//===-- llvm/CodeGen/MachineCodeEmitter.h - Code emission -------*- C++ -*-===// // // The LLVM Compiler Infrastructure // // This file was developed by the LLVM research group and is distributed under // the University of Illinois Open Source License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file defines an abstract interface that is used by the machine code // emission framework to output the code. This allows machine code emission to // be separated from concerns such as resolution of call targets, and where the // machine code will be written (memory or disk, f.e.). // //===----------------------------------------------------------------------===// #ifndef LLVM_CODEGEN_MACHINECODEEMITTER_H #define LLVM_CODEGEN_MACHINECODEEMITTER_H #include "llvm/Support/DataTypes.h" #include <vector> namespace llvm { class MachineBasicBlock; class MachineConstantPool; class MachineJumpTableInfo; class MachineFunction; class MachineRelocation; class Value; class GlobalValue; class Function; /// MachineCodeEmitter - This class defines two sorts of methods: those for /// emitting the actual bytes of machine code, and those for emitting auxillary /// structures, such as jump tables, relocations, etc. /// /// Emission of machine code is complicated by the fact that we don't (in /// general) know the size of the machine code that we're about to emit before /// we emit it. As such, we preallocate a certain amount of memory, and set the /// BufferBegin/BufferEnd pointers to the start and end of the buffer. As we /// emit machine instructions, we advance the CurBufferPtr to indicate the /// location of the next byte to emit. In the case of a buffer overflow (we /// need to emit more machine code than we have allocated space for), the /// CurBufferPtr will saturate to BufferEnd and ignore stores. Once the entire /// function has been emitted, the overflow condition is checked, and if it has /// occurred, more memory is allocated, and we reemit the code into it. /// class MachineCodeEmitter { protected: /// BufferBegin/BufferEnd - Pointers to the start and end of the memory /// allocated for this code buffer. unsigned char *BufferBegin, *BufferEnd; /// CurBufferPtr - Pointer to the next byte of memory to fill when emitting /// code. This is guranteed to be in the range [BufferBegin,BufferEnd]. If /// this pointer is at BufferEnd, it will never move due to code emission, and /// all code emission requests will be ignored (this is the buffer overflow /// condition). unsigned char *CurBufferPtr; public: virtual ~MachineCodeEmitter() {} /// startFunction - This callback is invoked when the specified function is /// about to be code generated. This initializes the BufferBegin/End/Ptr /// fields. /// virtual void startFunction(MachineFunction &F) = 0; /// finishFunction - This callback is invoked when the specified function has /// finished code generation. If a buffer overflow has occurred, this method /// returns true (the callee is required to try again), otherwise it returns /// false. /// virtual bool finishFunction(MachineFunction &F) = 0; /// startFunctionStub - This callback is invoked when the JIT needs the /// address of a function that has not been code generated yet. The StubSize /// specifies the total size required by the stub. Stubs are not allowed to /// have constant pools, the can only use the other emitByte*/emitWord* /// methods. /// virtual void startFunctionStub(unsigned StubSize, unsigned Alignment = 1) = 0; /// finishFunctionStub - This callback is invoked to terminate a function /// stub. /// virtual void *finishFunctionStub(const Function *F) = 0; /// emitByte - This callback is invoked when a byte needs to be written to the /// output stream. /// void emitByte(unsigned char B) { if (CurBufferPtr != BufferEnd) *CurBufferPtr++ = B; } /// emitWordLE - This callback is invoked when a 32-bit word needs to be /// written to the output stream in little-endian format. /// void emitWordLE(unsigned W) { if (CurBufferPtr+4 <= BufferEnd) { *CurBufferPtr++ = (unsigned char)(W >> 0); *CurBufferPtr++ = (unsigned char)(W >> 8); *CurBufferPtr++ = (unsigned char)(W >> 16); *CurBufferPtr++ = (unsigned char)(W >> 24); } else { CurBufferPtr = BufferEnd; } } /// emitWordBE - This callback is invoked when a 32-bit word needs to be /// written to the output stream in big-endian format. /// void emitWordBE(unsigned W) { if (CurBufferPtr+4 <= BufferEnd) { *CurBufferPtr++ = (unsigned char)(W >> 24); *CurBufferPtr++ = (unsigned char)(W >> 16); *CurBufferPtr++ = (unsigned char)(W >> 8); *CurBufferPtr++ = (unsigned char)(W >> 0); } else { CurBufferPtr = BufferEnd; } } /// emitAlignment - Move the CurBufferPtr pointer up the the specified /// alignment (saturated to BufferEnd of course). void emitAlignment(unsigned Alignment) { if (Alignment == 0) Alignment = 1; // Move the current buffer ptr up to the specified alignment. CurBufferPtr = (unsigned char*)(((intptr_t)CurBufferPtr+Alignment-1) & ~(intptr_t)(Alignment-1)); if (CurBufferPtr > BufferEnd) CurBufferPtr = BufferEnd; } /// allocateSpace - Allocate a block of space in the current output buffer, /// returning null (and setting conditions to indicate buffer overflow) on /// failure. Alignment is the alignment in bytes of the buffer desired. void *allocateSpace(intptr_t Size, unsigned Alignment) { emitAlignment(Alignment); void *Result = CurBufferPtr; // Allocate the space. CurBufferPtr += Size; // Check for buffer overflow. if (CurBufferPtr >= BufferEnd) { CurBufferPtr = BufferEnd; Result = 0; } return Result; } /// StartMachineBasicBlock - This should be called by the target when a new /// basic block is about to be emitted. This way the MCE knows where the /// start of the block is, and can implement getMachineBasicBlockAddress. virtual void StartMachineBasicBlock(MachineBasicBlock *MBB) = 0; /// getCurrentPCValue - This returns the address that the next emitted byte /// will be output to. /// virtual intptr_t getCurrentPCValue() const { return (intptr_t)CurBufferPtr; } /// getCurrentPCOffset - Return the offset from the start of the emitted /// buffer that we are currently writing to. intptr_t getCurrentPCOffset() const { return CurBufferPtr-BufferBegin; } /// addRelocation - Whenever a relocatable address is needed, it should be /// noted with this interface. virtual void addRelocation(const MachineRelocation &MR) = 0; /// FIXME: These should all be handled with relocations! /// getConstantPoolEntryAddress - Return the address of the 'Index' entry in /// the constant pool that was last emitted with the emitConstantPool method. /// virtual intptr_t getConstantPoolEntryAddress(unsigned Index) const = 0; /// getJumpTableEntryAddress - Return the address of the jump table with index /// 'Index' in the function that last called initJumpTableInfo. /// virtual intptr_t getJumpTableEntryAddress(unsigned Index) const = 0; /// getMachineBasicBlockAddress - Return the address of the specified /// MachineBasicBlock, only usable after the label for the MBB has been /// emitted. /// virtual intptr_t getMachineBasicBlockAddress(MachineBasicBlock *MBB) const= 0; }; } // End llvm namespace #endif