1 //===- Mips16FrameLowering.cpp - Mips16 Frame Information -----------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file contains the Mips16 implementation of TargetFrameLowering class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "Mips16FrameLowering.h"
14 #include "MCTargetDesc/MipsBaseInfo.h"
15 #include "Mips16InstrInfo.h"
16 #include "MipsInstrInfo.h"
17 #include "MipsRegisterInfo.h"
18 #include "MipsSubtarget.h"
19 #include "llvm/ADT/BitVector.h"
20 #include "llvm/CodeGen/MachineBasicBlock.h"
21 #include "llvm/CodeGen/MachineFrameInfo.h"
22 #include "llvm/CodeGen/MachineFunction.h"
23 #include "llvm/CodeGen/MachineInstr.h"
24 #include "llvm/CodeGen/MachineInstrBuilder.h"
25 #include "llvm/CodeGen/MachineModuleInfo.h"
26 #include "llvm/IR/DebugLoc.h"
27 #include "llvm/MC/MCContext.h"
28 #include "llvm/MC/MCDwarf.h"
29 #include "llvm/MC/MCRegisterInfo.h"
30 #include "llvm/MC/MachineLocation.h"
31 #include "llvm/Support/MathExtras.h"
32 #include "llvm/CodeGen/TargetFrameLowering.h"
33 #include <cassert>
34 #include <cstdint>
35 #include <vector>
36 
37 using namespace llvm;
38 
39 Mips16FrameLowering::Mips16FrameLowering(const MipsSubtarget &STI)
40     : MipsFrameLowering(STI, STI.getStackAlignment()) {}
41 
42 void Mips16FrameLowering::emitPrologue(MachineFunction &MF,
43                                        MachineBasicBlock &MBB) const {
44   MachineFrameInfo &MFI = MF.getFrameInfo();
45   const Mips16InstrInfo &TII =
46       *static_cast<const Mips16InstrInfo *>(STI.getInstrInfo());
47   MachineBasicBlock::iterator MBBI = MBB.begin();
48 
49   // Debug location must be unknown since the first debug location is used
50   // to determine the end of the prologue.
51   DebugLoc dl;
52 
53   uint64_t StackSize = MFI.getStackSize();
54 
55   // No need to allocate space on the stack.
56   if (StackSize == 0 && !MFI.adjustsStack()) return;
57 
58   MachineModuleInfo &MMI = MF.getMMI();
59   const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();
60 
61   // Adjust stack.
62   TII.makeFrame(Mips::SP, StackSize, MBB, MBBI);
63 
64   // emit ".cfi_def_cfa_offset StackSize"
65   unsigned CFIIndex =
66       MF.addFrameInst(MCCFIInstruction::cfiDefCfaOffset(nullptr, StackSize));
67   BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
68       .addCFIIndex(CFIIndex);
69 
70   const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
71 
72   if (!CSI.empty()) {
73     const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
74 
75     for (const CalleeSavedInfo &I : CSI) {
76       int64_t Offset = MFI.getObjectOffset(I.getFrameIdx());
77       Register Reg = I.getReg();
78       unsigned DReg = MRI->getDwarfRegNum(Reg, true);
79       unsigned CFIIndex = MF.addFrameInst(
80           MCCFIInstruction::createOffset(nullptr, DReg, Offset));
81       BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
82           .addCFIIndex(CFIIndex);
83     }
84   }
85   if (hasFP(MF))
86     BuildMI(MBB, MBBI, dl, TII.get(Mips::MoveR3216), Mips::S0)
87       .addReg(Mips::SP).setMIFlag(MachineInstr::FrameSetup);
88 }
89 
90 void Mips16FrameLowering::emitEpilogue(MachineFunction &MF,
91                                  MachineBasicBlock &MBB) const {
92   MachineBasicBlock::iterator MBBI = MBB.getFirstTerminator();
93   MachineFrameInfo &MFI = MF.getFrameInfo();
94   const Mips16InstrInfo &TII =
95       *static_cast<const Mips16InstrInfo *>(STI.getInstrInfo());
96   DebugLoc dl = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
97   uint64_t StackSize = MFI.getStackSize();
98 
99   if (!StackSize)
100     return;
101 
102   if (hasFP(MF))
103     BuildMI(MBB, MBBI, dl, TII.get(Mips::Move32R16), Mips::SP)
104       .addReg(Mips::S0);
105 
106   // Adjust stack.
107   // assumes stacksize multiple of 8
108   TII.restoreFrame(Mips::SP, StackSize, MBB, MBBI);
109 }
110 
111 bool Mips16FrameLowering::spillCalleeSavedRegisters(
112     MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
113     ArrayRef<CalleeSavedInfo> CSI, const TargetRegisterInfo *TRI) const {
114   MachineFunction *MF = MBB.getParent();
115 
116   //
117   // Registers RA, S0,S1 are the callee saved registers and they
118   // will be saved with the "save" instruction
119   // during emitPrologue
120   //
121   for (const CalleeSavedInfo &I : CSI) {
122     // Add the callee-saved register as live-in. Do not add if the register is
123     // RA and return address is taken, because it has already been added in
124     // method MipsTargetLowering::lowerRETURNADDR.
125     // It's killed at the spill, unless the register is RA and return address
126     // is taken.
127     Register Reg = I.getReg();
128     bool IsRAAndRetAddrIsTaken = (Reg == Mips::RA)
129       && MF->getFrameInfo().isReturnAddressTaken();
130     if (!IsRAAndRetAddrIsTaken)
131       MBB.addLiveIn(Reg);
132   }
133 
134   return true;
135 }
136 
137 bool Mips16FrameLowering::restoreCalleeSavedRegisters(
138     MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
139     MutableArrayRef<CalleeSavedInfo> CSI, const TargetRegisterInfo *TRI) const {
140   //
141   // Registers RA,S0,S1 are the callee saved registers and they will be restored
142   // with the restore instruction during emitEpilogue.
143   // We need to override this virtual function, otherwise llvm will try and
144   // restore the registers on it's on from the stack.
145   //
146 
147   return true;
148 }
149 
150 bool
151 Mips16FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
152   const MachineFrameInfo &MFI = MF.getFrameInfo();
153   // Reserve call frame if the size of the maximum call frame fits into 15-bit
154   // immediate field and there are no variable sized objects on the stack.
155   return isInt<15>(MFI.getMaxCallFrameSize()) && !MFI.hasVarSizedObjects();
156 }
157 
158 void Mips16FrameLowering::determineCalleeSaves(MachineFunction &MF,
159                                                BitVector &SavedRegs,
160                                                RegScavenger *RS) const {
161   TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);
162   const Mips16InstrInfo &TII =
163       *static_cast<const Mips16InstrInfo *>(STI.getInstrInfo());
164   const MipsRegisterInfo &RI = TII.getRegisterInfo();
165   const BitVector Reserved = RI.getReservedRegs(MF);
166   bool SaveS2 = Reserved[Mips::S2];
167   if (SaveS2)
168     SavedRegs.set(Mips::S2);
169   if (hasFP(MF))
170     SavedRegs.set(Mips::S0);
171 }
172 
173 const MipsFrameLowering *
174 llvm::createMips16FrameLowering(const MipsSubtarget &ST) {
175   return new Mips16FrameLowering(ST);
176 }
177