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/IR/DataLayout.h"
26 #include "llvm/IR/Function.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Target/TargetOptions.h"
29
30 using 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
create(MipsTargetMachine & TM,const MipsSubtarget & ST)85 const 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.
hasFP(const MachineFunction & MF) const96 bool 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
estimateStackSize(const MachineFunction & MF) const102 uint64_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