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