Home | History | Annotate | Download | only in Target 
      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 "llvm/MC/MCDwarf.h"
     19 #include "llvm/ADT/ArrayRef.h"
     20 
     21 #include <utility>
     22 #include <vector>
     23 
     24 namespace llvm {
     25   class CalleeSavedInfo;
     26   class MachineFunction;
     27   class MachineBasicBlock;
     28   class MachineMove;
     29   class RegScavenger;
     30 
     31 /// Information about stack frame layout on the target.  It holds the direction
     32 /// of stack growth, the known stack alignment on entry to each function, and
     33 /// the offset to the locals area.
     34 ///
     35 /// The offset to the local area is the offset from the stack pointer on
     36 /// function entry to the first location where function data (local variables,
     37 /// spill locations) can be stored.
     38 class TargetFrameLowering {
     39 public:
     40   enum StackDirection {
     41     StackGrowsUp,        // Adding to the stack increases the stack address
     42     StackGrowsDown       // Adding to the stack decreases the stack address
     43   };
     44 
     45   // Maps a callee saved register to a stack slot with a fixed offset.
     46   struct SpillSlot {
     47     unsigned Reg;
     48     int Offset; // Offset relative to stack pointer on function entry.
     49   };
     50 private:
     51   StackDirection StackDir;
     52   unsigned StackAlignment;
     53   unsigned TransientStackAlignment;
     54   int LocalAreaOffset;
     55 public:
     56   TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
     57                       unsigned TransAl = 1)
     58     : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
     59       LocalAreaOffset(LAO) {}
     60 
     61   virtual ~TargetFrameLowering();
     62 
     63   // These methods return information that describes the abstract stack layout
     64   // of the target machine.
     65 
     66   /// getStackGrowthDirection - Return the direction the stack grows
     67   ///
     68   StackDirection getStackGrowthDirection() const { return StackDir; }
     69 
     70   /// getStackAlignment - This method returns the number of bytes to which the
     71   /// stack pointer must be aligned on entry to a function.  Typically, this
     72   /// is the largest alignment for any data object in the target.
     73   ///
     74   unsigned getStackAlignment() const { return StackAlignment; }
     75 
     76   /// getTransientStackAlignment - This method returns the number of bytes to
     77   /// which the stack pointer must be aligned at all times, even between
     78   /// calls.
     79   ///
     80   unsigned getTransientStackAlignment() const {
     81     return TransientStackAlignment;
     82   }
     83 
     84   /// getOffsetOfLocalArea - This method returns the offset of the local area
     85   /// from the stack pointer on entrance to a function.
     86   ///
     87   int getOffsetOfLocalArea() const { return LocalAreaOffset; }
     88 
     89   /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
     90   /// pairs, that contains an entry for each callee saved register that must be
     91   /// spilled to a particular stack location if it is spilled.
     92   ///
     93   /// Each entry in this array contains a <register,offset> pair, indicating the
     94   /// fixed offset from the incoming stack pointer that each register should be
     95   /// spilled at. If a register is not listed here, the code generator is
     96   /// allowed to spill it anywhere it chooses.
     97   ///
     98   virtual const SpillSlot *
     99   getCalleeSavedSpillSlots(unsigned &NumEntries) const {
    100     NumEntries = 0;
    101     return 0;
    102   }
    103 
    104   /// targetHandlesStackFrameRounding - Returns true if the target is
    105   /// responsible for rounding up the stack frame (probably at emitPrologue
    106   /// time).
    107   virtual bool targetHandlesStackFrameRounding() const {
    108     return false;
    109   }
    110 
    111   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
    112   /// the function.
    113   virtual void emitPrologue(MachineFunction &MF) const = 0;
    114   virtual void emitEpilogue(MachineFunction &MF,
    115                             MachineBasicBlock &MBB) const = 0;
    116 
    117   /// Adjust the prologue to have the function use segmented stacks. This works
    118   /// by adding a check even before the "normal" function prologue.
    119   virtual void adjustForSegmentedStacks(MachineFunction &MF) const { }
    120 
    121   /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
    122   /// saved registers and returns true if it isn't possible / profitable to do
    123   /// so by issuing a series of store instructions via
    124   /// storeRegToStackSlot(). Returns false otherwise.
    125   virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
    126                                          MachineBasicBlock::iterator MI,
    127                                         const std::vector<CalleeSavedInfo> &CSI,
    128                                          const TargetRegisterInfo *TRI) const {
    129     return false;
    130   }
    131 
    132   /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
    133   /// saved registers and returns true if it isn't possible / profitable to do
    134   /// so by issuing a series of load instructions via loadRegToStackSlot().
    135   /// Returns false otherwise.
    136   virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
    137                                            MachineBasicBlock::iterator MI,
    138                                         const std::vector<CalleeSavedInfo> &CSI,
    139                                         const TargetRegisterInfo *TRI) const {
    140     return false;
    141   }
    142 
    143   /// hasFP - Return true if the specified function should have a dedicated
    144   /// frame pointer register. For most targets this is true only if the function
    145   /// has variable sized allocas or if frame pointer elimination is disabled.
    146   virtual bool hasFP(const MachineFunction &MF) const = 0;
    147 
    148   /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
    149   /// not required, we reserve argument space for call sites in the function
    150   /// immediately on entry to the current function. This eliminates the need for
    151   /// add/sub sp brackets around call sites. Returns true if the call frame is
    152   /// included as part of the stack frame.
    153   virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
    154     return !hasFP(MF);
    155   }
    156 
    157   /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
    158   /// call frame pseudo ops before doing frame index elimination. This is
    159   /// possible only when frame index references between the pseudos won't
    160   /// need adjusting for the call frame adjustments. Normally, that's true
    161   /// if the function has a reserved call frame or a frame pointer. Some
    162   /// targets (Thumb2, for example) may have more complicated criteria,
    163   /// however, and can override this behavior.
    164   virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
    165     return hasReservedCallFrame(MF) || hasFP(MF);
    166   }
    167 
    168   /// getFrameIndexOffset - Returns the displacement from the frame register to
    169   /// the stack frame of the specified index.
    170   virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;
    171 
    172   /// getFrameIndexReference - This method should return the base register
    173   /// and offset used to reference a frame index location. The offset is
    174   /// returned directly, and the base register is returned via FrameReg.
    175   virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
    176                                      unsigned &FrameReg) const;
    177 
    178   /// processFunctionBeforeCalleeSavedScan - This method is called immediately
    179   /// before PrologEpilogInserter scans the physical registers used to determine
    180   /// what callee saved registers should be spilled. This method is optional.
    181   virtual void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
    182                                                 RegScavenger *RS = NULL) const {
    183 
    184   }
    185 
    186   /// processFunctionBeforeFrameFinalized - This method is called immediately
    187   /// before the specified function's frame layout (MF.getFrameInfo()) is
    188   /// finalized.  Once the frame is finalized, MO_FrameIndex operands are
    189   /// replaced with direct constants.  This method is optional.
    190   ///
    191   virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF) const {
    192   }
    193 };
    194 
    195 } // End llvm namespace
    196 
    197 #endif
    198