X86RegisterInfo.cpp revision 7ad3e063f508218a2823bd5cf092ef622ed7ba6c 
1//===- X86RegisterInfo.cpp - X86 Register Information -----------*- C++ -*-===//
2//
3// This file contains the X86 implementation of the MRegisterInfo class.  This
4// file is responsible for the frame pointer elimination optimization on X86.
5//
6//===----------------------------------------------------------------------===//
7
8#include "X86.h"
9#include "X86RegisterInfo.h"
10#include "X86InstrBuilder.h"
11#include "llvm/Constants.h"
12#include "llvm/Type.h"
13#include "llvm/CodeGen/ValueTypes.h"
14#include "llvm/CodeGen/MachineInstrBuilder.h"
15#include "llvm/CodeGen/MachineFunction.h"
16#include "llvm/CodeGen/MachineFrameInfo.h"
17#include "llvm/Target/TargetMachine.h"
18#include "llvm/Target/TargetFrameInfo.h"
19#include "Support/CommandLine.h"
20
21namespace {
22  cl::opt<bool>
23  NoFPElim("disable-fp-elim",
24	   cl::desc("Disable frame pointer elimination optimization"));
25}
26
27X86RegisterInfo::X86RegisterInfo()
28  : X86GenRegisterInfo(X86::ADJCALLSTACKDOWN, X86::ADJCALLSTACKUP) {}
29
30static unsigned getIdx(const TargetRegisterClass *RC) {
31  switch (RC->getSize()) {
32  default: assert(0 && "Invalid data size!");
33  case 1:  return 0;
34  case 2:  return 1;
35  case 4:  return 2;
36  case 10: return 3;
37  }
38}
39
40void X86RegisterInfo::storeRegToStackSlot(MachineBasicBlock &MBB,
41					  MachineBasicBlock::iterator &MBBI,
42					  unsigned SrcReg, int FrameIdx,
43					  const TargetRegisterClass *RC) const {
44  static const unsigned Opcode[] =
45    { X86::MOVrm8, X86::MOVrm16, X86::MOVrm32, X86::FSTPr80 };
46  MachineInstr *MI = addFrameReference(BuildMI(Opcode[getIdx(RC)], 5),
47				       FrameIdx).addReg(SrcReg);
48  MBBI = MBB.insert(MBBI, MI)+1;
49}
50
51void X86RegisterInfo::loadRegFromStackSlot(MachineBasicBlock &MBB,
52					   MachineBasicBlock::iterator &MBBI,
53					   unsigned DestReg, int FrameIdx,
54					   const TargetRegisterClass *RC) const{
55  static const unsigned Opcode[] =
56    { X86::MOVmr8, X86::MOVmr16, X86::MOVmr32, X86::FLDr80 };
57  MachineInstr *MI = addFrameReference(BuildMI(Opcode[getIdx(RC)], 4, DestReg),
58				       FrameIdx);
59  MBBI = MBB.insert(MBBI, MI)+1;
60}
61
62void X86RegisterInfo::copyRegToReg(MachineBasicBlock &MBB,
63				   MachineBasicBlock::iterator &MBBI,
64				   unsigned DestReg, unsigned SrcReg,
65				   const TargetRegisterClass *RC) const {
66  static const unsigned Opcode[] =
67    { X86::MOVrr8, X86::MOVrr16, X86::MOVrr32, X86::FpMOV };
68  MachineInstr *MI = BuildMI(Opcode[getIdx(RC)],1,DestReg).addReg(SrcReg);
69  MBBI = MBB.insert(MBBI, MI)+1;
70}
71
72//===----------------------------------------------------------------------===//
73// Stack Frame Processing methods
74//===----------------------------------------------------------------------===//
75
76// hasFP - Return true if the specified function should have a dedicated frame
77// pointer register.  This is true if the function has variable sized allocas or
78// if frame pointer elimination is disabled.
79//
80static bool hasFP(MachineFunction &MF) {
81  return NoFPElim || MF.getFrameInfo()->hasVarSizedObjects();
82}
83
84// hasSPAdjust - Return true if this function has ESP adjustment instructions in
85// the prolog and epilog which allocate local stack space.  This is neccesary
86// because we elide these instructions if there are no function calls in the
87// current function (ie, this is a leaf function).  In this case, we can refer
88// beyond the stack pointer because we know that nothing will trample on that
89// part of the stack.
90//
91static bool hasSPAdjust(MachineFunction &MF) {
92  assert(!hasFP(MF) && "Can only eliminate SP adjustment if no frame-pointer!");
93  return MF.getFrameInfo()->hasCalls();
94}
95
96void X86RegisterInfo::eliminateCallFramePseudoInstr(MachineFunction &MF,
97						    MachineBasicBlock &MBB,
98	                                 MachineBasicBlock::iterator &I) const {
99  MachineInstr *New = 0, *Old = *I;;
100  if (hasFP(MF)) {
101    // If we have a frame pointer, turn the adjcallstackup instruction into a
102    // 'sub ESP, <amt>' and the adjcallstackdown instruction into 'add ESP,
103    // <amt>'
104    unsigned Amount = Old->getOperand(0).getImmedValue();
105    if (Amount != 0) {
106      // We need to keep the stack aligned properly.  To do this, we round the
107      // amount of space needed for the outgoing arguments up to the next
108      // alignment boundary.
109      unsigned Align = MF.getTarget().getFrameInfo().getStackAlignment();
110      Amount = (Amount+Align-1)/Align*Align;
111
112      if (Old->getOpcode() == X86::ADJCALLSTACKDOWN) {
113	New=BuildMI(X86::SUBri32, 2, X86::ESP).addReg(X86::ESP).addZImm(Amount);
114      } else {
115	assert(Old->getOpcode() == X86::ADJCALLSTACKUP);
116	New=BuildMI(X86::ADDri32, 2, X86::ESP).addReg(X86::ESP).addZImm(Amount);
117      }
118    }
119  }
120
121  if (New)
122    *I = New;        // Replace the pseudo instruction with a new instruction...
123  else
124    I = MBB.erase(I);// Just delete the pseudo instruction...
125  delete Old;
126}
127
128void X86RegisterInfo::eliminateFrameIndex(MachineFunction &MF,
129					MachineBasicBlock::iterator &II) const {
130  unsigned i = 0;
131  MachineInstr &MI = **II;
132  while (!MI.getOperand(i).isFrameIndex()) {
133    ++i;
134    assert(i < MI.getNumOperands() && "Instr doesn't have FrameIndex operand!");
135  }
136
137  int FrameIndex = MI.getOperand(i).getFrameIndex();
138
139  // This must be part of a four operand memory reference.  Replace the
140  // FrameIndex with base register with EBP.  Add add an offset to the offset.
141  MI.SetMachineOperandReg(i, hasFP(MF) ? X86::EBP : X86::ESP);
142
143  // Now add the frame object offset to the offset from EBP.
144  int Offset = MF.getFrameInfo()->getObjectOffset(FrameIndex) +
145               MI.getOperand(i+3).getImmedValue()+4;
146
147  if (!hasFP(MF) && hasSPAdjust(MF)) {
148    const MachineFrameInfo *MFI = MF.getFrameInfo();
149    Offset += MFI->getStackSize();
150  }
151
152  MI.SetMachineOperandConst(i+3, MachineOperand::MO_SignExtendedImmed, Offset);
153}
154
155void X86RegisterInfo::processFunctionBeforeFrameFinalized(MachineFunction &MF)
156  const {
157  if (hasFP(MF)) {
158    // Create a frame entry for the EBP register that must be saved.
159    int FrameIdx = MF.getFrameInfo()->CreateStackObject(4, 4);
160    assert(FrameIdx == MF.getFrameInfo()->getObjectIndexEnd()-1 &&
161	   "Slot for EBP register must be last in order to be found!");
162  }
163}
164
165void X86RegisterInfo::emitPrologue(MachineFunction &MF) const {
166  MachineBasicBlock &MBB = MF.front();   // Prolog goes in entry BB
167  MachineBasicBlock::iterator MBBI = MBB.begin();
168  MachineFrameInfo *MFI = MF.getFrameInfo();
169  MachineInstr *MI;
170
171  // Get the number of bytes to allocate from the FrameInfo
172  unsigned NumBytes = MFI->getStackSize();
173  if (hasFP(MF)) {
174    // Get the offset of the stack slot for the EBP register... which is
175    // guaranteed to be the last slot by processFunctionBeforeFrameFinalized.
176    int EBPOffset = MFI->getObjectOffset(MFI->getObjectIndexEnd()-1)+4;
177
178    MI = addRegOffset(BuildMI(X86::MOVrm32, 5),    // mov [ESP-<offset>], EBP
179		      X86::ESP, EBPOffset).addReg(X86::EBP);
180    MBBI = MBB.insert(MBBI, MI)+1;
181
182    MI = BuildMI(X86::MOVrr32, 2, X86::EBP).addReg(X86::ESP);
183    MBBI = MBB.insert(MBBI, MI)+1;
184  } else {
185    // If we don't have a frame pointer, and the function contains no call sites
186    // (it's a leaf function), we don't have to emit ANY stack adjustment
187    // instructions at all, we can just refer to the area beyond the stack
188    // pointer.  This can be important for small functions.
189    //
190    if (!hasSPAdjust(MF)) return;
191
192    // When we have no frame pointer, we reserve argument space for call sites
193    // in the function immediately on entry to the current function.  This
194    // eliminates the need for add/sub ESP brackets around call sites.
195    //
196    NumBytes += MFI->getMaxCallFrameSize();
197
198    // Round the size to a multiple of the alignment (don't forget the 4 byte
199    // offset though).
200    unsigned Align = MF.getTarget().getFrameInfo().getStackAlignment();
201    NumBytes = ((NumBytes+4)+Align-1)/Align*Align - 4;
202
203    // Update frame info to pretend that this is part of the stack...
204    MFI->setStackSize(NumBytes);
205  }
206
207  if (NumBytes) {
208    // adjust stack pointer: ESP -= numbytes
209    MI  = BuildMI(X86::SUBri32, 2, X86::ESP).addReg(X86::ESP).addZImm(NumBytes);
210    MBBI = 1+MBB.insert(MBBI, MI);
211  }
212}
213
214void X86RegisterInfo::emitEpilogue(MachineFunction &MF,
215				   MachineBasicBlock &MBB) const {
216  const MachineFrameInfo *MFI = MF.getFrameInfo();
217  MachineBasicBlock::iterator MBBI = MBB.end()-1;
218  MachineInstr *MI;
219  assert((*MBBI)->getOpcode() == X86::RET &&
220         "Can only insert epilog into returning blocks");
221
222  if (hasFP(MF)) {
223    // Get the offset of the stack slot for the EBP register... which is
224    // guaranteed to be the last slot by processFunctionBeforeFrameFinalized.
225    int EBPOffset = MFI->getObjectOffset(MFI->getObjectIndexEnd()-1)+4;
226
227    // mov ESP, EBP
228    MI = BuildMI(X86::MOVrr32, 1,X86::ESP).addReg(X86::EBP);
229    MBBI = 1+MBB.insert(MBBI, MI);
230
231    // mov EBP, [ESP-<offset>]
232    MI = addRegOffset(BuildMI(X86::MOVmr32, 5, X86::EBP), X86::ESP, EBPOffset);
233    MBBI = 1+MBB.insert(MBBI, MI);
234  } else {
235    if (!hasSPAdjust(MF)) return;
236
237    // Get the number of bytes allocated from the FrameInfo...
238    unsigned NumBytes = MFI->getStackSize();
239
240    if (NumBytes) {    // adjust stack pointer back: ESP += numbytes
241      MI =BuildMI(X86::ADDri32, 2, X86::ESP).addReg(X86::ESP).addZImm(NumBytes);
242      MBBI = 1+MBB.insert(MBBI, MI);
243    }
244  }
245}
246
247#include "X86GenRegisterInfo.inc"
248
249const TargetRegisterClass*
250X86RegisterInfo::getRegClassForType(const Type* Ty) const {
251  switch (Ty->getPrimitiveID()) {
252  case Type::LongTyID:
253  case Type::ULongTyID: assert(0 && "Long values can't fit in registers!");
254  default:              assert(0 && "Invalid type to getClass!");
255  case Type::BoolTyID:
256  case Type::SByteTyID:
257  case Type::UByteTyID:   return &r8Instance;
258  case Type::ShortTyID:
259  case Type::UShortTyID:  return &r16Instance;
260  case Type::IntTyID:
261  case Type::UIntTyID:
262  case Type::PointerTyID: return &r32Instance;
263
264  case Type::FloatTyID:
265  case Type::DoubleTyID: return &rFPInstance;
266  }
267}
268