1
//===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===//
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 implements the SSAUpdater class.
12
//===----------------------------------------------------------------------===//
14
#define DEBUG_TYPE "ssaupdater"
15
#include "llvm/Instructions.h"
16
#include "llvm/ADT/DenseMap.h"
17
#include "llvm/Support/AlignOf.h"
18
#include "llvm/Support/Allocator.h"
19
#include "llvm/Support/CFG.h"
20
#include "llvm/Support/Debug.h"
21
#include "llvm/Support/raw_ostream.h"
22
#include "llvm/Transforms/Utils/SSAUpdater.h"
23
#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
26
typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
27
static AvailableValsTy &getAvailableVals(void *AV) {
28
return *static_cast<AvailableValsTy*>(AV);
31
SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
32
: AV(0), ProtoType(0), ProtoName(), InsertedPHIs(NewPHI) {}
34
SSAUpdater::~SSAUpdater() {
35
delete &getAvailableVals(AV);
38
/// Initialize - Reset this object to get ready for a new set of SSA
39
/// updates with type 'Ty'. PHI nodes get a name based on 'Name'.
40
void SSAUpdater::Initialize(const Type *Ty, StringRef Name) {
42
AV = new AvailableValsTy();
44
getAvailableVals(AV).clear();
49
/// HasValueForBlock - Return true if the SSAUpdater already has a value for
50
/// the specified block.
51
bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
52
return getAvailableVals(AV).count(BB);
55
/// AddAvailableValue - Indicate that a rewritten value is available in the
56
/// specified block with the specified value.
57
void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
58
assert(ProtoType != 0 && "Need to initialize SSAUpdater");
59
assert(ProtoType == V->getType() &&
60
"All rewritten values must have the same type");
61
getAvailableVals(AV)[BB] = V;
64
/// IsEquivalentPHI - Check if PHI has the same incoming value as specified
65
/// in ValueMapping for each predecessor block.
66
static bool IsEquivalentPHI(PHINode *PHI,
67
DenseMap<BasicBlock*, Value*> &ValueMapping) {
68
unsigned PHINumValues = PHI->getNumIncomingValues();
69
if (PHINumValues != ValueMapping.size())
72
// Scan the phi to see if it matches.
73
for (unsigned i = 0, e = PHINumValues; i != e; ++i)
74
if (ValueMapping[PHI->getIncomingBlock(i)] !=
75
PHI->getIncomingValue(i)) {
82
/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
83
/// live at the end of the specified block.
84
Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
85
Value *Res = GetValueAtEndOfBlockInternal(BB);
89
/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
90
/// is live in the middle of the specified block.
92
/// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
93
/// important case: if there is a definition of the rewritten value after the
94
/// 'use' in BB. Consider code like this:
100
/// br Cond, SomeBB, OutBB
102
/// In this case, there are two values (X1 and X2) added to the AvailableVals
103
/// set by the client of the rewriter, and those values are both live out of
104
/// their respective blocks. However, the use of X happens in the *middle* of
105
/// a block. Because of this, we need to insert a new PHI node in SomeBB to
106
/// merge the appropriate values, and this value isn't live out of the block.
108
Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
109
// If there is no definition of the renamed variable in this block, just use
110
// GetValueAtEndOfBlock to do our work.
111
if (!HasValueForBlock(BB))
112
return GetValueAtEndOfBlock(BB);
114
// Otherwise, we have the hard case. Get the live-in values for each
116
SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
117
Value *SingularValue = 0;
119
// We can get our predecessor info by walking the pred_iterator list, but it
120
// is relatively slow. If we already have PHI nodes in this block, walk one
121
// of them to get the predecessor list instead.
122
if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
123
for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
124
BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
125
Value *PredVal = GetValueAtEndOfBlock(PredBB);
126
PredValues.push_back(std::make_pair(PredBB, PredVal));
128
// Compute SingularValue.
130
SingularValue = PredVal;
131
else if (PredVal != SingularValue)
135
bool isFirstPred = true;
136
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
137
BasicBlock *PredBB = *PI;
138
Value *PredVal = GetValueAtEndOfBlock(PredBB);
139
PredValues.push_back(std::make_pair(PredBB, PredVal));
141
// Compute SingularValue.
143
SingularValue = PredVal;
145
} else if (PredVal != SingularValue)
150
// If there are no predecessors, just return undef.
151
if (PredValues.empty())
152
return UndefValue::get(ProtoType);
154
// Otherwise, if all the merged values are the same, just use it.
155
if (SingularValue != 0)
156
return SingularValue;
158
// Otherwise, we do need a PHI: check to see if we already have one available
159
// in this block that produces the right value.
160
if (isa<PHINode>(BB->begin())) {
161
DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
164
for (BasicBlock::iterator It = BB->begin();
165
(SomePHI = dyn_cast<PHINode>(It)); ++It) {
166
if (IsEquivalentPHI(SomePHI, ValueMapping))
171
// Ok, we have no way out, insert a new one now.
172
PHINode *InsertedPHI = PHINode::Create(ProtoType, ProtoName, &BB->front());
173
InsertedPHI->reserveOperandSpace(PredValues.size());
175
// Fill in all the predecessors of the PHI.
176
for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
177
InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
179
// See if the PHI node can be merged to a single value. This can happen in
180
// loop cases when we get a PHI of itself and one other value.
181
if (Value *ConstVal = InsertedPHI->hasConstantValue()) {
182
InsertedPHI->eraseFromParent();
186
// If the client wants to know about all new instructions, tell it.
187
if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
189
DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
193
/// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
194
/// which use their value in the corresponding predecessor.
195
void SSAUpdater::RewriteUse(Use &U) {
196
Instruction *User = cast<Instruction>(U.getUser());
199
if (PHINode *UserPN = dyn_cast<PHINode>(User))
200
V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
202
V = GetValueInMiddleOfBlock(User->getParent());
207
/// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse. However,
208
/// this version of the method can rewrite uses in the same block as a
209
/// definition, because it assumes that all uses of a value are below any
211
void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
212
Instruction *User = cast<Instruction>(U.getUser());
215
if (PHINode *UserPN = dyn_cast<PHINode>(User))
216
V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
218
V = GetValueAtEndOfBlock(User->getParent());
223
/// PHIiter - Iterator for PHI operands. This is used for the PHI_iterator
224
/// in the SSAUpdaterImpl template.
232
explicit PHIiter(PHINode *P) // begin iterator
234
PHIiter(PHINode *P, bool) // end iterator
235
: PHI(P), idx(PHI->getNumIncomingValues()) {}
237
PHIiter &operator++() { ++idx; return *this; }
238
bool operator==(const PHIiter& x) const { return idx == x.idx; }
239
bool operator!=(const PHIiter& x) const { return !operator==(x); }
240
Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
241
BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
245
/// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
246
/// specialized for SSAUpdater.
249
class SSAUpdaterTraits<SSAUpdater> {
251
typedef BasicBlock BlkT;
253
typedef PHINode PhiT;
255
typedef succ_iterator BlkSucc_iterator;
256
static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
257
static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
259
typedef PHIiter PHI_iterator;
260
static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
261
static inline PHI_iterator PHI_end(PhiT *PHI) {
262
return PHI_iterator(PHI, true);
265
/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
266
/// vector, set Info->NumPreds, and allocate space in Info->Preds.
267
static void FindPredecessorBlocks(BasicBlock *BB,
268
SmallVectorImpl<BasicBlock*> *Preds) {
269
// We can get our predecessor info by walking the pred_iterator list,
270
// but it is relatively slow. If we already have PHI nodes in this
271
// block, walk one of them to get the predecessor list instead.
272
if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
273
for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
274
Preds->push_back(SomePhi->getIncomingBlock(PI));
276
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
277
Preds->push_back(*PI);
281
/// GetUndefVal - Get an undefined value of the same type as the value
283
static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
284
return UndefValue::get(Updater->ProtoType);
287
/// CreateEmptyPHI - Create a new PHI instruction in the specified block.
288
/// Reserve space for the operands but do not fill them in yet.
289
static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
290
SSAUpdater *Updater) {
291
PHINode *PHI = PHINode::Create(Updater->ProtoType, Updater->ProtoName,
293
PHI->reserveOperandSpace(NumPreds);
297
/// AddPHIOperand - Add the specified value as an operand of the PHI for
298
/// the specified predecessor block.
299
static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
300
PHI->addIncoming(Val, Pred);
303
/// InstrIsPHI - Check if an instruction is a PHI.
305
static PHINode *InstrIsPHI(Instruction *I) {
306
return dyn_cast<PHINode>(I);
309
/// ValueIsPHI - Check if a value is a PHI.
311
static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
312
return dyn_cast<PHINode>(Val);
315
/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
316
/// operands, i.e., it was just added.
317
static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
318
PHINode *PHI = ValueIsPHI(Val, Updater);
319
if (PHI && PHI->getNumIncomingValues() == 0)
324
/// GetPHIValue - For the specified PHI instruction, return the value
326
static Value *GetPHIValue(PHINode *PHI) {
331
} // End llvm namespace
333
/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
334
/// for the specified BB and if so, return it. If not, construct SSA form by
335
/// first calculating the required placement of PHIs and then inserting new
336
/// PHIs where needed.
337
Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
338
AvailableValsTy &AvailableVals = getAvailableVals(AV);
339
if (Value *V = AvailableVals[BB])
342
SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
343
return Impl.GetValue(BB);