LLVM API Documentation
00001 //===-- llvm/CodeGen/MachineCodeEmitter.h - Code emission -------*- 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 // This file defines an abstract interface that is used by the machine code 00011 // emission framework to output the code. This allows machine code emission to 00012 // be separated from concerns such as resolution of call targets, and where the 00013 // machine code will be written (memory or disk, f.e.). 00014 // 00015 //===----------------------------------------------------------------------===// 00016 00017 #ifndef LLVM_CODEGEN_MACHINECODEEMITTER_H 00018 #define LLVM_CODEGEN_MACHINECODEEMITTER_H 00019 00020 #include "llvm/Support/DataTypes.h" 00021 #include <vector> 00022 00023 namespace llvm { 00024 00025 class MachineBasicBlock; 00026 class MachineConstantPool; 00027 class MachineJumpTableInfo; 00028 class MachineFunction; 00029 class MachineRelocation; 00030 class Value; 00031 class GlobalValue; 00032 class Function; 00033 00034 /// MachineCodeEmitter - This class defines two sorts of methods: those for 00035 /// emitting the actual bytes of machine code, and those for emitting auxillary 00036 /// structures, such as jump tables, relocations, etc. 00037 /// 00038 /// Emission of machine code is complicated by the fact that we don't (in 00039 /// general) know the size of the machine code that we're about to emit before 00040 /// we emit it. As such, we preallocate a certain amount of memory, and set the 00041 /// BufferBegin/BufferEnd pointers to the start and end of the buffer. As we 00042 /// emit machine instructions, we advance the CurBufferPtr to indicate the 00043 /// location of the next byte to emit. In the case of a buffer overflow (we 00044 /// need to emit more machine code than we have allocated space for), the 00045 /// CurBufferPtr will saturate to BufferEnd and ignore stores. Once the entire 00046 /// function has been emitted, the overflow condition is checked, and if it has 00047 /// occurred, more memory is allocated, and we reemit the code into it. 00048 /// 00049 class MachineCodeEmitter { 00050 protected: 00051 /// BufferBegin/BufferEnd - Pointers to the start and end of the memory 00052 /// allocated for this code buffer. 00053 unsigned char *BufferBegin, *BufferEnd; 00054 00055 /// CurBufferPtr - Pointer to the next byte of memory to fill when emitting 00056 /// code. This is guranteed to be in the range [BufferBegin,BufferEnd]. If 00057 /// this pointer is at BufferEnd, it will never move due to code emission, and 00058 /// all code emission requests will be ignored (this is the buffer overflow 00059 /// condition). 00060 unsigned char *CurBufferPtr; 00061 public: 00062 virtual ~MachineCodeEmitter() {} 00063 00064 /// startFunction - This callback is invoked when the specified function is 00065 /// about to be code generated. This initializes the BufferBegin/End/Ptr 00066 /// fields. 00067 /// 00068 virtual void startFunction(MachineFunction &F) = 0; 00069 00070 /// finishFunction - This callback is invoked when the specified function has 00071 /// finished code generation. If a buffer overflow has occurred, this method 00072 /// returns true (the callee is required to try again), otherwise it returns 00073 /// false. 00074 /// 00075 virtual bool finishFunction(MachineFunction &F) = 0; 00076 00077 /// startFunctionStub - This callback is invoked when the JIT needs the 00078 /// address of a function that has not been code generated yet. The StubSize 00079 /// specifies the total size required by the stub. Stubs are not allowed to 00080 /// have constant pools, the can only use the other emitByte*/emitWord* 00081 /// methods. 00082 /// 00083 virtual void startFunctionStub(unsigned StubSize) = 0; 00084 00085 /// finishFunctionStub - This callback is invoked to terminate a function 00086 /// stub. 00087 /// 00088 virtual void *finishFunctionStub(const Function *F) = 0; 00089 00090 /// emitByte - This callback is invoked when a byte needs to be written to the 00091 /// output stream. 00092 /// 00093 void emitByte(unsigned char B) { 00094 if (CurBufferPtr != BufferEnd) 00095 *CurBufferPtr++ = B; 00096 } 00097 00098 /// emitWordLE - This callback is invoked when a 32-bit word needs to be 00099 /// written to the output stream in little-endian format. 00100 /// 00101 void emitWordLE(unsigned W) { 00102 if (CurBufferPtr+4 <= BufferEnd) { 00103 *CurBufferPtr++ = (unsigned char)(W >> 0); 00104 *CurBufferPtr++ = (unsigned char)(W >> 8); 00105 *CurBufferPtr++ = (unsigned char)(W >> 16); 00106 *CurBufferPtr++ = (unsigned char)(W >> 24); 00107 } else { 00108 CurBufferPtr = BufferEnd; 00109 } 00110 } 00111 00112 /// emitWordBE - This callback is invoked when a 32-bit word needs to be 00113 /// written to the output stream in big-endian format. 00114 /// 00115 void emitWordBE(unsigned W) { 00116 if (CurBufferPtr+4 <= BufferEnd) { 00117 *CurBufferPtr++ = (unsigned char)(W >> 24); 00118 *CurBufferPtr++ = (unsigned char)(W >> 16); 00119 *CurBufferPtr++ = (unsigned char)(W >> 8); 00120 *CurBufferPtr++ = (unsigned char)(W >> 0); 00121 } else { 00122 CurBufferPtr = BufferEnd; 00123 } 00124 } 00125 00126 /// emitAlignment - Move the CurBufferPtr pointer up the the specified 00127 /// alignment (saturated to BufferEnd of course). 00128 void emitAlignment(unsigned Alignment) { 00129 if (Alignment == 0) Alignment = 1; 00130 // Move the current buffer ptr up to the specified alignment. 00131 CurBufferPtr = 00132 (unsigned char*)(((intptr_t)CurBufferPtr+Alignment-1) & 00133 ~(intptr_t)(Alignment-1)); 00134 if (CurBufferPtr > BufferEnd) 00135 CurBufferPtr = BufferEnd; 00136 } 00137 00138 /// allocateSpace - Allocate a block of space in the current output buffer, 00139 /// returning null (and setting conditions to indicate buffer overflow) on 00140 /// failure. Alignment is the alignment in bytes of the buffer desired. 00141 void *allocateSpace(intptr_t Size, unsigned Alignment) { 00142 emitAlignment(Alignment); 00143 void *Result = CurBufferPtr; 00144 00145 // Allocate the space. 00146 CurBufferPtr += Size; 00147 00148 // Check for buffer overflow. 00149 if (CurBufferPtr >= BufferEnd) { 00150 CurBufferPtr = BufferEnd; 00151 Result = 0; 00152 } 00153 return Result; 00154 } 00155 00156 /// StartMachineBasicBlock - This should be called by the target when a new 00157 /// basic block is about to be emitted. This way the MCE knows where the 00158 /// start of the block is, and can implement getMachineBasicBlockAddress. 00159 virtual void StartMachineBasicBlock(MachineBasicBlock *MBB) = 0; 00160 00161 /// getCurrentPCValue - This returns the address that the next emitted byte 00162 /// will be output to. 00163 /// 00164 virtual intptr_t getCurrentPCValue() const { 00165 return (intptr_t)CurBufferPtr; 00166 } 00167 00168 /// getCurrentPCOffset - Return the offset from the start of the emitted 00169 /// buffer that we are currently writing to. 00170 intptr_t getCurrentPCOffset() const { 00171 return CurBufferPtr-BufferBegin; 00172 } 00173 00174 /// addRelocation - Whenever a relocatable address is needed, it should be 00175 /// noted with this interface. 00176 virtual void addRelocation(const MachineRelocation &MR) = 0; 00177 00178 00179 /// FIXME: These should all be handled with relocations! 00180 00181 /// getConstantPoolEntryAddress - Return the address of the 'Index' entry in 00182 /// the constant pool that was last emitted with the emitConstantPool method. 00183 /// 00184 virtual intptr_t getConstantPoolEntryAddress(unsigned Index) const = 0; 00185 00186 /// getJumpTableEntryAddress - Return the address of the jump table with index 00187 /// 'Index' in the function that last called initJumpTableInfo. 00188 /// 00189 virtual intptr_t getJumpTableEntryAddress(unsigned Index) const = 0; 00190 00191 /// getMachineBasicBlockAddress - Return the address of the specified 00192 /// MachineBasicBlock, only usable after the label for the MBB has been 00193 /// emitted. 00194 /// 00195 virtual intptr_t getMachineBasicBlockAddress(MachineBasicBlock *MBB) const= 0; 00196 }; 00197 00198 } // End llvm namespace 00199 00200 #endif