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1 //===-- MSP430FrameLowering.cpp - MSP430 Frame Information ----------------===//
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 contains the MSP430 implementation of TargetFrameLowering class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "MSP430FrameLowering.h"
15 #include "MSP430InstrInfo.h"
16 #include "MSP430MachineFunctionInfo.h"
17 #include "MSP430Subtarget.h"
18 #include "llvm/CodeGen/MachineFrameInfo.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineInstrBuilder.h"
21 #include "llvm/CodeGen/MachineModuleInfo.h"
22 #include "llvm/CodeGen/MachineRegisterInfo.h"
23 #include "llvm/IR/DataLayout.h"
24 #include "llvm/IR/Function.h"
25 #include "llvm/Support/CommandLine.h"
26 #include "llvm/Target/TargetOptions.h"
27 
28 using namespace llvm;
29 
hasFP(const MachineFunction & MF) const30 bool MSP430FrameLowering::hasFP(const MachineFunction &MF) const {
31   const MachineFrameInfo *MFI = MF.getFrameInfo();
32 
33   return (MF.getTarget().Options.DisableFramePointerElim(MF) ||
34           MF.getFrameInfo()->hasVarSizedObjects() ||
35           MFI->isFrameAddressTaken());
36 }
37 
hasReservedCallFrame(const MachineFunction & MF) const38 bool MSP430FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
39   return !MF.getFrameInfo()->hasVarSizedObjects();
40 }
41 
emitPrologue(MachineFunction & MF,MachineBasicBlock & MBB) const42 void MSP430FrameLowering::emitPrologue(MachineFunction &MF,
43                                        MachineBasicBlock &MBB) const {
44   assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
45   MachineFrameInfo *MFI = MF.getFrameInfo();
46   MSP430MachineFunctionInfo *MSP430FI = MF.getInfo<MSP430MachineFunctionInfo>();
47   const MSP430InstrInfo &TII =
48       *static_cast<const MSP430InstrInfo *>(MF.getSubtarget().getInstrInfo());
49 
50   MachineBasicBlock::iterator MBBI = MBB.begin();
51   DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
52 
53   // Get the number of bytes to allocate from the FrameInfo.
54   uint64_t StackSize = MFI->getStackSize();
55 
56   uint64_t NumBytes = 0;
57   if (hasFP(MF)) {
58     // Calculate required stack adjustment
59     uint64_t FrameSize = StackSize - 2;
60     NumBytes = FrameSize - MSP430FI->getCalleeSavedFrameSize();
61 
62     // Get the offset of the stack slot for the EBP register... which is
63     // guaranteed to be the last slot by processFunctionBeforeFrameFinalized.
64     // Update the frame offset adjustment.
65     MFI->setOffsetAdjustment(-NumBytes);
66 
67     // Save FP into the appropriate stack slot...
68     BuildMI(MBB, MBBI, DL, TII.get(MSP430::PUSH16r))
69       .addReg(MSP430::FP, RegState::Kill);
70 
71     // Update FP with the new base value...
72     BuildMI(MBB, MBBI, DL, TII.get(MSP430::MOV16rr), MSP430::FP)
73       .addReg(MSP430::SP);
74 
75     // Mark the FramePtr as live-in in every block except the entry.
76     for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
77          I != E; ++I)
78       I->addLiveIn(MSP430::FP);
79 
80   } else
81     NumBytes = StackSize - MSP430FI->getCalleeSavedFrameSize();
82 
83   // Skip the callee-saved push instructions.
84   while (MBBI != MBB.end() && (MBBI->getOpcode() == MSP430::PUSH16r))
85     ++MBBI;
86 
87   if (MBBI != MBB.end())
88     DL = MBBI->getDebugLoc();
89 
90   if (NumBytes) { // adjust stack pointer: SP -= numbytes
91     // If there is an SUB16ri of SP immediately before this instruction, merge
92     // the two.
93     //NumBytes -= mergeSPUpdates(MBB, MBBI, true);
94     // If there is an ADD16ri or SUB16ri of SP immediately after this
95     // instruction, merge the two instructions.
96     // mergeSPUpdatesDown(MBB, MBBI, &NumBytes);
97 
98     if (NumBytes) {
99       MachineInstr *MI =
100         BuildMI(MBB, MBBI, DL, TII.get(MSP430::SUB16ri), MSP430::SP)
101         .addReg(MSP430::SP).addImm(NumBytes);
102       // The SRW implicit def is dead.
103       MI->getOperand(3).setIsDead();
104     }
105   }
106 }
107 
emitEpilogue(MachineFunction & MF,MachineBasicBlock & MBB) const108 void MSP430FrameLowering::emitEpilogue(MachineFunction &MF,
109                                        MachineBasicBlock &MBB) const {
110   const MachineFrameInfo *MFI = MF.getFrameInfo();
111   MSP430MachineFunctionInfo *MSP430FI = MF.getInfo<MSP430MachineFunctionInfo>();
112   const MSP430InstrInfo &TII =
113       *static_cast<const MSP430InstrInfo *>(MF.getSubtarget().getInstrInfo());
114 
115   MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
116   unsigned RetOpcode = MBBI->getOpcode();
117   DebugLoc DL = MBBI->getDebugLoc();
118 
119   switch (RetOpcode) {
120   case MSP430::RET:
121   case MSP430::RETI: break;  // These are ok
122   default:
123     llvm_unreachable("Can only insert epilog into returning blocks");
124   }
125 
126   // Get the number of bytes to allocate from the FrameInfo
127   uint64_t StackSize = MFI->getStackSize();
128   unsigned CSSize = MSP430FI->getCalleeSavedFrameSize();
129   uint64_t NumBytes = 0;
130 
131   if (hasFP(MF)) {
132     // Calculate required stack adjustment
133     uint64_t FrameSize = StackSize - 2;
134     NumBytes = FrameSize - CSSize;
135 
136     // pop FP.
137     BuildMI(MBB, MBBI, DL, TII.get(MSP430::POP16r), MSP430::FP);
138   } else
139     NumBytes = StackSize - CSSize;
140 
141   // Skip the callee-saved pop instructions.
142   while (MBBI != MBB.begin()) {
143     MachineBasicBlock::iterator PI = std::prev(MBBI);
144     unsigned Opc = PI->getOpcode();
145     if (Opc != MSP430::POP16r && !PI->isTerminator())
146       break;
147     --MBBI;
148   }
149 
150   DL = MBBI->getDebugLoc();
151 
152   // If there is an ADD16ri or SUB16ri of SP immediately before this
153   // instruction, merge the two instructions.
154   //if (NumBytes || MFI->hasVarSizedObjects())
155   //  mergeSPUpdatesUp(MBB, MBBI, StackPtr, &NumBytes);
156 
157   if (MFI->hasVarSizedObjects()) {
158     BuildMI(MBB, MBBI, DL,
159             TII.get(MSP430::MOV16rr), MSP430::SP).addReg(MSP430::FP);
160     if (CSSize) {
161       MachineInstr *MI =
162         BuildMI(MBB, MBBI, DL,
163                 TII.get(MSP430::SUB16ri), MSP430::SP)
164         .addReg(MSP430::SP).addImm(CSSize);
165       // The SRW implicit def is dead.
166       MI->getOperand(3).setIsDead();
167     }
168   } else {
169     // adjust stack pointer back: SP += numbytes
170     if (NumBytes) {
171       MachineInstr *MI =
172         BuildMI(MBB, MBBI, DL, TII.get(MSP430::ADD16ri), MSP430::SP)
173         .addReg(MSP430::SP).addImm(NumBytes);
174       // The SRW implicit def is dead.
175       MI->getOperand(3).setIsDead();
176     }
177   }
178 }
179 
180 // FIXME: Can we eleminate these in favour of generic code?
181 bool
spillCalleeSavedRegisters(MachineBasicBlock & MBB,MachineBasicBlock::iterator MI,const std::vector<CalleeSavedInfo> & CSI,const TargetRegisterInfo * TRI) const182 MSP430FrameLowering::spillCalleeSavedRegisters(MachineBasicBlock &MBB,
183                                            MachineBasicBlock::iterator MI,
184                                         const std::vector<CalleeSavedInfo> &CSI,
185                                         const TargetRegisterInfo *TRI) const {
186   if (CSI.empty())
187     return false;
188 
189   DebugLoc DL;
190   if (MI != MBB.end()) DL = MI->getDebugLoc();
191 
192   MachineFunction &MF = *MBB.getParent();
193   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
194   MSP430MachineFunctionInfo *MFI = MF.getInfo<MSP430MachineFunctionInfo>();
195   MFI->setCalleeSavedFrameSize(CSI.size() * 2);
196 
197   for (unsigned i = CSI.size(); i != 0; --i) {
198     unsigned Reg = CSI[i-1].getReg();
199     // Add the callee-saved register as live-in. It's killed at the spill.
200     MBB.addLiveIn(Reg);
201     BuildMI(MBB, MI, DL, TII.get(MSP430::PUSH16r))
202       .addReg(Reg, RegState::Kill);
203   }
204   return true;
205 }
206 
207 bool
restoreCalleeSavedRegisters(MachineBasicBlock & MBB,MachineBasicBlock::iterator MI,const std::vector<CalleeSavedInfo> & CSI,const TargetRegisterInfo * TRI) const208 MSP430FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
209                                                  MachineBasicBlock::iterator MI,
210                                         const std::vector<CalleeSavedInfo> &CSI,
211                                         const TargetRegisterInfo *TRI) const {
212   if (CSI.empty())
213     return false;
214 
215   DebugLoc DL;
216   if (MI != MBB.end()) DL = MI->getDebugLoc();
217 
218   MachineFunction &MF = *MBB.getParent();
219   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
220 
221   for (unsigned i = 0, e = CSI.size(); i != e; ++i)
222     BuildMI(MBB, MI, DL, TII.get(MSP430::POP16r), CSI[i].getReg());
223 
224   return true;
225 }
226 
227 void MSP430FrameLowering::
eliminateCallFramePseudoInstr(MachineFunction & MF,MachineBasicBlock & MBB,MachineBasicBlock::iterator I) const228 eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
229                               MachineBasicBlock::iterator I) const {
230   const MSP430InstrInfo &TII =
231       *static_cast<const MSP430InstrInfo *>(MF.getSubtarget().getInstrInfo());
232   unsigned StackAlign = getStackAlignment();
233 
234   if (!hasReservedCallFrame(MF)) {
235     // If the stack pointer can be changed after prologue, turn the
236     // adjcallstackup instruction into a 'sub SP, <amt>' and the
237     // adjcallstackdown instruction into 'add SP, <amt>'
238     // TODO: consider using push / pop instead of sub + store / add
239     MachineInstr *Old = I;
240     uint64_t Amount = Old->getOperand(0).getImm();
241     if (Amount != 0) {
242       // We need to keep the stack aligned properly.  To do this, we round the
243       // amount of space needed for the outgoing arguments up to the next
244       // alignment boundary.
245       Amount = (Amount+StackAlign-1)/StackAlign*StackAlign;
246 
247       MachineInstr *New = nullptr;
248       if (Old->getOpcode() == TII.getCallFrameSetupOpcode()) {
249         New = BuildMI(MF, Old->getDebugLoc(),
250                       TII.get(MSP430::SUB16ri), MSP430::SP)
251           .addReg(MSP430::SP).addImm(Amount);
252       } else {
253         assert(Old->getOpcode() == TII.getCallFrameDestroyOpcode());
254         // factor out the amount the callee already popped.
255         uint64_t CalleeAmt = Old->getOperand(1).getImm();
256         Amount -= CalleeAmt;
257         if (Amount)
258           New = BuildMI(MF, Old->getDebugLoc(),
259                         TII.get(MSP430::ADD16ri), MSP430::SP)
260             .addReg(MSP430::SP).addImm(Amount);
261       }
262 
263       if (New) {
264         // The SRW implicit def is dead.
265         New->getOperand(3).setIsDead();
266 
267         // Replace the pseudo instruction with a new instruction...
268         MBB.insert(I, New);
269       }
270     }
271   } else if (I->getOpcode() == TII.getCallFrameDestroyOpcode()) {
272     // If we are performing frame pointer elimination and if the callee pops
273     // something off the stack pointer, add it back.
274     if (uint64_t CalleeAmt = I->getOperand(1).getImm()) {
275       MachineInstr *Old = I;
276       MachineInstr *New =
277         BuildMI(MF, Old->getDebugLoc(), TII.get(MSP430::SUB16ri),
278                 MSP430::SP).addReg(MSP430::SP).addImm(CalleeAmt);
279       // The SRW implicit def is dead.
280       New->getOperand(3).setIsDead();
281 
282       MBB.insert(I, New);
283     }
284   }
285 
286   MBB.erase(I);
287 }
288 
289 void
processFunctionBeforeFrameFinalized(MachineFunction & MF,RegScavenger *) const290 MSP430FrameLowering::processFunctionBeforeFrameFinalized(MachineFunction &MF,
291                                                          RegScavenger *) const {
292   // Create a frame entry for the FP register that must be saved.
293   if (hasFP(MF)) {
294     int FrameIdx = MF.getFrameInfo()->CreateFixedObject(2, -4, true);
295     (void)FrameIdx;
296     assert(FrameIdx == MF.getFrameInfo()->getObjectIndexBegin() &&
297            "Slot for FP register must be last in order to be found!");
298   }
299 }
300