src/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h

   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/IR/BasicBlock.h"
  21 #include "llvm/IR/CFG.h"
  22
  23 namespace llvm {
  24
  25 class AliasAnalysis;
  26 class DominatorTree;
  27 class Instruction;
  28 class MDNode;
  29 class Pass;
  30 class ReturnInst;
  31 class TargetLibraryInfo;
  32 class TerminatorInst;
  33
  34 /// DeleteDeadBlock - Delete the specified block, which must have no
  35 /// predecessors.
  36 void DeleteDeadBlock(BasicBlock *BB);
  37
  38 /// FoldSingleEntryPHINodes - We know that BB has one predecessor.  If there are
  39 /// any single-entry PHI nodes in it, fold them away.  This handles the case
  40 /// when all entries to the PHI nodes in a block are guaranteed equal, such as
  41 /// when the block has exactly one predecessor.
  42 void FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P = nullptr);
  43
  44 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
  45 /// is dead. Also recursively delete any operands that become dead as
  46 /// a result. This includes tracing the def-use list from the PHI to see if
  47 /// it is ultimately unused or if it reaches an unused cycle. Return true
  48 /// if any PHIs were deleted.
  49 bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr);
  50
  51 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
  52 /// if possible.  The return value indicates success or failure.
  53 bool MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P = nullptr);
  54
  55 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
  56 // with a value, then remove and delete the original instruction.
  57 //
  58 void ReplaceInstWithValue(BasicBlock::InstListType &BIL,
  59                           BasicBlock::iterator &BI, Value *V);
  60
  61 // ReplaceInstWithInst - Replace the instruction specified by BI with the
  62 // instruction specified by I.  The original instruction is deleted and BI is
  63 // updated to point to the new instruction.
  64 //
  65 void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
  66                          BasicBlock::iterator &BI, Instruction *I);
  67
  68 // ReplaceInstWithInst - Replace the instruction specified by From with the
  69 // instruction specified by To.
  70 //
  71 void ReplaceInstWithInst(Instruction *From, Instruction *To);
  72
  73 /// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
  74 /// split the critical edge.  This will update DominatorTree and
  75 /// DominatorFrontier information if it is available, thus calling this pass
  76 /// will not invalidate either of them. This returns the new block if the edge
  77 /// was split, null otherwise.
  78 ///
  79 /// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the
  80 /// specified successor will be merged into the same critical edge block.
  81 /// This is most commonly interesting with switch instructions, which may
  82 /// have many edges to any one destination.  This ensures that all edges to that
  83 /// dest go to one block instead of each going to a different block, but isn't
  84 /// the standard definition of a "critical edge".
  85 ///
  86 /// It is invalid to call this function on a critical edge that starts at an
  87 /// IndirectBrInst.  Splitting these edges will almost always create an invalid
  88 /// program because the address of the new block won't be the one that is jumped
  89 /// to.
  90 ///
  91 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
  92                               Pass *P = nullptr,
  93                               bool MergeIdenticalEdges = false,
  94                               bool DontDeleteUselessPHIs = false,
  95                               bool SplitLandingPads = false);
  96
  97 inline BasicBlock *SplitCriticalEdge(BasicBlock *BB, succ_iterator SI,
  98                                      Pass *P = nullptr) {
  99   return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), P);
 100 }
 101
 102 /// SplitCriticalEdge - If the edge from *PI to BB is not critical, return
 103 /// false.  Otherwise, split all edges between the two blocks and return true.
 104 /// This updates all of the same analyses as the other SplitCriticalEdge
 105 /// function.  If P is specified, it updates the analyses
 106 /// described above.
 107 inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI,
 108                               Pass *P = nullptr) {
 109   bool MadeChange = false;
 110   TerminatorInst *TI = (*PI)->getTerminator();
 111   for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
 112     if (TI->getSuccessor(i) == Succ)
 113       MadeChange |= !!SplitCriticalEdge(TI, i, P);
 114   return MadeChange;
 115 }
 116
 117 /// SplitCriticalEdge - If an edge from Src to Dst is critical, split the edge
 118 /// and return true, otherwise return false.  This method requires that there be
 119 /// an edge between the two blocks.  If P is specified, it updates the analyses
 120 /// described above.
 121 inline BasicBlock *SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
 122                                      Pass *P = nullptr,
 123                                      bool MergeIdenticalEdges = false,
 124                                      bool DontDeleteUselessPHIs = false) {
 125   TerminatorInst *TI = Src->getTerminator();
 126   unsigned i = 0;
 127   while (1) {
 128     assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
 129     if (TI->getSuccessor(i) == Dst)
 130       return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges,
 131                                DontDeleteUselessPHIs);
 132     ++i;
 133   }
 134 }
 135
 136 // SplitAllCriticalEdges - Loop over all of the edges in the CFG,
 137 // breaking critical edges as they are found. Pass P must not be NULL.
 138 // Returns the number of broken edges.
 139 unsigned SplitAllCriticalEdges(Function &F, Pass *P);
 140
 141 /// SplitEdge -  Split the edge connecting specified block. Pass P must
 142 /// not be NULL.
 143 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, Pass *P);
 144
 145 /// SplitBlock - Split the specified block at the specified instruction - every
 146 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
 147 /// to a new block.  The two blocks are joined by an unconditional branch and
 148 /// the loop info is updated.
 149 ///
 150 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P);
 151
 152 /// SplitBlockPredecessors - This method transforms BB by introducing a new
 153 /// basic block into the function, and moving some of the predecessors of BB to
 154 /// be predecessors of the new block.  The new predecessors are indicated by the
 155 /// Preds array, which has NumPreds elements in it.  The new block is given a
 156 /// suffix of 'Suffix'.  This function returns the new block.
 157 ///
 158 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
 159 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
 160 /// In particular, it does not preserve LoopSimplify (because it's
 161 /// complicated to handle the case where one of the edges being split
 162 /// is an exit of a loop with other exits).
 163 ///
 164 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock*> Preds,
 165                                    const char *Suffix, Pass *P = nullptr);
 166
 167 /// SplitLandingPadPredecessors - This method transforms the landing pad,
 168 /// OrigBB, by introducing two new basic blocks into the function. One of those
 169 /// new basic blocks gets the predecessors listed in Preds. The other basic
 170 /// block gets the remaining predecessors of OrigBB. The landingpad instruction
 171 /// OrigBB is clone into both of the new basic blocks. The new blocks are given
 172 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector.
 173 ///
 174 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
 175 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular,
 176 /// it does not preserve LoopSimplify (because it's complicated to handle the
 177 /// case where one of the edges being split is an exit of a loop with other
 178 /// exits).
 179 ///
 180 void SplitLandingPadPredecessors(BasicBlock *OrigBB,ArrayRef<BasicBlock*> Preds,
 181                                  const char *Suffix, const char *Suffix2,
 182                                  Pass *P, SmallVectorImpl<BasicBlock*> &NewBBs);
 183
 184 /// FoldReturnIntoUncondBranch - This method duplicates the specified return
 185 /// instruction into a predecessor which ends in an unconditional branch. If
 186 /// the return instruction returns a value defined by a PHI, propagate the
 187 /// right value into the return. It returns the new return instruction in the
 188 /// predecessor.
 189 ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
 190                                        BasicBlock *Pred);
 191
 192 /// SplitBlockAndInsertIfThen - Split the containing block at the
 193 /// specified instruction - everything before and including SplitBefore stays
 194 /// in the old basic block, and everything after SplitBefore is moved to a
 195 /// new block. The two blocks are connected by a conditional branch
 196 /// (with value of Cmp being the condition).
 197 /// Before:
 198 ///   Head
 199 ///   SplitBefore
 200 ///   Tail
 201 /// After:
 202 ///   Head
 203 ///   if (Cond)
 204 ///     ThenBlock
 205 ///   SplitBefore
 206 ///   Tail
 207 ///
 208 /// If Unreachable is true, then ThenBlock ends with
 209 /// UnreachableInst, otherwise it branches to Tail.
 210 /// Returns the NewBasicBlock's terminator.
 211 ///
 212 /// Updates DT if given.
 213 TerminatorInst *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
 214                                           bool Unreachable,
 215                                           MDNode *BranchWeights = nullptr,
 216                                           DominatorTree *DT = nullptr);
 217
 218 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
 219 /// but also creates the ElseBlock.
 220 /// Before:
 221 ///   Head
 222 ///   SplitBefore
 223 ///   Tail
 224 /// After:
 225 ///   Head
 226 ///   if (Cond)
 227 ///     ThenBlock
 228 ///   else
 229 ///     ElseBlock
 230 ///   SplitBefore
 231 ///   Tail
 232 void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
 233                                    TerminatorInst **ThenTerm,
 234                                    TerminatorInst **ElseTerm,
 235                                    MDNode *BranchWeights = nullptr);
 236
 237 ///
 238 /// GetIfCondition - Check whether BB is the merge point of a if-region.
 239 /// If so, return the boolean condition that determines which entry into
 240 /// BB will be taken.  Also, return by references the block that will be
 241 /// entered from if the condition is true, and the block that will be
 242 /// entered if the condition is false.
 243 Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
 244                       BasicBlock *&IfFalse);
 245 } // End llvm namespace
 246
 247 #endif