LCOV - code coverage report
Current view: top level - include/llvm/Transforms/Utils - BasicBlockUtils.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 9 9 100.0 %
Date: 2018-09-23 13:06:45 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/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        5550 :       : DT(DT), LI(LI), MSSAU(MSSAU) {}
      98             : 
      99             :   CriticalEdgeSplittingOptions &setMergeIdenticalEdges() {
     100         191 :     MergeIdenticalEdges = true;
     101             :     return *this;
     102             :   }
     103             : 
     104             :   CriticalEdgeSplittingOptions &setDontDeleteUselessPHIs() {
     105         171 :     DontDeleteUselessPHIs = true;
     106             :     return *this;
     107             :   }
     108             : 
     109             :   CriticalEdgeSplittingOptions &setPreserveLCSSA() {
     110        4172 :     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(TerminatorInst *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             :   TerminatorInst *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        4188 : SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
     163             :                   const CriticalEdgeSplittingOptions &Options =
     164             :                       CriticalEdgeSplittingOptions()) {
     165             :   TerminatorInst *TI = Src->getTerminator();
     166             :   unsigned i = 0;
     167             :   while (true) {
     168        1994 :     assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
     169        6182 :     if (TI->getSuccessor(i) == Dst)
     170        4188 :       return SplitCriticalEdge(TI, i, Options);
     171        1994 :     ++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             : TerminatorInst *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             :                                    TerminatorInst **ThenTerm,
     282             :                                    TerminatorInst **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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