1 //===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
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 family of functions perform manipulations on basic blocks, and
11 // instructions contained within basic blocks.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
16 #include "llvm/Function.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/Constant.h"
19 #include "llvm/Type.h"
20 #include "llvm/Analysis/AliasAnalysis.h"
21 #include "llvm/Analysis/LoopInfo.h"
22 #include "llvm/Analysis/Dominators.h"
26 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
27 /// if possible. The return value indicates success or failure.
28 bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) {
29 // Can't merge the entry block.
30 if (pred_begin(BB) == pred_end(BB)) return false;
31 // Can't merge if there are multiple preds.
32 if (++pred_begin(BB) != pred_end(BB)) return false;
34 BasicBlock* PredBB = *pred_begin(BB);
36 // Can't merge if the edge is critical.
37 if (PredBB->getTerminator()->getNumSuccessors() != 1) return false;
39 // Begin by getting rid of unneeded PHIs.
40 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
41 PN->replaceAllUsesWith(PN->getIncomingValue(0));
42 BB->getInstList().pop_front(); // Delete the phi node...
45 // Delete the unconditional branch from the predecessor...
46 PredBB->getInstList().pop_back();
48 // Move all definitions in the successor to the predecessor...
49 PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
51 // Make all PHI nodes that referred to BB now refer to Pred as their
53 BB->replaceAllUsesWith(PredBB);
55 // Finally, erase the old block and update dominator info.
57 if (DominatorTree* DT = P->getAnalysisToUpdate<DominatorTree>()) {
58 DomTreeNode* DTN = DT->getNode(BB);
59 DomTreeNode* PredDTN = DT->getNode(PredBB);
62 SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
63 for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(),
64 DE = Children.end(); DI != DE; ++DI)
65 DT->changeImmediateDominator(*DI, PredDTN);
72 BB->eraseFromParent();
78 /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
79 /// with a value, then remove and delete the original instruction.
81 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
82 BasicBlock::iterator &BI, Value *V) {
84 // Replaces all of the uses of the instruction with uses of the value
85 I.replaceAllUsesWith(V);
87 // Make sure to propagate a name if there is one already.
88 if (I.hasName() && !V->hasName())
91 // Delete the unnecessary instruction now...
96 /// ReplaceInstWithInst - Replace the instruction specified by BI with the
97 /// instruction specified by I. The original instruction is deleted and BI is
98 /// updated to point to the new instruction.
100 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
101 BasicBlock::iterator &BI, Instruction *I) {
102 assert(I->getParent() == 0 &&
103 "ReplaceInstWithInst: Instruction already inserted into basic block!");
105 // Insert the new instruction into the basic block...
106 BasicBlock::iterator New = BIL.insert(BI, I);
108 // Replace all uses of the old instruction, and delete it.
109 ReplaceInstWithValue(BIL, BI, I);
111 // Move BI back to point to the newly inserted instruction
115 /// ReplaceInstWithInst - Replace the instruction specified by From with the
116 /// instruction specified by To.
118 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
119 BasicBlock::iterator BI(From);
120 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
123 /// RemoveSuccessor - Change the specified terminator instruction such that its
124 /// successor SuccNum no longer exists. Because this reduces the outgoing
125 /// degree of the current basic block, the actual terminator instruction itself
126 /// may have to be changed. In the case where the last successor of the block
127 /// is deleted, a return instruction is inserted in its place which can cause a
128 /// surprising change in program behavior if it is not expected.
130 void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) {
131 assert(SuccNum < TI->getNumSuccessors() &&
132 "Trying to remove a nonexistant successor!");
134 // If our old successor block contains any PHI nodes, remove the entry in the
135 // PHI nodes that comes from this branch...
137 BasicBlock *BB = TI->getParent();
138 TI->getSuccessor(SuccNum)->removePredecessor(BB);
140 TerminatorInst *NewTI = 0;
141 switch (TI->getOpcode()) {
142 case Instruction::Br:
143 // If this is a conditional branch... convert to unconditional branch.
144 if (TI->getNumSuccessors() == 2) {
145 cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum));
146 } else { // Otherwise convert to a return instruction...
149 // Create a value to return... if the function doesn't return null...
150 if (BB->getParent()->getReturnType() != Type::VoidTy)
151 RetVal = Constant::getNullValue(BB->getParent()->getReturnType());
153 // Create the return...
154 NewTI = ReturnInst::Create(RetVal);
158 case Instruction::Invoke: // Should convert to call
159 case Instruction::Switch: // Should remove entry
161 case Instruction::Ret: // Cannot happen, has no successors!
162 assert(0 && "Unhandled terminator instruction type in RemoveSuccessor!");
166 if (NewTI) // If it's a different instruction, replace.
167 ReplaceInstWithInst(TI, NewTI);
170 /// SplitEdge - Split the edge connecting specified block. Pass P must
172 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
173 TerminatorInst *LatchTerm = BB->getTerminator();
174 unsigned SuccNum = 0;
175 for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) {
176 assert(i != e && "Didn't find edge?");
177 if (LatchTerm->getSuccessor(i) == Succ) {
183 // If this is a critical edge, let SplitCriticalEdge do it.
184 if (SplitCriticalEdge(BB->getTerminator(), SuccNum, P))
185 return LatchTerm->getSuccessor(SuccNum);
187 // If the edge isn't critical, then BB has a single successor or Succ has a
188 // single pred. Split the block.
189 BasicBlock::iterator SplitPoint;
190 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
191 // If the successor only has a single pred, split the top of the successor
193 assert(SP == BB && "CFG broken");
194 return SplitBlock(Succ, Succ->begin(), P);
196 // Otherwise, if BB has a single successor, split it at the bottom of the
198 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
199 "Should have a single succ!");
200 return SplitBlock(BB, BB->getTerminator(), P);
204 /// SplitBlock - Split the specified block at the specified instruction - every
205 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
206 /// to a new block. The two blocks are joined by an unconditional branch and
207 /// the loop info is updated.
209 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
211 LoopInfo &LI = P->getAnalysis<LoopInfo>();
212 BasicBlock::iterator SplitIt = SplitPt;
213 while (isa<PHINode>(SplitIt))
215 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
217 // The new block lives in whichever loop the old one did.
218 if (Loop *L = LI.getLoopFor(Old))
219 L->addBasicBlockToLoop(New, LI.getBase());
221 if (DominatorTree *DT = P->getAnalysisToUpdate<DominatorTree>())
223 // Old dominates New. New node domiantes all other nodes dominated by Old.
224 DomTreeNode *OldNode = DT->getNode(Old);
225 std::vector<DomTreeNode *> Children;
226 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
228 Children.push_back(*I);
230 DomTreeNode *NewNode = DT->addNewBlock(New,Old);
232 for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
233 E = Children.end(); I != E; ++I)
234 DT->changeImmediateDominator(*I, NewNode);
237 if (DominanceFrontier *DF = P->getAnalysisToUpdate<DominanceFrontier>())
244 /// SplitBlockPredecessors - This method transforms BB by introducing a new
245 /// basic block into the function, and moving some of the predecessors of BB to
246 /// be predecessors of the new block. The new predecessors are indicated by the
247 /// Preds array, which has NumPreds elements in it. The new block is given a
248 /// suffix of 'Suffix'.
250 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree and
251 /// DominanceFrontier, but no other analyses.
252 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
253 BasicBlock *const *Preds,
254 unsigned NumPreds, const char *Suffix,
256 // Create new basic block, insert right before the original block.
258 BasicBlock::Create(BB->getName()+Suffix, BB->getParent(), BB);
260 // The new block unconditionally branches to the old block.
261 BranchInst *BI = BranchInst::Create(BB, NewBB);
263 // Move the edges from Preds to point to NewBB instead of BB.
264 for (unsigned i = 0; i != NumPreds; ++i)
265 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
267 // Update dominator tree and dominator frontier if available.
268 DominatorTree *DT = P ? P->getAnalysisToUpdate<DominatorTree>() : 0;
270 DT->splitBlock(NewBB);
271 if (DominanceFrontier *DF = P ? P->getAnalysisToUpdate<DominanceFrontier>():0)
272 DF->splitBlock(NewBB);
273 AliasAnalysis *AA = P ? P->getAnalysisToUpdate<AliasAnalysis>() : 0;
276 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
277 // node becomes an incoming value for BB's phi node. However, if the Preds
278 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
279 // account for the newly created predecessor.
281 // Insert dummy values as the incoming value.
282 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
283 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
287 // Otherwise, create a new PHI node in NewBB for each PHI node in BB.
288 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
289 PHINode *PN = cast<PHINode>(I++);
291 // Check to see if all of the values coming in are the same. If so, we
292 // don't need to create a new PHI node.
293 Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
294 for (unsigned i = 1; i != NumPreds; ++i)
295 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
301 // If all incoming values for the new PHI would be the same, just don't
302 // make a new PHI. Instead, just remove the incoming values from the old
304 for (unsigned i = 0; i != NumPreds; ++i)
305 PN->removeIncomingValue(Preds[i], false);
307 // If the values coming into the block are not the same, we need a PHI.
308 // Create the new PHI node, insert it into NewBB at the end of the block
310 PHINode::Create(PN->getType(), PN->getName()+".ph", BI);
311 if (AA) AA->copyValue(PN, NewPHI);
313 // Move all of the PHI values for 'Preds' to the new PHI.
314 for (unsigned i = 0; i != NumPreds; ++i) {
315 Value *V = PN->removeIncomingValue(Preds[i], false);
316 NewPHI->addIncoming(V, Preds[i]);
321 // Add an incoming value to the PHI node in the loop for the preheader
323 PN->addIncoming(InVal, NewBB);
325 // Check to see if we can eliminate this phi node.
326 if (Value *V = PN->hasConstantValue(DT != 0)) {
327 Instruction *I = dyn_cast<Instruction>(V);
328 if (!I || DT == 0 || DT->dominates(I, PN)) {
329 PN->replaceAllUsesWith(V);
330 if (AA) AA->deleteValue(PN);
331 PN->eraseFromParent();