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.
8 //===----------------------------------------------------------------------===//
10 // This family of functions perform manipulations on basic blocks, and
11 // instructions contained within basic blocks.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_TRANSFORMS_UTILS_BASICBLOCK_H
16 #define LLVM_TRANSFORMS_UTILS_BASICBLOCK_H
18 // FIXME: Move to this file: BasicBlock::removePredecessor, BB::splitBasicBlock
20 #include "llvm/BasicBlock.h"
21 #include "llvm/Support/CFG.h"
29 /// DeleteDeadBlock - Delete the specified block, which must have no
31 void DeleteDeadBlock(BasicBlock *BB);
34 /// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are
35 /// any single-entry PHI nodes in it, fold them away. This handles the case
36 /// when all entries to the PHI nodes in a block are guaranteed equal, such as
37 /// when the block has exactly one predecessor.
38 void FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P = 0);
40 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
41 /// is dead. Also recursively delete any operands that become dead as
42 /// a result. This includes tracing the def-use list from the PHI to see if
43 /// it is ultimately unused or if it reaches an unused cycle. Return true
44 /// if any PHIs were deleted.
45 bool DeleteDeadPHIs(BasicBlock *BB);
47 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
48 /// if possible. The return value indicates success or failure.
49 bool MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P = 0);
51 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
52 // with a value, then remove and delete the original instruction.
54 void ReplaceInstWithValue(BasicBlock::InstListType &BIL,
55 BasicBlock::iterator &BI, Value *V);
57 // ReplaceInstWithInst - Replace the instruction specified by BI with the
58 // instruction specified by I. The original instruction is deleted and BI is
59 // updated to point to the new instruction.
61 void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
62 BasicBlock::iterator &BI, Instruction *I);
64 // ReplaceInstWithInst - Replace the instruction specified by From with the
65 // instruction specified by To.
67 void ReplaceInstWithInst(Instruction *From, Instruction *To);
69 /// FindFunctionBackedges - Analyze the specified function to find all of the
70 /// loop backedges in the function and return them. This is a relatively cheap
71 /// (compared to computing dominators and loop info) analysis.
73 /// The output is added to Result, as pairs of <from,to> edge info.
74 void FindFunctionBackedges(const Function &F,
75 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result);
78 /// GetSuccessorNumber - Search for the specified successor of basic block BB
79 /// and return its position in the terminator instruction's list of
80 /// successors. It is an error to call this with a block that is not a
82 unsigned GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ);
84 /// isCriticalEdge - Return true if the specified edge is a critical edge.
85 /// Critical edges are edges from a block with multiple successors to a block
86 /// with multiple predecessors.
88 bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
89 bool AllowIdenticalEdges = false);
91 /// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
92 /// split the critical edge. This will update DominatorTree and
93 /// DominatorFrontier information if it is available, thus calling this pass
94 /// will not invalidate either of them. This returns the new block if the edge
95 /// was split, null otherwise.
97 /// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the
98 /// specified successor will be merged into the same critical edge block.
99 /// This is most commonly interesting with switch instructions, which may
100 /// have many edges to any one destination. This ensures that all edges to that
101 /// dest go to one block instead of each going to a different block, but isn't
102 /// the standard definition of a "critical edge".
104 /// It is invalid to call this function on a critical edge that starts at an
105 /// IndirectBrInst. Splitting these edges will almost always create an invalid
106 /// program because the address of the new block won't be the one that is jumped
109 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
110 Pass *P = 0, bool MergeIdenticalEdges = false);
112 inline BasicBlock *SplitCriticalEdge(BasicBlock *BB, succ_iterator SI,
114 return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), P);
117 /// SplitCriticalEdge - If the edge from *PI to BB is not critical, return
118 /// false. Otherwise, split all edges between the two blocks and return true.
119 /// This updates all of the same analyses as the other SplitCriticalEdge
120 /// function. If P is specified, it updates the analyses
122 inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, Pass *P = 0) {
123 bool MadeChange = false;
124 TerminatorInst *TI = (*PI)->getTerminator();
125 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
126 if (TI->getSuccessor(i) == Succ)
127 MadeChange |= !!SplitCriticalEdge(TI, i, P);
131 /// SplitCriticalEdge - If an edge from Src to Dst is critical, split the edge
132 /// and return true, otherwise return false. This method requires that there be
133 /// an edge between the two blocks. If P is specified, it updates the analyses
135 inline BasicBlock *SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
137 bool MergeIdenticalEdges = false) {
138 TerminatorInst *TI = Src->getTerminator();
141 assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
142 if (TI->getSuccessor(i) == Dst)
143 return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges);
148 /// SplitEdge - Split the edge connecting specified block. Pass P must
150 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, Pass *P);
152 /// SplitBlock - Split the specified block at the specified instruction - every
153 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
154 /// to a new block. The two blocks are joined by an unconditional branch and
155 /// the loop info is updated.
157 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P);
159 /// SplitBlockPredecessors - This method transforms BB by introducing a new
160 /// basic block into the function, and moving some of the predecessors of BB to
161 /// be predecessors of the new block. The new predecessors are indicated by the
162 /// Preds array, which has NumPreds elements in it. The new block is given a
163 /// suffix of 'Suffix'. This function returns the new block.
165 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
166 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
167 /// In particular, it does not preserve LoopSimplify (because it's
168 /// complicated to handle the case where one of the edges being split
169 /// is an exit of a loop with other exits).
171 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, BasicBlock *const *Preds,
172 unsigned NumPreds, const char *Suffix,
175 } // End llvm namespace