LLVM  4.0.0
TargetFrameLowering.h
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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 
18 #include <utility>
19 #include <vector>
20 
21 namespace 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.
35 public:
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  };
46 private:
47  StackDirection StackDir;
48  unsigned StackAlignment;
49  unsigned TransientStackAlignment;
50  int LocalAreaOffset;
51  bool StackRealignable;
52 public:
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
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
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.
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.
180  MachineBasicBlock &PrologueMBB) const {}
181 
182  /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
183  /// saved registers and returns true if it isn't possible / profitable to do
184  /// so by issuing a series of store instructions via
185  /// storeRegToStackSlot(). Returns false otherwise.
188  const std::vector<CalleeSavedInfo> &CSI,
189  const TargetRegisterInfo *TRI) const {
190  return false;
191  }
192 
193  /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
194  /// saved registers and returns true if it isn't possible / profitable to do
195  /// so by issuing a series of load instructions via loadRegToStackSlot().
196  /// Returns false otherwise.
199  const std::vector<CalleeSavedInfo> &CSI,
200  const TargetRegisterInfo *TRI) const {
201  return false;
202  }
203 
204  /// Return true if the target needs to disable frame pointer elimination.
205  virtual bool noFramePointerElim(const MachineFunction &MF) const;
206 
207  /// hasFP - Return true if the specified function should have a dedicated
208  /// frame pointer register. For most targets this is true only if the function
209  /// has variable sized allocas or if frame pointer elimination is disabled.
210  virtual bool hasFP(const MachineFunction &MF) const = 0;
211 
212  /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
213  /// not required, we reserve argument space for call sites in the function
214  /// immediately on entry to the current function. This eliminates the need for
215  /// add/sub sp brackets around call sites. Returns true if the call frame is
216  /// included as part of the stack frame.
217  virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
218  return !hasFP(MF);
219  }
220 
221  /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
222  /// call frame pseudo ops before doing frame index elimination. This is
223  /// possible only when frame index references between the pseudos won't
224  /// need adjusting for the call frame adjustments. Normally, that's true
225  /// if the function has a reserved call frame or a frame pointer. Some
226  /// targets (Thumb2, for example) may have more complicated criteria,
227  /// however, and can override this behavior.
228  virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
229  return hasReservedCallFrame(MF) || hasFP(MF);
230  }
231 
232  // needsFrameIndexResolution - Do we need to perform FI resolution for
233  // this function. Normally, this is required only when the function
234  // has any stack objects. However, targets may want to override this.
235  virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
236 
237  /// getFrameIndexReference - This method should return the base register
238  /// and offset used to reference a frame index location. The offset is
239  /// returned directly, and the base register is returned via FrameReg.
240  virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
241  unsigned &FrameReg) const;
242 
243  /// Same as \c getFrameIndexReference, except that the stack pointer (as
244  /// opposed to the frame pointer) will be the preferred value for \p
245  /// FrameReg. This is generally used for emitting statepoint or EH tables that
246  /// use offsets from RSP. If \p IgnoreSPUpdates is true, the returned
247  /// offset is only guaranteed to be valid with respect to the value of SP at
248  /// the end of the prologue.
249  virtual int getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI,
250  unsigned &FrameReg,
251  bool IgnoreSPUpdates) const {
252  // Always safe to dispatch to getFrameIndexReference.
253  return getFrameIndexReference(MF, FI, FrameReg);
254  }
255 
256  /// This method determines which of the registers reported by
257  /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved.
258  /// The default implementation checks populates the \p SavedRegs bitset with
259  /// all registers which are modified in the function, targets may override
260  /// this function to save additional registers.
261  /// This method also sets up the register scavenger ensuring there is a free
262  /// register or a frameindex available.
263  virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
264  RegScavenger *RS = nullptr) const;
265 
266  /// processFunctionBeforeFrameFinalized - This method is called immediately
267  /// before the specified function's frame layout (MF.getFrameInfo()) is
268  /// finalized. Once the frame is finalized, MO_FrameIndex operands are
269  /// replaced with direct constants. This method is optional.
270  ///
272  RegScavenger *RS = nullptr) const {
273  }
274 
275  virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
276  report_fatal_error("WinEH not implemented for this target");
277  }
278 
279  /// This method is called during prolog/epilog code insertion to eliminate
280  /// call frame setup and destroy pseudo instructions (but only if the Target
281  /// is using them). It is responsible for eliminating these instructions,
282  /// replacing them with concrete instructions. This method need only be
283  /// implemented if using call frame setup/destroy pseudo instructions.
284  /// Returns an iterator pointing to the instruction after the replaced one.
289  llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
290  "target!");
291  }
292 
293 
294  /// Order the symbols in the local stack frame.
295  /// The list of objects that we want to order is in \p objectsToAllocate as
296  /// indices into the MachineFrameInfo. The array can be reordered in any way
297  /// upon return. The contents of the array, however, may not be modified (i.e.
298  /// only their order may be changed).
299  /// By default, just maintain the original order.
300  virtual void
302  SmallVectorImpl<int> &objectsToAllocate) const {
303  }
304 
305  /// Check whether or not the given \p MBB can be used as a prologue
306  /// for the target.
307  /// The prologue will be inserted first in this basic block.
308  /// This method is used by the shrink-wrapping pass to decide if
309  /// \p MBB will be correctly handled by the target.
310  /// As soon as the target enable shrink-wrapping without overriding
311  /// this method, we assume that each basic block is a valid
312  /// prologue.
313  virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
314  return true;
315  }
316 
317  /// Check whether or not the given \p MBB can be used as a epilogue
318  /// for the target.
319  /// The epilogue will be inserted before the first terminator of that block.
320  /// This method is used by the shrink-wrapping pass to decide if
321  /// \p MBB will be correctly handled by the target.
322  /// As soon as the target enable shrink-wrapping without overriding
323  /// this method, we assume that each basic block is a valid
324  /// epilogue.
325  virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
326  return true;
327  }
328 
329  /// Check if given function is safe for not having callee saved registers.
330  /// This is used when interprocedural register allocation is enabled.
331  static bool isSafeForNoCSROpt(const Function *F) {
332  if (!F->hasLocalLinkage() || F->hasAddressTaken() ||
333  !F->hasFnAttribute(Attribute::NoRecurse))
334  return false;
335  // Function should not be optimized as tail call.
336  for (const User *U : F->users())
337  if (auto CS = ImmutableCallSite(U))
338  if (CS.isTailCall())
339  return false;
340  return true;
341  }
342 };
343 
344 } // End llvm namespace
345 
346 #endif
unsigned getStackAlignment() const
getStackAlignment - This method returns the number of bytes to which the stack pointer must be aligne...
virtual void orderFrameObjects(const MachineFunction &MF, SmallVectorImpl< int > &objectsToAllocate) const
Order the symbols in the local stack frame.
LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err, bool gen_crash_diag=true)
Report a serious error, calling any installed error handler.
virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const
Check whether or not the given MBB can be used as a epilogue for the target.
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 unsigned getStackAlignmentSkew(const MachineFunction &MF) const
Return the skew that has to be applied to stack alignment under certain conditions (e...
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:664
virtual const SpillSlot * getCalleeSavedSpillSlots(unsigned &NumEntries) const
getCalleeSavedSpillSlots - This method returns a pointer to an array of pairs, that contains an entry...
bool isStackRealignable() const
isStackRealignable - This method returns whether the stack can be realigned.
virtual bool targetHandlesStackFrameRounding() const
targetHandlesStackFrameRounding - Returns true if the target is responsible for rounding up the stack...
virtual void inlineStackProbe(MachineFunction &MF, MachineBasicBlock &PrologueMBB) const
Replace a StackProbe stub (if any) with the actual probe code inline.
virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF, RegScavenger *RS=nullptr) const
processFunctionBeforeFrameFinalized - This method is called immediately before the specified function...
virtual bool hasFP(const MachineFunction &MF) const =0
hasFP - Return true if the specified function should have a dedicated frame pointer register...
static GCRegistry::Add< StatepointGC > D("statepoint-example","an example strategy for statepoint")
virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const
virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI, const std::vector< CalleeSavedInfo > &CSI, const TargetRegisterInfo *TRI) const
restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee saved registers and returns...
virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const
Check whether or not the given MBB can be used as a prologue for the target.
#define F(x, y, z)
Definition: MD5.cpp:51
virtual bool needsFrameIndexResolution(const MachineFunction &MF) const
MachineBasicBlock * MBB
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 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...
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...
virtual int getFrameIndexReference(const MachineFunction &MF, int FI, unsigned &FrameReg) const
getFrameIndexReference - This method should return the base register and offset used to reference a f...
unsigned getTransientStackAlignment() const
getTransientStackAlignment - This method returns the number of bytes to which the stack pointer must ...
virtual void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const =0
emitProlog/emitEpilog - These methods insert prolog and epilog code into the function.
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...
int alignSPAdjust(int SPAdj) const
alignSPAdjust - This method aligns the stack adjustment to the correct alignment. ...
TargetRegisterInfo base class - We assume that the target defines a static array of TargetRegisterDes...
#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 void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs, RegScavenger *RS=nullptr) const
This method determines which of the registers reported by TargetRegisterInfo::getCalleeSavedRegs() sh...
virtual bool noFramePointerElim(const MachineFunction &MF) const
Return true if the target needs to disable frame pointer elimination.
virtual void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const =0
int getOffsetOfLocalArea() const
getOffsetOfLocalArea - This method returns the offset of the local area from the stack pointer on ent...
Information about stack frame layout on the target.
virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const
canSimplifyCallFramePseudos - When possible, it's best to simplify the call frame pseudo ops before d...
TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO, unsigned TransAl=1, bool StackReal=true)
iterator_range< user_iterator > users()
Definition: Value.h:370
static bool isSafeForNoCSROpt(const Function *F)
Check if given function is safe for not having callee saved registers.
StackDirection getStackGrowthDirection() const
getStackGrowthDirection - Return the direction the stack grows
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:1171
bool hasFnAttribute(Attribute::AttrKind Kind) const
Return true if the function has the attribute.
Definition: Function.h:226
ImmutableCallSite - establish a view to a call site for examination.
Definition: CallSite.h:665
virtual void adjustForSegmentedStacks(MachineFunction &MF, MachineBasicBlock &PrologueMBB) const
Adjust the prologue to have the function use segmented stacks.
bool hasLocalLinkage() const
Definition: GlobalValue.h:415
virtual bool assignCalleeSavedSpillSlots(MachineFunction &MF, const TargetRegisterInfo *TRI, std::vector< CalleeSavedInfo > &CSI) const
assignCalleeSavedSpillSlots - Allows target to override spill slot assignment logic.
virtual bool enableShrinkWrapping(const MachineFunction &MF) const
Returns true if the target will correctly handle shrink wrapping.
IRTranslator LLVM IR MI
virtual bool isFPCloseToIncomingSP() const
isFPCloseToIncomingSP - Return true if the frame pointer is close to the incoming stack pointer...