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