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TargetFrameLowering.h
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1 //===-- llvm/CodeGen/TargetFrameLowering.h ----------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Interface to describe the layout of a stack frame on the target machine.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_CODEGEN_TARGETFRAMELOWERING_H
14 #define LLVM_CODEGEN_TARGETFRAMELOWERING_H
15 
17 #include "llvm/ADT/StringSwitch.h"
18 #include <utility>
19 #include <vector>
20 
21 namespace llvm {
22  class BitVector;
23  class CalleeSavedInfo;
24  class MachineFunction;
25  class RegScavenger;
26 
27 namespace TargetStackID {
28  enum Value {
29  Default = 0,
30  SGPRSpill = 1,
31  SVEVector = 2,
32  NoAlloc = 255
33  };
34 }
35 
36 /// Information about stack frame layout on the target. It holds the direction
37 /// of stack growth, the known stack alignment on entry to each function, and
38 /// the offset to the locals area.
39 ///
40 /// The offset to the local area is the offset from the stack pointer on
41 /// function entry to the first location where function data (local variables,
42 /// spill locations) can be stored.
44 public:
46  StackGrowsUp, // Adding to the stack increases the stack address
47  StackGrowsDown // Adding to the stack decreases the stack address
48  };
49 
50  // Maps a callee saved register to a stack slot with a fixed offset.
51  struct SpillSlot {
52  unsigned Reg;
53  int Offset; // Offset relative to stack pointer on function entry.
54  };
55 private:
56  StackDirection StackDir;
57  Align StackAlignment;
58  unsigned TransientStackAlignment;
59  int LocalAreaOffset;
60  bool StackRealignable;
61 public:
63  unsigned TransAl = 1, bool StackReal = true)
64  : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
65  LocalAreaOffset(LAO), StackRealignable(StackReal) {}
66 
67  virtual ~TargetFrameLowering();
68 
69  // These methods return information that describes the abstract stack layout
70  // of the target machine.
71 
72  /// getStackGrowthDirection - Return the direction the stack grows
73  ///
74  StackDirection getStackGrowthDirection() const { return StackDir; }
75 
76  /// getStackAlignment - This method returns the number of bytes to which the
77  /// stack pointer must be aligned on entry to a function. Typically, this
78  /// is the largest alignment for any data object in the target.
79  ///
80  unsigned getStackAlignment() const { return StackAlignment.value(); }
81 
82  /// alignSPAdjust - This method aligns the stack adjustment to the correct
83  /// alignment.
84  ///
85  int alignSPAdjust(int SPAdj) const {
86  if (SPAdj < 0) {
87  SPAdj = -alignTo(-SPAdj, StackAlignment);
88  } else {
89  SPAdj = alignTo(SPAdj, StackAlignment);
90  }
91  return SPAdj;
92  }
93 
94  /// getTransientStackAlignment - This method returns the number of bytes to
95  /// which the stack pointer must be aligned at all times, even between
96  /// calls.
97  ///
98  unsigned getTransientStackAlignment() const {
99  return TransientStackAlignment;
100  }
101 
102  /// isStackRealignable - This method returns whether the stack can be
103  /// realigned.
104  bool isStackRealignable() const {
105  return StackRealignable;
106  }
107 
108  /// Return the skew that has to be applied to stack alignment under
109  /// certain conditions (e.g. stack was adjusted before function \p MF
110  /// was called).
111  virtual unsigned getStackAlignmentSkew(const MachineFunction &MF) const;
112 
113  /// getOffsetOfLocalArea - This method returns the offset of the local area
114  /// from the stack pointer on entrance to a function.
115  ///
116  int getOffsetOfLocalArea() const { return LocalAreaOffset; }
117 
118  /// isFPCloseToIncomingSP - Return true if the frame pointer is close to
119  /// the incoming stack pointer, false if it is close to the post-prologue
120  /// stack pointer.
121  virtual bool isFPCloseToIncomingSP() const { return true; }
122 
123  /// assignCalleeSavedSpillSlots - Allows target to override spill slot
124  /// assignment logic. If implemented, assignCalleeSavedSpillSlots() should
125  /// assign frame slots to all CSI entries and return true. If this method
126  /// returns false, spill slots will be assigned using generic implementation.
127  /// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
128  /// CSI.
129  virtual bool
131  const TargetRegisterInfo *TRI,
132  std::vector<CalleeSavedInfo> &CSI) const {
133  return false;
134  }
135 
136  /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
137  /// pairs, that contains an entry for each callee saved register that must be
138  /// spilled to a particular stack location if it is spilled.
139  ///
140  /// Each entry in this array contains a <register,offset> pair, indicating the
141  /// fixed offset from the incoming stack pointer that each register should be
142  /// spilled at. If a register is not listed here, the code generator is
143  /// allowed to spill it anywhere it chooses.
144  ///
145  virtual const SpillSlot *
146  getCalleeSavedSpillSlots(unsigned &NumEntries) const {
147  NumEntries = 0;
148  return nullptr;
149  }
150 
151  /// targetHandlesStackFrameRounding - Returns true if the target is
152  /// responsible for rounding up the stack frame (probably at emitPrologue
153  /// time).
154  virtual bool targetHandlesStackFrameRounding() const {
155  return false;
156  }
157 
158  /// Returns true if the target will correctly handle shrink wrapping.
159  virtual bool enableShrinkWrapping(const MachineFunction &MF) const {
160  return false;
161  }
162 
163  /// Returns true if the stack slot holes in the fixed and callee-save stack
164  /// area should be used when allocating other stack locations to reduce stack
165  /// size.
166  virtual bool enableStackSlotScavenging(const MachineFunction &MF) const {
167  return false;
168  }
169 
170  /// Returns true if the target can safely skip saving callee-saved registers
171  /// for noreturn nounwind functions.
172  virtual bool enableCalleeSaveSkip(const MachineFunction &MF) const;
173 
174  /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
175  /// the function.
176  virtual void emitPrologue(MachineFunction &MF,
177  MachineBasicBlock &MBB) const = 0;
178  virtual void emitEpilogue(MachineFunction &MF,
179  MachineBasicBlock &MBB) const = 0;
180 
181  /// Replace a StackProbe stub (if any) with the actual probe code inline
183  MachineBasicBlock &PrologueMBB) const {}
184 
185  /// Adjust the prologue to have the function use segmented stacks. This works
186  /// by adding a check even before the "normal" function prologue.
188  MachineBasicBlock &PrologueMBB) const {}
189 
190  /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
191  /// the assembly prologue to explicitly handle the stack.
193  MachineBasicBlock &PrologueMBB) const {}
194 
195  /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
196  /// saved registers and returns true if it isn't possible / profitable to do
197  /// so by issuing a series of store instructions via
198  /// storeRegToStackSlot(). Returns false otherwise.
201  const std::vector<CalleeSavedInfo> &CSI,
202  const TargetRegisterInfo *TRI) const {
203  return false;
204  }
205 
206  /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
207  /// saved registers and returns true if it isn't possible / profitable to do
208  /// so by issuing a series of load instructions via loadRegToStackSlot().
209  /// If it returns true, and any of the registers in CSI is not restored,
210  /// it sets the corresponding Restored flag in CSI to false.
211  /// Returns false otherwise.
214  std::vector<CalleeSavedInfo> &CSI,
215  const TargetRegisterInfo *TRI) const {
216  return false;
217  }
218 
219  /// Return true if the target wants to keep the frame pointer regardless of
220  /// the function attribute "frame-pointer".
221  virtual bool keepFramePointer(const MachineFunction &MF) const {
222  return false;
223  }
224 
225  /// hasFP - Return true if the specified function should have a dedicated
226  /// frame pointer register. For most targets this is true only if the function
227  /// has variable sized allocas or if frame pointer elimination is disabled.
228  virtual bool hasFP(const MachineFunction &MF) const = 0;
229 
230  /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
231  /// not required, we reserve argument space for call sites in the function
232  /// immediately on entry to the current function. This eliminates the need for
233  /// add/sub sp brackets around call sites. Returns true if the call frame is
234  /// included as part of the stack frame.
235  virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
236  return !hasFP(MF);
237  }
238 
239  /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
240  /// call frame pseudo ops before doing frame index elimination. This is
241  /// possible only when frame index references between the pseudos won't
242  /// need adjusting for the call frame adjustments. Normally, that's true
243  /// if the function has a reserved call frame or a frame pointer. Some
244  /// targets (Thumb2, for example) may have more complicated criteria,
245  /// however, and can override this behavior.
246  virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
247  return hasReservedCallFrame(MF) || hasFP(MF);
248  }
249 
250  // needsFrameIndexResolution - Do we need to perform FI resolution for
251  // this function. Normally, this is required only when the function
252  // has any stack objects. However, targets may want to override this.
253  virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
254 
255  /// getFrameIndexReference - This method should return the base register
256  /// and offset used to reference a frame index location. The offset is
257  /// returned directly, and the base register is returned via FrameReg.
258  virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
259  unsigned &FrameReg) const;
260 
261  /// Same as \c getFrameIndexReference, except that the stack pointer (as
262  /// opposed to the frame pointer) will be the preferred value for \p
263  /// FrameReg. This is generally used for emitting statepoint or EH tables that
264  /// use offsets from RSP. If \p IgnoreSPUpdates is true, the returned
265  /// offset is only guaranteed to be valid with respect to the value of SP at
266  /// the end of the prologue.
267  virtual int getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI,
268  unsigned &FrameReg,
269  bool IgnoreSPUpdates) const {
270  // Always safe to dispatch to getFrameIndexReference.
271  return getFrameIndexReference(MF, FI, FrameReg);
272  }
273 
274  /// getNonLocalFrameIndexReference - This method returns the offset used to
275  /// reference a frame index location. The offset can be from either FP/BP/SP
276  /// based on which base register is returned by llvm.localaddress.
278  int FI) const {
279  // By default, dispatch to getFrameIndexReference. Interested targets can
280  // override this.
281  unsigned FrameReg;
282  return getFrameIndexReference(MF, FI, FrameReg);
283  }
284 
285  /// This method determines which of the registers reported by
286  /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved.
287  /// The default implementation checks populates the \p SavedRegs bitset with
288  /// all registers which are modified in the function, targets may override
289  /// this function to save additional registers.
290  /// This method also sets up the register scavenger ensuring there is a free
291  /// register or a frameindex available.
292  virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
293  RegScavenger *RS = nullptr) const;
294 
295  /// processFunctionBeforeFrameFinalized - This method is called immediately
296  /// before the specified function's frame layout (MF.getFrameInfo()) is
297  /// finalized. Once the frame is finalized, MO_FrameIndex operands are
298  /// replaced with direct constants. This method is optional.
299  ///
301  RegScavenger *RS = nullptr) const {
302  }
303 
304  virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
305  report_fatal_error("WinEH not implemented for this target");
306  }
307 
308  /// This method is called during prolog/epilog code insertion to eliminate
309  /// call frame setup and destroy pseudo instructions (but only if the Target
310  /// is using them). It is responsible for eliminating these instructions,
311  /// replacing them with concrete instructions. This method need only be
312  /// implemented if using call frame setup/destroy pseudo instructions.
313  /// Returns an iterator pointing to the instruction after the replaced one.
316  MachineBasicBlock &MBB,
318  llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
319  "target!");
320  }
321 
322 
323  /// Order the symbols in the local stack frame.
324  /// The list of objects that we want to order is in \p objectsToAllocate as
325  /// indices into the MachineFrameInfo. The array can be reordered in any way
326  /// upon return. The contents of the array, however, may not be modified (i.e.
327  /// only their order may be changed).
328  /// By default, just maintain the original order.
329  virtual void
331  SmallVectorImpl<int> &objectsToAllocate) const {
332  }
333 
334  /// Check whether or not the given \p MBB can be used as a prologue
335  /// for the target.
336  /// The prologue will be inserted first in this basic block.
337  /// This method is used by the shrink-wrapping pass to decide if
338  /// \p MBB will be correctly handled by the target.
339  /// As soon as the target enable shrink-wrapping without overriding
340  /// this method, we assume that each basic block is a valid
341  /// prologue.
342  virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
343  return true;
344  }
345 
346  /// Check whether or not the given \p MBB can be used as a epilogue
347  /// for the target.
348  /// The epilogue will be inserted before the first terminator of that block.
349  /// This method is used by the shrink-wrapping pass to decide if
350  /// \p MBB will be correctly handled by the target.
351  /// As soon as the target enable shrink-wrapping without overriding
352  /// this method, we assume that each basic block is a valid
353  /// epilogue.
354  virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
355  return true;
356  }
357 
359  switch (ID) {
360  default:
361  return false;
364  return true;
365  }
366  }
367 
368  /// Check if given function is safe for not having callee saved registers.
369  /// This is used when interprocedural register allocation is enabled.
370  static bool isSafeForNoCSROpt(const Function &F) {
371  if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
372  !F.hasFnAttribute(Attribute::NoRecurse))
373  return false;
374  // Function should not be optimized as tail call.
375  for (const User *U : F.users())
376  if (auto CS = ImmutableCallSite(U))
377  if (CS.isTailCall())
378  return false;
379  return true;
380  }
381 
382  /// Check if the no-CSR optimisation is profitable for the given function.
383  virtual bool isProfitableForNoCSROpt(const Function &F) const {
384  return true;
385  }
386 
387  /// Return initial CFA offset value i.e. the one valid at the beginning of the
388  /// function (before any stack operations).
389  virtual int getInitialCFAOffset(const MachineFunction &MF) const;
390 
391  /// Return initial CFA register value i.e. the one valid at the beginning of
392  /// the function (before any stack operations).
393  virtual unsigned getInitialCFARegister(const MachineFunction &MF) const;
394 };
395 
396 } // End llvm namespace
397 
398 #endif
bool hasLocalLinkage() const
Definition: GlobalValue.h:445
virtual bool enableShrinkWrapping(const MachineFunction &MF) const
Returns true if the target will correctly handle shrink wrapping.
virtual bool isSupportedStackID(TargetStackID::Value ID) const
LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err, bool gen_crash_diag=true)
Report a serious error, calling any installed error handler.
Definition: Error.cpp:139
This class represents lattice values for constants.
Definition: AllocatorList.h:23
virtual bool keepFramePointer(const MachineFunction &MF) const
Return true if the target wants to keep the frame pointer regardless of the function attribute "frame...
virtual void adjustForHiPEPrologue(MachineFunction &MF, MachineBasicBlock &PrologueMBB) const
Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in the assembly prologue to ex...
virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const
canSimplifyCallFramePseudos - When possible, it&#39;s best to simplify the call frame pseudo ops before d...
bool hasFnAttribute(Attribute::AttrKind Kind) const
Return true if the function has the attribute.
Definition: Function.h:323
virtual MachineBasicBlock::iterator eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB, MachineBasicBlock::iterator MI) const
This method is called during prolog/epilog code insertion to eliminate call frame setup and destroy p...
unsigned const TargetRegisterInfo * TRI
F(f)
int getOffsetOfLocalArea() const
getOffsetOfLocalArea - This method returns the offset of the local area from the stack pointer on ent...
virtual int getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI, unsigned &FrameReg, bool IgnoreSPUpdates) const
Same as getFrameIndexReference, except that the stack pointer (as opposed to the frame pointer) will ...
virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF, RegScavenger *RS=nullptr) const
processFunctionBeforeFrameFinalized - This method is called immediately before the specified function...
static bool isSafeForNoCSROpt(const Function &F)
Check if given function is safe for not having callee saved registers.
virtual const SpillSlot * getCalleeSavedSpillSlots(unsigned &NumEntries) const
getCalleeSavedSpillSlots - This method returns a pointer to an array of pairs, that contains an entry...
virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const
Check whether or not the given MBB can be used as a epilogue for the target.
virtual bool assignCalleeSavedSpillSlots(MachineFunction &MF, const TargetRegisterInfo *TRI, std::vector< CalleeSavedInfo > &CSI) const
assignCalleeSavedSpillSlots - Allows target to override spill slot assignment logic.
virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const
TargetFrameLowering(StackDirection D, Align StackAl, int LAO, unsigned TransAl=1, bool StackReal=true)
virtual int getNonLocalFrameIndexReference(const MachineFunction &MF, int FI) const
getNonLocalFrameIndexReference - This method returns the offset used to reference a frame index locat...
int alignSPAdjust(int SPAdj) const
alignSPAdjust - This method aligns the stack adjustment to the correct alignment. ...
virtual bool targetHandlesStackFrameRounding() const
targetHandlesStackFrameRounding - Returns true if the target is responsible for rounding up the stack...
uint64_t value() const
This is a hole in the type system and should not be abused.
Definition: Alignment.h:86
virtual void adjustForSegmentedStacks(MachineFunction &MF, MachineBasicBlock &PrologueMBB) const
Adjust the prologue to have the function use segmented stacks.
StackDirection getStackGrowthDirection() const
getStackGrowthDirection - Return the direction the stack grows
TargetRegisterInfo base class - We assume that the target defines a static array of TargetRegisterDes...
unsigned getStackAlignment() const
getStackAlignment - This method returns the number of bytes to which the stack pointer must be aligne...
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
virtual bool hasReservedCallFrame(const MachineFunction &MF) const
hasReservedCallFrame - Under normal circumstances, when a frame pointer is not required, we reserve argument space for call sites in the function immediately on entry to the current function.
This struct is a compact representation of a valid (non-zero power of two) alignment.
Definition: Alignment.h:40
virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI, std::vector< CalleeSavedInfo > &CSI, const TargetRegisterInfo *TRI) const
restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee saved registers and returns...
Information about stack frame layout on the target.
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
unsigned getTransientStackAlignment() const
getTransientStackAlignment - This method returns the number of bytes to which the stack pointer must ...
iterator_range< user_iterator > users()
Definition: Value.h:420
virtual bool isFPCloseToIncomingSP() const
isFPCloseToIncomingSP - Return true if the frame pointer is close to the incoming stack pointer...
virtual bool enableStackSlotScavenging(const MachineFunction &MF) const
Returns true if the stack slot holes in the fixed and callee-save stack area should be used when allo...
uint64_t alignTo(uint64_t Size, Align A)
Returns a multiple of A needed to store Size bytes.
Definition: Alignment.h:163
Establish a view to a call site for examination.
Definition: CallSite.h:906
virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI, const std::vector< CalleeSavedInfo > &CSI, const TargetRegisterInfo *TRI) const
spillCalleeSavedRegisters - Issues instruction(s) to spill all callee saved registers and returns tru...
virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const
Check whether or not the given MBB can be used as a prologue for the target.
virtual void inlineStackProbe(MachineFunction &MF, MachineBasicBlock &PrologueMBB) const
Replace a StackProbe stub (if any) with the actual probe code inline.
bool isStackRealignable() const
isStackRealignable - This method returns whether the stack can be realigned.
bool hasAddressTaken(const User **=nullptr) const
hasAddressTaken - returns true if there are any uses of this function other than direct calls or invo...
Definition: Function.cpp:1420
virtual void orderFrameObjects(const MachineFunction &MF, SmallVectorImpl< int > &objectsToAllocate) const
Order the symbols in the local stack frame.
IRTranslator LLVM IR MI
virtual bool isProfitableForNoCSROpt(const Function &F) const
Check if the no-CSR optimisation is profitable for the given function.