MipsFrameLowering.cpp revision d04a8d4b33ff316ca4cf961e06c9e312eff8e64f 
1//===-- MipsFrameLowering.cpp - Mips Frame Information --------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file contains the Mips implementation of TargetFrameLowering class.
11//
12//===----------------------------------------------------------------------===//
13
14#include "MipsFrameLowering.h"
15#include "MCTargetDesc/MipsBaseInfo.h"
16#include "MipsAnalyzeImmediate.h"
17#include "MipsInstrInfo.h"
18#include "MipsMachineFunction.h"
19#include "MipsTargetMachine.h"
20#include "llvm/CodeGen/MachineFrameInfo.h"
21#include "llvm/CodeGen/MachineFunction.h"
22#include "llvm/CodeGen/MachineInstrBuilder.h"
23#include "llvm/CodeGen/MachineModuleInfo.h"
24#include "llvm/CodeGen/MachineRegisterInfo.h"
25#include "llvm/DataLayout.h"
26#include "llvm/Function.h"
27#include "llvm/Support/CommandLine.h"
28#include "llvm/Target/TargetOptions.h"
29
30using namespace llvm;
31
32
33//===----------------------------------------------------------------------===//
34//
35// Stack Frame Processing methods
36// +----------------------------+
37//
38// The stack is allocated decrementing the stack pointer on
39// the first instruction of a function prologue. Once decremented,
40// all stack references are done thought a positive offset
41// from the stack/frame pointer, so the stack is considering
42// to grow up! Otherwise terrible hacks would have to be made
43// to get this stack ABI compliant :)
44//
45//  The stack frame required by the ABI (after call):
46//  Offset
47//
48//  0                 ----------
49//  4                 Args to pass
50//  .                 saved $GP  (used in PIC)
51//  .                 Alloca allocations
52//  .                 Local Area
53//  .                 CPU "Callee Saved" Registers
54//  .                 saved FP
55//  .                 saved RA
56//  .                 FPU "Callee Saved" Registers
57//  StackSize         -----------
58//
59// Offset - offset from sp after stack allocation on function prologue
60//
61// The sp is the stack pointer subtracted/added from the stack size
62// at the Prologue/Epilogue
63//
64// References to the previous stack (to obtain arguments) are done
65// with offsets that exceeds the stack size: (stacksize+(4*(num_arg-1))
66//
67// Examples:
68// - reference to the actual stack frame
69//   for any local area var there is smt like : FI >= 0, StackOffset: 4
70//     sw REGX, 4(SP)
71//
72// - reference to previous stack frame
73//   suppose there's a load to the 5th arguments : FI < 0, StackOffset: 16.
74//   The emitted instruction will be something like:
75//     lw REGX, 16+StackSize(SP)
76//
77// Since the total stack size is unknown on LowerFormalArguments, all
78// stack references (ObjectOffset) created to reference the function
79// arguments, are negative numbers. This way, on eliminateFrameIndex it's
80// possible to detect those references and the offsets are adjusted to
81// their real location.
82//
83//===----------------------------------------------------------------------===//
84
85const MipsFrameLowering *MipsFrameLowering::create(MipsTargetMachine &TM,
86                                                   const MipsSubtarget &ST) {
87  if (TM.getSubtargetImpl()->inMips16Mode())
88    return llvm::createMips16FrameLowering(ST);
89
90  return llvm::createMipsSEFrameLowering(ST);
91}
92
93// hasFP - Return true if the specified function should have a dedicated frame
94// pointer register.  This is true if the function has variable sized allocas or
95// if frame pointer elimination is disabled.
96bool MipsFrameLowering::hasFP(const MachineFunction &MF) const {
97  const MachineFrameInfo *MFI = MF.getFrameInfo();
98  return MF.getTarget().Options.DisableFramePointerElim(MF) ||
99      MFI->hasVarSizedObjects() || MFI->isFrameAddressTaken();
100}
101
102uint64_t MipsFrameLowering::estimateStackSize(const MachineFunction &MF) const {
103  const MachineFrameInfo *MFI = MF.getFrameInfo();
104  const TargetRegisterInfo &TRI = *MF.getTarget().getRegisterInfo();
105
106  int64_t Offset = 0;
107
108  // Iterate over fixed sized objects.
109  for (int I = MFI->getObjectIndexBegin(); I != 0; ++I)
110    Offset = std::max(Offset, -MFI->getObjectOffset(I));
111
112  // Conservatively assume all callee-saved registers will be saved.
113  for (const uint16_t *R = TRI.getCalleeSavedRegs(&MF); *R; ++R) {
114    unsigned Size = TRI.getMinimalPhysRegClass(*R)->getSize();
115    Offset = RoundUpToAlignment(Offset + Size, Size);
116  }
117
118  unsigned MaxAlign = MFI->getMaxAlignment();
119
120  // Check that MaxAlign is not zero if there is a stack object that is not a
121  // callee-saved spill.
122  assert(!MFI->getObjectIndexEnd() || MaxAlign);
123
124  // Iterate over other objects.
125  for (unsigned I = 0, E = MFI->getObjectIndexEnd(); I != E; ++I)
126    Offset = RoundUpToAlignment(Offset + MFI->getObjectSize(I), MaxAlign);
127
128  // Call frame.
129  if (MFI->adjustsStack() && hasReservedCallFrame(MF))
130    Offset = RoundUpToAlignment(Offset + MFI->getMaxCallFrameSize(),
131                                std::max(MaxAlign, getStackAlignment()));
132
133  return RoundUpToAlignment(Offset, getStackAlignment());
134}
135