1 //===-- llvm/CodeGen/MachineCodeEmitter.h - Code emission -------*- 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 // This file defines an abstract interface that is used by the machine code
11 // emission framework to output the code. This allows machine code emission to
12 // be separated from concerns such as resolution of call targets, and where the
13 // machine code will be written (memory or disk, f.e.).
15 //===----------------------------------------------------------------------===//
17 #ifndef LLVM_CODEGEN_MACHINECODEEMITTER_H
18 #define LLVM_CODEGEN_MACHINECODEEMITTER_H
20 #include "llvm/Support/DataTypes.h"
25 class MachineBasicBlock;
26 class MachineConstantPool;
27 class MachineJumpTableInfo;
28 class MachineFunction;
29 class MachineRelocation;
34 /// MachineCodeEmitter - This class defines two sorts of methods: those for
35 /// emitting the actual bytes of machine code, and those for emitting auxillary
36 /// structures, such as jump tables, relocations, etc.
38 /// Emission of machine code is complicated by the fact that we don't (in
39 /// general) know the size of the machine code that we're about to emit before
40 /// we emit it. As such, we preallocate a certain amount of memory, and set the
41 /// BufferBegin/BufferEnd pointers to the start and end of the buffer. As we
42 /// emit machine instructions, we advance the CurBufferPtr to indicate the
43 /// location of the next byte to emit. In the case of a buffer overflow (we
44 /// need to emit more machine code than we have allocated space for), the
45 /// CurBufferPtr will saturate to BufferEnd and ignore stores. Once the entire
46 /// function has been emitted, the overflow condition is checked, and if it has
47 /// occurred, more memory is allocated, and we reemit the code into it.
49 class MachineCodeEmitter {
51 /// BufferBegin/BufferEnd - Pointers to the start and end of the memory
52 /// allocated for this code buffer.
53 unsigned char *BufferBegin, *BufferEnd;
55 /// CurBufferPtr - Pointer to the next byte of memory to fill when emitting
56 /// code. This is guranteed to be in the range [BufferBegin,BufferEnd]. If
57 /// this pointer is at BufferEnd, it will never move due to code emission, and
58 /// all code emission requests will be ignored (this is the buffer overflow
60 unsigned char *CurBufferPtr;
62 virtual ~MachineCodeEmitter() {}
64 /// startFunction - This callback is invoked when the specified function is
65 /// about to be code generated. This initializes the BufferBegin/End/Ptr
68 virtual void startFunction(MachineFunction &F) = 0;
70 /// finishFunction - This callback is invoked when the specified function has
71 /// finished code generation. If a buffer overflow has occurred, this method
72 /// returns true (the callee is required to try again), otherwise it returns
75 virtual bool finishFunction(MachineFunction &F) = 0;
77 /// emitJumpTableInfo - This callback is invoked to output the jump tables
78 /// for the function. In addition to a pointer to the MachineJumpTableInfo,
79 /// this function also takes a map of MBBs to addresses, so that the final
80 /// addresses of the MBBs can be written to the jump tables.
81 virtual void emitJumpTableInfo(MachineJumpTableInfo *MJTI,
82 std::map<MachineBasicBlock*,uint64_t> &MBBM) = 0;
84 /// startFunctionStub - This callback is invoked when the JIT needs the
85 /// address of a function that has not been code generated yet. The StubSize
86 /// specifies the total size required by the stub. Stubs are not allowed to
87 /// have constant pools, the can only use the other emitByte*/emitWord*
90 virtual void startFunctionStub(unsigned StubSize) = 0;
92 /// finishFunctionStub - This callback is invoked to terminate a function
95 virtual void *finishFunctionStub(const Function *F) = 0;
97 /// emitByte - This callback is invoked when a byte needs to be written to the
100 void emitByte(unsigned char B) {
101 if (CurBufferPtr != BufferEnd)
105 /// emitWordLE - This callback is invoked when a 32-bit word needs to be
106 /// written to the output stream in little-endian format.
108 void emitWordLE(unsigned W) {
109 if (CurBufferPtr+4 <= BufferEnd) {
110 *CurBufferPtr++ = (unsigned char)(W >> 0);
111 *CurBufferPtr++ = (unsigned char)(W >> 8);
112 *CurBufferPtr++ = (unsigned char)(W >> 16);
113 *CurBufferPtr++ = (unsigned char)(W >> 24);
115 CurBufferPtr = BufferEnd;
119 /// emitWordBE - This callback is invoked when a 32-bit word needs to be
120 /// written to the output stream in big-endian format.
122 void emitWordBE(unsigned W) {
123 if (CurBufferPtr+4 <= BufferEnd) {
124 *CurBufferPtr++ = (unsigned char)(W >> 24);
125 *CurBufferPtr++ = (unsigned char)(W >> 16);
126 *CurBufferPtr++ = (unsigned char)(W >> 8);
127 *CurBufferPtr++ = (unsigned char)(W >> 0);
129 CurBufferPtr = BufferEnd;
133 /// allocateSpace - Allocate a block of space in the current output buffer,
134 /// returning null (and setting conditions to indicate buffer overflow) on
135 /// failure. Alignment is the alignment in bytes of the buffer desired.
136 void *allocateSpace(intptr_t Size, unsigned Alignment) {
137 if (Alignment == 0) Alignment = 1;
138 // Move the current buffer ptr up to the specified alignment.
140 (unsigned char*)(((intptr_t)CurBufferPtr+Alignment-1) & ~(Alignment-1));
141 void *Result = CurBufferPtr;
143 // Allocate the space.
144 CurBufferPtr += Size;
146 // Check for buffer overflow.
147 if (CurBufferPtr >= BufferEnd) {
148 CurBufferPtr = BufferEnd;
155 /// getCurrentPCValue - This returns the address that the next emitted byte
156 /// will be output to.
158 virtual intptr_t getCurrentPCValue() const {
159 return (intptr_t)CurBufferPtr;
162 /// getCurrentPCOffset - Return the offset from the start of the emitted
163 /// buffer that we are currently writing to.
164 intptr_t getCurrentPCOffset() const {
165 return CurBufferPtr-BufferBegin;
168 /// addRelocation - Whenever a relocatable address is needed, it should be
169 /// noted with this interface.
170 virtual void addRelocation(const MachineRelocation &MR) = 0;
172 /// getConstantPoolEntryAddress - Return the address of the 'Index' entry in
173 /// the constant pool that was last emitted with the emitConstantPool method.
175 virtual uint64_t getConstantPoolEntryAddress(unsigned Index) = 0;
177 /// getJumpTableEntryAddress - Return the address of the jump table with index
178 /// 'Index' in the function that last called initJumpTableInfo.
180 virtual uint64_t getJumpTableEntryAddress(unsigned Index) = 0;
183 } // End llvm namespace