1 //===-- CodeGen/MachineFrameInfo.h - Abstract Stack Frame Rep. --*- C++ -*-===//
3 // The MachineFrameInfo class represents an abstract stack frame until
4 // prolog/epilog code is inserted. This class is key to allowing stack frame
5 // representation optimizations, such as frame pointer elimination. It also
6 // allows more mundane (but still important) optimizations, such as reordering
7 // of abstract objects on the stack frame.
9 // To support this, the class assigns unique integer identifiers to stack
10 // objects requested clients. These identifiers are negative integers for fixed
11 // stack objects (such as arguments passed on the stack) or positive for objects
12 // that may be reordered. Instructions which refer to stack objects use a
13 // special MO_FrameIndex operand to represent these frame indexes.
15 // Because this class keeps track of all references to the stack frame, it knows
16 // when a variable sized object is allocated on the stack. This is the sole
17 // condition which prevents frame pointer elimination, which is an important
18 // optimization on register-poor architectures. Because original variable sized
19 // alloca's in the source program are the only source of variable sized stack
20 // objects, it is safe to decide whether there will be any variable sized
21 // objects before all stack objects are known (for example, register allocator
22 // spill code never needs variable sized objects).
24 // When prolog/epilog code emission is performed, the final stack frame is built
25 // and the machine instructions are modified to refer to the actual stack
26 // offsets of the object, eliminating all MO_FrameIndex operands from the
29 //===----------------------------------------------------------------------===//
31 #ifndef LLVM_CODEGEN_MACHINEFRAMEINFO_H
32 #define LLVM_CODEGEN_MACHINEFRAMEINFO_H
35 class TargetRegisterClass;
36 class MachineFunction;
39 class MachineFrameInfo {
41 // StackObject - Represent a single object allocated on the stack.
43 // The size of this object on the stack. 0 means a variable sized object
46 // Alignment - The required alignment of this stack slot.
49 // SPOffset - The offset of this object from the stack pointer on entry to
50 // the function. This field has no meaning for a variable sized element.
53 StackObject(unsigned Sz, unsigned Al, int SP)
54 : Size(Sz), Alignment(Al), SPOffset(SP) {}
57 /// Objects - The list of stack objects allocated...
59 std::vector<StackObject> Objects;
61 /// NumFixedObjects - This contains the number of fixed objects contained on
62 /// the stack. Because fixed objects are stored at a negative index in the
63 /// Objects list, this is also the index to the 0th object in the list.
65 unsigned NumFixedObjects;
67 /// HasVarSizedObjects - This boolean keeps track of whether any variable
68 /// sized objects have been allocated yet.
70 bool HasVarSizedObjects;
72 /// StackSize - The prolog/epilog code inserter calculates the final stack
73 /// offsets for all of the fixed size objects, updating the Objects list
74 /// above. It then updates StackSize to contain the number of bytes that need
75 /// to be allocated on entry to the function.
79 /// HasCalls - Set to true if this function has any function calls. This is
80 /// only valid during and after prolog/epilog code insertion.
83 /// MaxCallFrameSize - This contains the size of the largest call frame if the
84 /// target uses frame setup/destroy pseudo instructions (as defined in the
85 /// TargetFrameInfo class). This information is important for frame pointer
86 /// elimination. If is only valid during and after prolog/epilog code
89 unsigned MaxCallFrameSize;
92 NumFixedObjects = StackSize = 0;
93 HasVarSizedObjects = false;
98 /// hasStackObjects - Return true if there are any stack objects in this
101 bool hasStackObjects() const { return !Objects.empty(); }
103 /// hasVarSizedObjects - This method may be called any time after instruction
104 /// selection is complete to determine if the stack frame for this function
105 /// contains any variable sized objects.
107 bool hasVarSizedObjects() const { return HasVarSizedObjects; }
109 /// getObjectIndexBegin - Return the minimum frame object index...
111 int getObjectIndexBegin() const { return -NumFixedObjects; }
113 /// getObjectIndexEnd - Return one past the maximum frame object index...
115 int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; }
117 /// getObjectSize - Return the size of the specified object
119 int getObjectSize(int ObjectIdx) const {
120 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
121 return Objects[ObjectIdx+NumFixedObjects].Size;
124 /// getObjectAlignment - Return the alignment of the specified stack object...
125 int getObjectAlignment(int ObjectIdx) const {
126 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
127 return Objects[ObjectIdx+NumFixedObjects].Alignment;
130 /// getObjectOffset - Return the assigned stack offset of the specified object
131 /// from the incoming stack pointer.
133 int getObjectOffset(int ObjectIdx) const {
134 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
135 return Objects[ObjectIdx+NumFixedObjects].SPOffset;
138 /// setObjectOffset - Set the stack frame offset of the specified object. The
139 /// offset is relative to the stack pointer on entry to the function.
141 void setObjectOffset(int ObjectIdx, int SPOffset) {
142 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
143 Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset;
146 /// getStackSize - Return the number of bytes that must be allocated to hold
147 /// all of the fixed size frame objects. This is only valid after
148 /// Prolog/Epilog code insertion has finalized the stack frame layout.
150 unsigned getStackSize() const { return StackSize; }
152 /// setStackSize - Set the size of the stack...
154 void setStackSize(unsigned Size) { StackSize = Size; }
156 /// hasCalls - Return true if the current function has no function calls.
157 /// This is only valid during or after prolog/epilog code emission.
159 bool hasCalls() const { return HasCalls; }
160 void setHasCalls(bool V) { HasCalls = V; }
162 /// getMaxCallFrameSize - Return the maximum size of a call frame that must be
163 /// allocated for an outgoing function call. This is only available if
164 /// CallFrameSetup/Destroy pseudo instructions are used by the target, and
165 /// then only during or after prolog/epilog code insertion.
167 unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; }
168 void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; }
170 /// CreateFixedObject - Create a new object at a fixed location on the stack.
171 /// All fixed objects should be created before other objects are created for
172 /// efficiency. This returns an index with a negative value.
174 int CreateFixedObject(unsigned Size, int SPOffset) {
175 assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
176 Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset));
177 return -++NumFixedObjects;
180 /// CreateStackObject - Create a new statically sized stack object, returning
181 /// a postive identifier to represent it.
183 int CreateStackObject(unsigned Size, unsigned Alignment) {
184 assert(Size != 0 && "Cannot allocate zero size stack objects!");
185 Objects.push_back(StackObject(Size, Alignment, -1));
186 return Objects.size()-NumFixedObjects-1;
189 /// CreateStackObject - Create a stack object for a value of the specified
190 /// LLVM type or register class.
192 int CreateStackObject(const Type *Ty, const TargetData &TD);
193 int CreateStackObject(const TargetRegisterClass *RC);
195 /// CreateVariableSizedObject - Notify the MachineFrameInfo object that a
196 /// variable sized object has been created. This must be created whenever a
197 /// variable sized object is created, whether or not the index returned is
200 int CreateVariableSizedObject() {
201 HasVarSizedObjects = true;
202 Objects.push_back(StackObject(0, 1, -1));
203 return Objects.size()-NumFixedObjects-1;
206 /// print - Used by the MachineFunction printer to print information about
207 /// stack objects. Implemented in MachineFunction.cpp
209 void print(const MachineFunction &MF, std::ostream &OS) const;
211 /// dump - Call print(MF, std::cerr) to be called from the debugger.
212 void dump(const MachineFunction &MF) const;