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 21namespace 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. 34class TargetFrameLowering { 35public: 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 }; 46private: 47 StackDirection StackDir; 48 unsigned StackAlignment; 49 unsigned TransientStackAlignment; 50 int LocalAreaOffset; 51 bool StackRealignable; 52public: 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 /// Adjust the prologue to add an allocation at a fixed offset from the frame 183 /// pointer. 184 virtual void 185 adjustForFrameAllocatePrologue(MachineFunction &MF, 186 MachineBasicBlock &PrologueMBB) const {} 187 188 /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee 189 /// saved registers and returns true if it isn't possible / profitable to do 190 /// so by issuing a series of store instructions via 191 /// storeRegToStackSlot(). Returns false otherwise. 192 virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB, 193 MachineBasicBlock::iterator MI, 194 const std::vector<CalleeSavedInfo> &CSI, 195 const TargetRegisterInfo *TRI) const { 196 return false; 197 } 198 199 /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee 200 /// saved registers and returns true if it isn't possible / profitable to do 201 /// so by issuing a series of load instructions via loadRegToStackSlot(). 202 /// Returns false otherwise. 203 virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB, 204 MachineBasicBlock::iterator MI, 205 const std::vector<CalleeSavedInfo> &CSI, 206 const TargetRegisterInfo *TRI) const { 207 return false; 208 } 209 210 /// Return true if the target needs to disable frame pointer elimination. 211 virtual bool noFramePointerElim(const MachineFunction &MF) const; 212 213 /// 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; 217 218 /// 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 { 224 return !hasFP(MF); 225 } 226 227 /// 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); 236 } 237 238 // 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; 242 243 /// 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; 248 249 /// 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, 256 unsigned &FrameReg, 257 bool IgnoreSPUpdates) const { 258 // Always safe to dispatch to getFrameIndexReference. 259 return getFrameIndexReference(MF, FI, FrameReg); 260 } 261 262 /// 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; 271 272 /// 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. 276 /// 277 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF, 278 RegScavenger *RS = nullptr) const { 279 } 280 281 virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const { 282 report_fatal_error("WinEH not implemented for this target"); 283 } 284 285 /// 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 " 296 "target!"); 297 } 298 299 300 /// 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. 306 virtual void 307 orderFrameObjects(const MachineFunction &MF, 308 SmallVectorImpl<int> &objectsToAllocate) const { 309 } 310 311 /// Check whether or not the given \p MBB can be used as a prologue 312 /// for the target. 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 318 /// prologue. 319 virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const { 320 return true; 321 } 322 323 /// Check whether or not the given \p MBB can be used as a epilogue 324 /// for the target. 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 330 /// epilogue. 331 virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const { 332 return true; 333 } 334 335 /// 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)) 340 return false; 341 // Function should not be optimized as tail call. 342 for (const User *U : F->users()) 343 if (auto CS = ImmutableCallSite(U)) 344 if (CS.isTailCall()) 345 return false; 346 return true; 347 } 348}; 349 350} // End llvm namespace 351 352#endif 353