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