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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  NoAlloc = 255
32  };
33 }
34 
35 /// Information about stack frame layout on the target. It holds the direction
36 /// of stack growth, the known stack alignment on entry to each function, and
37 /// the offset to the locals area.
38 ///
39 /// The offset to the local area is the offset from the stack pointer on
40 /// function entry to the first location where function data (local variables,
41 /// spill locations) can be stored.
43 public:
45  StackGrowsUp, // Adding to the stack increases the stack address
46  StackGrowsDown // Adding to the stack decreases the stack address
47  };
48 
49  // Maps a callee saved register to a stack slot with a fixed offset.
50  struct SpillSlot {
51  unsigned Reg;
52  int Offset; // Offset relative to stack pointer on function entry.
53  };
54 private:
55  StackDirection StackDir;
56  unsigned StackAlignment;
57  unsigned TransientStackAlignment;
58  int LocalAreaOffset;
59  bool StackRealignable;
60 public:
61  TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
62  unsigned TransAl = 1, bool StackReal = true)
63  : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
64  LocalAreaOffset(LAO), StackRealignable(StackReal) {}
65 
66  virtual ~TargetFrameLowering();
67 
68  // These methods return information that describes the abstract stack layout
69  // of the target machine.
70 
71  /// getStackGrowthDirection - Return the direction the stack grows
72  ///
73  StackDirection getStackGrowthDirection() const { return StackDir; }
74 
75  /// getStackAlignment - This method returns the number of bytes to which the
76  /// stack pointer must be aligned on entry to a function. Typically, this
77  /// is the largest alignment for any data object in the target.
78  ///
79  unsigned getStackAlignment() const { return StackAlignment; }
80 
81  /// alignSPAdjust - This method aligns the stack adjustment to the correct
82  /// alignment.
83  ///
84  int alignSPAdjust(int SPAdj) const {
85  if (SPAdj < 0) {
86  SPAdj = -alignTo(-SPAdj, StackAlignment);
87  } else {
88  SPAdj = alignTo(SPAdj, StackAlignment);
89  }
90  return SPAdj;
91  }
92 
93  /// getTransientStackAlignment - This method returns the number of bytes to
94  /// which the stack pointer must be aligned at all times, even between
95  /// calls.
96  ///
97  unsigned getTransientStackAlignment() const {
98  return TransientStackAlignment;
99  }
100 
101  /// isStackRealignable - This method returns whether the stack can be
102  /// realigned.
103  bool isStackRealignable() const {
104  return StackRealignable;
105  }
106 
107  /// Return the skew that has to be applied to stack alignment under
108  /// certain conditions (e.g. stack was adjusted before function \p MF
109  /// was called).
110  virtual unsigned getStackAlignmentSkew(const MachineFunction &MF) const;
111 
112  /// getOffsetOfLocalArea - This method returns the offset of the local area
113  /// from the stack pointer on entrance to a function.
114  ///
115  int getOffsetOfLocalArea() const { return LocalAreaOffset; }
116 
117  /// isFPCloseToIncomingSP - Return true if the frame pointer is close to
118  /// the incoming stack pointer, false if it is close to the post-prologue
119  /// stack pointer.
120  virtual bool isFPCloseToIncomingSP() const { return true; }
121 
122  /// assignCalleeSavedSpillSlots - Allows target to override spill slot
123  /// assignment logic. If implemented, assignCalleeSavedSpillSlots() should
124  /// assign frame slots to all CSI entries and return true. If this method
125  /// returns false, spill slots will be assigned using generic implementation.
126  /// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
127  /// CSI.
128  virtual bool
130  const TargetRegisterInfo *TRI,
131  std::vector<CalleeSavedInfo> &CSI) const {
132  return false;
133  }
134 
135  /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
136  /// pairs, that contains an entry for each callee saved register that must be
137  /// spilled to a particular stack location if it is spilled.
138  ///
139  /// Each entry in this array contains a <register,offset> pair, indicating the
140  /// fixed offset from the incoming stack pointer that each register should be
141  /// spilled at. If a register is not listed here, the code generator is
142  /// allowed to spill it anywhere it chooses.
143  ///
144  virtual const SpillSlot *
145  getCalleeSavedSpillSlots(unsigned &NumEntries) const {
146  NumEntries = 0;
147  return nullptr;
148  }
149 
150  /// targetHandlesStackFrameRounding - Returns true if the target is
151  /// responsible for rounding up the stack frame (probably at emitPrologue
152  /// time).
153  virtual bool targetHandlesStackFrameRounding() const {
154  return false;
155  }
156 
157  /// Returns true if the target will correctly handle shrink wrapping.
158  virtual bool enableShrinkWrapping(const MachineFunction &MF) const {
159  return false;
160  }
161 
162  /// Returns true if the stack slot holes in the fixed and callee-save stack
163  /// area should be used when allocating other stack locations to reduce stack
164  /// size.
165  virtual bool enableStackSlotScavenging(const MachineFunction &MF) const {
166  return false;
167  }
168 
169  /// Returns true if the target can safely skip saving callee-saved registers
170  /// for noreturn nounwind functions.
171  virtual bool enableCalleeSaveSkip(const MachineFunction &MF) const;
172 
173  /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
174  /// the function.
175  virtual void emitPrologue(MachineFunction &MF,
176  MachineBasicBlock &MBB) const = 0;
177  virtual void emitEpilogue(MachineFunction &MF,
178  MachineBasicBlock &MBB) const = 0;
179 
180  /// Replace a StackProbe stub (if any) with the actual probe code inline
182  MachineBasicBlock &PrologueMBB) const {}
183 
184  /// Adjust the prologue to have the function use segmented stacks. This works
185  /// by adding a check even before the "normal" function prologue.
187  MachineBasicBlock &PrologueMBB) const {}
188 
189  /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
190  /// the assembly prologue to explicitly handle the stack.
192  MachineBasicBlock &PrologueMBB) const {}
193 
194  /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
195  /// saved registers and returns true if it isn't possible / profitable to do
196  /// so by issuing a series of store instructions via
197  /// storeRegToStackSlot(). Returns false otherwise.
200  const std::vector<CalleeSavedInfo> &CSI,
201  const TargetRegisterInfo *TRI) const {
202  return false;
203  }
204 
205  /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
206  /// saved registers and returns true if it isn't possible / profitable to do
207  /// so by issuing a series of load instructions via loadRegToStackSlot().
208  /// If it returns true, and any of the registers in CSI is not restored,
209  /// it sets the corresponding Restored flag in CSI to false.
210  /// Returns false otherwise.
213  std::vector<CalleeSavedInfo> &CSI,
214  const TargetRegisterInfo *TRI) const {
215  return false;
216  }
217 
218  /// Return true if the target wants to keep the frame pointer regardless of
219  /// the function attribute "frame-pointer".
220  virtual bool keepFramePointer(const MachineFunction &MF) const {
221  return false;
222  }
223 
224  /// hasFP - Return true if the specified function should have a dedicated
225  /// frame pointer register. For most targets this is true only if the function
226  /// has variable sized allocas or if frame pointer elimination is disabled.
227  virtual bool hasFP(const MachineFunction &MF) const = 0;
228 
229  /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
230  /// not required, we reserve argument space for call sites in the function
231  /// immediately on entry to the current function. This eliminates the need for
232  /// add/sub sp brackets around call sites. Returns true if the call frame is
233  /// included as part of the stack frame.
234  virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
235  return !hasFP(MF);
236  }
237 
238  /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
239  /// call frame pseudo ops before doing frame index elimination. This is
240  /// possible only when frame index references between the pseudos won't
241  /// need adjusting for the call frame adjustments. Normally, that's true
242  /// if the function has a reserved call frame or a frame pointer. Some
243  /// targets (Thumb2, for example) may have more complicated criteria,
244  /// however, and can override this behavior.
245  virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
246  return hasReservedCallFrame(MF) || hasFP(MF);
247  }
248 
249  // needsFrameIndexResolution - Do we need to perform FI resolution for
250  // this function. Normally, this is required only when the function
251  // has any stack objects. However, targets may want to override this.
252  virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
253 
254  /// getFrameIndexReference - This method should return the base register
255  /// and offset used to reference a frame index location. The offset is
256  /// returned directly, and the base register is returned via FrameReg.
257  virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
258  unsigned &FrameReg) const;
259 
260  /// Same as \c getFrameIndexReference, except that the stack pointer (as
261  /// opposed to the frame pointer) will be the preferred value for \p
262  /// FrameReg. This is generally used for emitting statepoint or EH tables that
263  /// use offsets from RSP. If \p IgnoreSPUpdates is true, the returned
264  /// offset is only guaranteed to be valid with respect to the value of SP at
265  /// the end of the prologue.
266  virtual int getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI,
267  unsigned &FrameReg,
268  bool IgnoreSPUpdates) const {
269  // Always safe to dispatch to getFrameIndexReference.
270  return getFrameIndexReference(MF, FI, FrameReg);
271  }
272 
273  /// getNonLocalFrameIndexReference - This method returns the offset used to
274  /// reference a frame index location. The offset can be from either FP/BP/SP
275  /// based on which base register is returned by llvm.localaddress.
277  int FI) const {
278  // By default, dispatch to getFrameIndexReference. Interested targets can
279  // override this.
280  unsigned FrameReg;
281  return getFrameIndexReference(MF, FI, FrameReg);
282  }
283 
284  /// This method determines which of the registers reported by
285  /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved.
286  /// The default implementation checks populates the \p SavedRegs bitset with
287  /// all registers which are modified in the function, targets may override
288  /// this function to save additional registers.
289  /// This method also sets up the register scavenger ensuring there is a free
290  /// register or a frameindex available.
291  virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
292  RegScavenger *RS = nullptr) const;
293 
294  /// processFunctionBeforeFrameFinalized - This method is called immediately
295  /// before the specified function's frame layout (MF.getFrameInfo()) is
296  /// finalized. Once the frame is finalized, MO_FrameIndex operands are
297  /// replaced with direct constants. This method is optional.
298  ///
300  RegScavenger *RS = nullptr) const {
301  }
302 
303  virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
304  report_fatal_error("WinEH not implemented for this target");
305  }
306 
307  /// This method is called during prolog/epilog code insertion to eliminate
308  /// call frame setup and destroy pseudo instructions (but only if the Target
309  /// is using them). It is responsible for eliminating these instructions,
310  /// replacing them with concrete instructions. This method need only be
311  /// implemented if using call frame setup/destroy pseudo instructions.
312  /// Returns an iterator pointing to the instruction after the replaced one.
315  MachineBasicBlock &MBB,
317  llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
318  "target!");
319  }
320 
321 
322  /// Order the symbols in the local stack frame.
323  /// The list of objects that we want to order is in \p objectsToAllocate as
324  /// indices into the MachineFrameInfo. The array can be reordered in any way
325  /// upon return. The contents of the array, however, may not be modified (i.e.
326  /// only their order may be changed).
327  /// By default, just maintain the original order.
328  virtual void
330  SmallVectorImpl<int> &objectsToAllocate) const {
331  }
332 
333  /// Check whether or not the given \p MBB can be used as a prologue
334  /// for the target.
335  /// The prologue will be inserted first in this basic block.
336  /// This method is used by the shrink-wrapping pass to decide if
337  /// \p MBB will be correctly handled by the target.
338  /// As soon as the target enable shrink-wrapping without overriding
339  /// this method, we assume that each basic block is a valid
340  /// prologue.
341  virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
342  return true;
343  }
344 
345  /// Check whether or not the given \p MBB can be used as a epilogue
346  /// for the target.
347  /// The epilogue will be inserted before the first terminator of that block.
348  /// This method is used by the shrink-wrapping pass to decide if
349  /// \p MBB will be correctly handled by the target.
350  /// As soon as the target enable shrink-wrapping without overriding
351  /// this method, we assume that each basic block is a valid
352  /// epilogue.
353  virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
354  return true;
355  }
356 
358  switch (ID) {
359  default:
360  return false;
363  return true;
364  }
365  }
366 
367  /// Check if given function is safe for not having callee saved registers.
368  /// This is used when interprocedural register allocation is enabled.
369  static bool isSafeForNoCSROpt(const Function &F) {
370  if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
371  !F.hasFnAttribute(Attribute::NoRecurse))
372  return false;
373  // Function should not be optimized as tail call.
374  for (const User *U : F.users())
375  if (auto CS = ImmutableCallSite(U))
376  if (CS.isTailCall())
377  return false;
378  return true;
379  }
380 
381  /// Return initial CFA offset value i.e. the one valid at the beginning of the
382  /// function (before any stack operations).
383  virtual int getInitialCFAOffset(const MachineFunction &MF) const;
384 
385  /// Return initial CFA register value i.e. the one valid at the beginning of
386  /// the function (before any stack operations).
387  virtual unsigned getInitialCFARegister(const MachineFunction &MF) const;
388 };
389 
390 } // End llvm namespace
391 
392 #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)
uint64_t alignTo(uint64_t Value, uint64_t Align, uint64_t Skew=0)
Returns the next integer (mod 2**64) that is greater than or equal to Value and is a multiple of Alig...
Definition: MathExtras.h:689
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
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...
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.
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 ...
TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO, unsigned TransAl=1, bool StackReal=true)
iterator_range< user_iterator > users()
Definition: Value.h:399
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...
Establish a view to a call site for examination.
Definition: CallSite.h:897
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:1339
virtual void orderFrameObjects(const MachineFunction &MF, SmallVectorImpl< int > &objectsToAllocate) const
Order the symbols in the local stack frame.
IRTranslator LLVM IR MI