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);
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 /// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the
70 /// instruction before ScanFrom) checking to see if we have the value at the
71 /// memory address *Ptr locally available within a small number of instructions.
72 /// If the value is available, return it.
74 /// If not, return the iterator for the last validated instruction that the
75 /// value would be live through. If we scanned the entire block and didn't find
76 /// something that invalidates *Ptr or provides it, ScanFrom would be left at
77 /// begin() and this returns null. ScanFrom could also be left
79 /// MaxInstsToScan specifies the maximum instructions to scan in the block. If
80 /// it is set to 0, it will scan the whole block. You can also optionally
81 /// specify an alias analysis implementation, which makes this more precise.
82 Value *FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
83 BasicBlock::iterator &ScanFrom,
84 unsigned MaxInstsToScan = 6,
85 AliasAnalysis *AA = 0);
87 /// FindFunctionBackedges - Analyze the specified function to find all of the
88 /// loop backedges in the function and return them. This is a relatively cheap
89 /// (compared to computing dominators and loop info) analysis.
91 /// The output is added to Result, as pairs of <from,to> edge info.
92 void FindFunctionBackedges(const Function &F,
93 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result);
96 // RemoveSuccessor - Change the specified terminator instruction such that its
97 // successor #SuccNum no longer exists. Because this reduces the outgoing
98 // degree of the current basic block, the actual terminator instruction itself
99 // may have to be changed. In the case where the last successor of the block is
100 // deleted, a return instruction is inserted in its place which can cause a
101 // suprising change in program behavior if it is not expected.
103 void RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum);
105 /// GetSuccessorNumber - Search for the specified successor of basic block BB
106 /// and return its position in the terminator instruction's list of
107 /// successors. It is an error to call this with a block that is not a
109 unsigned GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ);
111 /// isCriticalEdge - Return true if the specified edge is a critical edge.
112 /// Critical edges are edges from a block with multiple successors to a block
113 /// with multiple predecessors.
115 bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
116 bool AllowIdenticalEdges = false);
118 /// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
119 /// split the critical edge. This will update DominatorTree and
120 /// DominatorFrontier information if it is available, thus calling this pass
121 /// will not invalidate either of them. This returns the new block if the edge
122 /// was split, null otherwise.
124 /// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the
125 /// specified successor will be merged into the same critical edge block.
126 /// This is most commonly interesting with switch instructions, which may
127 /// have many edges to any one destination. This ensures that all edges to that
128 /// dest go to one block instead of each going to a different block, but isn't
129 /// the standard definition of a "critical edge".
131 /// It is invalid to call this function on a critical edge that starts at an
132 /// IndirectBrInst. Splitting these edges will almost always create an invalid
133 /// program because the address of the new block won't be the one that is jumped
136 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
137 Pass *P = 0, bool MergeIdenticalEdges = false);
139 inline BasicBlock *SplitCriticalEdge(BasicBlock *BB, succ_iterator SI,
141 return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), P);
144 /// SplitCriticalEdge - If the edge from *PI to BB is not critical, return
145 /// false. Otherwise, split all edges between the two blocks and return true.
146 /// This updates all of the same analyses as the other SplitCriticalEdge
147 /// function. If P is specified, it updates the analyses
149 inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, Pass *P = 0) {
150 bool MadeChange = false;
151 TerminatorInst *TI = (*PI)->getTerminator();
152 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
153 if (TI->getSuccessor(i) == Succ)
154 MadeChange |= !!SplitCriticalEdge(TI, i, P);
158 /// SplitCriticalEdge - If an edge from Src to Dst is critical, split the edge
159 /// and return true, otherwise return false. This method requires that there be
160 /// an edge between the two blocks. If P is specified, it updates the analyses
162 inline BasicBlock *SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
164 bool MergeIdenticalEdges = false) {
165 TerminatorInst *TI = Src->getTerminator();
168 assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
169 if (TI->getSuccessor(i) == Dst)
170 return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges);
175 /// SplitEdge - Split the edge connecting specified block. Pass P must
177 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, Pass *P);
179 /// SplitBlock - Split the specified block at the specified instruction - every
180 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
181 /// to a new block. The two blocks are joined by an unconditional branch and
182 /// the loop info is updated.
184 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P);
186 /// SplitBlockPredecessors - This method transforms BB by introducing a new
187 /// basic block into the function, and moving some of the predecessors of BB to
188 /// be predecessors of the new block. The new predecessors are indicated by the
189 /// Preds array, which has NumPreds elements in it. The new block is given a
190 /// suffix of 'Suffix'. This function returns the new block.
192 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
193 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
194 /// In particular, it does not preserve LoopSimplify (because it's
195 /// complicated to handle the case where one of the edges being split
196 /// is an exit of a loop with other exits).
198 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, BasicBlock *const *Preds,
199 unsigned NumPreds, const char *Suffix,
202 } // End llvm namespace