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
16#include "llvm/CodeGen/MachineBasicBlock.h"
17#include "llvm/Support/TypeSize.h"
18#include <vector>
19
20namespace llvm {
21 class BitVector;
22 class CalleeSavedInfo;
23 class MachineFunction;
24 class RegScavenger;
25
26namespace TargetStackID {
27 enum Value {
28 Default = 0,
29 SGPRSpill = 1,
30 ScalableVector = 2,
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.
42class TargetFrameLowering {
43public:
44 enum StackDirection {
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
55 struct DwarfFrameBase {
56 // The frame base may be either a register (the default), the CFA,
57 // or a WebAssembly-specific location description.
58 enum FrameBaseKind { Register, CFA, WasmFrameBase } Kind;
59 struct WasmFrameBase {
60 unsigned Kind; // Wasm local, global, or value stack
61 unsigned Index;
62 };
63 union {
64 unsigned Reg;
65 struct WasmFrameBase WasmLoc;
66 } Location;
67 };
68
69private:
70 StackDirection StackDir;
71 Align StackAlignment;
72 Align TransientStackAlignment;
73 int LocalAreaOffset;
74 bool StackRealignable;
75public:
76 TargetFrameLowering(StackDirection D, Align StackAl, int LAO,
77 Align TransAl = Align(1), bool StackReal = true)
78 : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
79 LocalAreaOffset(LAO), StackRealignable(StackReal) {}
80
81 virtual ~TargetFrameLowering();
82
83 // These methods return information that describes the abstract stack layout
84 // of the target machine.
85
86 /// getStackGrowthDirection - Return the direction the stack grows
87 ///
88 StackDirection getStackGrowthDirection() const { return StackDir; }
89
90 /// getStackAlignment - This method returns the number of bytes to which the
91 /// stack pointer must be aligned on entry to a function. Typically, this
92 /// is the largest alignment for any data object in the target.
93 ///
94 unsigned getStackAlignment() const { return StackAlignment.value(); }
95 /// getStackAlignment - This method returns the number of bytes to which the
96 /// stack pointer must be aligned on entry to a function. Typically, this
97 /// is the largest alignment for any data object in the target.
98 ///
99 Align getStackAlign() const { return StackAlignment; }
100
101 /// alignSPAdjust - This method aligns the stack adjustment to the correct
102 /// alignment.
103 ///
104 int alignSPAdjust(int SPAdj) const {
105 if (SPAdj < 0) {
106 SPAdj = -alignTo(-SPAdj, StackAlignment);
107 } else {
108 SPAdj = alignTo(SPAdj, StackAlignment);
109 }
110 return SPAdj;
111 }
112
113 /// getTransientStackAlignment - This method returns the number of bytes to
114 /// which the stack pointer must be aligned at all times, even between
115 /// calls.
116 ///
117 LLVM_ATTRIBUTE_DEPRECATED(unsigned getTransientStackAlignment() const,
118 "Use getTransientStackAlign instead") {
119 return TransientStackAlignment.value();
120 }
121 /// getTransientStackAlignment - This method returns the number of bytes to
122 /// which the stack pointer must be aligned at all times, even between
123 /// calls.
124 ///
125 Align getTransientStackAlign() const { return TransientStackAlignment; }
126
127 /// isStackRealignable - This method returns whether the stack can be
128 /// realigned.
129 bool isStackRealignable() const {
130 return StackRealignable;
131 }
132
133 /// Return the skew that has to be applied to stack alignment under
134 /// certain conditions (e.g. stack was adjusted before function \p MF
135 /// was called).
136 virtual unsigned getStackAlignmentSkew(const MachineFunction &MF) const;
137
138 /// This method returns whether or not it is safe for an object with the
139 /// given stack id to be bundled into the local area.
140 virtual bool isStackIdSafeForLocalArea(unsigned StackId) const {
141 return true;
142 }
143
144 /// getOffsetOfLocalArea - This method returns the offset of the local area
145 /// from the stack pointer on entrance to a function.
146 ///
147 int getOffsetOfLocalArea() const { return LocalAreaOffset; }
148
149 /// isFPCloseToIncomingSP - Return true if the frame pointer is close to
150 /// the incoming stack pointer, false if it is close to the post-prologue
151 /// stack pointer.
152 virtual bool isFPCloseToIncomingSP() const { return true; }
153
154 /// assignCalleeSavedSpillSlots - Allows target to override spill slot
155 /// assignment logic. If implemented, assignCalleeSavedSpillSlots() should
156 /// assign frame slots to all CSI entries and return true. If this method
157 /// returns false, spill slots will be assigned using generic implementation.
158 /// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
159 /// CSI.
160 virtual bool
161 assignCalleeSavedSpillSlots(MachineFunction &MF,
162 const TargetRegisterInfo *TRI,
163 std::vector<CalleeSavedInfo> &CSI) const {
164 return false;
165 }
166
167 /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
168 /// pairs, that contains an entry for each callee saved register that must be
169 /// spilled to a particular stack location if it is spilled.
170 ///
171 /// Each entry in this array contains a <register,offset> pair, indicating the
172 /// fixed offset from the incoming stack pointer that each register should be
173 /// spilled at. If a register is not listed here, the code generator is
174 /// allowed to spill it anywhere it chooses.
175 ///
176 virtual const SpillSlot *
177 getCalleeSavedSpillSlots(unsigned &NumEntries) const {
178 NumEntries = 0;
179 return nullptr;
180 }
181
182 /// targetHandlesStackFrameRounding - Returns true if the target is
183 /// responsible for rounding up the stack frame (probably at emitPrologue
184 /// time).
185 virtual bool targetHandlesStackFrameRounding() const {
186 return false;
187 }
188
189 /// Returns true if the target will correctly handle shrink wrapping.
190 virtual bool enableShrinkWrapping(const MachineFunction &MF) const {
191 return false;
192 }
193
194 /// Returns true if the stack slot holes in the fixed and callee-save stack
195 /// area should be used when allocating other stack locations to reduce stack
196 /// size.
197 virtual bool enableStackSlotScavenging(const MachineFunction &MF) const {
198 return false;
199 }
200
201 /// Returns true if the target can safely skip saving callee-saved registers
202 /// for noreturn nounwind functions.
203 virtual bool enableCalleeSaveSkip(const MachineFunction &MF) const;
204
205 /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
206 /// the function.
207 virtual void emitPrologue(MachineFunction &MF,
208 MachineBasicBlock &MBB) const = 0;
209 virtual void emitEpilogue(MachineFunction &MF,
210 MachineBasicBlock &MBB) const = 0;
211
212 /// With basic block sections, emit callee saved frame moves for basic blocks
213 /// that are in a different section.
214 virtual void
215 emitCalleeSavedFrameMoves(MachineBasicBlock &MBB,
216 MachineBasicBlock::iterator MBBI) const {}
217
218 virtual void emitCalleeSavedFrameMoves(MachineBasicBlock &MBB,
219 MachineBasicBlock::iterator MBBI,
220 const DebugLoc &DL,
221 bool IsPrologue) const {}
222
223 /// Replace a StackProbe stub (if any) with the actual probe code inline
224 virtual void inlineStackProbe(MachineFunction &MF,
225 MachineBasicBlock &PrologueMBB) const {}
226
227 /// Adjust the prologue to have the function use segmented stacks. This works
228 /// by adding a check even before the "normal" function prologue.
229 virtual void adjustForSegmentedStacks(MachineFunction &MF,
230 MachineBasicBlock &PrologueMBB) const {}
231
232 /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
233 /// the assembly prologue to explicitly handle the stack.
234 virtual void adjustForHiPEPrologue(MachineFunction &MF,
235 MachineBasicBlock &PrologueMBB) const {}
236
237 /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
238 /// saved registers and returns true if it isn't possible / profitable to do
239 /// so by issuing a series of store instructions via
240 /// storeRegToStackSlot(). Returns false otherwise.
241 virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
242 MachineBasicBlock::iterator MI,
243 ArrayRef<CalleeSavedInfo> CSI,
244 const TargetRegisterInfo *TRI) const {
245 return false;
246 }
247
248 /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
249 /// saved registers and returns true if it isn't possible / profitable to do
250 /// so by issuing a series of load instructions via loadRegToStackSlot().
251 /// If it returns true, and any of the registers in CSI is not restored,
252 /// it sets the corresponding Restored flag in CSI to false.
253 /// Returns false otherwise.
254 virtual bool
255 restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
256 MachineBasicBlock::iterator MI,
257 MutableArrayRef<CalleeSavedInfo> CSI,
258 const TargetRegisterInfo *TRI) const {
259 return false;
260 }
261
262 /// Return true if the target wants to keep the frame pointer regardless of
263 /// the function attribute "frame-pointer".
264 virtual bool keepFramePointer(const MachineFunction &MF) const {
265 return false;
266 }
267
268 /// hasFP - Return true if the specified function should have a dedicated
269 /// frame pointer register. For most targets this is true only if the function
270 /// has variable sized allocas or if frame pointer elimination is disabled.
271 virtual bool hasFP(const MachineFunction &MF) const = 0;
272
273 /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
274 /// not required, we reserve argument space for call sites in the function
275 /// immediately on entry to the current function. This eliminates the need for
276 /// add/sub sp brackets around call sites. Returns true if the call frame is
277 /// included as part of the stack frame.
278 virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
279 return !hasFP(MF);
280 }
281
282 /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
283 /// call frame pseudo ops before doing frame index elimination. This is
284 /// possible only when frame index references between the pseudos won't
285 /// need adjusting for the call frame adjustments. Normally, that's true
286 /// if the function has a reserved call frame or a frame pointer. Some
287 /// targets (Thumb2, for example) may have more complicated criteria,
288 /// however, and can override this behavior.
289 virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
290 return hasReservedCallFrame(MF) || hasFP(MF);
291 }
292
293 // needsFrameIndexResolution - Do we need to perform FI resolution for
294 // this function. Normally, this is required only when the function
295 // has any stack objects. However, targets may want to override this.
296 virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
297
298 /// getFrameIndexReference - This method should return the base register
299 /// and offset used to reference a frame index location. The offset is
300 /// returned directly, and the base register is returned via FrameReg.
301 virtual StackOffset getFrameIndexReference(const MachineFunction &MF, int FI,
302 Register &FrameReg) const;
303
304 /// Same as \c getFrameIndexReference, except that the stack pointer (as
305 /// opposed to the frame pointer) will be the preferred value for \p
306 /// FrameReg. This is generally used for emitting statepoint or EH tables that
307 /// use offsets from RSP. If \p IgnoreSPUpdates is true, the returned
308 /// offset is only guaranteed to be valid with respect to the value of SP at
309 /// the end of the prologue.
310 virtual StackOffset
311 getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI,
312 Register &FrameReg,
313 bool IgnoreSPUpdates) const {
314 // Always safe to dispatch to getFrameIndexReference.
315 return getFrameIndexReference(MF, FI, FrameReg);
316 }
317
318 /// getNonLocalFrameIndexReference - This method returns the offset used to
319 /// reference a frame index location. The offset can be from either FP/BP/SP
320 /// based on which base register is returned by llvm.localaddress.
321 virtual StackOffset getNonLocalFrameIndexReference(const MachineFunction &MF,
322 int FI) const {
323 // By default, dispatch to getFrameIndexReference. Interested targets can
324 // override this.
325 Register FrameReg;
326 return getFrameIndexReference(MF, FI, FrameReg);
327 }
328
329 /// Returns the callee-saved registers as computed by determineCalleeSaves
330 /// in the BitVector \p SavedRegs.
331 virtual void getCalleeSaves(const MachineFunction &MF,
332 BitVector &SavedRegs) const;
333
334 /// This method determines which of the registers reported by
335 /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved.
336 /// The default implementation checks populates the \p SavedRegs bitset with
337 /// all registers which are modified in the function, targets may override
338 /// this function to save additional registers.
339 /// This method also sets up the register scavenger ensuring there is a free
340 /// register or a frameindex available.
341 /// This method should not be called by any passes outside of PEI, because
342 /// it may change state passed in by \p MF and \p RS. The preferred
343 /// interface outside PEI is getCalleeSaves.
344 virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
345 RegScavenger *RS = nullptr) const;
346
347 /// processFunctionBeforeFrameFinalized - This method is called immediately
348 /// before the specified function's frame layout (MF.getFrameInfo()) is
349 /// finalized. Once the frame is finalized, MO_FrameIndex operands are
350 /// replaced with direct constants. This method is optional.
351 ///
352 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
353 RegScavenger *RS = nullptr) const {
354 }
355
356 /// processFunctionBeforeFrameIndicesReplaced - This method is called
357 /// immediately before MO_FrameIndex operands are eliminated, but after the
358 /// frame is finalized. This method is optional.
359 virtual void
360 processFunctionBeforeFrameIndicesReplaced(MachineFunction &MF,
361 RegScavenger *RS = nullptr) const {}
362
363 virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
364 report_fatal_error("WinEH not implemented for this target");
365 }
366
367 /// This method is called during prolog/epilog code insertion to eliminate
368 /// call frame setup and destroy pseudo instructions (but only if the Target
369 /// is using them). It is responsible for eliminating these instructions,
370 /// replacing them with concrete instructions. This method need only be
371 /// implemented if using call frame setup/destroy pseudo instructions.
372 /// Returns an iterator pointing to the instruction after the replaced one.
373 virtual MachineBasicBlock::iterator
374 eliminateCallFramePseudoInstr(MachineFunction &MF,
375 MachineBasicBlock &MBB,
376 MachineBasicBlock::iterator MI) const {
377 llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
378 "target!");
379 }
380
381
382 /// Order the symbols in the local stack frame.
383 /// The list of objects that we want to order is in \p objectsToAllocate as
384 /// indices into the MachineFrameInfo. The array can be reordered in any way
385 /// upon return. The contents of the array, however, may not be modified (i.e.
386 /// only their order may be changed).
387 /// By default, just maintain the original order.
388 virtual void
389 orderFrameObjects(const MachineFunction &MF,
390 SmallVectorImpl<int> &objectsToAllocate) const {
391 }
392
393 /// Check whether or not the given \p MBB can be used as a prologue
394 /// for the target.
395 /// The prologue will be inserted first in this basic block.
396 /// This method is used by the shrink-wrapping pass to decide if
397 /// \p MBB will be correctly handled by the target.
398 /// As soon as the target enable shrink-wrapping without overriding
399 /// this method, we assume that each basic block is a valid
400 /// prologue.
401 virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
402 return true;
403 }
404
405 /// Check whether or not the given \p MBB can be used as a epilogue
406 /// for the target.
407 /// The epilogue will be inserted before the first terminator of that block.
408 /// This method is used by the shrink-wrapping pass to decide if
409 /// \p MBB will be correctly handled by the target.
410 /// As soon as the target enable shrink-wrapping without overriding
411 /// this method, we assume that each basic block is a valid
412 /// epilogue.
413 virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
414 return true;
415 }
416
417 /// Returns the StackID that scalable vectors should be associated with.
418 virtual TargetStackID::Value getStackIDForScalableVectors() const {
419 return TargetStackID::Default;
420 }
421
422 virtual bool isSupportedStackID(TargetStackID::Value ID) const {
423 switch (ID) {
424 default:
425 return false;
426 case TargetStackID::Default:
427 case TargetStackID::NoAlloc:
428 return true;
429 }
430 }
431
432 /// Check if given function is safe for not having callee saved registers.
433 /// This is used when interprocedural register allocation is enabled.
434 static bool isSafeForNoCSROpt(const Function &F);
435
436 /// Check if the no-CSR optimisation is profitable for the given function.
437 virtual bool isProfitableForNoCSROpt(const Function &F) const {
438 return true;
439 }
440
441 /// Return initial CFA offset value i.e. the one valid at the beginning of the
442 /// function (before any stack operations).
443 virtual int getInitialCFAOffset(const MachineFunction &MF) const;
444
445 /// Return initial CFA register value i.e. the one valid at the beginning of
446 /// the function (before any stack operations).
447 virtual Register getInitialCFARegister(const MachineFunction &MF) const;
448
449 /// Return the frame base information to be encoded in the DWARF subprogram
450 /// debug info.
451 virtual DwarfFrameBase getDwarfFrameBase(const MachineFunction &MF) const;
452};
453
454} // End llvm namespace
455
456#endif
457