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/Type.h"
27 ValueSymbolTable *BasicBlock::getValueSymbolTable() {
28 if (Function *F = getParent())
29 return F->getValueSymbolTable();
33 LLVMContext &BasicBlock::getContext() const {
34 return getType()->getContext();
37 // Explicit instantiation of SymbolTableListTraits since some of the methods
38 // are not in the public header file...
39 template class llvm::SymbolTableListTraits<Instruction>;
41 BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent,
42 BasicBlock *InsertBefore)
43 : Value(Type::getLabelTy(C), Value::BasicBlockVal), Parent(nullptr) {
46 insertInto(NewParent, InsertBefore);
48 assert(!InsertBefore &&
49 "Cannot insert block before another block with no function!");
54 void BasicBlock::insertInto(Function *NewParent, BasicBlock *InsertBefore) {
55 assert(NewParent && "Expected a parent");
56 assert(!Parent && "Already has a parent");
59 NewParent->getBasicBlockList().insert(InsertBefore->getIterator(), this);
61 NewParent->getBasicBlockList().push_back(this);
64 BasicBlock::~BasicBlock() {
65 // If the address of the block is taken and it is being deleted (e.g. because
66 // it is dead), this means that there is either a dangling constant expr
67 // hanging off the block, or an undefined use of the block (source code
68 // expecting the address of a label to keep the block alive even though there
69 // is no indirect branch). Handle these cases by zapping the BlockAddress
70 // nodes. There are no other possible uses at this point.
71 if (hasAddressTaken()) {
72 assert(!use_empty() && "There should be at least one blockaddress!");
73 Constant *Replacement =
74 ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1);
75 while (!use_empty()) {
76 BlockAddress *BA = cast<BlockAddress>(user_back());
77 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
79 BA->destroyConstant();
83 assert(getParent() == nullptr && "BasicBlock still linked into the program!");
88 void BasicBlock::setParent(Function *parent) {
89 // Set Parent=parent, updating instruction symtab entries as appropriate.
90 InstList.setSymTabObject(&Parent, parent);
93 iterator_range<filter_iterator<BasicBlock::const_iterator,
94 std::function<bool(const Instruction &)>>>
95 BasicBlock::instructionsWithoutDebug() const {
96 std::function<bool(const Instruction &)> Fn = [](const Instruction &I) {
97 return !isa<DbgInfoIntrinsic>(I);
99 return make_filter_range(*this, Fn);
102 iterator_range<filter_iterator<BasicBlock::iterator,
103 std::function<bool(Instruction &)>>>
104 BasicBlock::instructionsWithoutDebug() {
105 std::function<bool(Instruction &)> Fn = [](Instruction &I) {
106 return !isa<DbgInfoIntrinsic>(I);
108 return make_filter_range(*this, Fn);
111 void BasicBlock::removeFromParent() {
112 getParent()->getBasicBlockList().remove(getIterator());
115 iplist<BasicBlock>::iterator BasicBlock::eraseFromParent() {
116 return getParent()->getBasicBlockList().erase(getIterator());
119 /// Unlink this basic block from its current function and
120 /// insert it into the function that MovePos lives in, right before MovePos.
121 void BasicBlock::moveBefore(BasicBlock *MovePos) {
122 MovePos->getParent()->getBasicBlockList().splice(
123 MovePos->getIterator(), getParent()->getBasicBlockList(), getIterator());
126 /// Unlink this basic block from its current function and
127 /// insert it into the function that MovePos lives in, right after MovePos.
128 void BasicBlock::moveAfter(BasicBlock *MovePos) {
129 MovePos->getParent()->getBasicBlockList().splice(
130 ++MovePos->getIterator(), getParent()->getBasicBlockList(),
134 const Module *BasicBlock::getModule() const {
135 return getParent()->getParent();
138 const Instruction *BasicBlock::getTerminator() const {
139 if (InstList.empty() || !InstList.back().isTerminator())
141 return &InstList.back();
144 const CallInst *BasicBlock::getTerminatingMustTailCall() const {
145 if (InstList.empty())
147 const ReturnInst *RI = dyn_cast<ReturnInst>(&InstList.back());
148 if (!RI || RI == &InstList.front())
151 const Instruction *Prev = RI->getPrevNode();
155 if (Value *RV = RI->getReturnValue()) {
159 // Look through the optional bitcast.
160 if (auto *BI = dyn_cast<BitCastInst>(Prev)) {
161 RV = BI->getOperand(0);
162 Prev = BI->getPrevNode();
163 if (!Prev || RV != Prev)
168 if (auto *CI = dyn_cast<CallInst>(Prev)) {
169 if (CI->isMustTailCall())
175 const CallInst *BasicBlock::getTerminatingDeoptimizeCall() const {
176 if (InstList.empty())
178 auto *RI = dyn_cast<ReturnInst>(&InstList.back());
179 if (!RI || RI == &InstList.front())
182 if (auto *CI = dyn_cast_or_null<CallInst>(RI->getPrevNode()))
183 if (Function *F = CI->getCalledFunction())
184 if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize)
190 const Instruction* BasicBlock::getFirstNonPHI() const {
191 for (const Instruction &I : *this)
192 if (!isa<PHINode>(I))
197 const Instruction* BasicBlock::getFirstNonPHIOrDbg() const {
198 for (const Instruction &I : *this)
199 if (!isa<PHINode>(I) && !isa<DbgInfoIntrinsic>(I))
204 const Instruction* BasicBlock::getFirstNonPHIOrDbgOrLifetime() const {
205 for (const Instruction &I : *this) {
206 if (isa<PHINode>(I) || isa<DbgInfoIntrinsic>(I))
209 if (I.isLifetimeStartOrEnd())
217 BasicBlock::const_iterator BasicBlock::getFirstInsertionPt() const {
218 const Instruction *FirstNonPHI = getFirstNonPHI();
222 const_iterator InsertPt = FirstNonPHI->getIterator();
223 if (InsertPt->isEHPad()) ++InsertPt;
227 void BasicBlock::dropAllReferences() {
228 for (Instruction &I : *this)
229 I.dropAllReferences();
232 /// If this basic block has a single predecessor block,
233 /// return the block, otherwise return a null pointer.
234 const BasicBlock *BasicBlock::getSinglePredecessor() const {
235 const_pred_iterator PI = pred_begin(this), E = pred_end(this);
236 if (PI == E) return nullptr; // No preds.
237 const BasicBlock *ThePred = *PI;
239 return (PI == E) ? ThePred : nullptr /*multiple preds*/;
242 /// If this basic block has a unique predecessor block,
243 /// return the block, otherwise return a null pointer.
244 /// Note that unique predecessor doesn't mean single edge, there can be
245 /// multiple edges from the unique predecessor to this block (for example
246 /// a switch statement with multiple cases having the same destination).
247 const BasicBlock *BasicBlock::getUniquePredecessor() const {
248 const_pred_iterator PI = pred_begin(this), E = pred_end(this);
249 if (PI == E) return nullptr; // No preds.
250 const BasicBlock *PredBB = *PI;
252 for (;PI != E; ++PI) {
255 // The same predecessor appears multiple times in the predecessor list.
261 bool BasicBlock::hasNPredecessors(unsigned N) const {
262 return hasNItems(pred_begin(this), pred_end(this), N);
265 bool BasicBlock::hasNPredecessorsOrMore(unsigned N) const {
266 return hasNItemsOrMore(pred_begin(this), pred_end(this), N);
269 const BasicBlock *BasicBlock::getSingleSuccessor() const {
270 succ_const_iterator SI = succ_begin(this), E = succ_end(this);
271 if (SI == E) return nullptr; // no successors
272 const BasicBlock *TheSucc = *SI;
274 return (SI == E) ? TheSucc : nullptr /* multiple successors */;
277 const BasicBlock *BasicBlock::getUniqueSuccessor() const {
278 succ_const_iterator SI = succ_begin(this), E = succ_end(this);
279 if (SI == E) return nullptr; // No successors
280 const BasicBlock *SuccBB = *SI;
282 for (;SI != E; ++SI) {
285 // The same successor appears multiple times in the successor list.
291 iterator_range<BasicBlock::phi_iterator> BasicBlock::phis() {
292 PHINode *P = empty() ? nullptr : dyn_cast<PHINode>(&*begin());
293 return make_range<phi_iterator>(P, nullptr);
296 /// This method is used to notify a BasicBlock that the
297 /// specified Predecessor of the block is no longer able to reach it. This is
298 /// actually not used to update the Predecessor list, but is actually used to
299 /// update the PHI nodes that reside in the block. Note that this should be
300 /// called while the predecessor still refers to this block.
302 void BasicBlock::removePredecessor(BasicBlock *Pred,
303 bool DontDeleteUselessPHIs) {
304 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
305 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
306 "removePredecessor: BB is not a predecessor!");
308 if (InstList.empty()) return;
309 PHINode *APN = dyn_cast<PHINode>(&front());
310 if (!APN) return; // Quick exit.
312 // If there are exactly two predecessors, then we want to nuke the PHI nodes
313 // altogether. However, we cannot do this, if this in this case:
316 // %x = phi [X, Loop]
317 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
318 // br Loop ;; %x2 does not dominate all uses
320 // This is because the PHI node input is actually taken from the predecessor
321 // basic block. The only case this can happen is with a self loop, so we
322 // check for this case explicitly now.
324 unsigned max_idx = APN->getNumIncomingValues();
325 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
327 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
329 // Disable PHI elimination!
330 if (this == Other) max_idx = 3;
333 // <= Two predecessors BEFORE I remove one?
334 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
335 // Yup, loop through and nuke the PHI nodes
336 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
337 // Remove the predecessor first.
338 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
340 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
342 if (PN->getIncomingValue(0) != PN)
343 PN->replaceAllUsesWith(PN->getIncomingValue(0));
345 // We are left with an infinite loop with no entries: kill the PHI.
346 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
347 getInstList().pop_front(); // Remove the PHI node
350 // If the PHI node already only had one entry, it got deleted by
351 // removeIncomingValue.
354 // Okay, now we know that we need to remove predecessor #pred_idx from all
355 // PHI nodes. Iterate over each PHI node fixing them up
357 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
359 PN->removeIncomingValue(Pred, false);
360 // If all incoming values to the Phi are the same, we can replace the Phi
362 Value* PNV = nullptr;
363 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue()))
365 PN->replaceAllUsesWith(PNV);
366 PN->eraseFromParent();
372 bool BasicBlock::canSplitPredecessors() const {
373 const Instruction *FirstNonPHI = getFirstNonPHI();
374 if (isa<LandingPadInst>(FirstNonPHI))
376 // This is perhaps a little conservative because constructs like
377 // CleanupBlockInst are pretty easy to split. However, SplitBlockPredecessors
378 // cannot handle such things just yet.
379 if (FirstNonPHI->isEHPad())
384 bool BasicBlock::isLegalToHoistInto() const {
385 auto *Term = getTerminator();
386 // No terminator means the block is under construction.
390 // If the block has no successors, there can be no instructions to hoist.
391 assert(Term->getNumSuccessors() > 0);
393 // Instructions should not be hoisted across exception handling boundaries.
394 return !Term->isExceptionalTerminator();
397 /// This splits a basic block into two at the specified
398 /// instruction. Note that all instructions BEFORE the specified iterator stay
399 /// as part of the original basic block, an unconditional branch is added to
400 /// the new BB, and the rest of the instructions in the BB are moved to the new
401 /// BB, including the old terminator. This invalidates the iterator.
403 /// Note that this only works on well formed basic blocks (must have a
404 /// terminator), and 'I' must not be the end of instruction list (which would
405 /// cause a degenerate basic block to be formed, having a terminator inside of
406 /// the basic block).
408 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
409 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
410 assert(I != InstList.end() &&
411 "Trying to get me to create degenerate basic block!");
413 BasicBlock *New = BasicBlock::Create(getContext(), BBName, getParent(),
414 this->getNextNode());
416 // Save DebugLoc of split point before invalidating iterator.
417 DebugLoc Loc = I->getDebugLoc();
418 // Move all of the specified instructions from the original basic block into
419 // the new basic block.
420 New->getInstList().splice(New->end(), this->getInstList(), I, end());
422 // Add a branch instruction to the newly formed basic block.
423 BranchInst *BI = BranchInst::Create(New, this);
424 BI->setDebugLoc(Loc);
426 // Now we must loop through all of the successors of the New block (which
427 // _were_ the successors of the 'this' block), and update any PHI nodes in
428 // successors. If there were PHI nodes in the successors, then they need to
429 // know that incoming branches will be from New, not from Old.
431 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
432 // Loop over any phi nodes in the basic block, updating the BB field of
433 // incoming values...
434 BasicBlock *Successor = *I;
435 for (auto &PN : Successor->phis()) {
436 int Idx = PN.getBasicBlockIndex(this);
438 PN.setIncomingBlock((unsigned)Idx, New);
439 Idx = PN.getBasicBlockIndex(this);
446 void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) {
447 Instruction *TI = getTerminator();
449 // Cope with being called on a BasicBlock that doesn't have a terminator
450 // yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this.
452 for (BasicBlock *Succ : successors(TI)) {
453 // N.B. Succ might not be a complete BasicBlock, so don't assume
454 // that it ends with a non-phi instruction.
455 for (iterator II = Succ->begin(), IE = Succ->end(); II != IE; ++II) {
456 PHINode *PN = dyn_cast<PHINode>(II);
460 while ((i = PN->getBasicBlockIndex(this)) >= 0)
461 PN->setIncomingBlock(i, New);
466 /// Return true if this basic block is a landing pad. I.e., it's
467 /// the destination of the 'unwind' edge of an invoke instruction.
468 bool BasicBlock::isLandingPad() const {
469 return isa<LandingPadInst>(getFirstNonPHI());
472 /// Return the landingpad instruction associated with the landing pad.
473 const LandingPadInst *BasicBlock::getLandingPadInst() const {
474 return dyn_cast<LandingPadInst>(getFirstNonPHI());
477 Optional<uint64_t> BasicBlock::getIrrLoopHeaderWeight() const {
478 const Instruction *TI = getTerminator();
479 if (MDNode *MDIrrLoopHeader =
480 TI->getMetadata(LLVMContext::MD_irr_loop)) {
481 MDString *MDName = cast<MDString>(MDIrrLoopHeader->getOperand(0));
482 if (MDName->getString().equals("loop_header_weight")) {
483 auto *CI = mdconst::extract<ConstantInt>(MDIrrLoopHeader->getOperand(1));
484 return Optional<uint64_t>(CI->getValue().getZExtValue());
487 return Optional<uint64_t>();
490 BasicBlock::iterator llvm::skipDebugIntrinsics(BasicBlock::iterator It) {
491 while (isa<DbgInfoIntrinsic>(It))