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 19 #include <utility> 20 #include <vector> 21 22 namespace llvm { 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 public: 52 TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO, 53 unsigned TransAl = 1) 54 : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl), 55 LocalAreaOffset(LAO) {} 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 /// getOffsetOfLocalArea - This method returns the offset of the local area 81 /// from the stack pointer on entrance to a function. 82 /// 83 int getOffsetOfLocalArea() const { return LocalAreaOffset; } 84 85 /// getCalleeSavedSpillSlots - This method returns a pointer to an array of 86 /// pairs, that contains an entry for each callee saved register that must be 87 /// spilled to a particular stack location if it is spilled. 88 /// 89 /// Each entry in this array contains a <register,offset> pair, indicating the 90 /// fixed offset from the incoming stack pointer that each register should be 91 /// spilled at. If a register is not listed here, the code generator is 92 /// allowed to spill it anywhere it chooses. 93 /// 94 virtual const SpillSlot * 95 getCalleeSavedSpillSlots(unsigned &NumEntries) const { 96 NumEntries = 0; 97 return 0; 98 } 99 100 /// targetHandlesStackFrameRounding - Returns true if the target is 101 /// responsible for rounding up the stack frame (probably at emitPrologue 102 /// time). 103 virtual bool targetHandlesStackFrameRounding() const { 104 return false; 105 } 106 107 /// emitProlog/emitEpilog - These methods insert prolog and epilog code into 108 /// the function. 109 virtual void emitPrologue(MachineFunction &MF) const = 0; 110 virtual void emitEpilogue(MachineFunction &MF, 111 MachineBasicBlock &MBB) const = 0; 112 113 /// Adjust the prologue to have the function use segmented stacks. This works 114 /// by adding a check even before the "normal" function prologue. 115 virtual void adjustForSegmentedStacks(MachineFunction &MF) const { } 116 117 /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee 118 /// saved registers and returns true if it isn't possible / profitable to do 119 /// so by issuing a series of store instructions via 120 /// storeRegToStackSlot(). Returns false otherwise. 121 virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB, 122 MachineBasicBlock::iterator MI, 123 const std::vector<CalleeSavedInfo> &CSI, 124 const TargetRegisterInfo *TRI) const { 125 return false; 126 } 127 128 /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee 129 /// saved registers and returns true if it isn't possible / profitable to do 130 /// so by issuing a series of load instructions via loadRegToStackSlot(). 131 /// Returns false otherwise. 132 virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB, 133 MachineBasicBlock::iterator MI, 134 const std::vector<CalleeSavedInfo> &CSI, 135 const TargetRegisterInfo *TRI) const { 136 return false; 137 } 138 139 /// hasFP - Return true if the specified function should have a dedicated 140 /// frame pointer register. For most targets this is true only if the function 141 /// has variable sized allocas or if frame pointer elimination is disabled. 142 virtual bool hasFP(const MachineFunction &MF) const = 0; 143 144 /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is 145 /// not required, we reserve argument space for call sites in the function 146 /// immediately on entry to the current function. This eliminates the need for 147 /// add/sub sp brackets around call sites. Returns true if the call frame is 148 /// included as part of the stack frame. 149 virtual bool hasReservedCallFrame(const MachineFunction &MF) const { 150 return !hasFP(MF); 151 } 152 153 /// canSimplifyCallFramePseudos - When possible, it's best to simplify the 154 /// call frame pseudo ops before doing frame index elimination. This is 155 /// possible only when frame index references between the pseudos won't 156 /// need adjusting for the call frame adjustments. Normally, that's true 157 /// if the function has a reserved call frame or a frame pointer. Some 158 /// targets (Thumb2, for example) may have more complicated criteria, 159 /// however, and can override this behavior. 160 virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const { 161 return hasReservedCallFrame(MF) || hasFP(MF); 162 } 163 164 /// getFrameIndexOffset - Returns the displacement from the frame register to 165 /// the stack frame of the specified index. 166 virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const; 167 168 /// getFrameIndexReference - This method should return the base register 169 /// and offset used to reference a frame index location. The offset is 170 /// returned directly, and the base register is returned via FrameReg. 171 virtual int getFrameIndexReference(const MachineFunction &MF, int FI, 172 unsigned &FrameReg) const; 173 174 /// processFunctionBeforeCalleeSavedScan - This method is called immediately 175 /// before PrologEpilogInserter scans the physical registers used to determine 176 /// what callee saved registers should be spilled. This method is optional. 177 virtual void processFunctionBeforeCalleeSavedScan(MachineFunction &MF, 178 RegScavenger *RS = NULL) const { 179 180 } 181 182 /// processFunctionBeforeFrameFinalized - This method is called immediately 183 /// before the specified function's frame layout (MF.getFrameInfo()) is 184 /// finalized. Once the frame is finalized, MO_FrameIndex operands are 185 /// replaced with direct constants. This method is optional. 186 /// 187 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF) const { 188 } 189 }; 190 191 } // End llvm namespace 192 193 #endif 194
