1//===-- MipsFrameLowering.cpp - Mips 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 Mips implementation of TargetFrameLowering class.
10//
11//===----------------------------------------------------------------------===//
12
13#include "MipsFrameLowering.h"
14#include "MCTargetDesc/MipsBaseInfo.h"
15#include "MipsInstrInfo.h"
16#include "MipsMachineFunction.h"
17#include "MipsTargetMachine.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/Target/TargetOptions.h"
26
27using namespace llvm;
28
29
30//===----------------------------------------------------------------------===//
31//
32// Stack Frame Processing methods
33// +----------------------------+
34//
35// The stack is allocated decrementing the stack pointer on
36// the first instruction of a function prologue. Once decremented,
37// all stack references are done thought a positive offset
38// from the stack/frame pointer, so the stack is considering
39// to grow up! Otherwise terrible hacks would have to be made
40// to get this stack ABI compliant :)
41//
42//  The stack frame required by the ABI (after call):
43//  Offset
44//
45//  0                 ----------
46//  4                 Args to pass
47//  .                 saved $GP  (used in PIC)
48//  .                 Alloca allocations
49//  .                 Local Area
50//  .                 CPU "Callee Saved" Registers
51//  .                 saved FP
52//  .                 saved RA
53//  .                 FPU "Callee Saved" Registers
54//  StackSize         -----------
55//
56// Offset - offset from sp after stack allocation on function prologue
57//
58// The sp is the stack pointer subtracted/added from the stack size
59// at the Prologue/Epilogue
60//
61// References to the previous stack (to obtain arguments) are done
62// with offsets that exceeds the stack size: (stacksize+(4*(num_arg-1))
63//
64// Examples:
65// - reference to the actual stack frame
66//   for any local area var there is smt like : FI >= 0, StackOffset: 4
67//     sw REGX, 4(SP)
68//
69// - reference to previous stack frame
70//   suppose there's a load to the 5th arguments : FI < 0, StackOffset: 16.
71//   The emitted instruction will be something like:
72//     lw REGX, 16+StackSize(SP)
73//
74// Since the total stack size is unknown on LowerFormalArguments, all
75// stack references (ObjectOffset) created to reference the function
76// arguments, are negative numbers. This way, on eliminateFrameIndex it's
77// possible to detect those references and the offsets are adjusted to
78// their real location.
79//
80//===----------------------------------------------------------------------===//
81
82const MipsFrameLowering *MipsFrameLowering::create(const MipsSubtarget &ST) {
83  if (ST.inMips16Mode())
84    return llvm::createMips16FrameLowering(ST);
85
86  return llvm::createMipsSEFrameLowering(ST);
87}
88
89// hasFP - Return true if the specified function should have a dedicated frame
90// pointer register.  This is true if the function has variable sized allocas,
91// if it needs dynamic stack realignment, if frame pointer elimination is
92// disabled, or if the frame address is taken.
93bool MipsFrameLowering::hasFP(const MachineFunction &MF) const {
94  const MachineFrameInfo &MFI = MF.getFrameInfo();
95  const TargetRegisterInfo *TRI = STI.getRegisterInfo();
96
97  return MF.getTarget().Options.DisableFramePointerElim(MF) ||
98      MFI.hasVarSizedObjects() || MFI.isFrameAddressTaken() ||
99      TRI->needsStackRealignment(MF);
100}
101
102bool MipsFrameLowering::hasBP(const MachineFunction &MF) const {
103  const MachineFrameInfo &MFI = MF.getFrameInfo();
104  const TargetRegisterInfo *TRI = STI.getRegisterInfo();
105
106  return MFI.hasVarSizedObjects() && TRI->needsStackRealignment(MF);
107}
108
109// Estimate the size of the stack, including the incoming arguments. We need to
110// account for register spills, local objects, reserved call frame and incoming
111// arguments. This is required to determine the largest possible positive offset
112// from $sp so that it can be determined if an emergency spill slot for stack
113// addresses is required.
114uint64_t MipsFrameLowering::estimateStackSize(const MachineFunction &MF) const {
115  const MachineFrameInfo &MFI = MF.getFrameInfo();
116  const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
117
118  int64_t Size = 0;
119
120  // Iterate over fixed sized objects which are incoming arguments.
121  for (int I = MFI.getObjectIndexBegin(); I != 0; ++I)
122    if (MFI.getObjectOffset(I) > 0)
123      Size += MFI.getObjectSize(I);
124
125  // Conservatively assume all callee-saved registers will be saved.
126  for (const MCPhysReg *R = TRI.getCalleeSavedRegs(&MF); *R; ++R) {
127    unsigned RegSize = TRI.getSpillSize(*TRI.getMinimalPhysRegClass(*R));
128    Size = alignTo(Size + RegSize, RegSize);
129  }
130
131  // Get the size of the rest of the frame objects and any possible reserved
132  // call frame, accounting for alignment.
133  return Size + MFI.estimateStackSize(MF);
134}
135
136// Eliminate ADJCALLSTACKDOWN, ADJCALLSTACKUP pseudo instructions
137MachineBasicBlock::iterator MipsFrameLowering::
138eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
139                              MachineBasicBlock::iterator I) const {
140  unsigned SP = STI.getABI().IsN64() ? Mips::SP_64 : Mips::SP;
141
142  if (!hasReservedCallFrame(MF)) {
143    int64_t Amount = I->getOperand(0).getImm();
144    if (I->getOpcode() == Mips::ADJCALLSTACKDOWN)
145      Amount = -Amount;
146
147    STI.getInstrInfo()->adjustStackPtr(SP, Amount, MBB, I);
148  }
149
150  return MBB.erase(I);
151}
152