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"
23 class CalleeSavedInfo;
24 class MachineFunction;
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.
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 {
37 StackGrowsUp, // Adding to the stack increases the stack address
38 StackGrowsDown // Adding to the stack decreases the stack address
41 // Maps a callee saved register to a stack slot with a fixed offset.
44 int Offset; // Offset relative to stack pointer on function entry.
47 StackDirection StackDir;
48 unsigned StackAlignment;
49 unsigned TransientStackAlignment;
52 TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
54 : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
55 LocalAreaOffset(LAO) {}
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 /// getOffsetOfLocalArea - This method returns the offset of the local area
81 /// from the stack pointer on entrance to a function.
83 int getOffsetOfLocalArea() const { return LocalAreaOffset; }
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.
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.
94 virtual const SpillSlot *
95 getCalleeSavedSpillSlots(unsigned &NumEntries) const {
100 /// targetHandlesStackFrameRounding - Returns true if the target is
101 /// responsible for rounding up the stack frame (probably at emitPrologue
103 virtual bool targetHandlesStackFrameRounding() const {
107 /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
109 virtual void emitPrologue(MachineFunction &MF) const = 0;
110 virtual void emitEpilogue(MachineFunction &MF,
111 MachineBasicBlock &MBB) const = 0;
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 { }
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 {
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 {
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;
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 {
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);
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;
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;
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 {
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.
187 virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF) const {
191 } // End llvm namespace