TargetFrameLowering.h revision 69261a644298bff1497d46c8cd38d688670f307b 
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 <utility>
19#include <vector>
20
21namespace llvm {
22  class CalleeSavedInfo;
23  class MachineFunction;
24  class RegScavenger;
25
26/// Information about stack frame layout on the target.  It holds the direction
27/// of stack growth, the known stack alignment on entry to each function, and
28/// the offset to the locals area.
29///
30/// The offset to the local area is the offset from the stack pointer on
31/// function entry to the first location where function data (local variables,
32/// spill locations) can be stored.
33class TargetFrameLowering {
34public:
35  enum StackDirection {
36    StackGrowsUp,        // Adding to the stack increases the stack address
37    StackGrowsDown       // Adding to the stack decreases the stack address
38  };
39
40  // Maps a callee saved register to a stack slot with a fixed offset.
41  struct SpillSlot {
42    unsigned Reg;
43    int Offset; // Offset relative to stack pointer on function entry.
44  };
45private:
46  StackDirection StackDir;
47  unsigned StackAlignment;
48  unsigned TransientStackAlignment;
49  int LocalAreaOffset;
50  bool StackRealignable;
51public:
52  TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
53                      unsigned TransAl = 1, bool StackReal = true)
54    : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
55      LocalAreaOffset(LAO), StackRealignable(StackReal) {}
56
57  virtual ~TargetFrameLowering();
58
59  // These methods return information that describes the abstract stack layout
60  // of the target machine.
61
62  /// getStackGrowthDirection - Return the direction the stack grows
63  ///
64  StackDirection getStackGrowthDirection() const { return StackDir; }
65
66  /// getStackAlignment - This method returns the number of bytes to which the
67  /// stack pointer must be aligned on entry to a function.  Typically, this
68  /// is the largest alignment for any data object in the target.
69  ///
70  unsigned getStackAlignment() const { return StackAlignment; }
71
72  /// getTransientStackAlignment - This method returns the number of bytes to
73  /// which the stack pointer must be aligned at all times, even between
74  /// calls.
75  ///
76  unsigned getTransientStackAlignment() const {
77    return TransientStackAlignment;
78  }
79
80  /// isStackRealignable - This method returns whether the stack can be
81  /// realigned.
82  bool isStackRealignable() const {
83    return StackRealignable;
84  }
85
86  /// getOffsetOfLocalArea - This method returns the offset of the local area
87  /// from the stack pointer on entrance to a function.
88  ///
89  int getOffsetOfLocalArea() const { return LocalAreaOffset; }
90
91  /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
92  /// pairs, that contains an entry for each callee saved register that must be
93  /// spilled to a particular stack location if it is spilled.
94  ///
95  /// Each entry in this array contains a <register,offset> pair, indicating the
96  /// fixed offset from the incoming stack pointer that each register should be
97  /// spilled at. If a register is not listed here, the code generator is
98  /// allowed to spill it anywhere it chooses.
99  ///
100  virtual const SpillSlot *
101  getCalleeSavedSpillSlots(unsigned &NumEntries) const {
102    NumEntries = 0;
103    return 0;
104  }
105
106  /// targetHandlesStackFrameRounding - Returns true if the target is
107  /// responsible for rounding up the stack frame (probably at emitPrologue
108  /// time).
109  virtual bool targetHandlesStackFrameRounding() const {
110    return false;
111  }
112
113  /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
114  /// the function.
115  virtual void emitPrologue(MachineFunction &MF) const = 0;
116  virtual void emitEpilogue(MachineFunction &MF,
117                            MachineBasicBlock &MBB) const = 0;
118
119  /// Adjust the prologue to have the function use segmented stacks. This works
120  /// by adding a check even before the "normal" function prologue.
121  virtual void adjustForSegmentedStacks(MachineFunction &MF) const { }
122
123  /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
124  /// saved registers and returns true if it isn't possible / profitable to do
125  /// so by issuing a series of store instructions via
126  /// storeRegToStackSlot(). Returns false otherwise.
127  virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
128                                         MachineBasicBlock::iterator MI,
129                                        const std::vector<CalleeSavedInfo> &CSI,
130                                         const TargetRegisterInfo *TRI) const {
131    return false;
132  }
133
134  /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
135  /// saved registers and returns true if it isn't possible / profitable to do
136  /// so by issuing a series of load instructions via loadRegToStackSlot().
137  /// Returns false otherwise.
138  virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
139                                           MachineBasicBlock::iterator MI,
140                                        const std::vector<CalleeSavedInfo> &CSI,
141                                        const TargetRegisterInfo *TRI) const {
142    return false;
143  }
144
145  /// hasFP - Return true if the specified function should have a dedicated
146  /// frame pointer register. For most targets this is true only if the function
147  /// has variable sized allocas or if frame pointer elimination is disabled.
148  virtual bool hasFP(const MachineFunction &MF) const = 0;
149
150  /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
151  /// not required, we reserve argument space for call sites in the function
152  /// immediately on entry to the current function. This eliminates the need for
153  /// add/sub sp brackets around call sites. Returns true if the call frame is
154  /// included as part of the stack frame.
155  virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
156    return !hasFP(MF);
157  }
158
159  /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
160  /// call frame pseudo ops before doing frame index elimination. This is
161  /// possible only when frame index references between the pseudos won't
162  /// need adjusting for the call frame adjustments. Normally, that's true
163  /// if the function has a reserved call frame or a frame pointer. Some
164  /// targets (Thumb2, for example) may have more complicated criteria,
165  /// however, and can override this behavior.
166  virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
167    return hasReservedCallFrame(MF) || hasFP(MF);
168  }
169
170  /// getFrameIndexOffset - Returns the displacement from the frame register to
171  /// the stack frame of the specified index.
172  virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;
173
174  /// getFrameIndexReference - This method should return the base register
175  /// and offset used to reference a frame index location. The offset is
176  /// returned directly, and the base register is returned via FrameReg.
177  virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
178                                     unsigned &FrameReg) const;
179
180  /// processFunctionBeforeCalleeSavedScan - This method is called immediately
181  /// before PrologEpilogInserter scans the physical registers used to determine
182  /// what callee saved registers should be spilled. This method is optional.
183  virtual void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
184                                                RegScavenger *RS = NULL) const {
185
186  }
187
188  /// processFunctionBeforeFrameFinalized - This method is called immediately
189  /// before the specified function's frame layout (MF.getFrameInfo()) is
190  /// finalized.  Once the frame is finalized, MO_FrameIndex operands are
191  /// replaced with direct constants.  This method is optional.
192  ///
193  virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF) const {
194  }
195};
196
197} // End llvm namespace
198
199#endif
200