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//===-- MipsFrameLowering.cpp - Mips Frame Information --------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains the Mips implementation of TargetFrameLowering class.
//
//===----------------------------------------------------------------------===//
#include "MipsFrameLowering.h"
#include "MCTargetDesc/MipsBaseInfo.h"
#include "MipsInstrInfo.h"
#include "MipsMachineFunction.h"
#include "MipsTargetMachine.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Function.h"
#include "llvm/Target/TargetOptions.h"
using namespace llvm;
//===----------------------------------------------------------------------===//
//
// Stack Frame Processing methods
// +----------------------------+
//
// The stack is allocated decrementing the stack pointer on
// the first instruction of a function prologue. Once decremented,
// all stack references are done thought a positive offset
// from the stack/frame pointer, so the stack is considering
// to grow up! Otherwise terrible hacks would have to be made
// to get this stack ABI compliant :)
//
// The stack frame required by the ABI (after call):
// Offset
//
// 0 ----------
// 4 Args to pass
// . saved $GP (used in PIC)
// . Alloca allocations
// . Local Area
// . CPU "Callee Saved" Registers
// . saved FP
// . saved RA
// . FPU "Callee Saved" Registers
// StackSize -----------
//
// Offset - offset from sp after stack allocation on function prologue
//
// The sp is the stack pointer subtracted/added from the stack size
// at the Prologue/Epilogue
//
// References to the previous stack (to obtain arguments) are done
// with offsets that exceeds the stack size: (stacksize+(4*(num_arg-1))
//
// Examples:
// - reference to the actual stack frame
// for any local area var there is smt like : FI >= 0, StackOffset: 4
// sw REGX, 4(SP)
//
// - reference to previous stack frame
// suppose there's a load to the 5th arguments : FI < 0, StackOffset: 16.
// The emitted instruction will be something like:
// lw REGX, 16+StackSize(SP)
//
// Since the total stack size is unknown on LowerFormalArguments, all
// stack references (ObjectOffset) created to reference the function
// arguments, are negative numbers. This way, on eliminateFrameIndex it's
// possible to detect those references and the offsets are adjusted to
// their real location.
//
//===----------------------------------------------------------------------===//
const MipsFrameLowering *MipsFrameLowering::create(const MipsSubtarget &ST) {
if (ST.inMips16Mode())
return llvm::createMips16FrameLowering(ST);
return llvm::createMipsSEFrameLowering(ST);
}
// hasFP - Return true if the specified function should have a dedicated frame
// pointer register. This is true if the function has variable sized allocas,
// if it needs dynamic stack realignment, if frame pointer elimination is
// disabled, or if the frame address is taken.
bool MipsFrameLowering::hasFP(const MachineFunction &MF) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetRegisterInfo *TRI = STI.getRegisterInfo();
return MF.getTarget().Options.DisableFramePointerElim(MF) ||
MFI.hasVarSizedObjects() || MFI.isFrameAddressTaken() ||
TRI->needsStackRealignment(MF);
}
bool MipsFrameLowering::hasBP(const MachineFunction &MF) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetRegisterInfo *TRI = STI.getRegisterInfo();
return MFI.hasVarSizedObjects() && TRI->needsStackRealignment(MF);
}
// Estimate the size of the stack, including the incoming arguments. We need to
// account for register spills, local objects, reserved call frame and incoming
// arguments. This is required to determine the largest possible positive offset
// from $sp so that it can be determined if an emergency spill slot for stack
// addresses is required.
uint64_t MipsFrameLowering::estimateStackSize(const MachineFunction &MF) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
int64_t Size = 0;
// Iterate over fixed sized objects which are incoming arguments.
for (int I = MFI.getObjectIndexBegin(); I != 0; ++I)
if (MFI.getObjectOffset(I) > 0)
Size += MFI.getObjectSize(I);
// Conservatively assume all callee-saved registers will be saved.
for (const MCPhysReg *R = TRI.getCalleeSavedRegs(&MF); *R; ++R) {
unsigned RegSize = TRI.getSpillSize(*TRI.getMinimalPhysRegClass(*R));
Size = alignTo(Size + RegSize, RegSize);
}
// Get the size of the rest of the frame objects and any possible reserved
// call frame, accounting for alignment.
return Size + MFI.estimateStackSize(MF);
}
// Eliminate ADJCALLSTACKDOWN, ADJCALLSTACKUP pseudo instructions
MachineBasicBlock::iterator MipsFrameLowering::
eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
MachineBasicBlock::iterator I) const {
unsigned SP = STI.getABI().IsN64() ? Mips::SP_64 : Mips::SP;
if (!hasReservedCallFrame(MF)) {
int64_t Amount = I->getOperand(0).getImm();
if (I->getOpcode() == Mips::ADJCALLSTACKDOWN)
Amount = -Amount;
STI.getInstrInfo()->adjustStackPtr(SP, Amount, MBB, I);
}
return MBB.erase(I);
}
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