lib/CodeGen/AllocationOrder.cpp

   1 //===-- llvm/CodeGen/AllocationOrder.cpp - Allocation Order ---------------===//
   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 file implements an allocation order for virtual registers.
  11 //
  12 // The preferred allocation order for a virtual register depends on allocation
  13 // hints and target hooks. The AllocationOrder class encapsulates all of that.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "AllocationOrder.h"
  18 #include "VirtRegMap.h"
  19 #include "llvm/CodeGen/MachineRegisterInfo.h"
  20
  21 using namespace llvm;
  22
  23 // Compare VirtRegMap::getRegAllocPref().
  24 AllocationOrder::AllocationOrder(unsigned VirtReg,
  25                                  const VirtRegMap &VRM,
  26                                  const BitVector &ReservedRegs)
  27   : Pos(0), Reserved(ReservedRegs) {
  28   const TargetRegisterClass *RC = VRM.getRegInfo().getRegClass(VirtReg);
  29   std::pair<unsigned, unsigned> HintPair =
  30     VRM.getRegInfo().getRegAllocationHint(VirtReg);
  31
  32   // HintPair.second is a register, phys or virt.
  33   Hint = HintPair.second;
  34
  35   // Translate to physreg, or 0 if not assigned yet.
  36   if (TargetRegisterInfo::isVirtualRegister(Hint))
  37     Hint = VRM.getPhys(Hint);
  38
  39   // The remaining allocation order may depend on the hint.
  40   tie(Begin, End) = VRM.getTargetRegInfo()
  41         .getAllocationOrder(RC, HintPair.first, Hint, VRM.getMachineFunction());
  42
  43   // Target-dependent hints require resolution.
  44   if (HintPair.first)
  45     Hint = VRM.getTargetRegInfo().ResolveRegAllocHint(HintPair.first, Hint,
  46                                                       VRM.getMachineFunction());
  47
  48   // The hint must be a valid physreg for allocation.
  49   if (Hint && (!TargetRegisterInfo::isPhysicalRegister(Hint) ||
  50                !RC->contains(Hint) || ReservedRegs.test(Hint)))
  51     Hint = 0;
  52 }
  53
  54 unsigned AllocationOrder::next() {
  55   // First take the hint.
  56   if (!Pos) {
  57     Pos = Begin;
  58     if (Hint)
  59       return Hint;
  60   }
  61   // Then look at the order from TRI.
  62   while(Pos != End) {
  63     unsigned Reg = *Pos++;
  64     if (Reg != Hint && !Reserved.test(Reg))
  65       return Reg;
  66   }
  67   return 0;
  68 }