lib/CodeGen/PHIElimination.h

   1 //===-- lib/CodeGen/PHIElimination.h ----------------------------*- 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 #ifndef LLVM_CODEGEN_PHIELIMINATION_HPP
  11 #define LLVM_CODEGEN_PHIELIMINATION_HPP
  12
  13 #include "llvm/ADT/DenseMap.h"
  14 #include "llvm/ADT/SmallSet.h"
  15 #include "llvm/ADT/SmallPtrSet.h"
  16 #include "llvm/CodeGen/MachineFunctionPass.h"
  17 #include "llvm/Target/TargetInstrInfo.h"
  18
  19 #include <map>
  20
  21 namespace llvm {
  22
  23   /// Lower PHI instructions to copies.
  24   class PHIElimination : public MachineFunctionPass {
  25     MachineRegisterInfo  *MRI; // Machine register information
  26   private:
  27
  28     typedef SmallSet<MachineBasicBlock*, 4> PHIKillList;
  29     typedef DenseMap<unsigned, PHIKillList> PHIKillMap;
  30     typedef DenseMap<unsigned, MachineBasicBlock*> PHIDefMap;
  31
  32   public:
  33
  34     typedef PHIKillList::iterator phi_kill_iterator;
  35     typedef PHIKillList::const_iterator const_phi_kill_iterator;
  36
  37     static char ID; // Pass identification, replacement for typeid
  38     PHIElimination() : MachineFunctionPass(&ID) {}
  39
  40     virtual bool runOnMachineFunction(MachineFunction &Fn);
  41
  42     virtual void getAnalysisUsage(AnalysisUsage &AU) const;
  43
  44     /// Return true if the given vreg was defined by a PHI intsr prior to
  45     /// lowering.
  46     bool hasPHIDef(unsigned vreg) const {
  47       return PHIDefs.count(vreg);
  48     }
  49
  50     /// Returns the block in which the PHI instruction which defined the
  51     /// given vreg used to reside.
  52     MachineBasicBlock* getPHIDefBlock(unsigned vreg) {
  53       PHIDefMap::iterator phiDefItr = PHIDefs.find(vreg);
  54       assert(phiDefItr != PHIDefs.end() && "vreg has no phi-def.");
  55       return phiDefItr->second;
  56     }
  57
  58     /// Returns true if the given vreg was killed by a PHI instr.
  59     bool hasPHIKills(unsigned vreg) const {
  60       return PHIKills.count(vreg);
  61     }
  62
  63     /// Returns an iterator over the BasicBlocks which contained PHI
  64     /// kills of this register prior to lowering.
  65     phi_kill_iterator phiKillsBegin(unsigned vreg) {
  66       PHIKillMap::iterator phiKillItr = PHIKills.find(vreg);
  67       assert(phiKillItr != PHIKills.end() && "vreg has no phi-kills.");
  68       return phiKillItr->second.begin();
  69     }
  70     phi_kill_iterator phiKillsEnd(unsigned vreg) {
  71       PHIKillMap::iterator phiKillItr = PHIKills.find(vreg);
  72       assert(phiKillItr != PHIKills.end() && "vreg has no phi-kills.");
  73       return phiKillItr->second.end();
  74     }
  75
  76   private:
  77     /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions
  78     /// in predecessor basic blocks.
  79     ///
  80     bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB);
  81     void LowerAtomicPHINode(MachineBasicBlock &MBB,
  82                             MachineBasicBlock::iterator AfterPHIsIt);
  83
  84     /// analyzePHINodes - Gather information about the PHI nodes in
  85     /// here. In particular, we want to map the number of uses of a virtual
  86     /// register which is used in a PHI node. We map that to the BB the
  87     /// vreg is coming from. This is used later to determine when the vreg
  88     /// is killed in the BB.
  89     ///
  90     void analyzePHINodes(const MachineFunction& Fn);
  91
  92     // FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
  93     // SrcReg.  This needs to be after any def or uses of SrcReg, but before
  94     // any subsequent point where control flow might jump out of the basic
  95     // block.
  96     MachineBasicBlock::iterator FindCopyInsertPoint(MachineBasicBlock &MBB,
  97                                                     unsigned SrcReg);
  98
  99     // SkipPHIsAndLabels - Copies need to be inserted after phi nodes and
 100     // also after any exception handling labels: in landing pads execution
 101     // starts at the label, so any copies placed before it won't be executed!
 102     MachineBasicBlock::iterator SkipPHIsAndLabels(MachineBasicBlock &MBB,
 103                                                 MachineBasicBlock::iterator I) {
 104       // Rather than assuming that EH labels come before other kinds of labels,
 105       // just skip all labels.
 106       while (I != MBB.end() &&
 107              (I->getOpcode() == TargetInstrInfo::PHI || I->isLabel()))
 108         ++I;
 109       return I;
 110     }
 111
 112     typedef std::pair<const MachineBasicBlock*, unsigned> BBVRegPair;
 113     typedef std::map<BBVRegPair, unsigned> VRegPHIUse;
 114
 115     VRegPHIUse VRegPHIUseCount;
 116     PHIDefMap PHIDefs;
 117     PHIKillMap PHIKills;
 118
 119     // Defs of PHI sources which are implicit_def.
 120     SmallPtrSet<MachineInstr*, 4> ImpDefs;
 121   };
 122
 123 }
 124
 125 #endif /* LLVM_CODEGEN_PHIELIMINATION_HPP */