1 //===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
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 BasicBlock class for the IR library.
12 //===----------------------------------------------------------------------===//
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/LeakDetector.h"
23 #include "llvm/IR/Type.h"
27 ValueSymbolTable *BasicBlock::getValueSymbolTable() {
28 if (Function *F = getParent())
29 return &F->getValueSymbolTable();
33 const DataLayout *BasicBlock::getDataLayout() const {
34 return getParent()->getDataLayout();
37 LLVMContext &BasicBlock::getContext() const {
38 return getType()->getContext();
41 // Explicit instantiation of SymbolTableListTraits since some of the methods
42 // are not in the public header file...
43 template class llvm::SymbolTableListTraits<Instruction, BasicBlock>;
46 BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent,
47 BasicBlock *InsertBefore)
48 : Value(Type::getLabelTy(C), Value::BasicBlockVal), Parent(nullptr) {
50 // Make sure that we get added to a function
51 LeakDetector::addGarbageObject(this);
55 "Cannot insert block before another block with no function!");
56 NewParent->getBasicBlockList().insert(InsertBefore, this);
57 } else if (NewParent) {
58 NewParent->getBasicBlockList().push_back(this);
65 BasicBlock::~BasicBlock() {
66 // If the address of the block is taken and it is being deleted (e.g. because
67 // it is dead), this means that there is either a dangling constant expr
68 // hanging off the block, or an undefined use of the block (source code
69 // expecting the address of a label to keep the block alive even though there
70 // is no indirect branch). Handle these cases by zapping the BlockAddress
71 // nodes. There are no other possible uses at this point.
72 if (hasAddressTaken()) {
73 assert(!use_empty() && "There should be at least one blockaddress!");
74 Constant *Replacement =
75 ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1);
76 while (!use_empty()) {
77 BlockAddress *BA = cast<BlockAddress>(user_back());
78 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
80 BA->destroyConstant();
84 assert(getParent() == nullptr && "BasicBlock still linked into the program!");
89 void BasicBlock::setParent(Function *parent) {
91 LeakDetector::addGarbageObject(this);
93 // Set Parent=parent, updating instruction symtab entries as appropriate.
94 InstList.setSymTabObject(&Parent, parent);
97 LeakDetector::removeGarbageObject(this);
100 void BasicBlock::removeFromParent() {
101 getParent()->getBasicBlockList().remove(this);
104 void BasicBlock::eraseFromParent() {
105 getParent()->getBasicBlockList().erase(this);
108 /// moveBefore - Unlink this basic block from its current function and
109 /// insert it into the function that MovePos lives in, right before MovePos.
110 void BasicBlock::moveBefore(BasicBlock *MovePos) {
111 MovePos->getParent()->getBasicBlockList().splice(MovePos,
112 getParent()->getBasicBlockList(), this);
115 /// moveAfter - Unlink this basic block from its current function and
116 /// insert it into the function that MovePos lives in, right after MovePos.
117 void BasicBlock::moveAfter(BasicBlock *MovePos) {
118 Function::iterator I = MovePos;
119 MovePos->getParent()->getBasicBlockList().splice(++I,
120 getParent()->getBasicBlockList(), this);
124 TerminatorInst *BasicBlock::getTerminator() {
125 if (InstList.empty()) return nullptr;
126 return dyn_cast<TerminatorInst>(&InstList.back());
129 const TerminatorInst *BasicBlock::getTerminator() const {
130 if (InstList.empty()) return nullptr;
131 return dyn_cast<TerminatorInst>(&InstList.back());
134 Instruction* BasicBlock::getFirstNonPHI() {
135 BasicBlock::iterator i = begin();
136 // All valid basic blocks should have a terminator,
137 // which is not a PHINode. If we have an invalid basic
138 // block we'll get an assertion failure when dereferencing
139 // a past-the-end iterator.
140 while (isa<PHINode>(i)) ++i;
144 Instruction* BasicBlock::getFirstNonPHIOrDbg() {
145 BasicBlock::iterator i = begin();
146 // All valid basic blocks should have a terminator,
147 // which is not a PHINode. If we have an invalid basic
148 // block we'll get an assertion failure when dereferencing
149 // a past-the-end iterator.
150 while (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i)) ++i;
154 Instruction* BasicBlock::getFirstNonPHIOrDbgOrLifetime() {
155 // All valid basic blocks should have a terminator,
156 // which is not a PHINode. If we have an invalid basic
157 // block we'll get an assertion failure when dereferencing
158 // a past-the-end iterator.
159 BasicBlock::iterator i = begin();
161 if (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i))
164 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(i);
167 if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
168 II->getIntrinsicID() != Intrinsic::lifetime_end)
174 BasicBlock::iterator BasicBlock::getFirstInsertionPt() {
175 iterator InsertPt = getFirstNonPHI();
176 if (isa<LandingPadInst>(InsertPt)) ++InsertPt;
180 void BasicBlock::dropAllReferences() {
181 for(iterator I = begin(), E = end(); I != E; ++I)
182 I->dropAllReferences();
185 /// getSinglePredecessor - If this basic block has a single predecessor block,
186 /// return the block, otherwise return a null pointer.
187 BasicBlock *BasicBlock::getSinglePredecessor() {
188 pred_iterator PI = pred_begin(this), E = pred_end(this);
189 if (PI == E) return nullptr; // No preds.
190 BasicBlock *ThePred = *PI;
192 return (PI == E) ? ThePred : nullptr /*multiple preds*/;
195 /// getUniquePredecessor - If this basic block has a unique predecessor block,
196 /// return the block, otherwise return a null pointer.
197 /// Note that unique predecessor doesn't mean single edge, there can be
198 /// multiple edges from the unique predecessor to this block (for example
199 /// a switch statement with multiple cases having the same destination).
200 BasicBlock *BasicBlock::getUniquePredecessor() {
201 pred_iterator PI = pred_begin(this), E = pred_end(this);
202 if (PI == E) return nullptr; // No preds.
203 BasicBlock *PredBB = *PI;
205 for (;PI != E; ++PI) {
208 // The same predecessor appears multiple times in the predecessor list.
214 /// removePredecessor - This method is used to notify a BasicBlock that the
215 /// specified Predecessor of the block is no longer able to reach it. This is
216 /// actually not used to update the Predecessor list, but is actually used to
217 /// update the PHI nodes that reside in the block. Note that this should be
218 /// called while the predecessor still refers to this block.
220 void BasicBlock::removePredecessor(BasicBlock *Pred,
221 bool DontDeleteUselessPHIs) {
222 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
223 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
224 "removePredecessor: BB is not a predecessor!");
226 if (InstList.empty()) return;
227 PHINode *APN = dyn_cast<PHINode>(&front());
228 if (!APN) return; // Quick exit.
230 // If there are exactly two predecessors, then we want to nuke the PHI nodes
231 // altogether. However, we cannot do this, if this in this case:
234 // %x = phi [X, Loop]
235 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
236 // br Loop ;; %x2 does not dominate all uses
238 // This is because the PHI node input is actually taken from the predecessor
239 // basic block. The only case this can happen is with a self loop, so we
240 // check for this case explicitly now.
242 unsigned max_idx = APN->getNumIncomingValues();
243 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
245 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
247 // Disable PHI elimination!
248 if (this == Other) max_idx = 3;
251 // <= Two predecessors BEFORE I remove one?
252 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
253 // Yup, loop through and nuke the PHI nodes
254 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
255 // Remove the predecessor first.
256 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
258 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
260 if (PN->getIncomingValue(0) != PN)
261 PN->replaceAllUsesWith(PN->getIncomingValue(0));
263 // We are left with an infinite loop with no entries: kill the PHI.
264 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
265 getInstList().pop_front(); // Remove the PHI node
268 // If the PHI node already only had one entry, it got deleted by
269 // removeIncomingValue.
272 // Okay, now we know that we need to remove predecessor #pred_idx from all
273 // PHI nodes. Iterate over each PHI node fixing them up
275 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
277 PN->removeIncomingValue(Pred, false);
278 // If all incoming values to the Phi are the same, we can replace the Phi
280 Value* PNV = nullptr;
281 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue()))
283 PN->replaceAllUsesWith(PNV);
284 PN->eraseFromParent();
291 /// splitBasicBlock - This splits a basic block into two at the specified
292 /// instruction. Note that all instructions BEFORE the specified iterator stay
293 /// as part of the original basic block, an unconditional branch is added to
294 /// the new BB, and the rest of the instructions in the BB are moved to the new
295 /// BB, including the old terminator. This invalidates the iterator.
297 /// Note that this only works on well formed basic blocks (must have a
298 /// terminator), and 'I' must not be the end of instruction list (which would
299 /// cause a degenerate basic block to be formed, having a terminator inside of
300 /// the basic block).
302 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
303 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
304 assert(I != InstList.end() &&
305 "Trying to get me to create degenerate basic block!");
307 BasicBlock *InsertBefore = std::next(Function::iterator(this))
308 .getNodePtrUnchecked();
309 BasicBlock *New = BasicBlock::Create(getContext(), BBName,
310 getParent(), InsertBefore);
312 // Move all of the specified instructions from the original basic block into
313 // the new basic block.
314 New->getInstList().splice(New->end(), this->getInstList(), I, end());
316 // Add a branch instruction to the newly formed basic block.
317 BranchInst::Create(New, this);
319 // Now we must loop through all of the successors of the New block (which
320 // _were_ the successors of the 'this' block), and update any PHI nodes in
321 // successors. If there were PHI nodes in the successors, then they need to
322 // know that incoming branches will be from New, not from Old.
324 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
325 // Loop over any phi nodes in the basic block, updating the BB field of
326 // incoming values...
327 BasicBlock *Successor = *I;
329 for (BasicBlock::iterator II = Successor->begin();
330 (PN = dyn_cast<PHINode>(II)); ++II) {
331 int IDX = PN->getBasicBlockIndex(this);
333 PN->setIncomingBlock((unsigned)IDX, New);
334 IDX = PN->getBasicBlockIndex(this);
341 void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) {
342 TerminatorInst *TI = getTerminator();
344 // Cope with being called on a BasicBlock that doesn't have a terminator
345 // yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this.
347 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
348 BasicBlock *Succ = TI->getSuccessor(i);
349 // N.B. Succ might not be a complete BasicBlock, so don't assume
350 // that it ends with a non-phi instruction.
351 for (iterator II = Succ->begin(), IE = Succ->end(); II != IE; ++II) {
352 PHINode *PN = dyn_cast<PHINode>(II);
356 while ((i = PN->getBasicBlockIndex(this)) >= 0)
357 PN->setIncomingBlock(i, New);
362 /// isLandingPad - Return true if this basic block is a landing pad. I.e., it's
363 /// the destination of the 'unwind' edge of an invoke instruction.
364 bool BasicBlock::isLandingPad() const {
365 return isa<LandingPadInst>(getFirstNonPHI());
368 /// getLandingPadInst() - Return the landingpad instruction associated with
370 LandingPadInst *BasicBlock::getLandingPadInst() {
371 return dyn_cast<LandingPadInst>(getFirstNonPHI());
373 const LandingPadInst *BasicBlock::getLandingPadInst() const {
374 return dyn_cast<LandingPadInst>(getFirstNonPHI());