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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/DomTreeUpdater.h"
24 : #include "llvm/IR/InstrTypes.h"
25 : #include <cassert>
26 :
27 : namespace llvm {
28 :
29 : class BlockFrequencyInfo;
30 : class BranchProbabilityInfo;
31 : class DominatorTree;
32 : class DomTreeUpdater;
33 : class Function;
34 : class Instruction;
35 : class LoopInfo;
36 : class MDNode;
37 : class MemoryDependenceResults;
38 : class MemorySSAUpdater;
39 : class ReturnInst;
40 : class TargetLibraryInfo;
41 : class Value;
42 :
43 : /// Delete the specified block, which must have no predecessors.
44 : void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU = nullptr);
45 :
46 : /// We know that BB has one predecessor. If there are any single-entry PHI nodes
47 : /// in it, fold them away. This handles the case when all entries to the PHI
48 : /// nodes in a block are guaranteed equal, such as when the block has exactly
49 : /// one predecessor.
50 : void FoldSingleEntryPHINodes(BasicBlock *BB,
51 : MemoryDependenceResults *MemDep = nullptr);
52 :
53 : /// Examine each PHI in the given block and delete it if it is dead. Also
54 : /// recursively delete any operands that become dead as a result. This includes
55 : /// tracing the def-use list from the PHI to see if it is ultimately unused or
56 : /// if it reaches an unused cycle. Return true if any PHIs were deleted.
57 : bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr);
58 :
59 : /// Attempts to merge a block into its predecessor, if possible. The return
60 : /// value indicates success or failure.
61 : bool MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU = nullptr,
62 : LoopInfo *LI = nullptr,
63 : MemorySSAUpdater *MSSAU = nullptr,
64 : MemoryDependenceResults *MemDep = nullptr);
65 :
66 : /// Replace all uses of an instruction (specified by BI) with a value, then
67 : /// remove and delete the original instruction.
68 : void ReplaceInstWithValue(BasicBlock::InstListType &BIL,
69 : BasicBlock::iterator &BI, Value *V);
70 :
71 : /// Replace the instruction specified by BI with the instruction specified by I.
72 : /// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The
73 : /// original instruction is deleted and BI is updated to point to the new
74 : /// instruction.
75 : void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
76 : BasicBlock::iterator &BI, Instruction *I);
77 :
78 : /// Replace the instruction specified by From with the instruction specified by
79 : /// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc.
80 : void ReplaceInstWithInst(Instruction *From, Instruction *To);
81 :
82 : /// Option class for critical edge splitting.
83 : ///
84 : /// This provides a builder interface for overriding the default options used
85 : /// during critical edge splitting.
86 : struct CriticalEdgeSplittingOptions {
87 : DominatorTree *DT;
88 : LoopInfo *LI;
89 : MemorySSAUpdater *MSSAU;
90 : bool MergeIdenticalEdges = false;
91 : bool DontDeleteUselessPHIs = false;
92 : bool PreserveLCSSA = false;
93 :
94 : CriticalEdgeSplittingOptions(DominatorTree *DT = nullptr,
95 : LoopInfo *LI = nullptr,
96 : MemorySSAUpdater *MSSAU = nullptr)
97 5625 : : DT(DT), LI(LI), MSSAU(MSSAU) {}
98 :
99 : CriticalEdgeSplittingOptions &setMergeIdenticalEdges() {
100 192 : MergeIdenticalEdges = true;
101 : return *this;
102 : }
103 :
104 : CriticalEdgeSplittingOptions &setDontDeleteUselessPHIs() {
105 172 : DontDeleteUselessPHIs = true;
106 : return *this;
107 : }
108 :
109 : CriticalEdgeSplittingOptions &setPreserveLCSSA() {
110 4210 : PreserveLCSSA = true;
111 : return *this;
112 : }
113 : };
114 :
115 : /// If this edge is a critical edge, insert a new node to split the critical
116 : /// edge. This will update the analyses passed in through the option struct.
117 : /// This returns the new block if the edge was split, null otherwise.
118 : ///
119 : /// If MergeIdenticalEdges in the options struct is true (not the default),
120 : /// *all* edges from TI to the specified successor will be merged into the same
121 : /// critical edge block. This is most commonly interesting with switch
122 : /// instructions, which may have many edges to any one destination. This
123 : /// ensures that all edges to that dest go to one block instead of each going
124 : /// to a different block, but isn't the standard definition of a "critical
125 : /// edge".
126 : ///
127 : /// It is invalid to call this function on a critical edge that starts at an
128 : /// IndirectBrInst. Splitting these edges will almost always create an invalid
129 : /// program because the address of the new block won't be the one that is jumped
130 : /// to.
131 : BasicBlock *SplitCriticalEdge(Instruction *TI, unsigned SuccNum,
132 : const CriticalEdgeSplittingOptions &Options =
133 : CriticalEdgeSplittingOptions());
134 :
135 : inline BasicBlock *
136 : SplitCriticalEdge(BasicBlock *BB, succ_iterator SI,
137 : const CriticalEdgeSplittingOptions &Options =
138 : CriticalEdgeSplittingOptions()) {
139 : return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(),
140 : Options);
141 : }
142 :
143 : /// If the edge from *PI to BB is not critical, return false. Otherwise, split
144 : /// all edges between the two blocks and return true. This updates all of the
145 : /// same analyses as the other SplitCriticalEdge function. If P is specified, it
146 : /// updates the analyses described above.
147 : inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI,
148 : const CriticalEdgeSplittingOptions &Options =
149 : CriticalEdgeSplittingOptions()) {
150 : bool MadeChange = false;
151 : Instruction *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, Options);
155 : return MadeChange;
156 : }
157 :
158 : /// If an edge from Src to Dst is critical, split the edge and return true,
159 : /// otherwise return false. This method requires that there be an edge between
160 : /// the two blocks. It updates the analyses passed in the options struct
161 : inline BasicBlock *
162 4249 : SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
163 : const CriticalEdgeSplittingOptions &Options =
164 : CriticalEdgeSplittingOptions()) {
165 : Instruction *TI = Src->getTerminator();
166 : unsigned i = 0;
167 : while (true) {
168 2018 : assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
169 6267 : if (TI->getSuccessor(i) == Dst)
170 4249 : return SplitCriticalEdge(TI, i, Options);
171 2018 : ++i;
172 : }
173 : }
174 :
175 : /// Loop over all of the edges in the CFG, breaking critical edges as they are
176 : /// found. Returns the number of broken edges.
177 : unsigned SplitAllCriticalEdges(Function &F,
178 : const CriticalEdgeSplittingOptions &Options =
179 : CriticalEdgeSplittingOptions());
180 :
181 : /// Split the edge connecting specified block.
182 : BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To,
183 : DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
184 : MemorySSAUpdater *MSSAU = nullptr);
185 :
186 : /// Split the specified block at the specified instruction - everything before
187 : /// SplitPt stays in Old and everything starting with SplitPt moves to a new
188 : /// block. The two blocks are joined by an unconditional branch and the loop
189 : /// info is updated.
190 : BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt,
191 : DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
192 : MemorySSAUpdater *MSSAU = nullptr);
193 :
194 : /// This method introduces at least one new basic block into the function and
195 : /// moves some of the predecessors of BB to be predecessors of the new block.
196 : /// The new predecessors are indicated by the Preds array. The new block is
197 : /// given a suffix of 'Suffix'. Returns new basic block to which predecessors
198 : /// from Preds are now pointing.
199 : ///
200 : /// If BB is a landingpad block then additional basicblock might be introduced.
201 : /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more
202 : /// details on this case.
203 : ///
204 : /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
205 : /// no other analyses. In particular, it does not preserve LoopSimplify
206 : /// (because it's complicated to handle the case where one of the edges being
207 : /// split is an exit of a loop with other exits).
208 : BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
209 : const char *Suffix,
210 : DominatorTree *DT = nullptr,
211 : LoopInfo *LI = nullptr,
212 : MemorySSAUpdater *MSSAU = nullptr,
213 : bool PreserveLCSSA = false);
214 :
215 : /// This method transforms the landing pad, OrigBB, by introducing two new basic
216 : /// blocks into the function. One of those new basic blocks gets the
217 : /// predecessors listed in Preds. The other basic block gets the remaining
218 : /// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both
219 : /// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and
220 : /// 'Suffix2', and are returned in the NewBBs vector.
221 : ///
222 : /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
223 : /// no other analyses. In particular, it does not preserve LoopSimplify
224 : /// (because it's complicated to handle the case where one of the edges being
225 : /// split is an exit of a loop with other exits).
226 : void SplitLandingPadPredecessors(
227 : BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix,
228 : const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs,
229 : DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
230 : MemorySSAUpdater *MSSAU = nullptr, bool PreserveLCSSA = false);
231 :
232 : /// This method duplicates the specified return instruction into a predecessor
233 : /// which ends in an unconditional branch. If the return instruction returns a
234 : /// value defined by a PHI, propagate the right value into the return. It
235 : /// returns the new return instruction in the predecessor.
236 : ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
237 : BasicBlock *Pred,
238 : DomTreeUpdater *DTU = nullptr);
239 :
240 : /// Split the containing block at the specified instruction - everything before
241 : /// SplitBefore stays in the old basic block, and the rest of the instructions
242 : /// in the BB are moved to a new block. The two blocks are connected by a
243 : /// conditional branch (with value of Cmp being the condition).
244 : /// Before:
245 : /// Head
246 : /// SplitBefore
247 : /// Tail
248 : /// After:
249 : /// Head
250 : /// if (Cond)
251 : /// ThenBlock
252 : /// SplitBefore
253 : /// Tail
254 : ///
255 : /// If Unreachable is true, then ThenBlock ends with
256 : /// UnreachableInst, otherwise it branches to Tail.
257 : /// Returns the NewBasicBlock's terminator.
258 : ///
259 : /// Updates DT and LI if given.
260 : Instruction *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
261 : bool Unreachable,
262 : MDNode *BranchWeights = nullptr,
263 : DominatorTree *DT = nullptr,
264 : LoopInfo *LI = nullptr);
265 :
266 : /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
267 : /// but also creates the ElseBlock.
268 : /// Before:
269 : /// Head
270 : /// SplitBefore
271 : /// Tail
272 : /// After:
273 : /// Head
274 : /// if (Cond)
275 : /// ThenBlock
276 : /// else
277 : /// ElseBlock
278 : /// SplitBefore
279 : /// Tail
280 : void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
281 : Instruction **ThenTerm,
282 : Instruction **ElseTerm,
283 : MDNode *BranchWeights = nullptr);
284 :
285 : /// Check whether BB is the merge point of a if-region.
286 : /// If so, return the boolean condition that determines which entry into
287 : /// BB will be taken. Also, return by references the block that will be
288 : /// entered from if the condition is true, and the block that will be
289 : /// entered if the condition is false.
290 : ///
291 : /// This does no checking to see if the true/false blocks have large or unsavory
292 : /// instructions in them.
293 : Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
294 : BasicBlock *&IfFalse);
295 :
296 : // Split critical edges where the source of the edge is an indirectbr
297 : // instruction. This isn't always possible, but we can handle some easy cases.
298 : // This is useful because MI is unable to split such critical edges,
299 : // which means it will not be able to sink instructions along those edges.
300 : // This is especially painful for indirect branches with many successors, where
301 : // we end up having to prepare all outgoing values in the origin block.
302 : //
303 : // Our normal algorithm for splitting critical edges requires us to update
304 : // the outgoing edges of the edge origin block, but for an indirectbr this
305 : // is hard, since it would require finding and updating the block addresses
306 : // the indirect branch uses. But if a block only has a single indirectbr
307 : // predecessor, with the others being regular branches, we can do it in a
308 : // different way.
309 : // Say we have A -> D, B -> D, I -> D where only I -> D is an indirectbr.
310 : // We can split D into D0 and D1, where D0 contains only the PHIs from D,
311 : // and D1 is the D block body. We can then duplicate D0 as D0A and D0B, and
312 : // create the following structure:
313 : // A -> D0A, B -> D0A, I -> D0B, D0A -> D1, D0B -> D1
314 : // If BPI and BFI aren't non-null, BPI/BFI will be updated accordingly.
315 : bool SplitIndirectBrCriticalEdges(Function &F,
316 : BranchProbabilityInfo *BPI = nullptr,
317 : BlockFrequencyInfo *BFI = nullptr);
318 :
319 : } // end namespace llvm
320 :
321 : #endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H
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