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 17 #include "llvm/CodeGen/MachineBasicBlock.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 /// 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. 34 class TargetFrameLowering { 35 public: 36 enum StackDirection { 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 121 assignCalleeSavedSpillSlots(MachineFunction &MF, 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 169 virtual void inlineStackProbe(MachineFunction &MF, 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. 174 virtual void adjustForSegmentedStacks(MachineFunction &MF, 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. 179 virtual void adjustForHiPEPrologue(MachineFunction &MF, 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. 186 virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB, 187 MachineBasicBlock::iterator MI, 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 /// If it returns true, and any of the registers in CSI is not restored, 197 /// it sets the corresponding Restored flag in CSI to false. 198 /// Returns false otherwise. 199 virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB, 200 MachineBasicBlock::iterator MI, 201 std::vector<CalleeSavedInfo> &CSI, 202 const TargetRegisterInfo *TRI) const { 203 return false; 204 } 205 206 /// Return true if the target needs to disable frame pointer elimination. 207 virtual bool noFramePointerElim(const MachineFunction &MF) const; 208 209 /// hasFP - Return true if the specified function should have a dedicated 210 /// frame pointer register. For most targets this is true only if the function 211 /// has variable sized allocas or if frame pointer elimination is disabled. 212 virtual bool hasFP(const MachineFunction &MF) const = 0; 213 214 /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is 215 /// not required, we reserve argument space for call sites in the function 216 /// immediately on entry to the current function. This eliminates the need for 217 /// add/sub sp brackets around call sites. Returns true if the call frame is 218 /// included as part of the stack frame. 219 virtual bool hasReservedCallFrame(const MachineFunction &MF) const { 220 return !hasFP(MF); 221 } 222 223 /// canSimplifyCallFramePseudos - When possible, it's best to simplify the 224 /// call frame pseudo ops before doing frame index elimination. This is 225 /// possible only when frame index references between the pseudos won't 226 /// need adjusting for the call frame adjustments. Normally, that's true 227 /// if the function has a reserved call frame or a frame pointer. Some 228 /// targets (Thumb2, for example) may have more complicated criteria, 229 /// however, and can override this behavior. 230 virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const { 231 return hasReservedCallFrame(MF) || hasFP(MF); 232 } 233 234 // needsFrameIndexResolution - Do we need to perform FI resolution for 235 // this function. Normally, this is required only when the function 236 // has any stack objects. However, targets may want to override this. 237 virtual bool needsFrameIndexResolution(const MachineFunction &MF) const; 238 239 /// getFrameIndexReference - This method should return the base register 240 /// and offset used to reference a frame index location. The offset is 241 /// returned directly, and the base register is returned via FrameReg. 242 virtual int getFrameIndexReference(const MachineFunction &MF, int FI, 243 unsigned &FrameReg) const; 244 245 /// Same as \c getFrameIndexReference, except that the stack pointer (as 246 /// opposed to the frame pointer) will be the preferred value for \p 247 /// FrameReg. This is generally used for emitting statepoint or EH tables that 248 /// use offsets from RSP. If \p IgnoreSPUpdates is true, the returned 249 /// offset is only guaranteed to be valid with respect to the value of SP at 250 /// the end of the prologue. 251 virtual int getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI, 252 unsigned &FrameReg, 253 bool IgnoreSPUpdates) const { 254 // Always safe to dispatch to getFrameIndexReference. 255 return getFrameIndexReference(MF, FI, FrameReg); 256 } 257 258 /// This method determines which of the registers reported by 259 /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved. 260 /// The default implementation checks populates the \p SavedRegs bitset with 261 /// all registers which are modified in the function, targets may override 262 /// this function to save additional registers. 263 /// This method also sets up the register scavenger ensuring there is a free 264 /// register or a frameindex available. 265 virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs, 266 RegScavenger *RS = nullptr) const; 267 268 /// processFunctionBeforeFrameFinalized - This method is called immediately 269 /// before the specified function's frame layout (MF.getFrameInfo()) is 270 /// finalized. Once the frame is finalized, MO_FrameIndex operands are 271 /// replaced with direct constants. This method is optional. 272 /// 273 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF, 274 RegScavenger *RS = nullptr) const { 275 } 276 277 virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const { 278 report_fatal_error("WinEH not implemented for this target"); 279 } 280 281 /// This method is called during prolog/epilog code insertion to eliminate 282 /// call frame setup and destroy pseudo instructions (but only if the Target 283 /// is using them). It is responsible for eliminating these instructions, 284 /// replacing them with concrete instructions. This method need only be 285 /// implemented if using call frame setup/destroy pseudo instructions. 286 /// Returns an iterator pointing to the instruction after the replaced one. 287 virtual MachineBasicBlock::iterator 288 eliminateCallFramePseudoInstr(MachineFunction &MF, 289 MachineBasicBlock &MBB, 290 MachineBasicBlock::iterator MI) const { 291 llvm_unreachable("Call Frame Pseudo Instructions do not exist on this " 292 "target!"); 293 } 294 295 296 /// Order the symbols in the local stack frame. 297 /// The list of objects that we want to order is in \p objectsToAllocate as 298 /// indices into the MachineFrameInfo. The array can be reordered in any way 299 /// upon return. The contents of the array, however, may not be modified (i.e. 300 /// only their order may be changed). 301 /// By default, just maintain the original order. 302 virtual void 303 orderFrameObjects(const MachineFunction &MF, 304 SmallVectorImpl<int> &objectsToAllocate) const { 305 } 306 307 /// Check whether or not the given \p MBB can be used as a prologue 308 /// for the target. 309 /// The prologue will be inserted first in this basic block. 310 /// This method is used by the shrink-wrapping pass to decide if 311 /// \p MBB will be correctly handled by the target. 312 /// As soon as the target enable shrink-wrapping without overriding 313 /// this method, we assume that each basic block is a valid 314 /// prologue. 315 virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const { 316 return true; 317 } 318 319 /// Check whether or not the given \p MBB can be used as a epilogue 320 /// for the target. 321 /// The epilogue will be inserted before the first terminator of that block. 322 /// This method is used by the shrink-wrapping pass to decide if 323 /// \p MBB will be correctly handled by the target. 324 /// As soon as the target enable shrink-wrapping without overriding 325 /// this method, we assume that each basic block is a valid 326 /// epilogue. 327 virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const { 328 return true; 329 } 330 331 /// Check if given function is safe for not having callee saved registers. 332 /// This is used when interprocedural register allocation is enabled. 333 static bool isSafeForNoCSROpt(const Function *F) { 334 if (!F->hasLocalLinkage() || F->hasAddressTaken() || 335 !F->hasFnAttribute(Attribute::NoRecurse)) 336 return false; 337 // Function should not be optimized as tail call. 338 for (const User *U : F->users()) 339 if (auto CS = ImmutableCallSite(U)) 340 if (CS.isTailCall()) 341 return false; 342 return true; 343 } 344 }; 345 346 } // End llvm namespace 347 348 #endif 349