TargetFrameLowering.h revision b99e412650d25776686b46e743751f4ba97a2e4e 
1//===-- llvm/Target/TargetFrameLowering.h ---------------------------*- C++ -*-===//
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// Interface to describe the layout of a stack frame on the target machine.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_TARGET_TARGETFRAMELOWERING_H
15#define LLVM_TARGET_TARGETFRAMELOWERING_H
16
17#include "llvm/CodeGen/MachineBasicBlock.h"
18#include "llvm/MC/MCDwarf.h"
19#include "llvm/ADT/ArrayRef.h"
20
21#include <utility>
22#include <vector>
23
24namespace llvm {
25  class CalleeSavedInfo;
26  class MachineFunction;
27  class MachineBasicBlock;
28  class MachineMove;
29  class RegScavenger;
30
31/// Information about stack frame layout on the target.  It holds the direction
32/// of stack growth, the known stack alignment on entry to each function, and
33/// the offset to the locals area.
34///
35/// The offset to the local area is the offset from the stack pointer on
36/// function entry to the first location where function data (local variables,
37/// spill locations) can be stored.
38class TargetFrameLowering {
39public:
40  enum StackDirection {
41    StackGrowsUp,        // Adding to the stack increases the stack address
42    StackGrowsDown       // Adding to the stack decreases the stack address
43  };
44
45  // Maps a callee saved register to a stack slot with a fixed offset.
46  struct SpillSlot {
47    unsigned Reg;
48    int Offset; // Offset relative to stack pointer on function entry.
49  };
50private:
51  StackDirection StackDir;
52  unsigned StackAlignment;
53  unsigned TransientStackAlignment;
54  int LocalAreaOffset;
55public:
56  TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
57                      unsigned TransAl = 1)
58    : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
59      LocalAreaOffset(LAO) {}
60
61  virtual ~TargetFrameLowering();
62
63  // These methods return information that describes the abstract stack layout
64  // of the target machine.
65
66  /// getStackGrowthDirection - Return the direction the stack grows
67  ///
68  StackDirection getStackGrowthDirection() const { return StackDir; }
69
70  /// getStackAlignment - This method returns the number of bytes to which the
71  /// stack pointer must be aligned on entry to a function.  Typically, this
72  /// is the largest alignment for any data object in the target.
73  ///
74  unsigned getStackAlignment() const { return StackAlignment; }
75
76  /// getTransientStackAlignment - This method returns the number of bytes to
77  /// which the stack pointer must be aligned at all times, even between
78  /// calls.
79  ///
80  unsigned getTransientStackAlignment() const {
81    return TransientStackAlignment;
82  }
83
84  /// getOffsetOfLocalArea - This method returns the offset of the local area
85  /// from the stack pointer on entrance to a function.
86  ///
87  int getOffsetOfLocalArea() const { return LocalAreaOffset; }
88
89  /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
90  /// pairs, that contains an entry for each callee saved register that must be
91  /// spilled to a particular stack location if it is spilled.
92  ///
93  /// Each entry in this array contains a <register,offset> pair, indicating the
94  /// fixed offset from the incoming stack pointer that each register should be
95  /// spilled at. If a register is not listed here, the code generator is
96  /// allowed to spill it anywhere it chooses.
97  ///
98  virtual const SpillSlot *
99  getCalleeSavedSpillSlots(unsigned &NumEntries) const {
100    NumEntries = 0;
101    return 0;
102  }
103
104  /// targetHandlesStackFrameRounding - Returns true if the target is
105  /// responsible for rounding up the stack frame (probably at emitPrologue
106  /// time).
107  virtual bool targetHandlesStackFrameRounding() const {
108    return false;
109  }
110
111  /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
112  /// the function.
113  virtual void emitPrologue(MachineFunction &MF) const = 0;
114  virtual void emitEpilogue(MachineFunction &MF,
115                            MachineBasicBlock &MBB) const = 0;
116
117  /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
118  /// saved registers and returns true if it isn't possible / profitable to do
119  /// so by issuing a series of store instructions via
120  /// storeRegToStackSlot(). Returns false otherwise.
121  virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
122                                         MachineBasicBlock::iterator MI,
123                                        const std::vector<CalleeSavedInfo> &CSI,
124                                         const TargetRegisterInfo *TRI) const {
125    return false;
126  }
127
128  /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
129  /// saved registers and returns true if it isn't possible / profitable to do
130  /// so by issuing a series of load instructions via loadRegToStackSlot().
131  /// Returns false otherwise.
132  virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
133                                           MachineBasicBlock::iterator MI,
134                                        const std::vector<CalleeSavedInfo> &CSI,
135                                        const TargetRegisterInfo *TRI) const {
136    return false;
137  }
138
139  /// hasFP - Return true if the specified function should have a dedicated
140  /// frame pointer register. For most targets this is true only if the function
141  /// has variable sized allocas or if frame pointer elimination is disabled.
142  virtual bool hasFP(const MachineFunction &MF) const = 0;
143
144  /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
145  /// not required, we reserve argument space for call sites in the function
146  /// immediately on entry to the current function. This eliminates the need for
147  /// add/sub sp brackets around call sites. Returns true if the call frame is
148  /// included as part of the stack frame.
149  virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
150    return !hasFP(MF);
151  }
152
153  /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
154  /// call frame pseudo ops before doing frame index elimination. This is
155  /// possible only when frame index references between the pseudos won't
156  /// need adjusting for the call frame adjustments. Normally, that's true
157  /// if the function has a reserved call frame or a frame pointer. Some
158  /// targets (Thumb2, for example) may have more complicated criteria,
159  /// however, and can override this behavior.
160  virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
161    return hasReservedCallFrame(MF) || hasFP(MF);
162  }
163
164  /// getInitialFrameState - Returns a list of machine moves that are assumed
165  /// on entry to all functions.  Note that LabelID is ignored (assumed to be
166  /// the beginning of the function.)
167  virtual void getInitialFrameState(std::vector<MachineMove> &Moves) const;
168
169  /// getFrameIndexOffset - Returns the displacement from the frame register to
170  /// the stack frame of the specified index.
171  virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;
172
173  /// getFrameIndexReference - This method should return the base register
174  /// and offset used to reference a frame index location. The offset is
175  /// returned directly, and the base register is returned via FrameReg.
176  virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
177                                     unsigned &FrameReg) const;
178
179  /// processFunctionBeforeCalleeSavedScan - This method is called immediately
180  /// before PrologEpilogInserter scans the physical registers used to determine
181  /// what callee saved registers should be spilled. This method is optional.
182  virtual void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
183                                                RegScavenger *RS = NULL) const {
184
185  }
186
187  /// processFunctionBeforeFrameFinalized - This method is called immediately
188  /// before the specified function's frame layout (MF.getFrameInfo()) is
189  /// finalized.  Once the frame is finalized, MO_FrameIndex operands are
190  /// replaced with direct constants.  This method is optional.
191  ///
192  virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF) const {
193  }
194
195  /// getCompactUnwindEncoding - Get the compact unwind encoding for the
196  /// function. Return 0 if the compact unwind isn't available.
197  virtual uint32_t getCompactUnwindEncoding(ArrayRef<MCCFIInstruction> Instrs,
198                                            int DataAlignmentFactor,
199                                            bool IsEH) const {
200    return 0;
201  }
202};
203
204} // End llvm namespace
205
206#endif
207