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 00011 #ifndef LLVM_CODEGEN_MACHINEFRAMEINFO_H 00012 #define LLVM_CODEGEN_MACHINEFRAMEINFO_H 00013 00014 #include <vector> 00015 00016 namespace llvm { 00017 class TargetData; 00018 class TargetRegisterClass; 00019 class Type; 00020 class MachineDebugInfo; 00021 class MachineFunction; 00022 00023 00024 /// The MachineFrameInfo class represents an abstract stack frame until 00025 /// prolog/epilog code is inserted. This class is key to allowing stack frame 00026 /// representation optimizations, such as frame pointer elimination. It also 00027 /// allows more mundane (but still important) optimizations, such as reordering 00028 /// of abstract objects on the stack frame. 00029 /// 00030 /// To support this, the class assigns unique integer identifiers to stack 00031 /// objects requested clients. These identifiers are negative integers for 00032 /// fixed stack objects (such as arguments passed on the stack) or positive 00033 /// for objects that may be reordered. Instructions which refer to stack 00034 /// objects use a special MO_FrameIndex operand to represent these frame 00035 /// indexes. 00036 /// 00037 /// Because this class keeps track of all references to the stack frame, it 00038 /// knows when a variable sized object is allocated on the stack. This is the 00039 /// sole condition which prevents frame pointer elimination, which is an 00040 /// important optimization on register-poor architectures. Because original 00041 /// variable sized alloca's in the source program are the only source of 00042 /// variable sized stack objects, it is safe to decide whether there will be 00043 /// any variable sized objects before all stack objects are known (for 00044 /// example, register allocator spill code never needs variable sized 00045 /// objects). 00046 /// 00047 /// When prolog/epilog code emission is performed, the final stack frame is 00048 /// built and the machine instructions are modified to refer to the actual 00049 /// stack offsets of the object, eliminating all MO_FrameIndex operands from 00050 /// the program. 00051 /// 00052 /// @brief Abstract Stack Frame Information 00053 class MachineFrameInfo { 00054 00055 // StackObject - Represent a single object allocated on the stack. 00056 struct StackObject { 00057 // The size of this object on the stack. 0 means a variable sized object 00058 unsigned Size; 00059 00060 // Alignment - The required alignment of this stack slot. 00061 unsigned Alignment; 00062 00063 // SPOffset - The offset of this object from the stack pointer on entry to 00064 // the function. This field has no meaning for a variable sized element. 00065 int SPOffset; 00066 00067 StackObject(unsigned Sz, unsigned Al, int SP) 00068 : Size(Sz), Alignment(Al), SPOffset(SP) {} 00069 }; 00070 00071 /// Objects - The list of stack objects allocated... 00072 /// 00073 std::vector<StackObject> Objects; 00074 00075 /// NumFixedObjects - This contains the number of fixed objects contained on 00076 /// the stack. Because fixed objects are stored at a negative index in the 00077 /// Objects list, this is also the index to the 0th object in the list. 00078 /// 00079 unsigned NumFixedObjects; 00080 00081 /// HasVarSizedObjects - This boolean keeps track of whether any variable 00082 /// sized objects have been allocated yet. 00083 /// 00084 bool HasVarSizedObjects; 00085 00086 /// StackSize - The prolog/epilog code inserter calculates the final stack 00087 /// offsets for all of the fixed size objects, updating the Objects list 00088 /// above. It then updates StackSize to contain the number of bytes that need 00089 /// to be allocated on entry to the function. 00090 /// 00091 unsigned StackSize; 00092 00093 /// MaxAlignment - The prolog/epilog code inserter may process objects 00094 /// that require greater alignment than the default alignment the target 00095 /// provides. To handle this, MaxAlignment is set to the maximum alignment 00096 /// needed by the objects on the current frame. If this is greater than the 00097 /// native alignment maintained by the compiler, dynamic alignment code will 00098 /// be needed. 00099 /// 00100 unsigned MaxAlignment; 00101 00102 /// HasCalls - Set to true if this function has any function calls. This is 00103 /// only valid during and after prolog/epilog code insertion. 00104 bool HasCalls; 00105 00106 /// MaxCallFrameSize - This contains the size of the largest call frame if the 00107 /// target uses frame setup/destroy pseudo instructions (as defined in the 00108 /// TargetFrameInfo class). This information is important for frame pointer 00109 /// elimination. If is only valid during and after prolog/epilog code 00110 /// insertion. 00111 /// 00112 unsigned MaxCallFrameSize; 00113 00114 /// DebugInfo - This field is set (via setMachineDebugInfo) by a debug info 00115 /// consumer (ex. DwarfWriter) to indicate that frame layout information 00116 /// should be acquired. Typically, it's the responsibility of the target's 00117 /// MRegisterInfo prologue/epilogue emitting code to inform MachineDebugInfo 00118 /// of frame layouts. 00119 MachineDebugInfo *DebugInfo; 00120 00121 public: 00122 MachineFrameInfo() { 00123 NumFixedObjects = StackSize = MaxAlignment = 0; 00124 HasVarSizedObjects = false; 00125 HasCalls = false; 00126 MaxCallFrameSize = 0; 00127 DebugInfo = 0; 00128 } 00129 00130 /// hasStackObjects - Return true if there are any stack objects in this 00131 /// function. 00132 /// 00133 bool hasStackObjects() const { return !Objects.empty(); } 00134 00135 /// hasVarSizedObjects - This method may be called any time after instruction 00136 /// selection is complete to determine if the stack frame for this function 00137 /// contains any variable sized objects. 00138 /// 00139 bool hasVarSizedObjects() const { return HasVarSizedObjects; } 00140 00141 /// getObjectIndexBegin - Return the minimum frame object index... 00142 /// 00143 int getObjectIndexBegin() const { return -NumFixedObjects; } 00144 00145 /// getObjectIndexEnd - Return one past the maximum frame object index... 00146 /// 00147 int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; } 00148 00149 /// getObjectSize - Return the size of the specified object 00150 /// 00151 int getObjectSize(int ObjectIdx) const { 00152 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!"); 00153 return Objects[ObjectIdx+NumFixedObjects].Size; 00154 } 00155 00156 /// getObjectAlignment - Return the alignment of the specified stack object... 00157 int getObjectAlignment(int ObjectIdx) const { 00158 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!"); 00159 return Objects[ObjectIdx+NumFixedObjects].Alignment; 00160 } 00161 00162 /// getObjectOffset - Return the assigned stack offset of the specified object 00163 /// from the incoming stack pointer. 00164 /// 00165 int getObjectOffset(int ObjectIdx) const { 00166 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!"); 00167 return Objects[ObjectIdx+NumFixedObjects].SPOffset; 00168 } 00169 00170 /// setObjectOffset - Set the stack frame offset of the specified object. The 00171 /// offset is relative to the stack pointer on entry to the function. 00172 /// 00173 void setObjectOffset(int ObjectIdx, int SPOffset) { 00174 assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!"); 00175 Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset; 00176 } 00177 00178 /// getStackSize - Return the number of bytes that must be allocated to hold 00179 /// all of the fixed size frame objects. This is only valid after 00180 /// Prolog/Epilog code insertion has finalized the stack frame layout. 00181 /// 00182 unsigned getStackSize() const { return StackSize; } 00183 00184 /// setStackSize - Set the size of the stack... 00185 /// 00186 void setStackSize(unsigned Size) { StackSize = Size; } 00187 00188 /// getMaxAlignment - Return the alignment in bytes that this function must be 00189 /// aligned to, which is greater than the default stack alignment provided by 00190 /// the target. 00191 /// 00192 unsigned getMaxAlignment() const { return MaxAlignment; } 00193 00194 /// setMaxAlignment - Set the preferred alignment. 00195 /// 00196 void setMaxAlignment(unsigned Align) { MaxAlignment = Align; } 00197 00198 /// hasCalls - Return true if the current function has no function calls. 00199 /// This is only valid during or after prolog/epilog code emission. 00200 /// 00201 bool hasCalls() const { return HasCalls; } 00202 void setHasCalls(bool V) { HasCalls = V; } 00203 00204 /// getMaxCallFrameSize - Return the maximum size of a call frame that must be 00205 /// allocated for an outgoing function call. This is only available if 00206 /// CallFrameSetup/Destroy pseudo instructions are used by the target, and 00207 /// then only during or after prolog/epilog code insertion. 00208 /// 00209 unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; } 00210 void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; } 00211 00212 /// CreateFixedObject - Create a new object at a fixed location on the stack. 00213 /// All fixed objects should be created before other objects are created for 00214 /// efficiency. This returns an index with a negative value. 00215 /// 00216 int CreateFixedObject(unsigned Size, int SPOffset) { 00217 assert(Size != 0 && "Cannot allocate zero size fixed stack objects!"); 00218 Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset)); 00219 return -++NumFixedObjects; 00220 } 00221 00222 /// CreateStackObject - Create a new statically sized stack object, returning 00223 /// a postive identifier to represent it. 00224 /// 00225 int CreateStackObject(unsigned Size, unsigned Alignment) { 00226 // Keep track of the maximum alignment. 00227 if (MaxAlignment < Alignment) MaxAlignment = Alignment; 00228 00229 assert(Size != 0 && "Cannot allocate zero size stack objects!"); 00230 Objects.push_back(StackObject(Size, Alignment, -1)); 00231 return Objects.size()-NumFixedObjects-1; 00232 } 00233 00234 /// CreateVariableSizedObject - Notify the MachineFrameInfo object that a 00235 /// variable sized object has been created. This must be created whenever a 00236 /// variable sized object is created, whether or not the index returned is 00237 /// actually used. 00238 /// 00239 int CreateVariableSizedObject() { 00240 HasVarSizedObjects = true; 00241 if (MaxAlignment < 1) MaxAlignment = 1; 00242 Objects.push_back(StackObject(0, 1, -1)); 00243 return Objects.size()-NumFixedObjects-1; 00244 } 00245 00246 /// getMachineDebugInfo - Used by a prologue/epilogue emitter (MRegisterInfo) 00247 /// to provide frame layout information. 00248 MachineDebugInfo *getMachineDebugInfo() const { return DebugInfo; } 00249 00250 /// setMachineDebugInfo - Used by a debug consumer (DwarfWriter) to indicate 00251 /// that frame layout information should be gathered. 00252 void setMachineDebugInfo(MachineDebugInfo *DI) { DebugInfo = DI; } 00253 00254 /// print - Used by the MachineFunction printer to print information about 00255 /// stack objects. Implemented in MachineFunction.cpp 00256 /// 00257 void print(const MachineFunction &MF, std::ostream &OS) const; 00258 00259 /// dump - Call print(MF, std::cerr) to be called from the debugger. 00260 void dump(const MachineFunction &MF) const; 00261 }; 00262 00263 } // End llvm namespace 00264 00265 #endif