1 //===-- Transform/Utils/BasicBlockUtils.h - BasicBlock Utils ----*- C++ -*-===//
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 family of functions perform manipulations on basic blocks, and
11 // instructions contained within basic blocks.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H
16 #define LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H
17 
18 // FIXME: Move to this file: BasicBlock::removePredecessor, BB::splitBasicBlock
19 
20 #include "llvm/IR/BasicBlock.h"
21 #include "llvm/IR/CFG.h"
22 
23 namespace llvm {
24 
25 class AliasAnalysis;
26 class DominatorTree;
27 class Instruction;
28 class MDNode;
29 class Pass;
30 class ReturnInst;
31 class TargetLibraryInfo;
32 class TerminatorInst;
33 
34 /// DeleteDeadBlock - Delete the specified block, which must have no
35 /// predecessors.
36 void DeleteDeadBlock(BasicBlock *BB);
37 
38 /// FoldSingleEntryPHINodes - We know that BB has one predecessor.  If there are
39 /// any single-entry PHI nodes in it, fold them away.  This handles the case
40 /// when all entries to the PHI nodes in a block are guaranteed equal, such as
41 /// when the block has exactly one predecessor.
42 void FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P = nullptr);
43 
44 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
45 /// is dead. Also recursively delete any operands that become dead as
46 /// a result. This includes tracing the def-use list from the PHI to see if
47 /// it is ultimately unused or if it reaches an unused cycle. Return true
48 /// if any PHIs were deleted.
49 bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr);
50 
51 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
52 /// if possible.  The return value indicates success or failure.
53 bool MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P = nullptr);
54 
55 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
56 // with a value, then remove and delete the original instruction.
57 //
58 void ReplaceInstWithValue(BasicBlock::InstListType &BIL,
59                           BasicBlock::iterator &BI, Value *V);
60 
61 // ReplaceInstWithInst - Replace the instruction specified by BI with the
62 // instruction specified by I.  The original instruction is deleted and BI is
63 // updated to point to the new instruction.
64 //
65 void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
66                          BasicBlock::iterator &BI, Instruction *I);
67 
68 // ReplaceInstWithInst - Replace the instruction specified by From with the
69 // instruction specified by To.
70 //
71 void ReplaceInstWithInst(Instruction *From, Instruction *To);
72 
73 /// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
74 /// split the critical edge.  This will update DominatorTree and
75 /// DominatorFrontier information if it is available, thus calling this pass
76 /// will not invalidate either of them. This returns the new block if the edge
77 /// was split, null otherwise.
78 ///
79 /// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the
80 /// specified successor will be merged into the same critical edge block.
81 /// This is most commonly interesting with switch instructions, which may
82 /// have many edges to any one destination.  This ensures that all edges to that
83 /// dest go to one block instead of each going to a different block, but isn't
84 /// the standard definition of a "critical edge".
85 ///
86 /// It is invalid to call this function on a critical edge that starts at an
87 /// IndirectBrInst.  Splitting these edges will almost always create an invalid
88 /// program because the address of the new block won't be the one that is jumped
89 /// to.
90 ///
91 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
92                               Pass *P = nullptr,
93                               bool MergeIdenticalEdges = false,
94                               bool DontDeleteUselessPHIs = false,
95                               bool SplitLandingPads = false);
96 
97 inline BasicBlock *SplitCriticalEdge(BasicBlock *BB, succ_iterator SI,
98                                      Pass *P = nullptr) {
99   return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), P);
100 }
101 
102 /// SplitCriticalEdge - If the edge from *PI to BB is not critical, return
103 /// false.  Otherwise, split all edges between the two blocks and return true.
104 /// This updates all of the same analyses as the other SplitCriticalEdge
105 /// function.  If P is specified, it updates the analyses
106 /// described above.
107 inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI,
108                               Pass *P = nullptr) {
109   bool MadeChange = false;
110   TerminatorInst *TI = (*PI)->getTerminator();
111   for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
112     if (TI->getSuccessor(i) == Succ)
113       MadeChange |= !!SplitCriticalEdge(TI, i, P);
114   return MadeChange;
115 }
116 
117 /// SplitCriticalEdge - If an edge from Src to Dst is critical, split the edge
118 /// and return true, otherwise return false.  This method requires that there be
119 /// an edge between the two blocks.  If P is specified, it updates the analyses
120 /// described above.
121 inline BasicBlock *SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
122                                      Pass *P = nullptr,
123                                      bool MergeIdenticalEdges = false,
124                                      bool DontDeleteUselessPHIs = false) {
125   TerminatorInst *TI = Src->getTerminator();
126   unsigned i = 0;
127   while (1) {
128     assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
129     if (TI->getSuccessor(i) == Dst)
130       return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges,
131                                DontDeleteUselessPHIs);
132     ++i;
133   }
134 }
135 
136 // SplitAllCriticalEdges - Loop over all of the edges in the CFG,
137 // breaking critical edges as they are found. Pass P must not be NULL.
138 // Returns the number of broken edges.
139 unsigned SplitAllCriticalEdges(Function &F, Pass *P);
140 
141 /// SplitEdge -  Split the edge connecting specified block. Pass P must
142 /// not be NULL.
143 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, Pass *P);
144 
145 /// SplitBlock - Split the specified block at the specified instruction - every
146 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
147 /// to a new block.  The two blocks are joined by an unconditional branch and
148 /// the loop info is updated.
149 ///
150 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P);
151 
152 /// SplitBlockPredecessors - This method transforms BB by introducing a new
153 /// basic block into the function, and moving some of the predecessors of BB to
154 /// be predecessors of the new block.  The new predecessors are indicated by the
155 /// Preds array, which has NumPreds elements in it.  The new block is given a
156 /// suffix of 'Suffix'.  This function returns the new block.
157 ///
158 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
159 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
160 /// In particular, it does not preserve LoopSimplify (because it's
161 /// complicated to handle the case where one of the edges being split
162 /// is an exit of a loop with other exits).
163 ///
164 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock*> Preds,
165                                    const char *Suffix, Pass *P = nullptr);
166 
167 /// SplitLandingPadPredecessors - This method transforms the landing pad,
168 /// OrigBB, by introducing two new basic blocks into the function. One of those
169 /// new basic blocks gets the predecessors listed in Preds. The other basic
170 /// block gets the remaining predecessors of OrigBB. The landingpad instruction
171 /// OrigBB is clone into both of the new basic blocks. The new blocks are given
172 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector.
173 ///
174 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
175 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular,
176 /// it does not preserve LoopSimplify (because it's complicated to handle the
177 /// case where one of the edges being split is an exit of a loop with other
178 /// exits).
179 ///
180 void SplitLandingPadPredecessors(BasicBlock *OrigBB,ArrayRef<BasicBlock*> Preds,
181                                  const char *Suffix, const char *Suffix2,
182                                  Pass *P, SmallVectorImpl<BasicBlock*> &NewBBs);
183 
184 /// FoldReturnIntoUncondBranch - This method duplicates the specified return
185 /// instruction into a predecessor which ends in an unconditional branch. If
186 /// the return instruction returns a value defined by a PHI, propagate the
187 /// right value into the return. It returns the new return instruction in the
188 /// predecessor.
189 ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
190                                        BasicBlock *Pred);
191 
192 /// SplitBlockAndInsertIfThen - Split the containing block at the
193 /// specified instruction - everything before and including SplitBefore stays
194 /// in the old basic block, and everything after SplitBefore is moved to a
195 /// new block. The two blocks are connected by a conditional branch
196 /// (with value of Cmp being the condition).
197 /// Before:
198 ///   Head
199 ///   SplitBefore
200 ///   Tail
201 /// After:
202 ///   Head
203 ///   if (Cond)
204 ///     ThenBlock
205 ///   SplitBefore
206 ///   Tail
207 ///
208 /// If Unreachable is true, then ThenBlock ends with
209 /// UnreachableInst, otherwise it branches to Tail.
210 /// Returns the NewBasicBlock's terminator.
211 ///
212 /// Updates DT if given.
213 TerminatorInst *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
214                                           bool Unreachable,
215                                           MDNode *BranchWeights = nullptr,
216                                           DominatorTree *DT = nullptr);
217 
218 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
219 /// but also creates the ElseBlock.
220 /// Before:
221 ///   Head
222 ///   SplitBefore
223 ///   Tail
224 /// After:
225 ///   Head
226 ///   if (Cond)
227 ///     ThenBlock
228 ///   else
229 ///     ElseBlock
230 ///   SplitBefore
231 ///   Tail
232 void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
233                                    TerminatorInst **ThenTerm,
234                                    TerminatorInst **ElseTerm,
235                                    MDNode *BranchWeights = nullptr);
236 
237 ///
238 /// GetIfCondition - Check whether BB is the merge point of a if-region.
239 /// If so, return the boolean condition that determines which entry into
240 /// BB will be taken.  Also, return by references the block that will be
241 /// entered from if the condition is true, and the block that will be
242 /// entered if the condition is false.
243 Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
244                       BasicBlock *&IfFalse);
245 } // End llvm namespace
246 
247 #endif
248