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;
38 class MachineFrameInfo {
40 // StackObject - Represent a single object allocated on the stack.
42 // The size of this object on the stack. 0 means a variable sized object
45 // Alignment - The required alignment of this stack slot.
48 // SPOffset - The offset of this object from the stack pointer on entry to
49 // the function. This field has no meaning for a variable sized element.
52 StackObject(unsigned Sz, unsigned Al, int SP)
53 : Size(Sz), Alignment(Al), SPOffset(SP) {}
56 /// Objects - The list of stack objects allocated...
58 std::vector<StackObject> Objects;
60 /// NumFixedObjects - This contains the number of fixed objects contained on
61 /// the stack. Because fixed objects are stored at a negative index in the
62 /// Objects list, this is also the index to the 0th object in the list.
64 unsigned NumFixedObjects;
66 /// HasVarSizedObjects - This boolean keeps track of whether any variable
67 /// sized objects have been allocated yet.
69 bool HasVarSizedObjects;
71 /// StackSize - The prolog/epilog code inserter calculates the final stack
72 /// offsets for all of the fixed size objects, updating the Objects list
73 /// above. It then updates StackSize to contain the number of bytes that need
74 /// to be allocated on entry to the function.
78 /// HasCalls - Set to true if this function has any function calls. This is
79 /// only valid during and after prolog/epilog code insertion.
82 /// MaxCallFrameSize - This contains the size of the largest call frame if the
83 /// target uses frame setup/destroy pseudo instructions (as defined in the
84 /// TargetFrameInfo class). This information is important for frame pointer
85 /// elimination. If is only valid during and after prolog/epilog code
88 unsigned MaxCallFrameSize;
91 NumFixedObjects = StackSize = 0;
92 HasVarSizedObjects = false;
97 /// hasStackObjects - Return true if there are any stack objects in this
100 bool hasStackObjects() const { return !Objects.empty(); }
102 /// hasVarSizedObjects - This method may be called any time after instruction
103 /// selection is complete to determine if the stack frame for this function
104 /// contains any variable sized objects.
106 bool hasVarSizedObjects() const { return HasVarSizedObjects; }
108 /// getObjectIndexBegin - Return the minimum frame object index...
110 int getObjectIndexBegin() const { return -NumFixedObjects; }
112 /// getObjectIndexEnd - Return one past the maximum frame object index...
114 int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; }
116 /// getObjectSize - Return the size of the specified object
118 int getObjectSize(int ObjectIdx) const {
119 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
120 return Objects[ObjectIdx+NumFixedObjects].Size;
123 /// getObjectAlignment - Return the alignment of the specified stack object...
124 int getObjectAlignment(int ObjectIdx) const {
125 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
126 return Objects[ObjectIdx+NumFixedObjects].Alignment;
129 /// getObjectOffset - Return the assigned stack offset of the specified object
130 /// from the incoming stack pointer.
132 int getObjectOffset(int ObjectIdx) const {
133 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
134 return Objects[ObjectIdx+NumFixedObjects].SPOffset;
137 /// setObjectOffset - Set the stack frame offset of the specified object. The
138 /// offset is relative to the stack pointer on entry to the function.
140 void setObjectOffset(int ObjectIdx, int SPOffset) {
141 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
142 Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset;
145 /// getStackSize - Return the number of bytes that must be allocated to hold
146 /// all of the fixed size frame objects. This is only valid after
147 /// Prolog/Epilog code insertion has finalized the stack frame layout.
149 unsigned getStackSize() const { return StackSize; }
151 /// setStackSize - Set the size of the stack...
153 void setStackSize(unsigned Size) { StackSize = Size; }
155 /// hasCalls - Return true if the current function has no function calls.
156 /// This is only valid during or after prolog/epilog code emission.
158 bool hasCalls() const { return HasCalls; }
159 void setHasCalls(bool V) { HasCalls = V; }
161 /// getMaxCallFrameSize - Return the maximum size of a call frame that must be
162 /// allocated for an outgoing function call. This is only available if
163 /// CallFrameSetup/Destroy pseudo instructions are used by the target, and
164 /// then only during or after prolog/epilog code insertion.
166 unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; }
167 void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; }
169 /// CreateFixedObject - Create a new object at a fixed location on the stack.
170 /// All fixed objects should be created before other objects are created for
171 /// efficiency. This returns an index with a negative value.
173 int CreateFixedObject(unsigned Size, int SPOffset) {
174 assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
175 Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset));
176 return -++NumFixedObjects;
179 /// CreateStackObject - Create a new statically sized stack object, returning
180 /// a postive identifier to represent it.
182 int CreateStackObject(unsigned Size, unsigned Alignment) {
183 assert(Size != 0 && "Cannot allocate zero size stack objects!");
184 Objects.push_back(StackObject(Size, Alignment, -1));
185 return Objects.size()-NumFixedObjects-1;
188 /// CreateStackObject - Create a stack object for a value of the specified
189 /// LLVM type or register class.
191 int CreateStackObject(const Type *Ty, const TargetData &TD);
192 int CreateStackObject(const TargetRegisterClass *RC);
194 /// CreateVariableSizedObject - Notify the MachineFrameInfo object that a
195 /// variable sized object has been created. This must be created whenever a
196 /// variable sized object is created, whether or not the index returned is
199 int CreateVariableSizedObject() {
200 HasVarSizedObjects = true;
201 Objects.push_back(StackObject(0, 1, -1));
202 return Objects.size()-NumFixedObjects-1;
205 /// print - Used by the MachineFunction printer to print information about
206 /// stack objects. Implemented in MachineFunction.cpp
208 void print(std::ostream &OS) const;
210 /// dump - Call print(std::cerr) to be called from the debugger.