1 //===-- llvm/Target/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_TARGET_TARGETFRAMELOWERING_H
15 #define LLVM_TARGET_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 /// getTransientStackAlignment - This method returns the number of bytes to
74 /// which the stack pointer must be aligned at all times, even between
77 unsigned getTransientStackAlignment() const {
78 return TransientStackAlignment;
81 /// isStackRealignable - This method returns whether the stack can be
83 bool isStackRealignable() const {
84 return StackRealignable;
87 /// getOffsetOfLocalArea - This method returns the offset of the local area
88 /// from the stack pointer on entrance to a function.
90 int getOffsetOfLocalArea() const { return LocalAreaOffset; }
92 /// isFPCloseToIncomingSP - Return true if the frame pointer is close to
93 /// the incoming stack pointer, false if it is close to the post-prologue
95 virtual bool isFPCloseToIncomingSP() const { return true; }
97 /// assignCalleeSavedSpillSlots - Allows target to override spill slot
98 /// assignment logic. If implemented, assignCalleeSavedSpillSlots() should
99 /// assign frame slots to all CSI entries and return true. If this method
100 /// returns false, spill slots will be assigned using generic implementation.
101 /// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
104 assignCalleeSavedSpillSlots(MachineFunction &MF,
105 const TargetRegisterInfo *TRI,
106 std::vector<CalleeSavedInfo> &CSI) const {
110 /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
111 /// pairs, that contains an entry for each callee saved register that must be
112 /// spilled to a particular stack location if it is spilled.
114 /// Each entry in this array contains a <register,offset> pair, indicating the
115 /// fixed offset from the incoming stack pointer that each register should be
116 /// spilled at. If a register is not listed here, the code generator is
117 /// allowed to spill it anywhere it chooses.
119 virtual const SpillSlot *
120 getCalleeSavedSpillSlots(unsigned &NumEntries) const {
125 /// targetHandlesStackFrameRounding - Returns true if the target is
126 /// responsible for rounding up the stack frame (probably at emitPrologue
128 virtual bool targetHandlesStackFrameRounding() const {
132 /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
134 virtual void emitPrologue(MachineFunction &MF,
135 MachineBasicBlock &MBB) const = 0;
136 virtual void emitEpilogue(MachineFunction &MF,
137 MachineBasicBlock &MBB) const = 0;
139 /// Adjust the prologue to have the function use segmented stacks. This works
140 /// by adding a check even before the "normal" function prologue.
141 virtual void adjustForSegmentedStacks(MachineFunction &MF,
142 MachineBasicBlock &PrologueMBB) const {}
144 /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
145 /// the assembly prologue to explicitly handle the stack.
146 virtual void adjustForHiPEPrologue(MachineFunction &MF,
147 MachineBasicBlock &PrologueMBB) const {}
149 /// Adjust the prologue to add an allocation at a fixed offset from the frame
152 adjustForFrameAllocatePrologue(MachineFunction &MF,
153 MachineBasicBlock &PrologueMBB) const {}
155 /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
156 /// saved registers and returns true if it isn't possible / profitable to do
157 /// so by issuing a series of store instructions via
158 /// storeRegToStackSlot(). Returns false otherwise.
159 virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
160 MachineBasicBlock::iterator MI,
161 const std::vector<CalleeSavedInfo> &CSI,
162 const TargetRegisterInfo *TRI) const {
166 /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
167 /// saved registers and returns true if it isn't possible / profitable to do
168 /// so by issuing a series of load instructions via loadRegToStackSlot().
169 /// Returns false otherwise.
170 virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
171 MachineBasicBlock::iterator MI,
172 const std::vector<CalleeSavedInfo> &CSI,
173 const TargetRegisterInfo *TRI) const {
177 /// Return true if the target needs to disable frame pointer elimination.
178 virtual bool noFramePointerElim(const MachineFunction &MF) const;
180 /// hasFP - Return true if the specified function should have a dedicated
181 /// frame pointer register. For most targets this is true only if the function
182 /// has variable sized allocas or if frame pointer elimination is disabled.
183 virtual bool hasFP(const MachineFunction &MF) const = 0;
185 /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
186 /// not required, we reserve argument space for call sites in the function
187 /// immediately on entry to the current function. This eliminates the need for
188 /// add/sub sp brackets around call sites. Returns true if the call frame is
189 /// included as part of the stack frame.
190 virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
194 /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
195 /// call frame pseudo ops before doing frame index elimination. This is
196 /// possible only when frame index references between the pseudos won't
197 /// need adjusting for the call frame adjustments. Normally, that's true
198 /// if the function has a reserved call frame or a frame pointer. Some
199 /// targets (Thumb2, for example) may have more complicated criteria,
200 /// however, and can override this behavior.
201 virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
202 return hasReservedCallFrame(MF) || hasFP(MF);
205 // needsFrameIndexResolution - Do we need to perform FI resolution for
206 // this function. Normally, this is required only when the function
207 // has any stack objects. However, targets may want to override this.
208 virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
210 /// getFrameIndexOffset - Returns the displacement from the frame register to
211 /// the stack frame of the specified index.
212 virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;
214 /// getFrameIndexReference - This method should return the base register
215 /// and offset used to reference a frame index location. The offset is
216 /// returned directly, and the base register is returned via FrameReg.
217 virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
218 unsigned &FrameReg) const;
220 /// Same as above, except that the 'base register' will always be RSP, not
221 /// RBP on x86. This is used exclusively for lowering STATEPOINT nodes.
222 /// TODO: This should really be a parameterizable choice.
223 virtual int getFrameIndexReferenceFromSP(const MachineFunction &MF, int FI,
224 unsigned &FrameReg) const {
225 // default to calling normal version, we override this on x86 only
226 llvm_unreachable("unimplemented for non-x86");
230 /// This method determines which of the registers reported by
231 /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved.
232 /// The default implementation checks populates the \p SavedRegs bitset with
233 /// all registers which are modified in the function, targets may override
234 /// this function to save additional registers.
235 /// This method also sets up the register scavenger ensuring there is a free
236 /// register or a frameindex available.
237 virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
238 RegScavenger *RS = nullptr) const;
240 /// processFunctionBeforeFrameFinalized - This method is called immediately
241 /// before the specified function's frame layout (MF.getFrameInfo()) is
242 /// finalized. Once the frame is finalized, MO_FrameIndex operands are
243 /// replaced with direct constants. This method is optional.
245 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
246 RegScavenger *RS = nullptr) const {
249 /// eliminateCallFramePseudoInstr - This method is called during prolog/epilog
250 /// code insertion to eliminate call frame setup and destroy pseudo
251 /// instructions (but only if the Target is using them). It is responsible
252 /// for eliminating these instructions, replacing them with concrete
253 /// instructions. This method need only be implemented if using call frame
254 /// setup/destroy pseudo instructions.
257 eliminateCallFramePseudoInstr(MachineFunction &MF,
258 MachineBasicBlock &MBB,
259 MachineBasicBlock::iterator MI) const {
260 llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
264 /// Check whether or not the given \p MBB can be used as a prologue
266 /// The prologue will be inserted first in this basic block.
267 /// This method is used by the shrink-wrapping pass to decide if
268 /// \p MBB will be correctly handled by the target.
269 /// As soon as the target enable shrink-wrapping without overriding
270 /// this method, we assume that each basic block is a valid
272 virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
276 /// Check whether or not the given \p MBB can be used as a epilogue
278 /// The epilogue will be inserted before the first terminator of that block.
279 /// This method is used by the shrink-wrapping pass to decide if
280 /// \p MBB will be correctly handled by the target.
281 /// As soon as the target enable shrink-wrapping without overriding
282 /// this method, we assume that each basic block is a valid
284 virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
289 } // End llvm namespace