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Current view: top level - include/llvm/Transforms/Utils - BasicBlockUtils.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 11 11 100.0 %
Date: 2017-09-14 15:23:50 Functions: 1 1 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       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 MemoryDependenceResults;
      29             : class DominatorTree;
      30             : class LoopInfo;
      31             : class Instruction;
      32             : class MDNode;
      33             : class ReturnInst;
      34             : class TargetLibraryInfo;
      35             : 
      36             : /// Delete the specified block, which must have no predecessors.
      37             : void DeleteDeadBlock(BasicBlock *BB);
      38             : 
      39             : /// We know that BB has one predecessor. If there are any single-entry PHI nodes
      40             : /// in it, fold them away. This handles the case when all entries to the PHI
      41             : /// nodes in a block are guaranteed equal, such as when the block has exactly
      42             : /// one predecessor.
      43             : void FoldSingleEntryPHINodes(BasicBlock *BB,
      44             :                              MemoryDependenceResults *MemDep = nullptr);
      45             : 
      46             : /// Examine each PHI in the given block and delete it if it is dead. Also
      47             : /// recursively delete any operands that become dead as a result. This includes
      48             : /// tracing the def-use list from the PHI to see if it is ultimately unused or
      49             : /// if it reaches an unused cycle. Return true if any PHIs were deleted.
      50             : bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr);
      51             : 
      52             : /// Attempts to merge a block into its predecessor, if possible. The return
      53             : /// value indicates success or failure.
      54             : bool MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT = nullptr,
      55             :                                LoopInfo *LI = nullptr,
      56             :                                MemoryDependenceResults *MemDep = nullptr);
      57             : 
      58             : /// Replace all uses of an instruction (specified by BI) with a value, then
      59             : /// remove and delete the original instruction.
      60             : void ReplaceInstWithValue(BasicBlock::InstListType &BIL,
      61             :                           BasicBlock::iterator &BI, Value *V);
      62             : 
      63             : /// Replace the instruction specified by BI with the instruction specified by I.
      64             : /// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The
      65             : /// original instruction is deleted and BI is updated to point to the new
      66             : /// instruction.
      67             : void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
      68             :                          BasicBlock::iterator &BI, Instruction *I);
      69             : 
      70             : /// Replace the instruction specified by From with the instruction specified by
      71             : /// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc.
      72             : void ReplaceInstWithInst(Instruction *From, Instruction *To);
      73             : 
      74             : /// Option class for critical edge splitting.
      75             : ///
      76             : /// This provides a builder interface for overriding the default options used
      77             : /// during critical edge splitting.
      78             : struct CriticalEdgeSplittingOptions {
      79             :   DominatorTree *DT;
      80             :   LoopInfo *LI;
      81             :   bool MergeIdenticalEdges = false;
      82             :   bool DontDeleteUselessPHIs = false;
      83             :   bool PreserveLCSSA = false;
      84             : 
      85             :   CriticalEdgeSplittingOptions(DominatorTree *DT = nullptr,
      86             :                                LoopInfo *LI = nullptr)
      87        3551 :       : DT(DT), LI(LI) {}
      88             : 
      89             :   CriticalEdgeSplittingOptions &setMergeIdenticalEdges() {
      90          56 :     MergeIdenticalEdges = true;
      91             :     return *this;
      92             :   }
      93             : 
      94             :   CriticalEdgeSplittingOptions &setDontDeleteUselessPHIs() {
      95          56 :     DontDeleteUselessPHIs = true;
      96             :     return *this;
      97             :   }
      98             : 
      99             :   CriticalEdgeSplittingOptions &setPreserveLCSSA() {
     100        2168 :     PreserveLCSSA = true;
     101             :     return *this;
     102             :   }
     103             : };
     104             : 
     105             : /// If this edge is a critical edge, insert a new node to split the critical
     106             : /// edge. This will update the analyses passed in through the option struct.
     107             : /// This returns the new block if the edge was split, null otherwise.
     108             : ///
     109             : /// If MergeIdenticalEdges in the options struct is true (not the default),
     110             : /// *all* edges from TI to the specified successor will be merged into the same
     111             : /// critical edge block. This is most commonly interesting with switch
     112             : /// instructions, which may have many edges to any one destination.  This
     113             : /// ensures that all edges to that dest go to one block instead of each going
     114             : /// to a different block, but isn't the standard definition of a "critical
     115             : /// edge".
     116             : ///
     117             : /// It is invalid to call this function on a critical edge that starts at an
     118             : /// IndirectBrInst.  Splitting these edges will almost always create an invalid
     119             : /// program because the address of the new block won't be the one that is jumped
     120             : /// to.
     121             : ///
     122             : BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
     123             :                               const CriticalEdgeSplittingOptions &Options =
     124             :                                   CriticalEdgeSplittingOptions());
     125             : 
     126             : inline BasicBlock *
     127             : SplitCriticalEdge(BasicBlock *BB, succ_iterator SI,
     128             :                   const CriticalEdgeSplittingOptions &Options =
     129             :                       CriticalEdgeSplittingOptions()) {
     130             :   return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(),
     131             :                            Options);
     132             : }
     133             : 
     134             : /// If the edge from *PI to BB is not critical, return false. Otherwise, split
     135             : /// all edges between the two blocks and return true. This updates all of the
     136             : /// same analyses as the other SplitCriticalEdge function. If P is specified, it
     137             : /// updates the analyses described above.
     138             : inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI,
     139             :                               const CriticalEdgeSplittingOptions &Options =
     140             :                                   CriticalEdgeSplittingOptions()) {
     141             :   bool MadeChange = false;
     142             :   TerminatorInst *TI = (*PI)->getTerminator();
     143             :   for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
     144             :     if (TI->getSuccessor(i) == Succ)
     145             :       MadeChange |= !!SplitCriticalEdge(TI, i, Options);
     146             :   return MadeChange;
     147             : }
     148             : 
     149             : /// If an edge from Src to Dst is critical, split the edge and return true,
     150             : /// otherwise return false. This method requires that there be an edge between
     151             : /// the two blocks. It updates the analyses passed in the options struct
     152             : inline BasicBlock *
     153        2294 : SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
     154             :                   const CriticalEdgeSplittingOptions &Options =
     155             :                       CriticalEdgeSplittingOptions()) {
     156        2294 :   TerminatorInst *TI = Src->getTerminator();
     157        2294 :   unsigned i = 0;
     158             :   while (true) {
     159        1135 :     assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
     160        3429 :     if (TI->getSuccessor(i) == Dst)
     161        2294 :       return SplitCriticalEdge(TI, i, Options);
     162        1135 :     ++i;
     163             :   }
     164             : }
     165             : 
     166             : /// Loop over all of the edges in the CFG, breaking critical edges as they are
     167             : /// found. Returns the number of broken edges.
     168             : unsigned SplitAllCriticalEdges(Function &F,
     169             :                                const CriticalEdgeSplittingOptions &Options =
     170             :                                    CriticalEdgeSplittingOptions());
     171             : 
     172             : /// Split the edge connecting specified block.
     173             : BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To,
     174             :                       DominatorTree *DT = nullptr, LoopInfo *LI = nullptr);
     175             : 
     176             : /// Split the specified block at the specified instruction - everything before
     177             : /// SplitPt stays in Old and everything starting with SplitPt moves to a new
     178             : /// block. The two blocks are joined by an unconditional branch and the loop
     179             : /// info is updated.
     180             : BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt,
     181             :                        DominatorTree *DT = nullptr, LoopInfo *LI = nullptr);
     182             : 
     183             : /// This method introduces at least one new basic block into the function and
     184             : /// moves some of the predecessors of BB to be predecessors of the new block.
     185             : /// The new predecessors are indicated by the Preds array. The new block is
     186             : /// given a suffix of 'Suffix'. Returns new basic block to which predecessors
     187             : /// from Preds are now pointing.
     188             : ///
     189             : /// If BB is a landingpad block then additional basicblock might be introduced.
     190             : /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more
     191             : /// details on this case.
     192             : ///
     193             : /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
     194             : /// no other analyses. In particular, it does not preserve LoopSimplify
     195             : /// (because it's complicated to handle the case where one of the edges being
     196             : /// split is an exit of a loop with other exits).
     197             : ///
     198             : BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
     199             :                                    const char *Suffix,
     200             :                                    DominatorTree *DT = nullptr,
     201             :                                    LoopInfo *LI = nullptr,
     202             :                                    bool PreserveLCSSA = false);
     203             : 
     204             : /// This method transforms the landing pad, OrigBB, by introducing two new basic
     205             : /// blocks into the function. One of those new basic blocks gets the
     206             : /// predecessors listed in Preds. The other basic block gets the remaining
     207             : /// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both
     208             : /// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and
     209             : /// 'Suffix2', and are returned in the NewBBs vector.
     210             : ///
     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             : ///
     216             : void SplitLandingPadPredecessors(BasicBlock *OrigBB,
     217             :                                  ArrayRef<BasicBlock *> Preds,
     218             :                                  const char *Suffix, const char *Suffix2,
     219             :                                  SmallVectorImpl<BasicBlock *> &NewBBs,
     220             :                                  DominatorTree *DT = nullptr,
     221             :                                  LoopInfo *LI = nullptr,
     222             :                                  bool PreserveLCSSA = false);
     223             : 
     224             : /// This method duplicates the specified return instruction into a predecessor
     225             : /// which ends in an unconditional branch. If the return instruction returns a
     226             : /// value defined by a PHI, propagate the right value into the return. It
     227             : /// returns the new return instruction in the predecessor.
     228             : ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
     229             :                                        BasicBlock *Pred);
     230             : 
     231             : /// Split the containing block at the specified instruction - everything before
     232             : /// SplitBefore stays in the old basic block, and the rest of the instructions
     233             : /// in the BB are moved to a new block. The two blocks are connected by a
     234             : /// conditional branch (with value of Cmp being the condition).
     235             : /// Before:
     236             : ///   Head
     237             : ///   SplitBefore
     238             : ///   Tail
     239             : /// After:
     240             : ///   Head
     241             : ///   if (Cond)
     242             : ///     ThenBlock
     243             : ///   SplitBefore
     244             : ///   Tail
     245             : ///
     246             : /// If Unreachable is true, then ThenBlock ends with
     247             : /// UnreachableInst, otherwise it branches to Tail.
     248             : /// Returns the NewBasicBlock's terminator.
     249             : ///
     250             : /// Updates DT and LI if given.
     251             : TerminatorInst *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
     252             :                                           bool Unreachable,
     253             :                                           MDNode *BranchWeights = nullptr,
     254             :                                           DominatorTree *DT = nullptr,
     255             :                                           LoopInfo *LI = nullptr);
     256             : 
     257             : /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
     258             : /// but also creates the ElseBlock.
     259             : /// Before:
     260             : ///   Head
     261             : ///   SplitBefore
     262             : ///   Tail
     263             : /// After:
     264             : ///   Head
     265             : ///   if (Cond)
     266             : ///     ThenBlock
     267             : ///   else
     268             : ///     ElseBlock
     269             : ///   SplitBefore
     270             : ///   Tail
     271             : void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
     272             :                                    TerminatorInst **ThenTerm,
     273             :                                    TerminatorInst **ElseTerm,
     274             :                                    MDNode *BranchWeights = nullptr);
     275             : 
     276             : /// Check whether BB is the merge point of a if-region.
     277             : /// If so, return the boolean condition that determines which entry into
     278             : /// BB will be taken.  Also, return by references the block that will be
     279             : /// entered from if the condition is true, and the block that will be
     280             : /// entered if the condition is false.
     281             : ///
     282             : /// This does no checking to see if the true/false blocks have large or unsavory
     283             : /// instructions in them.
     284             : Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
     285             :                       BasicBlock *&IfFalse);
     286             : 
     287             : } // end namespace llvm
     288             : 
     289             : #endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H

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