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