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1 //===-- MipsFrameLowering.cpp - Mips Frame Information --------------------===//
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2 //
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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3 // The LLVM Compiler Infrastructure
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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4 //
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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9 //
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10 // This file contains the Mips implementation of TargetFrameLowering class.
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11 //
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12 //===----------------------------------------------------------------------===//
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13
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14 #include "MipsFrameLowering.h"
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15 #include "MCTargetDesc/MipsBaseInfo.h"
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16 #include "MipsAnalyzeImmediate.h"
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17 #include "MipsInstrInfo.h"
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18 #include "MipsMachineFunction.h"
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19 #include "MipsTargetMachine.h"
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20 #include "llvm/CodeGen/MachineFrameInfo.h"
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21 #include "llvm/CodeGen/MachineFunction.h"
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22 #include "llvm/CodeGen/MachineInstrBuilder.h"
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23 #include "llvm/CodeGen/MachineModuleInfo.h"
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24 #include "llvm/CodeGen/MachineRegisterInfo.h"
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25 #include "llvm/IR/DataLayout.h"
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26 #include "llvm/IR/Function.h"
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27 #include "llvm/Support/CommandLine.h"
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28 #include "llvm/Target/TargetOptions.h"
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29
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30 using namespace llvm;
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31
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32
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33 //===----------------------------------------------------------------------===//
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34 //
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35 // Stack Frame Processing methods
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36 // +----------------------------+
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37 //
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38 // The stack is allocated decrementing the stack pointer on
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39 // the first instruction of a function prologue. Once decremented,
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40 // all stack references are done thought a positive offset
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41 // from the stack/frame pointer, so the stack is considering
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42 // to grow up! Otherwise terrible hacks would have to be made
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43 // to get this stack ABI compliant :)
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44 //
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45 // The stack frame required by the ABI (after call):
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46 // Offset
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47 //
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48 // 0 ----------
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49 // 4 Args to pass
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50 // . saved $GP (used in PIC)
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51 // . Alloca allocations
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52 // . Local Area
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53 // . CPU "Callee Saved" Registers
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54 // . saved FP
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55 // . saved RA
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56 // . FPU "Callee Saved" Registers
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57 // StackSize -----------
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58 //
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59 // Offset - offset from sp after stack allocation on function prologue
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60 //
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61 // The sp is the stack pointer subtracted/added from the stack size
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62 // at the Prologue/Epilogue
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63 //
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64 // References to the previous stack (to obtain arguments) are done
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65 // with offsets that exceeds the stack size: (stacksize+(4*(num_arg-1))
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66 //
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67 // Examples:
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68 // - reference to the actual stack frame
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69 // for any local area var there is smt like : FI >= 0, StackOffset: 4
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70 // sw REGX, 4(SP)
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71 //
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72 // - reference to previous stack frame
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73 // suppose there's a load to the 5th arguments : FI < 0, StackOffset: 16.
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74 // The emitted instruction will be something like:
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75 // lw REGX, 16+StackSize(SP)
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76 //
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77 // Since the total stack size is unknown on LowerFormalArguments, all
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78 // stack references (ObjectOffset) created to reference the function
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79 // arguments, are negative numbers. This way, on eliminateFrameIndex it's
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80 // possible to detect those references and the offsets are adjusted to
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81 // their real location.
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82 //
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83 //===----------------------------------------------------------------------===//
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84
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77
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85 const MipsFrameLowering *MipsFrameLowering::create(const MipsSubtarget &ST) {
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86 if (ST.inMips16Mode())
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87 return llvm::createMips16FrameLowering(ST);
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88
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89 return llvm::createMipsSEFrameLowering(ST);
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90 }
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91
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92 // hasFP - Return true if the specified function should have a dedicated frame
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93 // pointer register. This is true if the function has variable sized allocas or
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94 // if frame pointer elimination is disabled.
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95 bool MipsFrameLowering::hasFP(const MachineFunction &MF) const {
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96 const MachineFrameInfo *MFI = MF.getFrameInfo();
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97 return MF.getTarget().Options.DisableFramePointerElim(MF) ||
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98 MFI->hasVarSizedObjects() || MFI->isFrameAddressTaken();
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99 }
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100
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101 uint64_t MipsFrameLowering::estimateStackSize(const MachineFunction &MF) const {
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102 const MachineFrameInfo *MFI = MF.getFrameInfo();
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83
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103 const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
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104
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105 int64_t Offset = 0;
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106
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107 // Iterate over fixed sized objects.
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108 for (int I = MFI->getObjectIndexBegin(); I != 0; ++I)
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109 Offset = std::max(Offset, -MFI->getObjectOffset(I));
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110
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111 // Conservatively assume all callee-saved registers will be saved.
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112 for (const MCPhysReg *R = TRI.getCalleeSavedRegs(&MF); *R; ++R) {
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113 unsigned Size = TRI.getMinimalPhysRegClass(*R)->getSize();
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114 Offset = RoundUpToAlignment(Offset + Size, Size);
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115 }
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116
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117 unsigned MaxAlign = MFI->getMaxAlignment();
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118
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119 // Check that MaxAlign is not zero if there is a stack object that is not a
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120 // callee-saved spill.
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121 assert(!MFI->getObjectIndexEnd() || MaxAlign);
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122
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123 // Iterate over other objects.
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124 for (unsigned I = 0, E = MFI->getObjectIndexEnd(); I != E; ++I)
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125 Offset = RoundUpToAlignment(Offset + MFI->getObjectSize(I), MaxAlign);
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126
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127 // Call frame.
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128 if (MFI->adjustsStack() && hasReservedCallFrame(MF))
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129 Offset = RoundUpToAlignment(Offset + MFI->getMaxCallFrameSize(),
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130 std::max(MaxAlign, getStackAlignment()));
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131
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132 return RoundUpToAlignment(Offset, getStackAlignment());
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133 }
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