1 //===-- llvm/CodeGen/TargetFrameLowering.h ----------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Interface to describe the layout of a stack frame on the target machine.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_CODEGEN_TARGETFRAMELOWERING_H
15 #define LLVM_CODEGEN_TARGETFRAMELOWERING_H
17 #include "llvm/CodeGen/MachineBasicBlock.h"
23 class CalleeSavedInfo;
24 class MachineFunction;
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.
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.
34 class TargetFrameLowering {
37 StackGrowsUp, // Adding to the stack increases the stack address
38 StackGrowsDown // Adding to the stack decreases the stack address
41 // Maps a callee saved register to a stack slot with a fixed offset.
44 int Offset; // Offset relative to stack pointer on function entry.
47 StackDirection StackDir;
48 unsigned StackAlignment;
49 unsigned TransientStackAlignment;
51 bool StackRealignable;
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) {}
58 virtual ~TargetFrameLowering();
60 // These methods return information that describes the abstract stack layout
61 // of the target machine.
63 /// getStackGrowthDirection - Return the direction the stack grows
65 StackDirection getStackGrowthDirection() const { return StackDir; }
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.
71 unsigned getStackAlignment() const { return StackAlignment; }
73 /// alignSPAdjust - This method aligns the stack adjustment to the correct
76 int alignSPAdjust(int SPAdj) const {
78 SPAdj = -alignTo(-SPAdj, StackAlignment);
80 SPAdj = alignTo(SPAdj, StackAlignment);
85 /// getTransientStackAlignment - This method returns the number of bytes to
86 /// which the stack pointer must be aligned at all times, even between
89 unsigned getTransientStackAlignment() const {
90 return TransientStackAlignment;
93 /// isStackRealignable - This method returns whether the stack can be
95 bool isStackRealignable() const {
96 return StackRealignable;
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
102 virtual unsigned getStackAlignmentSkew(const MachineFunction &MF) const;
104 /// getOffsetOfLocalArea - This method returns the offset of the local area
105 /// from the stack pointer on entrance to a function.
107 int getOffsetOfLocalArea() const { return LocalAreaOffset; }
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
112 virtual bool isFPCloseToIncomingSP() const { return true; }
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
121 assignCalleeSavedSpillSlots(MachineFunction &MF,
122 const TargetRegisterInfo *TRI,
123 std::vector<CalleeSavedInfo> &CSI) const {
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.
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.
136 virtual const SpillSlot *
137 getCalleeSavedSpillSlots(unsigned &NumEntries) const {
142 /// targetHandlesStackFrameRounding - Returns true if the target is
143 /// responsible for rounding up the stack frame (probably at emitPrologue
145 virtual bool targetHandlesStackFrameRounding() const {
149 /// Returns true if the target will correctly handle shrink wrapping.
150 virtual bool enableShrinkWrapping(const MachineFunction &MF) const {
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
157 virtual bool enableStackSlotScavenging(const MachineFunction &MF) const {
161 /// Returns true if the target can safely skip saving callee-saved registers
162 /// for noreturn nounwind functions.
163 virtual bool enableCalleeSaveSkip(const MachineFunction &MF) const;
165 /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
167 virtual void emitPrologue(MachineFunction &MF,
168 MachineBasicBlock &MBB) const = 0;
169 virtual void emitEpilogue(MachineFunction &MF,
170 MachineBasicBlock &MBB) const = 0;
172 /// Replace a StackProbe stub (if any) with the actual probe code inline
173 virtual void inlineStackProbe(MachineFunction &MF,
174 MachineBasicBlock &PrologueMBB) const {}
176 /// Adjust the prologue to have the function use segmented stacks. This works
177 /// by adding a check even before the "normal" function prologue.
178 virtual void adjustForSegmentedStacks(MachineFunction &MF,
179 MachineBasicBlock &PrologueMBB) const {}
181 /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
182 /// the assembly prologue to explicitly handle the stack.
183 virtual void adjustForHiPEPrologue(MachineFunction &MF,
184 MachineBasicBlock &PrologueMBB) const {}
186 /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
187 /// saved registers and returns true if it isn't possible / profitable to do
188 /// so by issuing a series of store instructions via
189 /// storeRegToStackSlot(). Returns false otherwise.
190 virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
191 MachineBasicBlock::iterator MI,
192 const std::vector<CalleeSavedInfo> &CSI,
193 const TargetRegisterInfo *TRI) const {
197 /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
198 /// saved registers and returns true if it isn't possible / profitable to do
199 /// so by issuing a series of load instructions via loadRegToStackSlot().
200 /// If it returns true, and any of the registers in CSI is not restored,
201 /// it sets the corresponding Restored flag in CSI to false.
202 /// Returns false otherwise.
203 virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
204 MachineBasicBlock::iterator MI,
205 std::vector<CalleeSavedInfo> &CSI,
206 const TargetRegisterInfo *TRI) const {
210 /// Return true if the target needs to disable frame pointer elimination.
211 virtual bool noFramePointerElim(const MachineFunction &MF) const;
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;
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 {
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);
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;
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;
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,
257 bool IgnoreSPUpdates) const {
258 // Always safe to dispatch to getFrameIndexReference.
259 return getFrameIndexReference(MF, FI, FrameReg);
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;
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.
277 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
278 RegScavenger *RS = nullptr) const {
281 virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
282 report_fatal_error("WinEH not implemented for this target");
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 "
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.
307 orderFrameObjects(const MachineFunction &MF,
308 SmallVectorImpl<int> &objectsToAllocate) const {
311 /// Check whether or not the given \p MBB can be used as a prologue
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
319 virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
323 /// Check whether or not the given \p MBB can be used as a epilogue
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
331 virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
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))
341 // Function should not be optimized as tail call.
342 for (const User *U : F.users())
343 if (auto CS = ImmutableCallSite(U))
349 /// Return initial CFA offset value i.e. the one valid at the beginning of the
350 /// function (before any stack operations).
351 virtual int getInitialCFAOffset(const MachineFunction &MF) const;
353 /// Return initial CFA register value i.e. the one valid at the beginning of
354 /// the function (before any stack operations).
355 virtual unsigned getInitialCFARegister(const MachineFunction &MF) const;
358 } // End llvm namespace