Mercurial > hg > CbC > CbC_llvm

comparison lib/CodeGen/MachineSSAUpdater.cpp @ 0:95c75e76d11b LLVM3.4

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
LLVM 3.4
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Thu, 12 Dec 2013 13:56:28 +0900
parents
children 54457678186b
comparison
equal deleted inserted replaced
-1:000000000000 0:95c75e76d11b
1 //===- MachineSSAUpdater.cpp - Unstructured SSA Update Tool ---------------===//
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 // This file implements the MachineSSAUpdater class. It's based on SSAUpdater
11 // class in lib/Transforms/Utils.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "llvm/CodeGen/MachineSSAUpdater.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/CodeGen/MachineInstr.h"
19 #include "llvm/CodeGen/MachineInstrBuilder.h"
20 #include "llvm/CodeGen/MachineRegisterInfo.h"
21 #include "llvm/Support/AlignOf.h"
22 #include "llvm/Support/Allocator.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/ErrorHandling.h"
25 #include "llvm/Support/raw_ostream.h"
26 #include "llvm/Target/TargetInstrInfo.h"
27 #include "llvm/Target/TargetMachine.h"
28 #include "llvm/Target/TargetRegisterInfo.h"
29 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
30 using namespace llvm;
31
32 typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
33 static AvailableValsTy &getAvailableVals(void *AV) {
34 return *static_cast<AvailableValsTy*>(AV);
35 }
36
37 MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
38 SmallVectorImpl<MachineInstr*> *NewPHI)
39 : AV(0), InsertedPHIs(NewPHI) {
40 TII = MF.getTarget().getInstrInfo();
41 MRI = &MF.getRegInfo();
42 }
43
44 MachineSSAUpdater::~MachineSSAUpdater() {
45 delete static_cast<AvailableValsTy*>(AV);
46 }
47
48 /// Initialize - Reset this object to get ready for a new set of SSA
49 /// updates. ProtoValue is the value used to name PHI nodes.
50 void MachineSSAUpdater::Initialize(unsigned V) {
51 if (AV == 0)
52 AV = new AvailableValsTy();
53 else
54 getAvailableVals(AV).clear();
55
56 VR = V;
57 VRC = MRI->getRegClass(VR);
58 }
59
60 /// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
61 /// the specified block.
62 bool MachineSSAUpdater::HasValueForBlock(MachineBasicBlock *BB) const {
63 return getAvailableVals(AV).count(BB);
64 }
65
66 /// AddAvailableValue - Indicate that a rewritten value is available in the
67 /// specified block with the specified value.
68 void MachineSSAUpdater::AddAvailableValue(MachineBasicBlock *BB, unsigned V) {
69 getAvailableVals(AV)[BB] = V;
70 }
71
72 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
73 /// live at the end of the specified block.
74 unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
75 return GetValueAtEndOfBlockInternal(BB);
76 }
77
78 static
79 unsigned LookForIdenticalPHI(MachineBasicBlock *BB,
80 SmallVectorImpl<std::pair<MachineBasicBlock*, unsigned> > &PredValues) {
81 if (BB->empty())
82 return 0;
83
84 MachineBasicBlock::iterator I = BB->begin();
85 if (!I->isPHI())
86 return 0;
87
88 AvailableValsTy AVals;
89 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
90 AVals[PredValues[i].first] = PredValues[i].second;
91 while (I != BB->end() && I->isPHI()) {
92 bool Same = true;
93 for (unsigned i = 1, e = I->getNumOperands(); i != e; i += 2) {
94 unsigned SrcReg = I->getOperand(i).getReg();
95 MachineBasicBlock *SrcBB = I->getOperand(i+1).getMBB();
96 if (AVals[SrcBB] != SrcReg) {
97 Same = false;
98 break;
99 }
100 }
101 if (Same)
102 return I->getOperand(0).getReg();
103 ++I;
104 }
105 return 0;
106 }
107
108 /// InsertNewDef - Insert an empty PHI or IMPLICIT_DEF instruction which define
109 /// a value of the given register class at the start of the specified basic
110 /// block. It returns the virtual register defined by the instruction.
111 static
112 MachineInstrBuilder InsertNewDef(unsigned Opcode,
113 MachineBasicBlock *BB, MachineBasicBlock::iterator I,
114 const TargetRegisterClass *RC,
115 MachineRegisterInfo *MRI,
116 const TargetInstrInfo *TII) {
117 unsigned NewVR = MRI->createVirtualRegister(RC);
118 return BuildMI(*BB, I, DebugLoc(), TII->get(Opcode), NewVR);
119 }
120
121 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
122 /// is live in the middle of the specified block.
123 ///
124 /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
125 /// important case: if there is a definition of the rewritten value after the
126 /// 'use' in BB. Consider code like this:
127 ///
128 /// X1 = ...
129 /// SomeBB:
130 /// use(X)
131 /// X2 = ...
132 /// br Cond, SomeBB, OutBB
133 ///
134 /// In this case, there are two values (X1 and X2) added to the AvailableVals
135 /// set by the client of the rewriter, and those values are both live out of
136 /// their respective blocks. However, the use of X happens in the *middle* of
137 /// a block. Because of this, we need to insert a new PHI node in SomeBB to
138 /// merge the appropriate values, and this value isn't live out of the block.
139 ///
140 unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
141 // If there is no definition of the renamed variable in this block, just use
142 // GetValueAtEndOfBlock to do our work.
143 if (!HasValueForBlock(BB))
144 return GetValueAtEndOfBlockInternal(BB);
145
146 // If there are no predecessors, just return undef.
147 if (BB->pred_empty()) {
148 // Insert an implicit_def to represent an undef value.
149 MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
150 BB, BB->getFirstTerminator(),
151 VRC, MRI, TII);
152 return NewDef->getOperand(0).getReg();
153 }
154
155 // Otherwise, we have the hard case. Get the live-in values for each
156 // predecessor.
157 SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> PredValues;
158 unsigned SingularValue = 0;
159
160 bool isFirstPred = true;
161 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
162 E = BB->pred_end(); PI != E; ++PI) {
163 MachineBasicBlock *PredBB = *PI;
164 unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
165 PredValues.push_back(std::make_pair(PredBB, PredVal));
166
167 // Compute SingularValue.
168 if (isFirstPred) {
169 SingularValue = PredVal;
170 isFirstPred = false;
171 } else if (PredVal != SingularValue)
172 SingularValue = 0;
173 }
174
175 // Otherwise, if all the merged values are the same, just use it.
176 if (SingularValue != 0)
177 return SingularValue;
178
179 // If an identical PHI is already in BB, just reuse it.
180 unsigned DupPHI = LookForIdenticalPHI(BB, PredValues);
181 if (DupPHI)
182 return DupPHI;
183
184 // Otherwise, we do need a PHI: insert one now.
185 MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
186 MachineInstrBuilder InsertedPHI = InsertNewDef(TargetOpcode::PHI, BB,
187 Loc, VRC, MRI, TII);
188
189 // Fill in all the predecessors of the PHI.
190 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
191 InsertedPHI.addReg(PredValues[i].second).addMBB(PredValues[i].first);
192
193 // See if the PHI node can be merged to a single value. This can happen in
194 // loop cases when we get a PHI of itself and one other value.
195 if (unsigned ConstVal = InsertedPHI->isConstantValuePHI()) {
196 InsertedPHI->eraseFromParent();
197 return ConstVal;
198 }
199
200 // If the client wants to know about all new instructions, tell it.
201 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
202
203 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
204 return InsertedPHI->getOperand(0).getReg();
205 }
206
207 static
208 MachineBasicBlock *findCorrespondingPred(const MachineInstr *MI,
209 MachineOperand *U) {
210 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
211 if (&MI->getOperand(i) == U)
212 return MI->getOperand(i+1).getMBB();
213 }
214
215 llvm_unreachable("MachineOperand::getParent() failure?");
216 }
217
218 /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
219 /// which use their value in the corresponding predecessor.
220 void MachineSSAUpdater::RewriteUse(MachineOperand &U) {
221 MachineInstr *UseMI = U.getParent();
222 unsigned NewVR = 0;
223 if (UseMI->isPHI()) {
224 MachineBasicBlock *SourceBB = findCorrespondingPred(UseMI, &U);
225 NewVR = GetValueAtEndOfBlockInternal(SourceBB);
226 } else {
227 NewVR = GetValueInMiddleOfBlock(UseMI->getParent());
228 }
229
230 U.setReg(NewVR);
231 }
232
233 void MachineSSAUpdater::ReplaceRegWith(unsigned OldReg, unsigned NewReg) {
234 MRI->replaceRegWith(OldReg, NewReg);
235
236 AvailableValsTy &AvailableVals = getAvailableVals(AV);
237 for (DenseMap<MachineBasicBlock*, unsigned>::iterator
238 I = AvailableVals.begin(), E = AvailableVals.end(); I != E; ++I)
239 if (I->second == OldReg)
240 I->second = NewReg;
241 }
242
243 /// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
244 /// template, specialized for MachineSSAUpdater.
245 namespace llvm {
246 template<>
247 class SSAUpdaterTraits<MachineSSAUpdater> {
248 public:
249 typedef MachineBasicBlock BlkT;
250 typedef unsigned ValT;
251 typedef MachineInstr PhiT;
252
253 typedef MachineBasicBlock::succ_iterator BlkSucc_iterator;
254 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
255 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
256
257 /// Iterator for PHI operands.
258 class PHI_iterator {
259 private:
260 MachineInstr *PHI;
261 unsigned idx;
262
263 public:
264 explicit PHI_iterator(MachineInstr *P) // begin iterator
265 : PHI(P), idx(1) {}
266 PHI_iterator(MachineInstr *P, bool) // end iterator
267 : PHI(P), idx(PHI->getNumOperands()) {}
268
269 PHI_iterator &operator++() { idx += 2; return *this; }
270 bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
271 bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
272 unsigned getIncomingValue() { return PHI->getOperand(idx).getReg(); }
273 MachineBasicBlock *getIncomingBlock() {
274 return PHI->getOperand(idx+1).getMBB();
275 }
276 };
277 static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
278 static inline PHI_iterator PHI_end(PhiT *PHI) {
279 return PHI_iterator(PHI, true);
280 }
281
282 /// FindPredecessorBlocks - Put the predecessors of BB into the Preds
283 /// vector.
284 static void FindPredecessorBlocks(MachineBasicBlock *BB,
285 SmallVectorImpl<MachineBasicBlock*> *Preds){
286 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
287 E = BB->pred_end(); PI != E; ++PI)
288 Preds->push_back(*PI);
289 }
290
291 /// GetUndefVal - Create an IMPLICIT_DEF instruction with a new register.
292 /// Add it into the specified block and return the register.
293 static unsigned GetUndefVal(MachineBasicBlock *BB,
294 MachineSSAUpdater *Updater) {
295 // Insert an implicit_def to represent an undef value.
296 MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
297 BB, BB->getFirstTerminator(),
298 Updater->VRC, Updater->MRI,
299 Updater->TII);
300 return NewDef->getOperand(0).getReg();
301 }
302
303 /// CreateEmptyPHI - Create a PHI instruction that defines a new register.
304 /// Add it into the specified block and return the register.
305 static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
306 MachineSSAUpdater *Updater) {
307 MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
308 MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
309 Updater->VRC, Updater->MRI,
310 Updater->TII);
311 return PHI->getOperand(0).getReg();
312 }
313
314 /// AddPHIOperand - Add the specified value as an operand of the PHI for
315 /// the specified predecessor block.
316 static void AddPHIOperand(MachineInstr *PHI, unsigned Val,
317 MachineBasicBlock *Pred) {
318 MachineInstrBuilder(*Pred->getParent(), PHI).addReg(Val).addMBB(Pred);
319 }
320
321 /// InstrIsPHI - Check if an instruction is a PHI.
322 ///
323 static MachineInstr *InstrIsPHI(MachineInstr *I) {
324 if (I && I->isPHI())
325 return I;
326 return 0;
327 }
328
329 /// ValueIsPHI - Check if the instruction that defines the specified register
330 /// is a PHI instruction.
331 static MachineInstr *ValueIsPHI(unsigned Val, MachineSSAUpdater *Updater) {
332 return InstrIsPHI(Updater->MRI->getVRegDef(Val));
333 }
334
335 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
336 /// operands, i.e., it was just added.
337 static MachineInstr *ValueIsNewPHI(unsigned Val, MachineSSAUpdater *Updater) {
338 MachineInstr *PHI = ValueIsPHI(Val, Updater);
339 if (PHI && PHI->getNumOperands() <= 1)
340 return PHI;
341 return 0;
342 }
343
344 /// GetPHIValue - For the specified PHI instruction, return the register
345 /// that it defines.
346 static unsigned GetPHIValue(MachineInstr *PHI) {
347 return PHI->getOperand(0).getReg();
348 }
349 };
350
351 } // End llvm namespace
352
353 /// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
354 /// for the specified BB and if so, return it. If not, construct SSA form by
355 /// first calculating the required placement of PHIs and then inserting new
356 /// PHIs where needed.
357 unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
358 AvailableValsTy &AvailableVals = getAvailableVals(AV);
359 if (unsigned V = AvailableVals[BB])
360 return V;
361
362 SSAUpdaterImpl<MachineSSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
363 return Impl.GetValue(BB);
364 }