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//===-- MipsFrameLowering.cpp - Mips Frame Information --------------------===//
//
// 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 "MCTargetDesc/MipsBaseInfo.h"
#include "MipsAnalyzeImmediate.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/Support/CommandLine.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 or
// if frame pointer elimination is disabled.
bool MipsFrameLowering::hasFP(const MachineFunction &MF) const {
const MachineFrameInfo *MFI = MF.getFrameInfo();
return MF.getTarget().Options.DisableFramePointerElim(MF) ||
MFI->hasVarSizedObjects() || MFI->isFrameAddressTaken();
}
uint64_t MipsFrameLowering::estimateStackSize(const MachineFunction &MF) const {
const MachineFrameInfo *MFI = MF.getFrameInfo();
const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
int64_t Offset = 0;
// Iterate over fixed sized objects.
for (int I = MFI->getObjectIndexBegin(); I != 0; ++I)
Offset = std::max(Offset, -MFI->getObjectOffset(I));
// Conservatively assume all callee-saved registers will be saved.
for (const MCPhysReg *R = TRI.getCalleeSavedRegs(&MF); *R; ++R) {
unsigned Size = TRI.getMinimalPhysRegClass(*R)->getSize();
Offset = RoundUpToAlignment(Offset + Size, Size);
}
unsigned MaxAlign = MFI->getMaxAlignment();
// Check that MaxAlign is not zero if there is a stack object that is not a
// callee-saved spill.
assert(!MFI->getObjectIndexEnd() || MaxAlign);
// Iterate over other objects.
for (unsigned I = 0, E = MFI->getObjectIndexEnd(); I != E; ++I)
Offset = RoundUpToAlignment(Offset + MFI->getObjectSize(I), MaxAlign);
// Call frame.
if (MFI->adjustsStack() && hasReservedCallFrame(MF))
Offset = RoundUpToAlignment(Offset + MFI->getMaxCallFrameSize(),
std::max(MaxAlign, getStackAlignment()));
return RoundUpToAlignment(Offset, getStackAlignment());
}
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