include/llvm/CodeGen/MachineLoopInfo.h

   1 //===- llvm/CodeGen/MachineLoopInfo.h - Natural Loop Calculator -*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines the MachineLoopInfo class that is used to identify natural
  10 // loops and determine the loop depth of various nodes of the CFG.  Note that
  11 // natural loops may actually be several loops that share the same header node.
  12 //
  13 // This analysis calculates the nesting structure of loops in a function.  For
  14 // each natural loop identified, this analysis identifies natural loops
  15 // contained entirely within the loop and the basic blocks the make up the loop.
  16 //
  17 // It can calculate on the fly various bits of information, for example:
  18 //
  19 //  * whether there is a preheader for the loop
  20 //  * the number of back edges to the header
  21 //  * whether or not a particular block branches out of the loop
  22 //  * the successor blocks of the loop
  23 //  * the loop depth
  24 //  * the trip count
  25 //  * etc...
  26 //
  27 //===----------------------------------------------------------------------===//
  28
  29 #ifndef LLVM_CODEGEN_MACHINELOOPINFO_H
  30 #define LLVM_CODEGEN_MACHINELOOPINFO_H
  31
  32 #include "llvm/Analysis/LoopInfo.h"
  33 #include "llvm/CodeGen/MachineBasicBlock.h"
  34 #include "llvm/CodeGen/MachineFunctionPass.h"
  35 #include "llvm/IR/DebugLoc.h"
  36 #include "llvm/Pass.h"
  37
  38 namespace llvm {
  39
  40 // Implementation in LoopInfoImpl.h
  41 class MachineLoop;
  42 extern template class LoopBase<MachineBasicBlock, MachineLoop>;
  43
  44 class MachineLoop : public LoopBase<MachineBasicBlock, MachineLoop> {
  45 public:
  46   /// Return the "top" block in the loop, which is the first block in the linear
  47   /// layout, ignoring any parts of the loop not contiguous with the part that
  48   /// contains the header.
  49   MachineBasicBlock *getTopBlock();
  50
  51   /// Return the "bottom" block in the loop, which is the last block in the
  52   /// linear layout, ignoring any parts of the loop not contiguous with the part
  53   /// that contains the header.
  54   MachineBasicBlock *getBottomBlock();
  55
  56   /// Find the block that contains the loop control variable and the
  57   /// loop test. This will return the latch block if it's one of the exiting
  58   /// blocks. Otherwise, return the exiting block. Return 'null' when
  59   /// multiple exiting blocks are present.
  60   MachineBasicBlock *findLoopControlBlock();
  61
  62   /// Return the debug location of the start of this loop.
  63   /// This looks for a BB terminating instruction with a known debug
  64   /// location by looking at the preheader and header blocks. If it
  65   /// cannot find a terminating instruction with location information,
  66   /// it returns an unknown location.
  67   DebugLoc getStartLoc() const;
  68
  69   void dump() const;
  70
  71 private:
  72   friend class LoopInfoBase<MachineBasicBlock, MachineLoop>;
  73
  74   explicit MachineLoop(MachineBasicBlock *MBB)
  75     : LoopBase<MachineBasicBlock, MachineLoop>(MBB) {}
  76
  77   MachineLoop() = default;
  78 };
  79
  80 // Implementation in LoopInfoImpl.h
  81 extern template class LoopInfoBase<MachineBasicBlock, MachineLoop>;
  82
  83 class MachineLoopInfo : public MachineFunctionPass {
  84   friend class LoopBase<MachineBasicBlock, MachineLoop>;
  85
  86   LoopInfoBase<MachineBasicBlock, MachineLoop> LI;
  87
  88 public:
  89   static char ID; // Pass identification, replacement for typeid
  90
  91   MachineLoopInfo() : MachineFunctionPass(ID) {
  92     initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
  93   }
  94   MachineLoopInfo(const MachineLoopInfo &) = delete;
  95   MachineLoopInfo &operator=(const MachineLoopInfo &) = delete;
  96
  97   LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
  98
  99   /// Find the block that either is the loop preheader, or could
 100   /// speculatively be used as the preheader. This is e.g. useful to place
 101   /// loop setup code. Code that cannot be speculated should not be placed
 102   /// here. SpeculativePreheader is controlling whether it also tries to
 103   /// find the speculative preheader if the regular preheader is not present.
 104   MachineBasicBlock *findLoopPreheader(MachineLoop *L,
 105                                        bool SpeculativePreheader = false) const;
 106
 107   /// The iterator interface to the top-level loops in the current function.
 108   using iterator = LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator;
 109   inline iterator begin() const { return LI.begin(); }
 110   inline iterator end() const { return LI.end(); }
 111   bool empty() const { return LI.empty(); }
 112
 113   /// Return the innermost loop that BB lives in. If a basic block is in no loop
 114   /// (for example the entry node), null is returned.
 115   inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const {
 116     return LI.getLoopFor(BB);
 117   }
 118
 119   /// Same as getLoopFor.
 120   inline const MachineLoop *operator[](const MachineBasicBlock *BB) const {
 121     return LI.getLoopFor(BB);
 122   }
 123
 124   /// Return the loop nesting level of the specified block.
 125   inline unsigned getLoopDepth(const MachineBasicBlock *BB) const {
 126     return LI.getLoopDepth(BB);
 127   }
 128
 129   /// True if the block is a loop header node.
 130   inline bool isLoopHeader(const MachineBasicBlock *BB) const {
 131     return LI.isLoopHeader(BB);
 132   }
 133
 134   /// Calculate the natural loop information.
 135   bool runOnMachineFunction(MachineFunction &F) override;
 136
 137   void releaseMemory() override { LI.releaseMemory(); }
 138
 139   void getAnalysisUsage(AnalysisUsage &AU) const override;
 140
 141   /// This removes the specified top-level loop from this loop info object. The
 142   /// loop is not deleted, as it will presumably be inserted into another loop.
 143   inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); }
 144
 145   /// Change the top-level loop that contains BB to the specified loop. This
 146   /// should be used by transformations that restructure the loop hierarchy
 147   /// tree.
 148   inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) {
 149     LI.changeLoopFor(BB, L);
 150   }
 151
 152   /// Replace the specified loop in the top-level loops list with the indicated
 153   /// loop.
 154   inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) {
 155     LI.changeTopLevelLoop(OldLoop, NewLoop);
 156   }
 157
 158   /// This adds the specified loop to the collection of top-level loops.
 159   inline void addTopLevelLoop(MachineLoop *New) {
 160     LI.addTopLevelLoop(New);
 161   }
 162
 163   /// This method completely removes BB from all data structures, including all
 164   /// of the Loop objects it is nested in and our mapping from
 165   /// MachineBasicBlocks to loops.
 166   void removeBlock(MachineBasicBlock *BB) {
 167     LI.removeBlock(BB);
 168   }
 169 };
 170
 171 // Allow clients to walk the list of nested loops...
 172 template <> struct GraphTraits<const MachineLoop*> {
 173   using NodeRef = const MachineLoop *;
 174   using ChildIteratorType = MachineLoopInfo::iterator;
 175
 176   static NodeRef getEntryNode(const MachineLoop *L) { return L; }
 177   static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
 178   static ChildIteratorType child_end(NodeRef N) { return N->end(); }
 179 };
 180
 181 template <> struct GraphTraits<MachineLoop*> {
 182   using NodeRef = MachineLoop *;
 183   using ChildIteratorType = MachineLoopInfo::iterator;
 184
 185   static NodeRef getEntryNode(MachineLoop *L) { return L; }
 186   static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
 187   static ChildIteratorType child_end(NodeRef N) { return N->end(); }
 188 };
 189
 190 } // end namespace llvm
 191
 192 #endif // LLVM_CODEGEN_MACHINELOOPINFO_H