1 //===- Mips16FrameLowering.cpp - Mips16 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 Mips16 implementation of TargetFrameLowering class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "Mips16FrameLowering.h"
15 #include "MCTargetDesc/MipsBaseInfo.h"
16 #include "Mips16InstrInfo.h"
17 #include "MipsInstrInfo.h"
18 #include "MipsRegisterInfo.h"
19 #include "MipsSubtarget.h"
20 #include "llvm/ADT/BitVector.h"
21 #include "llvm/CodeGen/MachineBasicBlock.h"
22 #include "llvm/CodeGen/MachineFrameInfo.h"
23 #include "llvm/CodeGen/MachineFunction.h"
24 #include "llvm/CodeGen/MachineInstr.h"
25 #include "llvm/CodeGen/MachineInstrBuilder.h"
26 #include "llvm/CodeGen/MachineModuleInfo.h"
27 #include "llvm/IR/DebugLoc.h"
28 #include "llvm/MC/MCContext.h"
29 #include "llvm/MC/MCDwarf.h"
30 #include "llvm/MC/MCRegisterInfo.h"
31 #include "llvm/MC/MachineLocation.h"
32 #include "llvm/Support/MathExtras.h"
33 #include "llvm/Target/TargetFrameLowering.h"
34 #include <cassert>
35 #include <cstdint>
36 #include <vector>
37 
38 using namespace llvm;
39 
40 Mips16FrameLowering::Mips16FrameLowering(const MipsSubtarget &STI)
41     : MipsFrameLowering(STI, STI.stackAlignment()) {}
42 
43 void Mips16FrameLowering::emitPrologue(MachineFunction &MF,
44                                        MachineBasicBlock &MBB) const {
45   assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
46   MachineFrameInfo &MFI = MF.getFrameInfo();
47   const Mips16InstrInfo &TII =
48       *static_cast<const Mips16InstrInfo *>(STI.getInstrInfo());
49   MachineBasicBlock::iterator MBBI = MBB.begin();
50 
51   // Debug location must be unknown since the first debug location is used
52   // to determine the end of the prologue.
53   DebugLoc dl;
54 
55   uint64_t StackSize = MFI.getStackSize();
56 
57   // No need to allocate space on the stack.
58   if (StackSize == 0 && !MFI.adjustsStack()) return;
59 
60   MachineModuleInfo &MMI = MF.getMMI();
61   const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();
62   MachineLocation DstML, SrcML;
63 
64   // Adjust stack.
65   TII.makeFrame(Mips::SP, StackSize, MBB, MBBI);
66 
67   // emit ".cfi_def_cfa_offset StackSize"
68   unsigned CFIIndex = MF.addFrameInst(
69       MCCFIInstruction::createDefCfaOffset(nullptr, -StackSize));
70   BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
71       .addCFIIndex(CFIIndex);
72 
73   const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
74 
75   if (!CSI.empty()) {
76     const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
77 
78     for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
79          E = CSI.end(); I != E; ++I) {
80       int64_t Offset = MFI.getObjectOffset(I->getFrameIdx());
81       unsigned Reg = I->getReg();
82       unsigned DReg = MRI->getDwarfRegNum(Reg, true);
83       unsigned CFIIndex = MF.addFrameInst(
84           MCCFIInstruction::createOffset(nullptr, DReg, Offset));
85       BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
86           .addCFIIndex(CFIIndex);
87     }
88   }
89   if (hasFP(MF))
90     BuildMI(MBB, MBBI, dl, TII.get(Mips::MoveR3216), Mips::S0)
91       .addReg(Mips::SP).setMIFlag(MachineInstr::FrameSetup);
92 }
93 
94 void Mips16FrameLowering::emitEpilogue(MachineFunction &MF,
95                                  MachineBasicBlock &MBB) const {
96   MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
97   MachineFrameInfo &MFI = MF.getFrameInfo();
98   const Mips16InstrInfo &TII =
99       *static_cast<const Mips16InstrInfo *>(STI.getInstrInfo());
100   DebugLoc dl = MBBI->getDebugLoc();
101   uint64_t StackSize = MFI.getStackSize();
102 
103   if (!StackSize)
104     return;
105 
106   if (hasFP(MF))
107     BuildMI(MBB, MBBI, dl, TII.get(Mips::Move32R16), Mips::SP)
108       .addReg(Mips::S0);
109 
110   // Adjust stack.
111   // assumes stacksize multiple of 8
112   TII.restoreFrame(Mips::SP, StackSize, MBB, MBBI);
113 }
114 
115 bool Mips16FrameLowering::
116 spillCalleeSavedRegisters(MachineBasicBlock &MBB,
117                           MachineBasicBlock::iterator MI,
118                           const std::vector<CalleeSavedInfo> &CSI,
119                           const TargetRegisterInfo *TRI) const {
120   MachineFunction *MF = MBB.getParent();
121   MachineBasicBlock *EntryBlock = &MF->front();
122 
123   //
124   // Registers RA, S0,S1 are the callee saved registers and they
125   // will be saved with the "save" instruction
126   // during emitPrologue
127   //
128   for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
129     // Add the callee-saved register as live-in. Do not add if the register is
130     // RA and return address is taken, because it has already been added in
131     // method MipsTargetLowering::lowerRETURNADDR.
132     // It's killed at the spill, unless the register is RA and return address
133     // is taken.
134     unsigned Reg = CSI[i].getReg();
135     bool IsRAAndRetAddrIsTaken = (Reg == Mips::RA)
136       && MF->getFrameInfo().isReturnAddressTaken();
137     if (!IsRAAndRetAddrIsTaken)
138       EntryBlock->addLiveIn(Reg);
139   }
140 
141   return true;
142 }
143 
144 bool Mips16FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
145                                           MachineBasicBlock::iterator MI,
146                                        const std::vector<CalleeSavedInfo> &CSI,
147                                        const TargetRegisterInfo *TRI) const {
148   //
149   // Registers RA,S0,S1 are the callee saved registers and they will be restored
150   // with the restore instruction during emitEpilogue.
151   // We need to override this virtual function, otherwise llvm will try and
152   // restore the registers on it's on from the stack.
153   //
154 
155   return true;
156 }
157 
158 bool
159 Mips16FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
160   const MachineFrameInfo &MFI = MF.getFrameInfo();
161   // Reserve call frame if the size of the maximum call frame fits into 15-bit
162   // immediate field and there are no variable sized objects on the stack.
163   return isInt<15>(MFI.getMaxCallFrameSize()) && !MFI.hasVarSizedObjects();
164 }
165 
166 void Mips16FrameLowering::determineCalleeSaves(MachineFunction &MF,
167                                                BitVector &SavedRegs,
168                                                RegScavenger *RS) const {
169   TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);
170   const Mips16InstrInfo &TII =
171       *static_cast<const Mips16InstrInfo *>(STI.getInstrInfo());
172   const MipsRegisterInfo &RI = TII.getRegisterInfo();
173   const BitVector Reserved = RI.getReservedRegs(MF);
174   bool SaveS2 = Reserved[Mips::S2];
175   if (SaveS2)
176     SavedRegs.set(Mips::S2);
177   if (hasFP(MF))
178     SavedRegs.set(Mips::S0);
179 }
180 
181 const MipsFrameLowering *
182 llvm::createMips16FrameLowering(const MipsSubtarget &ST) {
183   return new Mips16FrameLowering(ST);
184 }
185