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