LLVM API Documentation
00001 //===-- CodeGen/MachineFrameInfo.h - Abstract Stack Frame Rep. --*- C++ -*-===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // The MachineFrameInfo class represents an abstract stack frame until 00011 // prolog/epilog code is inserted. This class is key to allowing stack frame 00012 // representation optimizations, such as frame pointer elimination. It also 00013 // allows more mundane (but still important) optimizations, such as reordering 00014 // of abstract objects on the stack frame. 00015 // 00016 // To support this, the class assigns unique integer identifiers to stack 00017 // objects requested clients. These identifiers are negative integers for fixed 00018 // stack objects (such as arguments passed on the stack) or positive for objects 00019 // that may be reordered. Instructions which refer to stack objects use a 00020 // special MO_FrameIndex operand to represent these frame indexes. 00021 // 00022 // Because this class keeps track of all references to the stack frame, it knows 00023 // when a variable sized object is allocated on the stack. This is the sole 00024 // condition which prevents frame pointer elimination, which is an important 00025 // optimization on register-poor architectures. Because original variable sized 00026 // alloca's in the source program are the only source of variable sized stack 00027 // objects, it is safe to decide whether there will be any variable sized 00028 // objects before all stack objects are known (for example, register allocator 00029 // spill code never needs variable sized objects). 00030 // 00031 // When prolog/epilog code emission is performed, the final stack frame is built 00032 // and the machine instructions are modified to refer to the actual stack 00033 // offsets of the object, eliminating all MO_FrameIndex operands from the 00034 // program. 00035 // 00036 //===----------------------------------------------------------------------===// 00037 00038 #ifndef LLVM_CODEGEN_MACHINEFRAMEINFO_H 00039 #define LLVM_CODEGEN_MACHINEFRAMEINFO_H 00040 00041 #include <vector> 00042 00043 namespace llvm { 00044 class TargetData; 00045 class TargetRegisterClass; 00046 class Type; 00047 class MachineDebugInfo; 00048 class MachineFunction; 00049 00050 class MachineFrameInfo { 00051 00052 // StackObject - Represent a single object allocated on the stack. 00053 struct StackObject { 00054 // The size of this object on the stack. 0 means a variable sized object 00055 unsigned Size; 00056 00057 // Alignment - The required alignment of this stack slot. 00058 unsigned Alignment; 00059 00060 // SPOffset - The offset of this object from the stack pointer on entry to 00061 // the function. This field has no meaning for a variable sized element. 00062 int SPOffset; 00063 00064 StackObject(unsigned Sz, unsigned Al, int SP) 00065 : Size(Sz), Alignment(Al), SPOffset(SP) {} 00066 }; 00067 00068 /// Objects - The list of stack objects allocated... 00069 /// 00070 std::vector<StackObject> Objects; 00071 00072 /// NumFixedObjects - This contains the number of fixed objects contained on 00073 /// the stack. Because fixed objects are stored at a negative index in the 00074 /// Objects list, this is also the index to the 0th object in the list. 00075 /// 00076 unsigned NumFixedObjects; 00077 00078 /// HasVarSizedObjects - This boolean keeps track of whether any variable 00079 /// sized objects have been allocated yet. 00080 /// 00081 bool HasVarSizedObjects; 00082 00083 /// StackSize - The prolog/epilog code inserter calculates the final stack 00084 /// offsets for all of the fixed size objects, updating the Objects list 00085 /// above. It then updates StackSize to contain the number of bytes that need 00086 /// to be allocated on entry to the function. 00087 /// 00088 unsigned StackSize; 00089 00090 /// MaxAlignment - The prolog/epilog code inserter may process objects 00091 /// that require greater alignment than the default alignment the target 00092 /// provides. To handle this, MaxAlignment is set to the maximum alignment 00093 /// needed by the objects on the current frame. If this is greater than the 00094 /// native alignment maintained by the compiler, dynamic alignment code will 00095 /// be needed. 00096 /// 00097 unsigned MaxAlignment; 00098 00099 /// HasCalls - Set to true if this function has any function calls. This is 00100 /// only valid during and after prolog/epilog code insertion. 00101 bool HasCalls; 00102 00103 /// MaxCallFrameSize - This contains the size of the largest call frame if the 00104 /// target uses frame setup/destroy pseudo instructions (as defined in the 00105 /// TargetFrameInfo class). This information is important for frame pointer 00106 /// elimination. If is only valid during and after prolog/epilog code 00107 /// insertion. 00108 /// 00109 unsigned MaxCallFrameSize; 00110 00111 /// DebugInfo - This field is set (via setMachineDebugInfo) by a debug info 00112 /// consumer (ex. DwarfWriter) to indicate that frame layout information 00113 /// should be acquired. Typically, it's the responsibility of the target's 00114 /// MRegisterInfo prologue/epilogue emitting code to inform MachineDebugInfo 00115 /// of frame layouts. 00116 MachineDebugInfo *DebugInfo; 00117 00118 public: 00119 MachineFrameInfo() { 00120 NumFixedObjects = StackSize = MaxAlignment = 0; 00121 HasVarSizedObjects = false; 00122 HasCalls = false; 00123 MaxCallFrameSize = 0; 00124 DebugInfo = 0; 00125 } 00126 00127 /// hasStackObjects - Return true if there are any stack objects in this 00128 /// function. 00129 /// 00130 bool hasStackObjects() const { return !Objects.empty(); } 00131 00132 /// hasVarSizedObjects - This method may be called any time after instruction 00133 /// selection is complete to determine if the stack frame for this function 00134 /// contains any variable sized objects. 00135 /// 00136 bool hasVarSizedObjects() const { return HasVarSizedObjects; } 00137 00138 /// getObjectIndexBegin - Return the minimum frame object index... 00139 /// 00140 int getObjectIndexBegin() const { return -NumFixedObjects; } 00141 00142 /// getObjectIndexEnd - Return one past the maximum frame object index... 00143 /// 00144 int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; } 00145 00146 /// getObjectSize - Return the size of the specified object 00147 /// 00148 int getObjectSize(int ObjectIdx) const { 00149 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!"); 00150 return Objects[ObjectIdx+NumFixedObjects].Size; 00151 } 00152 00153 /// getObjectAlignment - Return the alignment of the specified stack object... 00154 int getObjectAlignment(int ObjectIdx) const { 00155 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!"); 00156 return Objects[ObjectIdx+NumFixedObjects].Alignment; 00157 } 00158 00159 /// getObjectOffset - Return the assigned stack offset of the specified object 00160 /// from the incoming stack pointer. 00161 /// 00162 int getObjectOffset(int ObjectIdx) const { 00163 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!"); 00164 return Objects[ObjectIdx+NumFixedObjects].SPOffset; 00165 } 00166 00167 /// setObjectOffset - Set the stack frame offset of the specified object. The 00168 /// offset is relative to the stack pointer on entry to the function. 00169 /// 00170 void setObjectOffset(int ObjectIdx, int SPOffset) { 00171 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!"); 00172 Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset; 00173 } 00174 00175 /// getStackSize - Return the number of bytes that must be allocated to hold 00176 /// all of the fixed size frame objects. This is only valid after 00177 /// Prolog/Epilog code insertion has finalized the stack frame layout. 00178 /// 00179 unsigned getStackSize() const { return StackSize; } 00180 00181 /// setStackSize - Set the size of the stack... 00182 /// 00183 void setStackSize(unsigned Size) { StackSize = Size; } 00184 00185 /// getMaxAlignment - Return the alignment in bytes that this function must be 00186 /// aligned to, which is greater than the default stack alignment provided by 00187 /// the target. 00188 /// 00189 unsigned getMaxAlignment() const { return MaxAlignment; } 00190 00191 /// setMaxAlignment - Set the preferred alignment. 00192 /// 00193 void setMaxAlignment(unsigned Align) { MaxAlignment = Align; } 00194 00195 /// hasCalls - Return true if the current function has no function calls. 00196 /// This is only valid during or after prolog/epilog code emission. 00197 /// 00198 bool hasCalls() const { return HasCalls; } 00199 void setHasCalls(bool V) { HasCalls = V; } 00200 00201 /// getMaxCallFrameSize - Return the maximum size of a call frame that must be 00202 /// allocated for an outgoing function call. This is only available if 00203 /// CallFrameSetup/Destroy pseudo instructions are used by the target, and 00204 /// then only during or after prolog/epilog code insertion. 00205 /// 00206 unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; } 00207 void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; } 00208 00209 /// CreateFixedObject - Create a new object at a fixed location on the stack. 00210 /// All fixed objects should be created before other objects are created for 00211 /// efficiency. This returns an index with a negative value. 00212 /// 00213 int CreateFixedObject(unsigned Size, int SPOffset) { 00214 assert(Size != 0 && "Cannot allocate zero size fixed stack objects!"); 00215 Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset)); 00216 return -++NumFixedObjects; 00217 } 00218 00219 /// CreateStackObject - Create a new statically sized stack object, returning 00220 /// a postive identifier to represent it. 00221 /// 00222 int CreateStackObject(unsigned Size, unsigned Alignment) { 00223 // Keep track of the maximum alignment. 00224 if (MaxAlignment < Alignment) MaxAlignment = Alignment; 00225 00226 assert(Size != 0 && "Cannot allocate zero size stack objects!"); 00227 Objects.push_back(StackObject(Size, Alignment, -1)); 00228 return Objects.size()-NumFixedObjects-1; 00229 } 00230 00231 /// CreateVariableSizedObject - Notify the MachineFrameInfo object that a 00232 /// variable sized object has been created. This must be created whenever a 00233 /// variable sized object is created, whether or not the index returned is 00234 /// actually used. 00235 /// 00236 int CreateVariableSizedObject() { 00237 HasVarSizedObjects = true; 00238 if (MaxAlignment < 1) MaxAlignment = 1; 00239 Objects.push_back(StackObject(0, 1, -1)); 00240 return Objects.size()-NumFixedObjects-1; 00241 } 00242 00243 /// getMachineDebugInfo - Used by a prologue/epilogue emitter (MRegisterInfo) 00244 /// to provide frame layout information. 00245 MachineDebugInfo *getMachineDebugInfo() const { return DebugInfo; } 00246 00247 /// setMachineDebugInfo - Used by a debug consumer (DwarfWriter) to indicate 00248 /// that frame layout information should be gathered. 00249 void setMachineDebugInfo(MachineDebugInfo *DI) { DebugInfo = DI; } 00250 00251 /// print - Used by the MachineFunction printer to print information about 00252 /// stack objects. Implemented in MachineFunction.cpp 00253 /// 00254 void print(const MachineFunction &MF, std::ostream &OS) const; 00255 00256 /// dump - Call print(MF, std::cerr) to be called from the debugger. 00257 void dump(const MachineFunction &MF) const; 00258 }; 00259 00260 } // End llvm namespace 00261 00262 #endif