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/MachineBasicBlock.h"
  17 #include "llvm/CodeGen/MachineFunctionPass.h"
  18
  19 namespace llvm {
  20   class LiveVariables;
  21   class MachineRegisterInfo;
  22   class MachineLoopInfo;
  23
  24   /// Lower PHI instructions to copies.
  25   class PHIElimination : public MachineFunctionPass {
  26     MachineRegisterInfo *MRI; // Machine register information
  27
  28   public:
  29     static char ID; // Pass identification, replacement for typeid
  30     PHIElimination() : MachineFunctionPass(ID) {
  31       initializePHIEliminationPass(*PassRegistry::getPassRegistry());
  32     }
  33
  34     virtual bool runOnMachineFunction(MachineFunction &Fn);
  35
  36     virtual void getAnalysisUsage(AnalysisUsage &AU) const;
  37
  38   private:
  39     /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions
  40     /// in predecessor basic blocks.
  41     ///
  42     bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB);
  43     void LowerAtomicPHINode(MachineBasicBlock &MBB,
  44                             MachineBasicBlock::iterator AfterPHIsIt);
  45
  46     /// analyzePHINodes - Gather information about the PHI nodes in
  47     /// here. In particular, we want to map the number of uses of a virtual
  48     /// register which is used in a PHI node. We map that to the BB the
  49     /// vreg is coming from. This is used later to determine when the vreg
  50     /// is killed in the BB.
  51     ///
  52     void analyzePHINodes(const MachineFunction& Fn);
  53
  54     /// Split critical edges where necessary for good coalescer performance.
  55     bool SplitPHIEdges(MachineFunction &MF, MachineBasicBlock &MBB,
  56                        LiveVariables &LV, MachineLoopInfo *MLI);
  57
  58     /// SplitCriticalEdge - Split a critical edge from A to B by
  59     /// inserting a new MBB. Update branches in A and PHI instructions
  60     /// in B. Return the new block.
  61     MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *A,
  62                                          MachineBasicBlock *B);
  63
  64     /// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
  65     /// SrcReg when following the CFG edge to SuccMBB. This needs to be after
  66     /// any def of SrcReg, but before any subsequent point where control flow
  67     /// might jump out of the basic block.
  68     MachineBasicBlock::iterator FindCopyInsertPoint(MachineBasicBlock &MBB,
  69                                                     MachineBasicBlock &SuccMBB,
  70                                                     unsigned SrcReg);
  71
  72     // SkipPHIsAndLabels - Copies need to be inserted after phi nodes and
  73     // also after any exception handling labels: in landing pads execution
  74     // starts at the label, so any copies placed before it won't be executed!
  75     // We also deal with DBG_VALUEs, which are a bit tricky:
  76     //  PHI
  77     //  DBG_VALUE
  78     //  LABEL
  79     // Here the DBG_VALUE needs to be skipped, and if it refers to a PHI it
  80     // needs to be annulled or, better, moved to follow the label, as well.
  81     //  PHI
  82     //  DBG_VALUE
  83     //  no label
  84     // Here it is not a good idea to skip the DBG_VALUE.
  85     // FIXME: For now we skip and annul all DBG_VALUEs, maximally simple and
  86     // maximally stupid.
  87     MachineBasicBlock::iterator SkipPHIsAndLabels(MachineBasicBlock &MBB,
  88                                                 MachineBasicBlock::iterator I) {
  89       // Rather than assuming that EH labels come before other kinds of labels,
  90       // just skip all labels.
  91       while (I != MBB.end() &&
  92              (I->isPHI() || I->isLabel() || I->isDebugValue())) {
  93         if (I->isDebugValue() && I->getNumOperands()==3 &&
  94             I->getOperand(0).isReg())
  95           I->getOperand(0).setReg(0U);
  96         ++I;
  97       }
  98       return I;
  99     }
 100
 101     typedef std::pair<unsigned, unsigned> BBVRegPair;
 102     typedef DenseMap<BBVRegPair, unsigned> VRegPHIUse;
 103
 104     VRegPHIUse VRegPHIUseCount;
 105
 106     // Defs of PHI sources which are implicit_def.
 107     SmallPtrSet<MachineInstr*, 4> ImpDefs;
 108
 109     // Map reusable lowered PHI node -> incoming join register.
 110     typedef DenseMap<MachineInstr*, unsigned,
 111                      MachineInstrExpressionTrait> LoweredPHIMap;
 112     LoweredPHIMap LoweredPHIs;
 113   };
 114
 115 }
 116
 117 #endif /* LLVM_CODEGEN_PHIELIMINATION_HPP */