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 BitVector;
23  class CalleeSavedInfo;
24  class MachineFunction;
25  class RegScavenger;
26
27/// Information about stack frame layout on the target.  It holds the direction
28/// of stack growth, the known stack alignment on entry to each function, and
29/// the offset to the locals area.
30///
31/// The offset to the local area is the offset from the stack pointer on
32/// function entry to the first location where function data (local variables,
33/// spill locations) can be stored.
34class TargetFrameLowering {
35public:
36  enum StackDirection {
37    StackGrowsUp,        // Adding to the stack increases the stack address
38    StackGrowsDown       // Adding to the stack decreases the stack address
39  };
40
41  // Maps a callee saved register to a stack slot with a fixed offset.
42  struct SpillSlot {
43    unsigned Reg;
44    int Offset; // Offset relative to stack pointer on function entry.
45  };
46private:
47  StackDirection StackDir;
48  unsigned StackAlignment;
49  unsigned TransientStackAlignment;
50  int LocalAreaOffset;
51  bool StackRealignable;
52public:
53  TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
54                      unsigned TransAl = 1, bool StackReal = true)
55    : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
56      LocalAreaOffset(LAO), StackRealignable(StackReal) {}
57
58  virtual ~TargetFrameLowering();
59
60  // These methods return information that describes the abstract stack layout
61  // of the target machine.
62
63  /// getStackGrowthDirection - Return the direction the stack grows
64  ///
65  StackDirection getStackGrowthDirection() const { return StackDir; }
66
67  /// getStackAlignment - This method returns the number of bytes to which the
68  /// stack pointer must be aligned on entry to a function.  Typically, this
69  /// is the largest alignment for any data object in the target.
70  ///
71  unsigned getStackAlignment() const { return StackAlignment; }
72
73  /// alignSPAdjust - This method aligns the stack adjustment to the correct
74  /// alignment.
75  ///
76  int alignSPAdjust(int SPAdj) const {
77    if (SPAdj < 0) {
78      SPAdj = -RoundUpToAlignment(-SPAdj, StackAlignment);
79    } else {
80      SPAdj = RoundUpToAlignment(SPAdj, StackAlignment);
81    }
82    return SPAdj;
83  }
84
85  /// getTransientStackAlignment - This method returns the number of bytes to
86  /// which the stack pointer must be aligned at all times, even between
87  /// calls.
88  ///
89  unsigned getTransientStackAlignment() const {
90    return TransientStackAlignment;
91  }
92
93  /// isStackRealignable - This method returns whether the stack can be
94  /// realigned.
95  bool isStackRealignable() const {
96    return StackRealignable;
97  }
98
99  /// Return the skew that has to be applied to stack alignment under
100  /// certain conditions (e.g. stack was adjusted before function \p MF
101  /// was called).
102  virtual unsigned getStackAlignmentSkew(const MachineFunction &MF) const;
103
104  /// getOffsetOfLocalArea - This method returns the offset of the local area
105  /// from the stack pointer on entrance to a function.
106  ///
107  int getOffsetOfLocalArea() const { return LocalAreaOffset; }
108
109  /// isFPCloseToIncomingSP - Return true if the frame pointer is close to
110  /// the incoming stack pointer, false if it is close to the post-prologue
111  /// stack pointer.
112  virtual bool isFPCloseToIncomingSP() const { return true; }
113
114  /// assignCalleeSavedSpillSlots - Allows target to override spill slot
115  /// assignment logic.  If implemented, assignCalleeSavedSpillSlots() should
116  /// assign frame slots to all CSI entries and return true.  If this method
117  /// returns false, spill slots will be assigned using generic implementation.
118  /// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
119  /// CSI.
120  virtual bool
121  assignCalleeSavedSpillSlots(MachineFunction &MF,
122                              const TargetRegisterInfo *TRI,
123                              std::vector<CalleeSavedInfo> &CSI) const {
124    return false;
125  }
126
127  /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
128  /// pairs, that contains an entry for each callee saved register that must be
129  /// spilled to a particular stack location if it is spilled.
130  ///
131  /// Each entry in this array contains a <register,offset> pair, indicating the
132  /// fixed offset from the incoming stack pointer that each register should be
133  /// spilled at. If a register is not listed here, the code generator is
134  /// allowed to spill it anywhere it chooses.
135  ///
136  virtual const SpillSlot *
137  getCalleeSavedSpillSlots(unsigned &NumEntries) const {
138    NumEntries = 0;
139    return nullptr;
140  }
141
142  /// targetHandlesStackFrameRounding - Returns true if the target is
143  /// responsible for rounding up the stack frame (probably at emitPrologue
144  /// time).
145  virtual bool targetHandlesStackFrameRounding() const {
146    return false;
147  }
148
149  /// Returns true if the target will correctly handle shrink wrapping.
150  virtual bool enableShrinkWrapping(const MachineFunction &MF) const {
151    return false;
152  }
153
154  /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
155  /// the function.
156  virtual void emitPrologue(MachineFunction &MF,
157                            MachineBasicBlock &MBB) const = 0;
158  virtual void emitEpilogue(MachineFunction &MF,
159                            MachineBasicBlock &MBB) const = 0;
160
161  /// Replace a StackProbe stub (if any) with the actual probe code inline
162  virtual void inlineStackProbe(MachineFunction &MF,
163                                MachineBasicBlock &PrologueMBB) const {}
164
165  /// Adjust the prologue to have the function use segmented stacks. This works
166  /// by adding a check even before the "normal" function prologue.
167  virtual void adjustForSegmentedStacks(MachineFunction &MF,
168                                        MachineBasicBlock &PrologueMBB) const {}
169
170  /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
171  /// the assembly prologue to explicitly handle the stack.
172  virtual void adjustForHiPEPrologue(MachineFunction &MF,
173                                     MachineBasicBlock &PrologueMBB) const {}
174
175  /// Adjust the prologue to add an allocation at a fixed offset from the frame
176  /// pointer.
177  virtual void
178  adjustForFrameAllocatePrologue(MachineFunction &MF,
179                                 MachineBasicBlock &PrologueMBB) const {}
180
181  /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
182  /// saved registers and returns true if it isn't possible / profitable to do
183  /// so by issuing a series of store instructions via
184  /// storeRegToStackSlot(). Returns false otherwise.
185  virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
186                                         MachineBasicBlock::iterator MI,
187                                        const std::vector<CalleeSavedInfo> &CSI,
188                                         const TargetRegisterInfo *TRI) const {
189    return false;
190  }
191
192  /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
193  /// saved registers and returns true if it isn't possible / profitable to do
194  /// so by issuing a series of load instructions via loadRegToStackSlot().
195  /// Returns false otherwise.
196  virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
197                                           MachineBasicBlock::iterator MI,
198                                        const std::vector<CalleeSavedInfo> &CSI,
199                                        const TargetRegisterInfo *TRI) const {
200    return false;
201  }
202
203  /// Return true if the target needs to disable frame pointer elimination.
204  virtual bool noFramePointerElim(const MachineFunction &MF) const;
205
206  /// hasFP - Return true if the specified function should have a dedicated
207  /// frame pointer register. For most targets this is true only if the function
208  /// has variable sized allocas or if frame pointer elimination is disabled.
209  virtual bool hasFP(const MachineFunction &MF) const = 0;
210
211  /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
212  /// not required, we reserve argument space for call sites in the function
213  /// immediately on entry to the current function. This eliminates the need for
214  /// add/sub sp brackets around call sites. Returns true if the call frame is
215  /// included as part of the stack frame.
216  virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
217    return !hasFP(MF);
218  }
219
220  /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
221  /// call frame pseudo ops before doing frame index elimination. This is
222  /// possible only when frame index references between the pseudos won't
223  /// need adjusting for the call frame adjustments. Normally, that's true
224  /// if the function has a reserved call frame or a frame pointer. Some
225  /// targets (Thumb2, for example) may have more complicated criteria,
226  /// however, and can override this behavior.
227  virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
228    return hasReservedCallFrame(MF) || hasFP(MF);
229  }
230
231  // needsFrameIndexResolution - Do we need to perform FI resolution for
232  // this function. Normally, this is required only when the function
233  // has any stack objects. However, targets may want to override this.
234  virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
235
236  /// getFrameIndexReference - This method should return the base register
237  /// and offset used to reference a frame index location. The offset is
238  /// returned directly, and the base register is returned via FrameReg.
239  virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
240                                     unsigned &FrameReg) const;
241
242  /// Same as above, except that the 'base register' will always be RSP, not
243  /// RBP on x86. This is generally used for emitting statepoint or EH tables
244  /// that use offsets from RSP.
245  /// TODO: This should really be a parameterizable choice.
246  virtual int getFrameIndexReferenceFromSP(const MachineFunction &MF, int FI,
247                                           unsigned &FrameReg) const {
248    // default to calling normal version, we override this on x86 only
249    llvm_unreachable("unimplemented for non-x86");
250    return 0;
251  }
252
253  /// This method determines which of the registers reported by
254  /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved.
255  /// The default implementation checks populates the \p SavedRegs bitset with
256  /// all registers which are modified in the function, targets may override
257  /// this function to save additional registers.
258  /// This method also sets up the register scavenger ensuring there is a free
259  /// register or a frameindex available.
260  virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
261                                    RegScavenger *RS = nullptr) const;
262
263  /// processFunctionBeforeFrameFinalized - This method is called immediately
264  /// before the specified function's frame layout (MF.getFrameInfo()) is
265  /// finalized.  Once the frame is finalized, MO_FrameIndex operands are
266  /// replaced with direct constants.  This method is optional.
267  ///
268  virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
269                                             RegScavenger *RS = nullptr) const {
270  }
271
272  virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
273    report_fatal_error("WinEH not implemented for this target");
274  }
275
276  /// eliminateCallFramePseudoInstr - This method is called during prolog/epilog
277  /// code insertion to eliminate call frame setup and destroy pseudo
278  /// instructions (but only if the Target is using them).  It is responsible
279  /// for eliminating these instructions, replacing them with concrete
280  /// instructions.  This method need only be implemented if using call frame
281  /// setup/destroy pseudo instructions.
282  ///
283  virtual void
284  eliminateCallFramePseudoInstr(MachineFunction &MF,
285                                MachineBasicBlock &MBB,
286                                MachineBasicBlock::iterator MI) const {
287    llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
288                     "target!");
289  }
290
291  /// Check whether or not the given \p MBB can be used as a prologue
292  /// for the target.
293  /// The prologue will be inserted first in this basic block.
294  /// This method is used by the shrink-wrapping pass to decide if
295  /// \p MBB will be correctly handled by the target.
296  /// As soon as the target enable shrink-wrapping without overriding
297  /// this method, we assume that each basic block is a valid
298  /// prologue.
299  virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
300    return true;
301  }
302
303  /// Check whether or not the given \p MBB can be used as a epilogue
304  /// for the target.
305  /// The epilogue will be inserted before the first terminator of that block.
306  /// This method is used by the shrink-wrapping pass to decide if
307  /// \p MBB will be correctly handled by the target.
308  /// As soon as the target enable shrink-wrapping without overriding
309  /// this method, we assume that each basic block is a valid
310  /// epilogue.
311  virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
312    return true;
313  }
314};
315
316} // End llvm namespace
317
318#endif
319