1 //===-- llvm/Target/TargetFrameLowering.h ---------------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Interface to describe the layout of a stack frame on the target machine.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_TARGET_TARGETFRAMELOWERING_H
15 #define LLVM_TARGET_TARGETFRAMELOWERING_H
17 #include "llvm/CodeGen/MachineBasicBlock.h"
22 class CalleeSavedInfo;
23 class MachineFunction;
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.
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 {
36 StackGrowsUp, // Adding to the stack increases the stack address
37 StackGrowsDown // Adding to the stack decreases the stack address
40 // Maps a callee saved register to a stack slot with a fixed offset.
43 int Offset; // Offset relative to stack pointer on function entry.
46 StackDirection StackDir;
47 unsigned StackAlignment;
48 unsigned TransientStackAlignment;
50 bool StackRealignable;
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) {}
57 virtual ~TargetFrameLowering();
59 // These methods return information that describes the abstract stack layout
60 // of the target machine.
62 /// getStackGrowthDirection - Return the direction the stack grows
64 StackDirection getStackGrowthDirection() const { return StackDir; }
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.
70 unsigned getStackAlignment() const { return StackAlignment; }
72 /// getTransientStackAlignment - This method returns the number of bytes to
73 /// which the stack pointer must be aligned at all times, even between
76 unsigned getTransientStackAlignment() const {
77 return TransientStackAlignment;
80 /// isStackRealignable - This method returns whether the stack can be
82 bool isStackRealignable() const {
83 return StackRealignable;
86 /// getOffsetOfLocalArea - This method returns the offset of the local area
87 /// from the stack pointer on entrance to a function.
89 int getOffsetOfLocalArea() const { return LocalAreaOffset; }
91 /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
92 /// pairs, that contains an entry for each callee saved register that must be
93 /// spilled to a particular stack location if it is spilled.
95 /// Each entry in this array contains a <register,offset> pair, indicating the
96 /// fixed offset from the incoming stack pointer that each register should be
97 /// spilled at. If a register is not listed here, the code generator is
98 /// allowed to spill it anywhere it chooses.
100 virtual const SpillSlot *
101 getCalleeSavedSpillSlots(unsigned &NumEntries) const {
106 /// targetHandlesStackFrameRounding - Returns true if the target is
107 /// responsible for rounding up the stack frame (probably at emitPrologue
109 virtual bool targetHandlesStackFrameRounding() const {
113 /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
115 virtual void emitPrologue(MachineFunction &MF) const = 0;
116 virtual void emitEpilogue(MachineFunction &MF,
117 MachineBasicBlock &MBB) const = 0;
119 /// Adjust the prologue to have the function use segmented stacks. This works
120 /// by adding a check even before the "normal" function prologue.
121 virtual void adjustForSegmentedStacks(MachineFunction &MF) const { }
123 /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
124 /// saved registers and returns true if it isn't possible / profitable to do
125 /// so by issuing a series of store instructions via
126 /// storeRegToStackSlot(). Returns false otherwise.
127 virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
128 MachineBasicBlock::iterator MI,
129 const std::vector<CalleeSavedInfo> &CSI,
130 const TargetRegisterInfo *TRI) const {
134 /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
135 /// saved registers and returns true if it isn't possible / profitable to do
136 /// so by issuing a series of load instructions via loadRegToStackSlot().
137 /// Returns false otherwise.
138 virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
139 MachineBasicBlock::iterator MI,
140 const std::vector<CalleeSavedInfo> &CSI,
141 const TargetRegisterInfo *TRI) const {
145 /// hasFP - Return true if the specified function should have a dedicated
146 /// frame pointer register. For most targets this is true only if the function
147 /// has variable sized allocas or if frame pointer elimination is disabled.
148 virtual bool hasFP(const MachineFunction &MF) const = 0;
150 /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
151 /// not required, we reserve argument space for call sites in the function
152 /// immediately on entry to the current function. This eliminates the need for
153 /// add/sub sp brackets around call sites. Returns true if the call frame is
154 /// included as part of the stack frame.
155 virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
159 /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
160 /// call frame pseudo ops before doing frame index elimination. This is
161 /// possible only when frame index references between the pseudos won't
162 /// need adjusting for the call frame adjustments. Normally, that's true
163 /// if the function has a reserved call frame or a frame pointer. Some
164 /// targets (Thumb2, for example) may have more complicated criteria,
165 /// however, and can override this behavior.
166 virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
167 return hasReservedCallFrame(MF) || hasFP(MF);
170 /// getFrameIndexOffset - Returns the displacement from the frame register to
171 /// the stack frame of the specified index.
172 virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;
174 /// getFrameIndexReference - This method should return the base register
175 /// and offset used to reference a frame index location. The offset is
176 /// returned directly, and the base register is returned via FrameReg.
177 virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
178 unsigned &FrameReg) const;
180 /// processFunctionBeforeCalleeSavedScan - This method is called immediately
181 /// before PrologEpilogInserter scans the physical registers used to determine
182 /// what callee saved registers should be spilled. This method is optional.
183 virtual void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
184 RegScavenger *RS = NULL) const {
188 /// processFunctionBeforeFrameFinalized - This method is called immediately
189 /// before the specified function's frame layout (MF.getFrameInfo()) is
190 /// finalized. Once the frame is finalized, MO_FrameIndex operands are
191 /// replaced with direct constants. This method is optional.
193 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF) const {
197 } // End llvm namespace