src/llvm/include/llvm/Target/TargetFrameLowering.h

   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 CalleeSavedInfo;
  23   class MachineFunction;
  24   class RegScavenger;
  25
  26 /// Information about stack frame layout on the target.  It holds the direction
  27 /// of stack growth, the known stack alignment on entry to each function, and
  28 /// the offset to the locals area.
  29 ///
  30 /// The offset to the local area is the offset from the stack pointer on
  31 /// function entry to the first location where function data (local variables,
  32 /// spill locations) can be stored.
  33 class TargetFrameLowering {
  34 public:
  35   enum StackDirection {
  36     StackGrowsUp,        // Adding to the stack increases the stack address
  37     StackGrowsDown       // Adding to the stack decreases the stack address
  38   };
  39
  40   // Maps a callee saved register to a stack slot with a fixed offset.
  41   struct SpillSlot {
  42     unsigned Reg;
  43     int Offset; // Offset relative to stack pointer on function entry.
  44   };
  45 private:
  46   StackDirection StackDir;
  47   unsigned StackAlignment;
  48   unsigned TransientStackAlignment;
  49   int LocalAreaOffset;
  50   bool StackRealignable;
  51 public:
  52   TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
  53                       unsigned TransAl = 1, bool StackReal = true)
  54     : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
  55       LocalAreaOffset(LAO), StackRealignable(StackReal) {}
  56
  57   virtual ~TargetFrameLowering();
  58
  59   // These methods return information that describes the abstract stack layout
  60   // of the target machine.
  61
  62   /// getStackGrowthDirection - Return the direction the stack grows
  63   ///
  64   StackDirection getStackGrowthDirection() const { return StackDir; }
  65
  66   /// getStackAlignment - This method returns the number of bytes to which the
  67   /// stack pointer must be aligned on entry to a function.  Typically, this
  68   /// is the largest alignment for any data object in the target.
  69   ///
  70   unsigned getStackAlignment() const { return StackAlignment; }
  71
  72   /// getTransientStackAlignment - This method returns the number of bytes to
  73   /// which the stack pointer must be aligned at all times, even between
  74   /// calls.
  75   ///
  76   unsigned getTransientStackAlignment() const {
  77     return TransientStackAlignment;
  78   }
  79
  80   /// isStackRealignable - This method returns whether the stack can be
  81   /// realigned.
  82   bool isStackRealignable() const {
  83     return StackRealignable;
  84   }
  85
  86   /// getOffsetOfLocalArea - This method returns the offset of the local area
  87   /// from the stack pointer on entrance to a function.
  88   ///
  89   int getOffsetOfLocalArea() const { return LocalAreaOffset; }
  90
  91   /// isFPCloseToIncomingSP - Return true if the frame pointer is close to
  92   /// the incoming stack pointer, false if it is close to the post-prologue
  93   /// stack pointer.
  94   virtual bool isFPCloseToIncomingSP() const { return true; }
  95
  96   /// assignCalleeSavedSpillSlots - Allows target to override spill slot
  97   /// assignment logic.  If implemented, assignCalleeSavedSpillSlots() should
  98   /// assign frame slots to all CSI entries and return true.  If this method
  99   /// returns false, spill slots will be assigned using generic implementation.
 100   /// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
 101   /// CSI.
 102   virtual bool
 103   assignCalleeSavedSpillSlots(MachineFunction &MF,
 104                               const TargetRegisterInfo *TRI,
 105                               std::vector<CalleeSavedInfo> &CSI) const {
 106     return false;
 107   }
 108
 109   /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
 110   /// pairs, that contains an entry for each callee saved register that must be
 111   /// spilled to a particular stack location if it is spilled.
 112   ///
 113   /// Each entry in this array contains a <register,offset> pair, indicating the
 114   /// fixed offset from the incoming stack pointer that each register should be
 115   /// spilled at. If a register is not listed here, the code generator is
 116   /// allowed to spill it anywhere it chooses.
 117   ///
 118   virtual const SpillSlot *
 119   getCalleeSavedSpillSlots(unsigned &NumEntries) const {
 120     NumEntries = 0;
 121     return nullptr;
 122   }
 123
 124   /// targetHandlesStackFrameRounding - Returns true if the target is
 125   /// responsible for rounding up the stack frame (probably at emitPrologue
 126   /// time).
 127   virtual bool targetHandlesStackFrameRounding() const {
 128     return false;
 129   }
 130
 131   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
 132   /// the function.
 133   virtual void emitPrologue(MachineFunction &MF) const = 0;
 134   virtual void emitEpilogue(MachineFunction &MF,
 135                             MachineBasicBlock &MBB) const = 0;
 136
 137   /// Adjust the prologue to have the function use segmented stacks. This works
 138   /// by adding a check even before the "normal" function prologue.
 139   virtual void adjustForSegmentedStacks(MachineFunction &MF) const { }
 140
 141   /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
 142   /// the assembly prologue to explicitly handle the stack.
 143   virtual void adjustForHiPEPrologue(MachineFunction &MF) const { }
 144
 145   /// Adjust the prologue to add an allocation at a fixed offset from the frame
 146   /// pointer.
 147   virtual void adjustForFrameAllocatePrologue(MachineFunction &MF) const { }
 148
 149   /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
 150   /// saved registers and returns true if it isn't possible / profitable to do
 151   /// so by issuing a series of store instructions via
 152   /// storeRegToStackSlot(). Returns false otherwise.
 153   virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
 154                                          MachineBasicBlock::iterator MI,
 155                                         const std::vector<CalleeSavedInfo> &CSI,
 156                                          const TargetRegisterInfo *TRI) const {
 157     return false;
 158   }
 159
 160   /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
 161   /// saved registers and returns true if it isn't possible / profitable to do
 162   /// so by issuing a series of load instructions via loadRegToStackSlot().
 163   /// Returns false otherwise.
 164   virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
 165                                            MachineBasicBlock::iterator MI,
 166                                         const std::vector<CalleeSavedInfo> &CSI,
 167                                         const TargetRegisterInfo *TRI) const {
 168     return false;
 169   }
 170
 171   /// hasFP - Return true if the specified function should have a dedicated
 172   /// frame pointer register. For most targets this is true only if the function
 173   /// has variable sized allocas or if frame pointer elimination is disabled.
 174   virtual bool hasFP(const MachineFunction &MF) const = 0;
 175
 176   /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
 177   /// not required, we reserve argument space for call sites in the function
 178   /// immediately on entry to the current function. This eliminates the need for
 179   /// add/sub sp brackets around call sites. Returns true if the call frame is
 180   /// included as part of the stack frame.
 181   virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
 182     return !hasFP(MF);
 183   }
 184
 185   /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
 186   /// call frame pseudo ops before doing frame index elimination. This is
 187   /// possible only when frame index references between the pseudos won't
 188   /// need adjusting for the call frame adjustments. Normally, that's true
 189   /// if the function has a reserved call frame or a frame pointer. Some
 190   /// targets (Thumb2, for example) may have more complicated criteria,
 191   /// however, and can override this behavior.
 192   virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
 193     return hasReservedCallFrame(MF) || hasFP(MF);
 194   }
 195
 196   /// getFrameIndexOffset - Returns the displacement from the frame register to
 197   /// the stack frame of the specified index.
 198   virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;
 199
 200   /// getFrameIndexReference - This method should return the base register
 201   /// and offset used to reference a frame index location. The offset is
 202   /// returned directly, and the base register is returned via FrameReg.
 203   virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
 204                                      unsigned &FrameReg) const;
 205
 206   /// Same as above, except that the 'base register' will always be RSP, not
 207   /// RBP on x86.  This is used exclusively for lowering STATEPOINT nodes.
 208   /// TODO: This should really be a parameterizable choice.
 209   virtual int getFrameIndexReferenceFromSP(const MachineFunction &MF, int FI,
 210                                           unsigned &FrameReg) const {
 211     // default to calling normal version, we override this on x86 only
 212     llvm_unreachable("unimplemented for non-x86");
 213     return 0;
 214   }
 215
 216   /// processFunctionBeforeCalleeSavedScan - This method is called immediately
 217   /// before PrologEpilogInserter scans the physical registers used to determine
 218   /// what callee saved registers should be spilled. This method is optional.
 219   virtual void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
 220                                              RegScavenger *RS = nullptr) const {
 221
 222   }
 223
 224   /// processFunctionBeforeFrameFinalized - This method is called immediately
 225   /// before the specified function's frame layout (MF.getFrameInfo()) is
 226   /// finalized.  Once the frame is finalized, MO_FrameIndex operands are
 227   /// replaced with direct constants.  This method is optional.
 228   ///
 229   virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
 230                                              RegScavenger *RS = nullptr) const {
 231   }
 232
 233   /// eliminateCallFramePseudoInstr - This method is called during prolog/epilog
 234   /// code insertion to eliminate call frame setup and destroy pseudo
 235   /// instructions (but only if the Target is using them).  It is responsible
 236   /// for eliminating these instructions, replacing them with concrete
 237   /// instructions.  This method need only be implemented if using call frame
 238   /// setup/destroy pseudo instructions.
 239   ///
 240   virtual void
 241   eliminateCallFramePseudoInstr(MachineFunction &MF,
 242                                 MachineBasicBlock &MBB,
 243                                 MachineBasicBlock::iterator MI) const {
 244     llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
 245                      "target!");
 246   }
 247 };
 248
 249 } // End llvm namespace
 250
 251 #endif