1 //===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
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 BasicBlock class for the IR library.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/IR/BasicBlock.h"
15 #include "SymbolTableListTraitsImpl.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/IR/CFG.h"
18 #include "llvm/IR/Constants.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/IR/IntrinsicInst.h"
21 #include "llvm/IR/LLVMContext.h"
22 #include "llvm/IR/Type.h"
23 #include <algorithm>
24 using namespace llvm;
25
getValueSymbolTable()26 ValueSymbolTable *BasicBlock::getValueSymbolTable() {
27 if (Function *F = getParent())
28 return &F->getValueSymbolTable();
29 return nullptr;
30 }
31
getDataLayout() const32 const DataLayout *BasicBlock::getDataLayout() const {
33 return getParent()->getDataLayout();
34 }
35
getContext() const36 LLVMContext &BasicBlock::getContext() const {
37 return getType()->getContext();
38 }
39
40 // Explicit instantiation of SymbolTableListTraits since some of the methods
41 // are not in the public header file...
42 template class llvm::SymbolTableListTraits<Instruction, BasicBlock>;
43
44
BasicBlock(LLVMContext & C,const Twine & Name,Function * NewParent,BasicBlock * InsertBefore)45 BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent,
46 BasicBlock *InsertBefore)
47 : Value(Type::getLabelTy(C), Value::BasicBlockVal), Parent(nullptr) {
48
49 if (NewParent)
50 insertInto(NewParent, InsertBefore);
51 else
52 assert(!InsertBefore &&
53 "Cannot insert block before another block with no function!");
54
55 setName(Name);
56 }
57
insertInto(Function * NewParent,BasicBlock * InsertBefore)58 void BasicBlock::insertInto(Function *NewParent, BasicBlock *InsertBefore) {
59 assert(NewParent && "Expected a parent");
60 assert(!Parent && "Already has a parent");
61
62 if (InsertBefore)
63 NewParent->getBasicBlockList().insert(InsertBefore, this);
64 else
65 NewParent->getBasicBlockList().push_back(this);
66 }
67
~BasicBlock()68 BasicBlock::~BasicBlock() {
69 // If the address of the block is taken and it is being deleted (e.g. because
70 // it is dead), this means that there is either a dangling constant expr
71 // hanging off the block, or an undefined use of the block (source code
72 // expecting the address of a label to keep the block alive even though there
73 // is no indirect branch). Handle these cases by zapping the BlockAddress
74 // nodes. There are no other possible uses at this point.
75 if (hasAddressTaken()) {
76 assert(!use_empty() && "There should be at least one blockaddress!");
77 Constant *Replacement =
78 ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1);
79 while (!use_empty()) {
80 BlockAddress *BA = cast<BlockAddress>(user_back());
81 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
82 BA->getType()));
83 BA->destroyConstant();
84 }
85 }
86
87 assert(getParent() == nullptr && "BasicBlock still linked into the program!");
88 dropAllReferences();
89 InstList.clear();
90 }
91
setParent(Function * parent)92 void BasicBlock::setParent(Function *parent) {
93 // Set Parent=parent, updating instruction symtab entries as appropriate.
94 InstList.setSymTabObject(&Parent, parent);
95 }
96
removeFromParent()97 void BasicBlock::removeFromParent() {
98 getParent()->getBasicBlockList().remove(this);
99 }
100
eraseFromParent()101 void BasicBlock::eraseFromParent() {
102 getParent()->getBasicBlockList().erase(this);
103 }
104
105 /// moveBefore - Unlink this basic block from its current function and
106 /// insert it into the function that MovePos lives in, right before MovePos.
moveBefore(BasicBlock * MovePos)107 void BasicBlock::moveBefore(BasicBlock *MovePos) {
108 MovePos->getParent()->getBasicBlockList().splice(MovePos,
109 getParent()->getBasicBlockList(), this);
110 }
111
112 /// moveAfter - Unlink this basic block from its current function and
113 /// insert it into the function that MovePos lives in, right after MovePos.
moveAfter(BasicBlock * MovePos)114 void BasicBlock::moveAfter(BasicBlock *MovePos) {
115 Function::iterator I = MovePos;
116 MovePos->getParent()->getBasicBlockList().splice(++I,
117 getParent()->getBasicBlockList(), this);
118 }
119
120
getTerminator()121 TerminatorInst *BasicBlock::getTerminator() {
122 if (InstList.empty()) return nullptr;
123 return dyn_cast<TerminatorInst>(&InstList.back());
124 }
125
getTerminator() const126 const TerminatorInst *BasicBlock::getTerminator() const {
127 if (InstList.empty()) return nullptr;
128 return dyn_cast<TerminatorInst>(&InstList.back());
129 }
130
getTerminatingMustTailCall()131 CallInst *BasicBlock::getTerminatingMustTailCall() {
132 if (InstList.empty())
133 return nullptr;
134 ReturnInst *RI = dyn_cast<ReturnInst>(&InstList.back());
135 if (!RI || RI == &InstList.front())
136 return nullptr;
137
138 Instruction *Prev = RI->getPrevNode();
139 if (!Prev)
140 return nullptr;
141
142 if (Value *RV = RI->getReturnValue()) {
143 if (RV != Prev)
144 return nullptr;
145
146 // Look through the optional bitcast.
147 if (auto *BI = dyn_cast<BitCastInst>(Prev)) {
148 RV = BI->getOperand(0);
149 Prev = BI->getPrevNode();
150 if (!Prev || RV != Prev)
151 return nullptr;
152 }
153 }
154
155 if (auto *CI = dyn_cast<CallInst>(Prev)) {
156 if (CI->isMustTailCall())
157 return CI;
158 }
159 return nullptr;
160 }
161
getFirstNonPHI()162 Instruction* BasicBlock::getFirstNonPHI() {
163 BasicBlock::iterator i = begin();
164 // All valid basic blocks should have a terminator,
165 // which is not a PHINode. If we have an invalid basic
166 // block we'll get an assertion failure when dereferencing
167 // a past-the-end iterator.
168 while (isa<PHINode>(i)) ++i;
169 return &*i;
170 }
171
getFirstNonPHIOrDbg()172 Instruction* BasicBlock::getFirstNonPHIOrDbg() {
173 BasicBlock::iterator i = begin();
174 // All valid basic blocks should have a terminator,
175 // which is not a PHINode. If we have an invalid basic
176 // block we'll get an assertion failure when dereferencing
177 // a past-the-end iterator.
178 while (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i)) ++i;
179 return &*i;
180 }
181
getFirstNonPHIOrDbgOrLifetime()182 Instruction* BasicBlock::getFirstNonPHIOrDbgOrLifetime() {
183 // All valid basic blocks should have a terminator,
184 // which is not a PHINode. If we have an invalid basic
185 // block we'll get an assertion failure when dereferencing
186 // a past-the-end iterator.
187 BasicBlock::iterator i = begin();
188 for (;; ++i) {
189 if (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i))
190 continue;
191
192 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(i);
193 if (!II)
194 break;
195 if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
196 II->getIntrinsicID() != Intrinsic::lifetime_end)
197 break;
198 }
199 return &*i;
200 }
201
getFirstInsertionPt()202 BasicBlock::iterator BasicBlock::getFirstInsertionPt() {
203 iterator InsertPt = getFirstNonPHI();
204 if (isa<LandingPadInst>(InsertPt)) ++InsertPt;
205 return InsertPt;
206 }
207
dropAllReferences()208 void BasicBlock::dropAllReferences() {
209 for(iterator I = begin(), E = end(); I != E; ++I)
210 I->dropAllReferences();
211 }
212
213 /// getSinglePredecessor - If this basic block has a single predecessor block,
214 /// return the block, otherwise return a null pointer.
getSinglePredecessor()215 BasicBlock *BasicBlock::getSinglePredecessor() {
216 pred_iterator PI = pred_begin(this), E = pred_end(this);
217 if (PI == E) return nullptr; // No preds.
218 BasicBlock *ThePred = *PI;
219 ++PI;
220 return (PI == E) ? ThePred : nullptr /*multiple preds*/;
221 }
222
223 /// getUniquePredecessor - If this basic block has a unique predecessor block,
224 /// return the block, otherwise return a null pointer.
225 /// Note that unique predecessor doesn't mean single edge, there can be
226 /// multiple edges from the unique predecessor to this block (for example
227 /// a switch statement with multiple cases having the same destination).
getUniquePredecessor()228 BasicBlock *BasicBlock::getUniquePredecessor() {
229 pred_iterator PI = pred_begin(this), E = pred_end(this);
230 if (PI == E) return nullptr; // No preds.
231 BasicBlock *PredBB = *PI;
232 ++PI;
233 for (;PI != E; ++PI) {
234 if (*PI != PredBB)
235 return nullptr;
236 // The same predecessor appears multiple times in the predecessor list.
237 // This is OK.
238 }
239 return PredBB;
240 }
241
242 /// removePredecessor - This method is used to notify a BasicBlock that the
243 /// specified Predecessor of the block is no longer able to reach it. This is
244 /// actually not used to update the Predecessor list, but is actually used to
245 /// update the PHI nodes that reside in the block. Note that this should be
246 /// called while the predecessor still refers to this block.
247 ///
removePredecessor(BasicBlock * Pred,bool DontDeleteUselessPHIs)248 void BasicBlock::removePredecessor(BasicBlock *Pred,
249 bool DontDeleteUselessPHIs) {
250 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
251 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
252 "removePredecessor: BB is not a predecessor!");
253
254 if (InstList.empty()) return;
255 PHINode *APN = dyn_cast<PHINode>(&front());
256 if (!APN) return; // Quick exit.
257
258 // If there are exactly two predecessors, then we want to nuke the PHI nodes
259 // altogether. However, we cannot do this, if this in this case:
260 //
261 // Loop:
262 // %x = phi [X, Loop]
263 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
264 // br Loop ;; %x2 does not dominate all uses
265 //
266 // This is because the PHI node input is actually taken from the predecessor
267 // basic block. The only case this can happen is with a self loop, so we
268 // check for this case explicitly now.
269 //
270 unsigned max_idx = APN->getNumIncomingValues();
271 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
272 if (max_idx == 2) {
273 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
274
275 // Disable PHI elimination!
276 if (this == Other) max_idx = 3;
277 }
278
279 // <= Two predecessors BEFORE I remove one?
280 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
281 // Yup, loop through and nuke the PHI nodes
282 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
283 // Remove the predecessor first.
284 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
285
286 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
287 if (max_idx == 2) {
288 if (PN->getIncomingValue(0) != PN)
289 PN->replaceAllUsesWith(PN->getIncomingValue(0));
290 else
291 // We are left with an infinite loop with no entries: kill the PHI.
292 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
293 getInstList().pop_front(); // Remove the PHI node
294 }
295
296 // If the PHI node already only had one entry, it got deleted by
297 // removeIncomingValue.
298 }
299 } else {
300 // Okay, now we know that we need to remove predecessor #pred_idx from all
301 // PHI nodes. Iterate over each PHI node fixing them up
302 PHINode *PN;
303 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
304 ++II;
305 PN->removeIncomingValue(Pred, false);
306 // If all incoming values to the Phi are the same, we can replace the Phi
307 // with that value.
308 Value* PNV = nullptr;
309 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue()))
310 if (PNV != PN) {
311 PN->replaceAllUsesWith(PNV);
312 PN->eraseFromParent();
313 }
314 }
315 }
316 }
317
318
319 /// splitBasicBlock - This splits a basic block into two at the specified
320 /// instruction. Note that all instructions BEFORE the specified iterator stay
321 /// as part of the original basic block, an unconditional branch is added to
322 /// the new BB, and the rest of the instructions in the BB are moved to the new
323 /// BB, including the old terminator. This invalidates the iterator.
324 ///
325 /// Note that this only works on well formed basic blocks (must have a
326 /// terminator), and 'I' must not be the end of instruction list (which would
327 /// cause a degenerate basic block to be formed, having a terminator inside of
328 /// the basic block).
329 ///
splitBasicBlock(iterator I,const Twine & BBName)330 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
331 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
332 assert(I != InstList.end() &&
333 "Trying to get me to create degenerate basic block!");
334
335 BasicBlock *InsertBefore = std::next(Function::iterator(this))
336 .getNodePtrUnchecked();
337 BasicBlock *New = BasicBlock::Create(getContext(), BBName,
338 getParent(), InsertBefore);
339
340 // Move all of the specified instructions from the original basic block into
341 // the new basic block.
342 New->getInstList().splice(New->end(), this->getInstList(), I, end());
343
344 // Add a branch instruction to the newly formed basic block.
345 BranchInst::Create(New, this);
346
347 // Now we must loop through all of the successors of the New block (which
348 // _were_ the successors of the 'this' block), and update any PHI nodes in
349 // successors. If there were PHI nodes in the successors, then they need to
350 // know that incoming branches will be from New, not from Old.
351 //
352 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
353 // Loop over any phi nodes in the basic block, updating the BB field of
354 // incoming values...
355 BasicBlock *Successor = *I;
356 PHINode *PN;
357 for (BasicBlock::iterator II = Successor->begin();
358 (PN = dyn_cast<PHINode>(II)); ++II) {
359 int IDX = PN->getBasicBlockIndex(this);
360 while (IDX != -1) {
361 PN->setIncomingBlock((unsigned)IDX, New);
362 IDX = PN->getBasicBlockIndex(this);
363 }
364 }
365 }
366 return New;
367 }
368
replaceSuccessorsPhiUsesWith(BasicBlock * New)369 void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) {
370 TerminatorInst *TI = getTerminator();
371 if (!TI)
372 // Cope with being called on a BasicBlock that doesn't have a terminator
373 // yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this.
374 return;
375 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
376 BasicBlock *Succ = TI->getSuccessor(i);
377 // N.B. Succ might not be a complete BasicBlock, so don't assume
378 // that it ends with a non-phi instruction.
379 for (iterator II = Succ->begin(), IE = Succ->end(); II != IE; ++II) {
380 PHINode *PN = dyn_cast<PHINode>(II);
381 if (!PN)
382 break;
383 int i;
384 while ((i = PN->getBasicBlockIndex(this)) >= 0)
385 PN->setIncomingBlock(i, New);
386 }
387 }
388 }
389
390 /// isLandingPad - Return true if this basic block is a landing pad. I.e., it's
391 /// the destination of the 'unwind' edge of an invoke instruction.
isLandingPad() const392 bool BasicBlock::isLandingPad() const {
393 return isa<LandingPadInst>(getFirstNonPHI());
394 }
395
396 /// getLandingPadInst() - Return the landingpad instruction associated with
397 /// the landing pad.
getLandingPadInst()398 LandingPadInst *BasicBlock::getLandingPadInst() {
399 return dyn_cast<LandingPadInst>(getFirstNonPHI());
400 }
getLandingPadInst() const401 const LandingPadInst *BasicBlock::getLandingPadInst() const {
402 return dyn_cast<LandingPadInst>(getFirstNonPHI());
403 }
404