llvm/llvm/lib/Target/Lanai/LanaiFrameLowering.cpp

//===-- LanaiFrameLowering.cpp - Lanai 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 Lanai implementation of TargetFrameLowering class.
//
//===----------------------------------------------------------------------===//

#include "LanaiFrameLowering.h"

#include "LanaiAluCode.h"
#include "LanaiInstrInfo.h"
#include "LanaiSubtarget.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Function.h"

usingnamespacellvm;

// Determines the size of the frame and maximum call frame size.
void LanaiFrameLowering::determineFrameLayout(MachineFunction &MF) const { … }

// Iterates through each basic block in a machine function and replaces
// ADJDYNALLOC pseudo instructions with a Lanai:ADDI with the
// maximum call frame size as the immediate.
void LanaiFrameLowering::replaceAdjDynAllocPseudo(MachineFunction &MF) const { … }

// Generates the following sequence for function entry:
//   st %fp,-4[*%sp]        !push old FP
//   add %sp,8,%fp          !generate new FP
//   sub %sp,0x4,%sp        !allocate stack space (as needed)
void LanaiFrameLowering::emitPrologue(MachineFunction &MF,
                                      MachineBasicBlock &MBB) const { … }

MachineBasicBlock::iterator LanaiFrameLowering::eliminateCallFramePseudoInstr(
    MachineFunction & /*MF*/, MachineBasicBlock &MBB,
    MachineBasicBlock::iterator I) const { … }

// The function epilogue should not depend on the current stack pointer!
// It should use the frame pointer only.  This is mandatory because
// of alloca; we also take advantage of it to omit stack adjustments
// before returning.
//
// Note that when we go to restore the preserved register values we must
// not try to address their slots by using offsets from the stack pointer.
// That's because the stack pointer may have been moved during the function
// execution due to a call to alloca().  Rather, we must restore all
// preserved registers via offsets from the frame pointer value.
//
// Note also that when the current frame is being "popped" (by adjusting
// the value of the stack pointer) on function exit, we must (for the
// sake of alloca) set the new value of the stack pointer based upon
// the current value of the frame pointer.  We can't just add what we
// believe to be the (static) frame size to the stack pointer because
// if we did that, and alloca() had been called during this function,
// we would end up returning *without* having fully deallocated all of
// the space grabbed by alloca.  If that happened, and a function
// containing one or more alloca() calls was called over and over again,
// then the stack would grow without limit!
//
// RET is lowered to
//      ld -4[%fp],%pc  # modify %pc (two delay slots)
// as the return address is in the stack frame and mov to pc is allowed.
// emitEpilogue emits
//      mov %fp,%sp     # restore the stack pointer
//      ld -8[%fp],%fp  # restore the caller's frame pointer
// before RET and the delay slot filler will move RET such that these
// instructions execute in the delay slots of the load to PC.
void LanaiFrameLowering::emitEpilogue(MachineFunction & /*MF*/,
                                      MachineBasicBlock &MBB) const { … }

void LanaiFrameLowering::determineCalleeSaves(MachineFunction &MF,
                                              BitVector &SavedRegs,
                                              RegScavenger *RS) const { … }