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llvm-project/llvm/lib/Target/Mips/MipsFrameLowering.cpp

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//=======- MipsFrameLowering.cpp - Mips Frame Information ------*- C++ -*-====//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the Mips implementation of TargetFrameLowering class.
//
//===----------------------------------------------------------------------===//
#include "MipsFrameLowering.h"
#include "MipsInstrInfo.h"
#include "MipsMachineFunction.h"
#include "llvm/Function.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/Target/TargetData.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/CommandLine.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.
//
//===----------------------------------------------------------------------===//
// hasFP - Return true if the specified function should have a dedicated frame
// pointer register. This is true if the function has variable sized allocas or
// if frame pointer elimination is disabled.
bool MipsFrameLowering::hasFP(const MachineFunction &MF) const {
const MachineFrameInfo *MFI = MF.getFrameInfo();
return DisableFramePointerElim(MF) || MFI->hasVarSizedObjects();
}
bool MipsFrameLowering::targetHandlesStackFrameRounding() const {
return true;
}
static unsigned AlignOffset(unsigned Offset, unsigned Align) {
return (Offset + Align - 1) / Align * Align;
}
// expand pair of register and immediate if the immediate doesn't fit in the
// 16-bit offset field.
// e.g.
// if OrigImm = 0x10000, OrigReg = $sp:
// generate the following sequence of instrs:
// lui $at, hi(0x10000)
// addu $at, $sp, $at
//
// (NewReg, NewImm) = ($at, lo(Ox10000))
// return true
static bool expandRegLargeImmPair(unsigned OrigReg, int OrigImm,
unsigned& NewReg, int& NewImm,
MachineBasicBlock& MBB,
MachineBasicBlock::iterator I) {
// OrigImm fits in the 16-bit field
if (OrigImm < 0x8000 && OrigImm >= -0x8000) {
NewReg = OrigReg;
NewImm = OrigImm;
return false;
}
MachineFunction* MF = MBB.getParent();
const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
DebugLoc DL = I->getDebugLoc();
int ImmLo = (short)(OrigImm & 0xffff);
int ImmHi = (((unsigned)OrigImm & 0xffff0000) >> 16) +
((OrigImm & 0x8000) != 0);
// FIXME: change this when mips goes MC".
BuildMI(MBB, I, DL, TII->get(Mips::NOAT));
BuildMI(MBB, I, DL, TII->get(Mips::LUi), Mips::AT).addImm(ImmHi);
BuildMI(MBB, I, DL, TII->get(Mips::ADDu), Mips::AT).addReg(OrigReg)
.addReg(Mips::AT);
NewReg = Mips::AT;
NewImm = ImmLo;
return true;
}
void MipsFrameLowering::emitPrologue(MachineFunction &MF) const {
MachineBasicBlock &MBB = MF.front();
MachineFrameInfo *MFI = MF.getFrameInfo();
MipsFunctionInfo *MipsFI = MF.getInfo<MipsFunctionInfo>();
const MipsRegisterInfo *RegInfo =
static_cast<const MipsRegisterInfo*>(MF.getTarget().getRegisterInfo());
const MipsInstrInfo &TII =
*static_cast<const MipsInstrInfo*>(MF.getTarget().getInstrInfo());
MachineBasicBlock::iterator MBBI = MBB.begin();
DebugLoc dl = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
bool isPIC = (MF.getTarget().getRelocationModel() == Reloc::PIC_);
unsigned NewReg = 0;
int NewImm = 0;
bool ATUsed;
// First, compute final stack size.
unsigned RegSize = STI.isGP32bit() ? 4 : 8;
unsigned StackAlign = getStackAlignment();
unsigned LocalVarAreaOffset = MipsFI->needGPSaveRestore() ?
(MFI->getObjectOffset(MipsFI->getGPFI()) + RegSize) :
MipsFI->getMaxCallFrameSize();
unsigned StackSize = AlignOffset(LocalVarAreaOffset, StackAlign) +
AlignOffset(MFI->getStackSize(), StackAlign);
// Update stack size
MFI->setStackSize(StackSize);
BuildMI(MBB, MBBI, dl, TII.get(Mips::NOREORDER));
// TODO: check need from GP here.
if (isPIC && STI.isABI_O32())
BuildMI(MBB, MBBI, dl, TII.get(Mips::CPLOAD))
.addReg(RegInfo->getPICCallReg());
BuildMI(MBB, MBBI, dl, TII.get(Mips::NOMACRO));
// No need to allocate space on the stack.
if (StackSize == 0 && !MFI->adjustsStack()) return;
// Adjust stack : addi sp, sp, (-imm)
ATUsed = expandRegLargeImmPair(Mips::SP, -StackSize, NewReg, NewImm, MBB,
MBBI);
BuildMI(MBB, MBBI, dl, TII.get(Mips::ADDiu), Mips::SP)
.addReg(NewReg).addImm(NewImm);
// FIXME: change this when mips goes MC".
if (ATUsed)
BuildMI(MBB, MBBI, dl, TII.get(Mips::ATMACRO));
// Find the instruction past the last instruction that saves a callee-saved
// register to the stack.
const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
for (unsigned i = 0; i < CSI.size(); ++i)
++MBBI;
// if framepointer enabled, set it to point to the stack pointer.
if (hasFP(MF))
// Insert instruction "move $fp, $sp" at this location.
BuildMI(MBB, MBBI, dl, TII.get(Mips::ADDu), Mips::FP)
.addReg(Mips::SP).addReg(Mips::ZERO);
// Restore GP from the saved stack location
if (MipsFI->needGPSaveRestore())
BuildMI(MBB, MBBI, dl, TII.get(Mips::CPRESTORE))
.addImm(MFI->getObjectOffset(MipsFI->getGPFI()));
// EH Frame infomation.
MachineModuleInfo &MMI = MF.getMMI();
std::vector<MachineMove> &Moves = MMI.getFrameMoves();
MCSymbol *FrameLabel = MMI.getContext().CreateTempSymbol();
BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::PROLOG_LABEL)).addSym(FrameLabel);
if (hasFP(MF)) {
MachineLocation SPDst(Mips::FP);
MachineLocation SPSrc(Mips::SP);
Moves.push_back(MachineMove(FrameLabel, SPDst, SPSrc));
}
if (StackSize) {
MachineLocation SPDst(MachineLocation::VirtualFP);
MachineLocation SPSrc(MachineLocation::VirtualFP, -StackSize);
Moves.push_back(MachineMove(FrameLabel, SPDst, SPSrc));
}
for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
E = CSI.end(); I != E; ++I) {
int64_t Offset = MFI->getObjectOffset(I->getFrameIdx());
MachineLocation CSDst(MachineLocation::VirtualFP, Offset);
MachineLocation CSSrc(I->getReg());
Moves.push_back(MachineMove(FrameLabel, CSDst, CSSrc));
}
}
void MipsFrameLowering::emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
MachineFrameInfo *MFI = MF.getFrameInfo();
const MipsInstrInfo &TII =
*static_cast<const MipsInstrInfo*>(MF.getTarget().getInstrInfo());
DebugLoc dl = MBBI->getDebugLoc();
// Get the number of bytes from FrameInfo
unsigned StackSize = MFI->getStackSize();
unsigned NewReg = 0;
int NewImm = 0;
bool ATUsed = false;
// if framepointer enabled, restore the stack pointer.
if (hasFP(MF)) {
// Find the first instruction that restores a callee-saved register.
MachineBasicBlock::iterator I = MBBI;
for (unsigned i = 0; i < MFI->getCalleeSavedInfo().size(); ++i)
--I;
// Insert instruction "move $sp, $fp" at this location.
BuildMI(MBB, I, dl, TII.get(Mips::ADDu), Mips::SP)
.addReg(Mips::FP).addReg(Mips::ZERO);
}
// adjust stack : insert addi sp, sp, (imm)
if (StackSize) {
ATUsed = expandRegLargeImmPair(Mips::SP, StackSize, NewReg, NewImm, MBB,
MBBI);
BuildMI(MBB, MBBI, dl, TII.get(Mips::ADDiu), Mips::SP)
.addReg(NewReg).addImm(NewImm);
// FIXME: change this when mips goes MC".
if (ATUsed)
BuildMI(MBB, MBBI, dl, TII.get(Mips::ATMACRO));
}
}
void
MipsFrameLowering::getInitialFrameState(std::vector<MachineMove> &Moves) const {
MachineLocation Dst(MachineLocation::VirtualFP);
MachineLocation Src(Mips::SP, 0);
Moves.push_back(MachineMove(0, Dst, Src));
}
void MipsFrameLowering::
processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
RegScavenger *RS) const {
MachineRegisterInfo& MRI = MF.getRegInfo();
// FIXME: remove this code if register allocator can correctly mark
// $fp and $ra used or unused.
// Mark $fp and $ra as used or unused.
if (hasFP(MF))
MRI.setPhysRegUsed(Mips::FP);
// The register allocator might determine $ra is used after seeing
// instruction "jr $ra", but we do not want PrologEpilogInserter to insert
// instructions to save/restore $ra unless there is a function call.
// To correct this, $ra is explicitly marked unused if there is no
// function call.
if (MF.getFrameInfo()->hasCalls())
MRI.setPhysRegUsed(Mips::RA);
else
MRI.setPhysRegUnused(Mips::RA);
}
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