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 = -RoundUpToAlignment(-SPAdj, StackAlignment); 79 } else { 80 SPAdj = RoundUpToAlignment(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 /// emitProlog/emitEpilog - These methods insert prolog and epilog code into 155 /// the function. 156 virtual void emitPrologue(MachineFunction &MF, 157 MachineBasicBlock &MBB) const = 0; 158 virtual void emitEpilogue(MachineFunction &MF, 159 MachineBasicBlock &MBB) const = 0; 160 161 /// Replace a StackProbe stub (if any) with the actual probe code inline 162 virtual void inlineStackProbe(MachineFunction &MF, 163 MachineBasicBlock &PrologueMBB) const {} 164 165 /// Adjust the prologue to have the function use segmented stacks. This works 166 /// by adding a check even before the "normal" function prologue. 167 virtual void adjustForSegmentedStacks(MachineFunction &MF, 168 MachineBasicBlock &PrologueMBB) const {} 169 170 /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in 171 /// the assembly prologue to explicitly handle the stack. 172 virtual void adjustForHiPEPrologue(MachineFunction &MF, 173 MachineBasicBlock &PrologueMBB) const {} 174 175 /// Adjust the prologue to add an allocation at a fixed offset from the frame 176 /// pointer. 177 virtual void 178 adjustForFrameAllocatePrologue(MachineFunction &MF, 179 MachineBasicBlock &PrologueMBB) const {} 180 181 /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee 182 /// saved registers and returns true if it isn't possible / profitable to do 183 /// so by issuing a series of store instructions via 184 /// storeRegToStackSlot(). Returns false otherwise. 185 virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB, 186 MachineBasicBlock::iterator MI, 187 const std::vector<CalleeSavedInfo> &CSI, 188 const TargetRegisterInfo *TRI) const { 189 return false; 190 } 191 192 /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee 193 /// saved registers and returns true if it isn't possible / profitable to do 194 /// so by issuing a series of load instructions via loadRegToStackSlot(). 195 /// Returns false otherwise. 196 virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB, 197 MachineBasicBlock::iterator MI, 198 const std::vector<CalleeSavedInfo> &CSI, 199 const TargetRegisterInfo *TRI) const { 200 return false; 201 } 202 203 /// Return true if the target needs to disable frame pointer elimination. 204 virtual bool noFramePointerElim(const MachineFunction &MF) const; 205 206 /// hasFP - Return true if the specified function should have a dedicated 207 /// frame pointer register. For most targets this is true only if the function 208 /// has variable sized allocas or if frame pointer elimination is disabled. 209 virtual bool hasFP(const MachineFunction &MF) const = 0; 210 211 /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is 212 /// not required, we reserve argument space for call sites in the function 213 /// immediately on entry to the current function. This eliminates the need for 214 /// add/sub sp brackets around call sites. Returns true if the call frame is 215 /// included as part of the stack frame. 216 virtual bool hasReservedCallFrame(const MachineFunction &MF) const { 217 return !hasFP(MF); 218 } 219 220 /// canSimplifyCallFramePseudos - When possible, it's best to simplify the 221 /// call frame pseudo ops before doing frame index elimination. This is 222 /// possible only when frame index references between the pseudos won't 223 /// need adjusting for the call frame adjustments. Normally, that's true 224 /// if the function has a reserved call frame or a frame pointer. Some 225 /// targets (Thumb2, for example) may have more complicated criteria, 226 /// however, and can override this behavior. 227 virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const { 228 return hasReservedCallFrame(MF) || hasFP(MF); 229 } 230 231 // needsFrameIndexResolution - Do we need to perform FI resolution for 232 // this function. Normally, this is required only when the function 233 // has any stack objects. However, targets may want to override this. 234 virtual bool needsFrameIndexResolution(const MachineFunction &MF) const; 235 236 /// getFrameIndexReference - This method should return the base register 237 /// and offset used to reference a frame index location. The offset is 238 /// returned directly, and the base register is returned via FrameReg. 239 virtual int getFrameIndexReference(const MachineFunction &MF, int FI, 240 unsigned &FrameReg) const; 241 242 /// Same as above, except that the 'base register' will always be RSP, not 243 /// RBP on x86. This is generally used for emitting statepoint or EH tables 244 /// that use offsets from RSP. 245 /// TODO: This should really be a parameterizable choice. 246 virtual int getFrameIndexReferenceFromSP(const MachineFunction &MF, int FI, 247 unsigned &FrameReg) const { 248 // default to calling normal version, we override this on x86 only 249 llvm_unreachable("unimplemented for non-x86"); 250 return 0; 251 } 252 253 /// This method determines which of the registers reported by 254 /// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved. 255 /// The default implementation checks populates the \p SavedRegs bitset with 256 /// all registers which are modified in the function, targets may override 257 /// this function to save additional registers. 258 /// This method also sets up the register scavenger ensuring there is a free 259 /// register or a frameindex available. 260 virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs, 261 RegScavenger *RS = nullptr) const; 262 263 /// processFunctionBeforeFrameFinalized - This method is called immediately 264 /// before the specified function's frame layout (MF.getFrameInfo()) is 265 /// finalized. Once the frame is finalized, MO_FrameIndex operands are 266 /// replaced with direct constants. This method is optional. 267 /// 268 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF, 269 RegScavenger *RS = nullptr) const { 270 } 271 272 virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const { 273 report_fatal_error("WinEH not implemented for this target"); 274 } 275 276 /// eliminateCallFramePseudoInstr - This method is called during prolog/epilog 277 /// code insertion to eliminate call frame setup and destroy pseudo 278 /// instructions (but only if the Target is using them). It is responsible 279 /// for eliminating these instructions, replacing them with concrete 280 /// instructions. This method need only be implemented if using call frame 281 /// setup/destroy pseudo instructions. 282 /// 283 virtual void 284 eliminateCallFramePseudoInstr(MachineFunction &MF, 285 MachineBasicBlock &MBB, 286 MachineBasicBlock::iterator MI) const { 287 llvm_unreachable("Call Frame Pseudo Instructions do not exist on this " 288 "target!"); 289 } 290 291 /// Check whether or not the given \p MBB can be used as a prologue 292 /// for the target. 293 /// The prologue will be inserted first in this basic block. 294 /// This method is used by the shrink-wrapping pass to decide if 295 /// \p MBB will be correctly handled by the target. 296 /// As soon as the target enable shrink-wrapping without overriding 297 /// this method, we assume that each basic block is a valid 298 /// prologue. 299 virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const { 300 return true; 301 } 302 303 /// Check whether or not the given \p MBB can be used as a epilogue 304 /// for the target. 305 /// The epilogue will be inserted before the first terminator of that block. 306 /// This method is used by the shrink-wrapping pass to decide if 307 /// \p MBB will be correctly handled by the target. 308 /// As soon as the target enable shrink-wrapping without overriding 309 /// this method, we assume that each basic block is a valid 310 /// epilogue. 311 virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const { 312 return true; 313 } 314 }; 315 316 } // End llvm namespace 317 318 #endif 319
