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BasicBlockUtils.h
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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/ADT/ArrayRef.h"
21 #include "llvm/IR/BasicBlock.h"
22 #include "llvm/IR/CFG.h"
23 #include "llvm/IR/InstrTypes.h"
24 #include <cassert>
25 
26 namespace llvm {
27 
28 class BlockFrequencyInfo;
29 class BranchProbabilityInfo;
30 class DeferredDominance;
31 class DominatorTree;
32 class Function;
33 class Instruction;
34 class LoopInfo;
35 class MDNode;
36 class MemoryDependenceResults;
37 class ReturnInst;
38 class TargetLibraryInfo;
39 class Value;
40 
41 /// Delete the specified block, which must have no predecessors.
42 void DeleteDeadBlock(BasicBlock *BB, DeferredDominance *DDT = nullptr);
43 
44 /// We know that BB has one predecessor. If there are any single-entry PHI nodes
45 /// in it, fold them away. This handles the case when all entries to the PHI
46 /// nodes in a block are guaranteed equal, such as when the block has exactly
47 /// one predecessor.
49  MemoryDependenceResults *MemDep = nullptr);
50 
51 /// Examine each PHI in the given block and delete it if it is dead. Also
52 /// recursively delete any operands that become dead as a result. This includes
53 /// tracing the def-use list from the PHI to see if it is ultimately unused or
54 /// if it reaches an unused cycle. Return true if any PHIs were deleted.
55 bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr);
56 
57 /// Attempts to merge a block into its predecessor, if possible. The return
58 /// value indicates success or failure.
59 bool MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT = nullptr,
60  LoopInfo *LI = nullptr,
61  MemoryDependenceResults *MemDep = nullptr,
62  DeferredDominance *DDT = nullptr);
63 
64 /// Replace all uses of an instruction (specified by BI) with a value, then
65 /// remove and delete the original instruction.
67  BasicBlock::iterator &BI, Value *V);
68 
69 /// Replace the instruction specified by BI with the instruction specified by I.
70 /// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The
71 /// original instruction is deleted and BI is updated to point to the new
72 /// instruction.
74  BasicBlock::iterator &BI, Instruction *I);
75 
76 /// Replace the instruction specified by From with the instruction specified by
77 /// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc.
78 void ReplaceInstWithInst(Instruction *From, Instruction *To);
79 
80 /// Option class for critical edge splitting.
81 ///
82 /// This provides a builder interface for overriding the default options used
83 /// during critical edge splitting.
87  bool MergeIdenticalEdges = false;
88  bool DontDeleteUselessPHIs = false;
89  bool PreserveLCSSA = false;
90 
92  LoopInfo *LI = nullptr)
93  : DT(DT), LI(LI) {}
94 
96  MergeIdenticalEdges = true;
97  return *this;
98  }
99 
101  DontDeleteUselessPHIs = true;
102  return *this;
103  }
104 
106  PreserveLCSSA = true;
107  return *this;
108  }
109 };
110 
111 /// If this edge is a critical edge, insert a new node to split the critical
112 /// edge. This will update the analyses passed in through the option struct.
113 /// This returns the new block if the edge was split, null otherwise.
114 ///
115 /// If MergeIdenticalEdges in the options struct is true (not the default),
116 /// *all* edges from TI to the specified successor will be merged into the same
117 /// critical edge block. This is most commonly interesting with switch
118 /// instructions, which may have many edges to any one destination. This
119 /// ensures that all edges to that dest go to one block instead of each going
120 /// to a different block, but isn't the standard definition of a "critical
121 /// edge".
122 ///
123 /// It is invalid to call this function on a critical edge that starts at an
124 /// IndirectBrInst. Splitting these edges will almost always create an invalid
125 /// program because the address of the new block won't be the one that is jumped
126 /// to.
127 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
128  const CriticalEdgeSplittingOptions &Options =
130 
131 inline BasicBlock *
133  const CriticalEdgeSplittingOptions &Options =
136  Options);
137 }
138 
139 /// If the edge from *PI to BB is not critical, return false. Otherwise, split
140 /// all edges between the two blocks and return true. This updates all of the
141 /// same analyses as the other SplitCriticalEdge function. If P is specified, it
142 /// updates the analyses described above.
144  const CriticalEdgeSplittingOptions &Options =
146  bool MadeChange = false;
147  TerminatorInst *TI = (*PI)->getTerminator();
148  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
149  if (TI->getSuccessor(i) == Succ)
150  MadeChange |= !!SplitCriticalEdge(TI, i, Options);
151  return MadeChange;
152 }
153 
154 /// If an edge from Src to Dst is critical, split the edge and return true,
155 /// otherwise return false. This method requires that there be an edge between
156 /// the two blocks. It updates the analyses passed in the options struct
157 inline BasicBlock *
159  const CriticalEdgeSplittingOptions &Options =
161  TerminatorInst *TI = Src->getTerminator();
162  unsigned i = 0;
163  while (true) {
164  assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
165  if (TI->getSuccessor(i) == Dst)
166  return SplitCriticalEdge(TI, i, Options);
167  ++i;
168  }
169 }
170 
171 /// Loop over all of the edges in the CFG, breaking critical edges as they are
172 /// found. Returns the number of broken edges.
174  const CriticalEdgeSplittingOptions &Options =
176 
177 /// Split the edge connecting specified block.
179  DominatorTree *DT = nullptr, LoopInfo *LI = nullptr);
180 
181 /// Split the specified block at the specified instruction - everything before
182 /// SplitPt stays in Old and everything starting with SplitPt moves to a new
183 /// block. The two blocks are joined by an unconditional branch and the loop
184 /// info is updated.
186  DominatorTree *DT = nullptr, LoopInfo *LI = nullptr);
187 
188 /// This method introduces at least one new basic block into the function and
189 /// moves some of the predecessors of BB to be predecessors of the new block.
190 /// The new predecessors are indicated by the Preds array. The new block is
191 /// given a suffix of 'Suffix'. Returns new basic block to which predecessors
192 /// from Preds are now pointing.
193 ///
194 /// If BB is a landingpad block then additional basicblock might be introduced.
195 /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more
196 /// details on this case.
197 ///
198 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
199 /// no other analyses. In particular, it does not preserve LoopSimplify
200 /// (because it's complicated to handle the case where one of the edges being
201 /// split is an exit of a loop with other exits).
203  const char *Suffix,
204  DominatorTree *DT = nullptr,
205  LoopInfo *LI = nullptr,
206  bool PreserveLCSSA = false);
207 
208 /// This method transforms the landing pad, OrigBB, by introducing two new basic
209 /// blocks into the function. One of those new basic blocks gets the
210 /// predecessors listed in Preds. The other basic block gets the remaining
211 /// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both
212 /// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and
213 /// 'Suffix2', and are returned in the NewBBs vector.
214 ///
215 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
216 /// no other analyses. In particular, it does not preserve LoopSimplify
217 /// (because it's complicated to handle the case where one of the edges being
218 /// split is an exit of a loop with other exits).
221  const char *Suffix, const char *Suffix2,
223  DominatorTree *DT = nullptr,
224  LoopInfo *LI = nullptr,
225  bool PreserveLCSSA = false);
226 
227 /// This method duplicates the specified return instruction into a predecessor
228 /// which ends in an unconditional branch. If the return instruction returns a
229 /// value defined by a PHI, propagate the right value into the return. It
230 /// returns the new return instruction in the predecessor.
232  BasicBlock *Pred);
233 
234 /// Split the containing block at the specified instruction - everything before
235 /// SplitBefore stays in the old basic block, and the rest of the instructions
236 /// in the BB are moved to a new block. The two blocks are connected by a
237 /// conditional branch (with value of Cmp being the condition).
238 /// Before:
239 /// Head
240 /// SplitBefore
241 /// Tail
242 /// After:
243 /// Head
244 /// if (Cond)
245 /// ThenBlock
246 /// SplitBefore
247 /// Tail
248 ///
249 /// If Unreachable is true, then ThenBlock ends with
250 /// UnreachableInst, otherwise it branches to Tail.
251 /// Returns the NewBasicBlock's terminator.
252 ///
253 /// Updates DT and LI if given.
255  bool Unreachable,
256  MDNode *BranchWeights = nullptr,
257  DominatorTree *DT = nullptr,
258  LoopInfo *LI = nullptr);
259 
260 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
261 /// but also creates the ElseBlock.
262 /// Before:
263 /// Head
264 /// SplitBefore
265 /// Tail
266 /// After:
267 /// Head
268 /// if (Cond)
269 /// ThenBlock
270 /// else
271 /// ElseBlock
272 /// SplitBefore
273 /// Tail
274 void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
275  TerminatorInst **ThenTerm,
276  TerminatorInst **ElseTerm,
277  MDNode *BranchWeights = nullptr);
278 
279 /// Check whether BB is the merge point of a if-region.
280 /// If so, return the boolean condition that determines which entry into
281 /// BB will be taken. Also, return by references the block that will be
282 /// entered from if the condition is true, and the block that will be
283 /// entered if the condition is false.
284 ///
285 /// This does no checking to see if the true/false blocks have large or unsavory
286 /// instructions in them.
288  BasicBlock *&IfFalse);
289 
290 // Split critical edges where the source of the edge is an indirectbr
291 // instruction. This isn't always possible, but we can handle some easy cases.
292 // This is useful because MI is unable to split such critical edges,
293 // which means it will not be able to sink instructions along those edges.
294 // This is especially painful for indirect branches with many successors, where
295 // we end up having to prepare all outgoing values in the origin block.
296 //
297 // Our normal algorithm for splitting critical edges requires us to update
298 // the outgoing edges of the edge origin block, but for an indirectbr this
299 // is hard, since it would require finding and updating the block addresses
300 // the indirect branch uses. But if a block only has a single indirectbr
301 // predecessor, with the others being regular branches, we can do it in a
302 // different way.
303 // Say we have A -> D, B -> D, I -> D where only I -> D is an indirectbr.
304 // We can split D into D0 and D1, where D0 contains only the PHIs from D,
305 // and D1 is the D block body. We can then duplicate D0 as D0A and D0B, and
306 // create the following structure:
307 // A -> D0A, B -> D0A, I -> D0B, D0A -> D1, D0B -> D1
308 // If BPI and BFI aren't non-null, BPI/BFI will be updated accordingly.
310  BranchProbabilityInfo *BPI = nullptr,
311  BlockFrequencyInfo *BFI = nullptr);
312 
313 } // end namespace llvm
314 
315 #endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H
Return a value (possibly void), from a function.
void ReplaceInstWithInst(BasicBlock::InstListType &BIL, BasicBlock::iterator &BI, Instruction *I)
Replace the instruction specified by BI with the instruction specified by I.
bool MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, MemoryDependenceResults *MemDep=nullptr, DeferredDominance *DDT=nullptr)
Attempts to merge a block into its predecessor, if possible.
unsigned getSuccessorIndex() const
This is used to interface between code that wants to operate on terminator instructions directly...
Definition: InstrTypes.h:162
void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, TerminatorInst **ThenTerm, TerminatorInst **ElseTerm, MDNode *BranchWeights=nullptr)
SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, but also creates the ElseBlock...
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
BasicBlock * SplitBlock(BasicBlock *Old, Instruction *SplitPt, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
Split the specified block at the specified instruction - everything before SplitPt stays in Old and e...
Various leaf nodes.
Definition: ISDOpcodes.h:60
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
Metadata node.
Definition: Metadata.h:862
F(f)
unsigned SplitAllCriticalEdges(Function &F, const CriticalEdgeSplittingOptions &Options=CriticalEdgeSplittingOptions())
Loop over all of the edges in the CFG, breaking critical edges as they are found. ...
Option class for critical edge splitting.
bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI=nullptr)
Examine each PHI in the given block and delete it if it is dead.
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory)...
Definition: APInt.h:33
void SplitLandingPadPredecessors(BasicBlock *OrigBB, ArrayRef< BasicBlock *> Preds, const char *Suffix, const char *Suffix2, SmallVectorImpl< BasicBlock *> &NewBBs, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, bool PreserveLCSSA=false)
This method transforms the landing pad, OrigBB, by introducing two new basic blocks into the function...
void ReplaceInstWithValue(BasicBlock::InstListType &BIL, BasicBlock::iterator &BI, Value *V)
Replace all uses of an instruction (specified by BI) with a value, then remove and delete the origina...
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:142
BasicBlock * SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, const CriticalEdgeSplittingOptions &Options=CriticalEdgeSplittingOptions())
If this edge is a critical edge, insert a new node to split the critical edge.
BlockFrequencyInfo pass uses BlockFrequencyInfoImpl implementation to estimate IR basic block frequen...
CriticalEdgeSplittingOptions & setMergeIdenticalEdges()
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:55
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
SymbolTableList< Instruction > InstListType
Definition: BasicBlock.h:62
BasicBlock * SplitBlockPredecessors(BasicBlock *BB, ArrayRef< BasicBlock *> Preds, const char *Suffix, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, bool PreserveLCSSA=false)
This method introduces at least one new basic block into the function and moves some of the predecess...
Value * GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, BasicBlock *&IfFalse)
Check whether BB is the merge point of a if-region.
TerminatorInst * SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, bool Unreachable, MDNode *BranchWeights=nullptr, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
Split the containing block at the specified instruction - everything before SplitBefore stays in the ...
CriticalEdgeSplittingOptions & setPreserveLCSSA()
CriticalEdgeSplittingOptions(DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:91
void FoldSingleEntryPHINodes(BasicBlock *BB, MemoryDependenceResults *MemDep=nullptr)
We know that BB has one predecessor.
Analysis providing branch probability information.
bool SplitIndirectBrCriticalEdges(Function &F, BranchProbabilityInfo *BPI=nullptr, BlockFrequencyInfo *BFI=nullptr)
#define I(x, y, z)
Definition: MD5.cpp:58
ReturnInst * FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, BasicBlock *Pred)
This method duplicates the specified return instruction into a predecessor which ends in an unconditi...
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
void DeleteDeadBlock(BasicBlock *BB, DeferredDominance *DDT=nullptr)
Delete the specified block, which must have no predecessors.
CriticalEdgeSplittingOptions & setDontDeleteUselessPHIs()
LLVM Value Representation.
Definition: Value.h:73
BasicBlock * SplitEdge(BasicBlock *From, BasicBlock *To, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
Split the edge connecting specified block.
const TerminatorInst * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:138