalyzePhysregInMachineLoopInfo(Reg))
239 return false;
240
241 return !llvm::any_of(
242 MRI->def_instructions(Reg),
243 [this](const MachineInstr &MI) { return this->contains(&MI); });
244 }
245
isLoopInvariant(MachineInstr & I,const Register ExcludeReg) const246 bool MachineLoop::isLoopInvariant(MachineInstr &I,
247 const Register ExcludeReg) const {
248 MachineFunction *MF = I.getParent()->getParent();
249 MachineRegisterInfo *MRI = &MF->getRegInfo();
250 const TargetSubtargetInfo &ST = MF->getSubtarget();
251 const TargetRegisterInfo *TRI = ST.getRegisterInfo();
252 const TargetInstrInfo *TII = ST.getInstrInfo();
253
254 // The instruction is loop invariant if all of its operands are.
255 for (const MachineOperand &MO : I.operands()) {
256 if (!MO.isReg())
257 continue;
258
259 Register Reg = MO.getReg();
260 if (Reg == 0) continue;
261
262 if (ExcludeReg == Reg)
263 continue;
264
265 // An instruction that uses or defines a physical register can't e.g. be
266 // hoisted, so mark this as not invariant.
267 if (Reg.isPhysical()) {
268 if (MO.isUse()) {
269 // If the physreg has no defs anywhere, it's just an ambient register
270 // and we can freely move its uses. Alternatively, if it's allocatable,
271 // it could get allocated to something with a def during allocation.
272 // However, if the physreg is known to always be caller saved/restored
273 // then this use is safe to hoist.
274 if (!isLoopInvariantImplicitPhysReg(Reg) &&
275 !(TRI->isCallerPreservedPhysReg(Reg.asMCReg(), *I.getMF())) &&
276 !TII->isIgnorableUse(MO))
277 return false;
278 // Otherwise it's safe to move.
279 continue;
280 } else if (!MO.isDead()) {
281 // A def that isn't dead can't be moved.
282 return false;
283 } else if (getHeader()->isLiveIn(Reg)) {
284 // If the reg is live into the loop, we can't hoist an instruction
285 // which would clobber it.
286 return false;
287 }
288 }
289
290 if (!MO.isUse())
291 continue;
292
293 assert(MRI->getVRegDef(Reg) &&
294 "Machine instr not mapped for this vreg?!");
295
296 // If the loop contains the definition of an operand, then the instruction
297 // isn't loop invariant.
298 if (contains(MRI->getVRegDef(Reg)))
299 return false;
300 }
301
302 // If we got this far, the instruction is loop invariant!
303 return true;
304 }
305
306 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dump() const307 LLVM_DUMP_METHOD void MachineLoop::dump() const {
308 print(dbgs());
309 }
310 #endif
311