1 //===-- CodeGen/MachineFrameInfo.h - Abstract Stack Frame Rep. --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 #ifndef LLVM_CODEGEN_MACHINEFRAMEINFO_H
12 #define LLVM_CODEGEN_MACHINEFRAMEINFO_H
18 class TargetRegisterClass;
20 class MachineDebugInfo;
21 class MachineFunction;
24 /// The MachineFrameInfo class represents an abstract stack frame until
25 /// prolog/epilog code is inserted. This class is key to allowing stack frame
26 /// representation optimizations, such as frame pointer elimination. It also
27 /// allows more mundane (but still important) optimizations, such as reordering
28 /// of abstract objects on the stack frame.
30 /// To support this, the class assigns unique integer identifiers to stack
31 /// objects requested clients. These identifiers are negative integers for
32 /// fixed stack objects (such as arguments passed on the stack) or positive
33 /// for objects that may be reordered. Instructions which refer to stack
34 /// objects use a special MO_FrameIndex operand to represent these frame
37 /// Because this class keeps track of all references to the stack frame, it
38 /// knows when a variable sized object is allocated on the stack. This is the
39 /// sole condition which prevents frame pointer elimination, which is an
40 /// important optimization on register-poor architectures. Because original
41 /// variable sized alloca's in the source program are the only source of
42 /// variable sized stack objects, it is safe to decide whether there will be
43 /// any variable sized objects before all stack objects are known (for
44 /// example, register allocator spill code never needs variable sized
47 /// When prolog/epilog code emission is performed, the final stack frame is
48 /// built and the machine instructions are modified to refer to the actual
49 /// stack offsets of the object, eliminating all MO_FrameIndex operands from
52 /// @brief Abstract Stack Frame Information
53 class MachineFrameInfo {
55 // StackObject - Represent a single object allocated on the stack.
57 // The size of this object on the stack. 0 means a variable sized object
60 // Alignment - The required alignment of this stack slot.
63 // SPOffset - The offset of this object from the stack pointer on entry to
64 // the function. This field has no meaning for a variable sized element.
67 StackObject(unsigned Sz, unsigned Al, int SP)
68 : Size(Sz), Alignment(Al), SPOffset(SP) {}
71 /// Objects - The list of stack objects allocated...
73 std::vector<StackObject> Objects;
75 /// NumFixedObjects - This contains the number of fixed objects contained on
76 /// the stack. Because fixed objects are stored at a negative index in the
77 /// Objects list, this is also the index to the 0th object in the list.
79 unsigned NumFixedObjects;
81 /// HasVarSizedObjects - This boolean keeps track of whether any variable
82 /// sized objects have been allocated yet.
84 bool HasVarSizedObjects;
86 /// StackSize - The prolog/epilog code inserter calculates the final stack
87 /// offsets for all of the fixed size objects, updating the Objects list
88 /// above. It then updates StackSize to contain the number of bytes that need
89 /// to be allocated on entry to the function.
93 /// MaxAlignment - The prolog/epilog code inserter may process objects
94 /// that require greater alignment than the default alignment the target
95 /// provides. To handle this, MaxAlignment is set to the maximum alignment
96 /// needed by the objects on the current frame. If this is greater than the
97 /// native alignment maintained by the compiler, dynamic alignment code will
100 unsigned MaxAlignment;
102 /// HasCalls - Set to true if this function has any function calls. This is
103 /// only valid during and after prolog/epilog code insertion.
106 /// MaxCallFrameSize - This contains the size of the largest call frame if the
107 /// target uses frame setup/destroy pseudo instructions (as defined in the
108 /// TargetFrameInfo class). This information is important for frame pointer
109 /// elimination. If is only valid during and after prolog/epilog code
112 unsigned MaxCallFrameSize;
114 /// DebugInfo - This field is set (via setMachineDebugInfo) by a debug info
115 /// consumer (ex. DwarfWriter) to indicate that frame layout information
116 /// should be acquired. Typically, it's the responsibility of the target's
117 /// MRegisterInfo prologue/epilogue emitting code to inform MachineDebugInfo
118 /// of frame layouts.
119 MachineDebugInfo *DebugInfo;
123 NumFixedObjects = StackSize = MaxAlignment = 0;
124 HasVarSizedObjects = false;
126 MaxCallFrameSize = 0;
130 /// hasStackObjects - Return true if there are any stack objects in this
133 bool hasStackObjects() const { return !Objects.empty(); }
135 /// hasVarSizedObjects - This method may be called any time after instruction
136 /// selection is complete to determine if the stack frame for this function
137 /// contains any variable sized objects.
139 bool hasVarSizedObjects() const { return HasVarSizedObjects; }
141 /// getObjectIndexBegin - Return the minimum frame object index...
143 int getObjectIndexBegin() const { return -NumFixedObjects; }
145 /// getObjectIndexEnd - Return one past the maximum frame object index...
147 int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; }
149 /// getObjectSize - Return the size of the specified object
151 int getObjectSize(int ObjectIdx) const {
152 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
153 return Objects[ObjectIdx+NumFixedObjects].Size;
156 /// getObjectAlignment - Return the alignment of the specified stack object...
157 int getObjectAlignment(int ObjectIdx) const {
158 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
159 return Objects[ObjectIdx+NumFixedObjects].Alignment;
162 /// getObjectOffset - Return the assigned stack offset of the specified object
163 /// from the incoming stack pointer.
165 int getObjectOffset(int ObjectIdx) const {
166 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
167 return Objects[ObjectIdx+NumFixedObjects].SPOffset;
170 /// setObjectOffset - Set the stack frame offset of the specified object. The
171 /// offset is relative to the stack pointer on entry to the function.
173 void setObjectOffset(int ObjectIdx, int SPOffset) {
174 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
175 Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset;
178 /// getStackSize - Return the number of bytes that must be allocated to hold
179 /// all of the fixed size frame objects. This is only valid after
180 /// Prolog/Epilog code insertion has finalized the stack frame layout.
182 unsigned getStackSize() const { return StackSize; }
184 /// setStackSize - Set the size of the stack...
186 void setStackSize(unsigned Size) { StackSize = Size; }
188 /// getMaxAlignment - Return the alignment in bytes that this function must be
189 /// aligned to, which is greater than the default stack alignment provided by
192 unsigned getMaxAlignment() const { return MaxAlignment; }
194 /// setMaxAlignment - Set the preferred alignment.
196 void setMaxAlignment(unsigned Align) { MaxAlignment = Align; }
198 /// hasCalls - Return true if the current function has no function calls.
199 /// This is only valid during or after prolog/epilog code emission.
201 bool hasCalls() const { return HasCalls; }
202 void setHasCalls(bool V) { HasCalls = V; }
204 /// getMaxCallFrameSize - Return the maximum size of a call frame that must be
205 /// allocated for an outgoing function call. This is only available if
206 /// CallFrameSetup/Destroy pseudo instructions are used by the target, and
207 /// then only during or after prolog/epilog code insertion.
209 unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; }
210 void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; }
212 /// CreateFixedObject - Create a new object at a fixed location on the stack.
213 /// All fixed objects should be created before other objects are created for
214 /// efficiency. This returns an index with a negative value.
216 int CreateFixedObject(unsigned Size, int SPOffset) {
217 assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
218 Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset));
219 return -++NumFixedObjects;
222 /// CreateStackObject - Create a new statically sized stack object, returning
223 /// a postive identifier to represent it.
225 int CreateStackObject(unsigned Size, unsigned Alignment) {
226 // Keep track of the maximum alignment.
227 if (MaxAlignment < Alignment) MaxAlignment = Alignment;
229 assert(Size != 0 && "Cannot allocate zero size stack objects!");
230 Objects.push_back(StackObject(Size, Alignment, -1));
231 return Objects.size()-NumFixedObjects-1;
234 /// CreateVariableSizedObject - Notify the MachineFrameInfo object that a
235 /// variable sized object has been created. This must be created whenever a
236 /// variable sized object is created, whether or not the index returned is
239 int CreateVariableSizedObject() {
240 HasVarSizedObjects = true;
241 if (MaxAlignment < 1) MaxAlignment = 1;
242 Objects.push_back(StackObject(0, 1, -1));
243 return Objects.size()-NumFixedObjects-1;
246 /// getMachineDebugInfo - Used by a prologue/epilogue emitter (MRegisterInfo)
247 /// to provide frame layout information.
248 MachineDebugInfo *getMachineDebugInfo() const { return DebugInfo; }
250 /// setMachineDebugInfo - Used by a debug consumer (DwarfWriter) to indicate
251 /// that frame layout information should be gathered.
252 void setMachineDebugInfo(MachineDebugInfo *DI) { DebugInfo = DI; }
254 /// print - Used by the MachineFunction printer to print information about
255 /// stack objects. Implemented in MachineFunction.cpp
257 void print(const MachineFunction &MF, std::ostream &OS) const;
259 /// dump - Call print(MF, std::cerr) to be called from the debugger.
260 void dump(const MachineFunction &MF) const;
263 } // End llvm namespace