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 = -alignTo(-SPAdj, StackAlignment);
79    } else {
80      SPAdj = alignTo(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  /// Returns true if the stack slot holes in the fixed and callee-save stack
155  /// area should be used when allocating other stack locations to reduce stack
156  /// size.
157  virtual bool enableStackSlotScavenging(const MachineFunction &MF) const {
158    return false;
159  }
160
161  /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
162  /// the function.
163  virtual void emitPrologue(MachineFunction &MF,
164                            MachineBasicBlock &MBB) const = 0;
165  virtual void emitEpilogue(MachineFunction &MF,
166                            MachineBasicBlock &MBB) const = 0;
167
168  /// Replace a StackProbe stub (if any) with the actual probe code inline
169  virtual void inlineStackProbe(MachineFunction &MF,
170                                MachineBasicBlock &PrologueMBB) const {}
171
172  /// Adjust the prologue to have the function use segmented stacks. This works
173  /// by adding a check even before the "normal" function prologue.
174  virtual void adjustForSegmentedStacks(MachineFunction &MF,
175                                        MachineBasicBlock &PrologueMBB) const {}
176
177  /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
178  /// the assembly prologue to explicitly handle the stack.
179  virtual void adjustForHiPEPrologue(MachineFunction &MF,
180                                     MachineBasicBlock &PrologueMBB) const {}
181
182  /// Adjust the prologue to add an allocation at a fixed offset from the frame
183  /// pointer.
184  virtual void
185  adjustForFrameAllocatePrologue(MachineFunction &MF,
186                                 MachineBasicBlock &PrologueMBB) const {}
187
188  /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
189  /// saved registers and returns true if it isn't possible / profitable to do
190  /// so by issuing a series of store instructions via
191  /// storeRegToStackSlot(). Returns false otherwise.
192  virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
193                                         MachineBasicBlock::iterator MI,
194                                        const std::vector<CalleeSavedInfo> &CSI,
195                                         const TargetRegisterInfo *TRI) const {
196    return false;
197  }
198
199  /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
200  /// saved registers and returns true if it isn't possible / profitable to do
201  /// so by issuing a series of load instructions via loadRegToStackSlot().
202  /// Returns false otherwise.
203  virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
204                                           MachineBasicBlock::iterator MI,
205                                        const std::vector<CalleeSavedInfo> &CSI,
206                                        const TargetRegisterInfo *TRI) const {
207    return false;
208  }
209
210  /// Return true if the target needs to disable frame pointer elimination.
211  virtual bool noFramePointerElim(const MachineFunction &MF) const;
212
213  /// hasFP - Return true if the specified function should have a dedicated
214  /// frame pointer register. For most targets this is true only if the function
215  /// has variable sized allocas or if frame pointer elimination is disabled.
216  virtual bool hasFP(const MachineFunction &MF) const = 0;
217
218  /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
219  /// not required, we reserve argument space for call sites in the function
220  /// immediately on entry to the current function. This eliminates the need for
221  /// add/sub sp brackets around call sites. Returns true if the call frame is
222  /// included as part of the stack frame.
223  virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
224    return !hasFP(MF);
225  }
226
227  /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
228  /// call frame pseudo ops before doing frame index elimination. This is
229  /// possible only when frame index references between the pseudos won't
230  /// need adjusting for the call frame adjustments. Normally, that's true
231  /// if the function has a reserved call frame or a frame pointer. Some
232  /// targets (Thumb2, for example) may have more complicated criteria,
233  /// however, and can override this behavior.
234  virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
235    return hasReservedCallFrame(MF) || hasFP(MF);
236  }
237
238  // needsFrameIndexResolution - Do we need to perform FI resolution for
239  // this function. Normally, this is required only when the function
240  // has any stack objects. However, targets may want to override this.
241  virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
242
243  /// getFrameIndexReference - This method should return the base register
244  /// and offset used to reference a frame index location. The offset is
245  /// returned directly, and the base register is returned via FrameReg.
246  virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
247                                     unsigned &FrameReg) const;
248
249  /// Same as \c getFrameIndexReference, except that the stack pointer (as
250  /// opposed to the frame pointer) will be the preferred value for \p
251  /// FrameReg. This is generally used for emitting statepoint or EH tables that
252  /// use offsets from RSP.  If \p IgnoreSPUpdates is true, the returned
253  /// offset is only guaranteed to be valid with respect to the value of SP at
254  /// the end of the prologue.
255  virtual int getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI,
256                                             unsigned &FrameReg,
257                                             bool IgnoreSPUpdates) const {
258    // Always safe to dispatch to getFrameIndexReference.
259    return getFrameIndexReference(MF, FI, FrameReg);
260  }
261
262  /// This method determines which of the registers reported by
263  /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved.
264  /// The default implementation checks populates the \p SavedRegs bitset with
265  /// all registers which are modified in the function, targets may override
266  /// this function to save additional registers.
267  /// This method also sets up the register scavenger ensuring there is a free
268  /// register or a frameindex available.
269  virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
270                                    RegScavenger *RS = nullptr) const;
271
272  /// processFunctionBeforeFrameFinalized - This method is called immediately
273  /// before the specified function's frame layout (MF.getFrameInfo()) is
274  /// finalized.  Once the frame is finalized, MO_FrameIndex operands are
275  /// replaced with direct constants.  This method is optional.
276  ///
277  virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
278                                             RegScavenger *RS = nullptr) const {
279  }
280
281  virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
282    report_fatal_error("WinEH not implemented for this target");
283  }
284
285  /// This method is called during prolog/epilog code insertion to eliminate
286  /// call frame setup and destroy pseudo instructions (but only if the Target
287  /// is using them).  It is responsible for eliminating these instructions,
288  /// replacing them with concrete instructions.  This method need only be
289  /// implemented if using call frame setup/destroy pseudo instructions.
290  /// Returns an iterator pointing to the instruction after the replaced one.
291  virtual MachineBasicBlock::iterator
292  eliminateCallFramePseudoInstr(MachineFunction &MF,
293                                MachineBasicBlock &MBB,
294                                MachineBasicBlock::iterator MI) const {
295    llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
296                     "target!");
297  }
298
299
300  /// Order the symbols in the local stack frame.
301  /// The list of objects that we want to order is in \p objectsToAllocate as
302  /// indices into the MachineFrameInfo. The array can be reordered in any way
303  /// upon return. The contents of the array, however, may not be modified (i.e.
304  /// only their order may be changed).
305  /// By default, just maintain the original order.
306  virtual void
307  orderFrameObjects(const MachineFunction &MF,
308                    SmallVectorImpl<int> &objectsToAllocate) const {
309  }
310
311  /// Check whether or not the given \p MBB can be used as a prologue
312  /// for the target.
313  /// The prologue will be inserted first in this basic block.
314  /// This method is used by the shrink-wrapping pass to decide if
315  /// \p MBB will be correctly handled by the target.
316  /// As soon as the target enable shrink-wrapping without overriding
317  /// this method, we assume that each basic block is a valid
318  /// prologue.
319  virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
320    return true;
321  }
322
323  /// Check whether or not the given \p MBB can be used as a epilogue
324  /// for the target.
325  /// The epilogue will be inserted before the first terminator of that block.
326  /// This method is used by the shrink-wrapping pass to decide if
327  /// \p MBB will be correctly handled by the target.
328  /// As soon as the target enable shrink-wrapping without overriding
329  /// this method, we assume that each basic block is a valid
330  /// epilogue.
331  virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
332    return true;
333  }
334
335  /// Check if given function is safe for not having callee saved registers.
336  /// This is used when interprocedural register allocation is enabled.
337  static bool isSafeForNoCSROpt(const Function *F) {
338    if (!F->hasLocalLinkage() || F->hasAddressTaken() ||
339        !F->hasFnAttribute(Attribute::NoRecurse))
340      return false;
341    // Function should not be optimized as tail call.
342    for (const User *U : F->users())
343      if (auto CS = ImmutableCallSite(U))
344        if (CS.isTailCall())
345          return false;
346    return true;
347  }
348};
349
350} // End llvm namespace
351
352#endif
353