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 //===----------------------------------------------------------------------===//
10 // The MachineFrameInfo class represents an abstract stack frame until
11 // prolog/epilog code is inserted. This class is key to allowing stack frame
12 // representation optimizations, such as frame pointer elimination. It also
13 // allows more mundane (but still important) optimizations, such as reordering
14 // of abstract objects on the stack frame.
16 // To support this, the class assigns unique integer identifiers to stack
17 // objects requested clients. These identifiers are negative integers for fixed
18 // stack objects (such as arguments passed on the stack) or positive for objects
19 // that may be reordered. Instructions which refer to stack objects use a
20 // special MO_FrameIndex operand to represent these frame indexes.
22 // Because this class keeps track of all references to the stack frame, it knows
23 // when a variable sized object is allocated on the stack. This is the sole
24 // condition which prevents frame pointer elimination, which is an important
25 // optimization on register-poor architectures. Because original variable sized
26 // alloca's in the source program are the only source of variable sized stack
27 // objects, it is safe to decide whether there will be any variable sized
28 // objects before all stack objects are known (for example, register allocator
29 // spill code never needs variable sized objects).
31 // When prolog/epilog code emission is performed, the final stack frame is built
32 // and the machine instructions are modified to refer to the actual stack
33 // offsets of the object, eliminating all MO_FrameIndex operands from the
36 //===----------------------------------------------------------------------===//
38 #ifndef LLVM_CODEGEN_MACHINEFRAMEINFO_H
39 #define LLVM_CODEGEN_MACHINEFRAMEINFO_H
45 class TargetRegisterClass;
47 class MachineDebugInfo;
48 class MachineFunction;
50 class MachineFrameInfo {
52 // StackObject - Represent a single object allocated on the stack.
54 // The size of this object on the stack. 0 means a variable sized object
57 // Alignment - The required alignment of this stack slot.
60 // SPOffset - The offset of this object from the stack pointer on entry to
61 // the function. This field has no meaning for a variable sized element.
64 StackObject(unsigned Sz, unsigned Al, int SP)
65 : Size(Sz), Alignment(Al), SPOffset(SP) {}
68 /// Objects - The list of stack objects allocated...
70 std::vector<StackObject> Objects;
72 /// NumFixedObjects - This contains the number of fixed objects contained on
73 /// the stack. Because fixed objects are stored at a negative index in the
74 /// Objects list, this is also the index to the 0th object in the list.
76 unsigned NumFixedObjects;
78 /// HasVarSizedObjects - This boolean keeps track of whether any variable
79 /// sized objects have been allocated yet.
81 bool HasVarSizedObjects;
83 /// StackSize - The prolog/epilog code inserter calculates the final stack
84 /// offsets for all of the fixed size objects, updating the Objects list
85 /// above. It then updates StackSize to contain the number of bytes that need
86 /// to be allocated on entry to the function.
90 /// MaxAlignment - The prolog/epilog code inserter may process objects
91 /// that require greater alignment than the default alignment the target
92 /// provides. To handle this, MaxAlignment is set to the maximum alignment
93 /// needed by the objects on the current frame. If this is greater than the
94 /// native alignment maintained by the compiler, dynamic alignment code will
97 unsigned MaxAlignment;
99 /// HasCalls - Set to true if this function has any function calls. This is
100 /// only valid during and after prolog/epilog code insertion.
103 /// MaxCallFrameSize - This contains the size of the largest call frame if the
104 /// target uses frame setup/destroy pseudo instructions (as defined in the
105 /// TargetFrameInfo class). This information is important for frame pointer
106 /// elimination. If is only valid during and after prolog/epilog code
109 unsigned MaxCallFrameSize;
111 /// DebugInfo - This field is set (via setMachineDebugInfo) by a debug info
112 /// consumer (ex. DwarfWriter) to indicate that frame layout information
113 /// should be acquired. Typically, it's the responsibility of the target's
114 /// MRegisterInfo prologue/epilogue emitting code to inform MachineDebugInfo
115 /// of frame layouts.
116 MachineDebugInfo *DebugInfo;
120 NumFixedObjects = StackSize = MaxAlignment = 0;
121 HasVarSizedObjects = false;
123 MaxCallFrameSize = 0;
127 /// hasStackObjects - Return true if there are any stack objects in this
130 bool hasStackObjects() const { return !Objects.empty(); }
132 /// hasVarSizedObjects - This method may be called any time after instruction
133 /// selection is complete to determine if the stack frame for this function
134 /// contains any variable sized objects.
136 bool hasVarSizedObjects() const { return HasVarSizedObjects; }
138 /// getObjectIndexBegin - Return the minimum frame object index...
140 int getObjectIndexBegin() const { return -NumFixedObjects; }
142 /// getObjectIndexEnd - Return one past the maximum frame object index...
144 int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; }
146 /// getObjectSize - Return the size of the specified object
148 int getObjectSize(int ObjectIdx) const {
149 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
150 return Objects[ObjectIdx+NumFixedObjects].Size;
153 /// getObjectAlignment - Return the alignment of the specified stack object...
154 int getObjectAlignment(int ObjectIdx) const {
155 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
156 return Objects[ObjectIdx+NumFixedObjects].Alignment;
159 /// getObjectOffset - Return the assigned stack offset of the specified object
160 /// from the incoming stack pointer.
162 int getObjectOffset(int ObjectIdx) const {
163 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
164 return Objects[ObjectIdx+NumFixedObjects].SPOffset;
167 /// setObjectOffset - Set the stack frame offset of the specified object. The
168 /// offset is relative to the stack pointer on entry to the function.
170 void setObjectOffset(int ObjectIdx, int SPOffset) {
171 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
172 Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset;
175 /// getStackSize - Return the number of bytes that must be allocated to hold
176 /// all of the fixed size frame objects. This is only valid after
177 /// Prolog/Epilog code insertion has finalized the stack frame layout.
179 unsigned getStackSize() const { return StackSize; }
181 /// setStackSize - Set the size of the stack...
183 void setStackSize(unsigned Size) { StackSize = Size; }
185 /// getMaxAlignment - Return the alignment in bytes that this function must be
186 /// aligned to, which is greater than the default stack alignment provided by
189 unsigned getMaxAlignment() const { return MaxAlignment; }
191 /// setMaxAlignment - Set the preferred alignment.
193 void setMaxAlignment(unsigned Align) { MaxAlignment = Align; }
195 /// hasCalls - Return true if the current function has no function calls.
196 /// This is only valid during or after prolog/epilog code emission.
198 bool hasCalls() const { return HasCalls; }
199 void setHasCalls(bool V) { HasCalls = V; }
201 /// getMaxCallFrameSize - Return the maximum size of a call frame that must be
202 /// allocated for an outgoing function call. This is only available if
203 /// CallFrameSetup/Destroy pseudo instructions are used by the target, and
204 /// then only during or after prolog/epilog code insertion.
206 unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; }
207 void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; }
209 /// CreateFixedObject - Create a new object at a fixed location on the stack.
210 /// All fixed objects should be created before other objects are created for
211 /// efficiency. This returns an index with a negative value.
213 int CreateFixedObject(unsigned Size, int SPOffset) {
214 assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
215 Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset));
216 return -++NumFixedObjects;
219 /// CreateStackObject - Create a new statically sized stack object, returning
220 /// a postive identifier to represent it.
222 int CreateStackObject(unsigned Size, unsigned Alignment) {
223 // Keep track of the maximum alignment.
224 if (MaxAlignment < Alignment) MaxAlignment = Alignment;
226 assert(Size != 0 && "Cannot allocate zero size stack objects!");
227 Objects.push_back(StackObject(Size, Alignment, -1));
228 return Objects.size()-NumFixedObjects-1;
231 /// CreateVariableSizedObject - Notify the MachineFrameInfo object that a
232 /// variable sized object has been created. This must be created whenever a
233 /// variable sized object is created, whether or not the index returned is
236 int CreateVariableSizedObject() {
237 HasVarSizedObjects = true;
238 if (MaxAlignment < 1) MaxAlignment = 1;
239 Objects.push_back(StackObject(0, 1, -1));
240 return Objects.size()-NumFixedObjects-1;
243 /// getMachineDebugInfo - Used by a prologue/epilogue emitter (MRegisterInfo)
244 /// to provide frame layout information.
245 MachineDebugInfo *getMachineDebugInfo() const { return DebugInfo; }
247 /// setMachineDebugInfo - Used by a debug consumer (DwarfWriter) to indicate
248 /// that frame layout information should be gathered.
249 void setMachineDebugInfo(MachineDebugInfo *DI) { DebugInfo = DI; }
251 /// print - Used by the MachineFunction printer to print information about
252 /// stack objects. Implemented in MachineFunction.cpp
254 void print(const MachineFunction &MF, std::ostream &OS) const;
256 /// dump - Call print(MF, std::cerr) to be called from the debugger.
257 void dump(const MachineFunction &MF) const;
260 } // End llvm namespace