1 //===-- llvm/CodeGen/MachineCodeEmitter.h - Code emission -------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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"
24 class MachineBasicBlock;
25 class MachineConstantPool;
26 class MachineJumpTableInfo;
27 class MachineFunction;
28 class MachineModuleInfo;
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;
63 virtual ~MachineCodeEmitter() {}
65 /// startFunction - This callback is invoked when the specified function is
66 /// about to be code generated. This initializes the BufferBegin/End/Ptr
69 virtual void startFunction(MachineFunction &F) = 0;
71 /// finishFunction - This callback is invoked when the specified function has
72 /// finished code generation. If a buffer overflow has occurred, this method
73 /// returns true (the callee is required to try again), otherwise it returns
76 virtual bool finishFunction(MachineFunction &F) = 0;
78 /// startFunctionStub - This callback is invoked when the JIT needs the
79 /// address of a function that has not been code generated yet. The StubSize
80 /// specifies the total size required by the stub. Stubs are not allowed to
81 /// have constant pools, the can only use the other emitByte*/emitWord*
84 virtual void startFunctionStub(const GlobalValue* F, unsigned StubSize,
85 unsigned Alignment = 1) = 0;
87 /// finishFunctionStub - This callback is invoked to terminate a function
90 virtual void *finishFunctionStub(const GlobalValue* F) = 0;
92 /// emitByte - This callback is invoked when a byte needs to be written to the
95 void emitByte(unsigned char B) {
96 if (CurBufferPtr != BufferEnd)
100 /// emitWordLE - This callback is invoked when a 32-bit word needs to be
101 /// written to the output stream in little-endian format.
103 void emitWordLE(unsigned W) {
104 if (CurBufferPtr+4 <= BufferEnd) {
105 *CurBufferPtr++ = (unsigned char)(W >> 0);
106 *CurBufferPtr++ = (unsigned char)(W >> 8);
107 *CurBufferPtr++ = (unsigned char)(W >> 16);
108 *CurBufferPtr++ = (unsigned char)(W >> 24);
110 CurBufferPtr = BufferEnd;
114 /// emitWordBE - This callback is invoked when a 32-bit word needs to be
115 /// written to the output stream in big-endian format.
117 void emitWordBE(unsigned W) {
118 if (CurBufferPtr+4 <= BufferEnd) {
119 *CurBufferPtr++ = (unsigned char)(W >> 24);
120 *CurBufferPtr++ = (unsigned char)(W >> 16);
121 *CurBufferPtr++ = (unsigned char)(W >> 8);
122 *CurBufferPtr++ = (unsigned char)(W >> 0);
124 CurBufferPtr = BufferEnd;
128 /// emitAlignment - Move the CurBufferPtr pointer up the the specified
129 /// alignment (saturated to BufferEnd of course).
130 void emitAlignment(unsigned Alignment) {
131 if (Alignment == 0) Alignment = 1;
132 // Move the current buffer ptr up to the specified alignment.
134 (unsigned char*)(((intptr_t)CurBufferPtr+Alignment-1) &
135 ~(intptr_t)(Alignment-1));
136 if (CurBufferPtr > BufferEnd)
137 CurBufferPtr = BufferEnd;
141 /// emitULEB128Bytes - This callback is invoked when a ULEB128 needs to be
142 /// written to the output stream.
143 void emitULEB128Bytes(unsigned Value) {
145 unsigned char Byte = Value & 0x7f;
147 if (Value) Byte |= 0x80;
152 /// emitSLEB128Bytes - This callback is invoked when a SLEB128 needs to be
153 /// written to the output stream.
154 void emitSLEB128Bytes(int Value) {
155 int Sign = Value >> (8 * sizeof(Value) - 1);
159 unsigned char Byte = Value & 0x7f;
161 IsMore = Value != Sign || ((Byte ^ Sign) & 0x40) != 0;
162 if (IsMore) Byte |= 0x80;
167 /// emitString - This callback is invoked when a String needs to be
168 /// written to the output stream.
169 void emitString(const std::string &String) {
170 for (unsigned i = 0, N = static_cast<unsigned>(String.size());
172 unsigned char C = String[i];
178 /// emitInt32 - Emit a int32 directive.
179 void emitInt32(int Value) {
180 if (CurBufferPtr+4 <= BufferEnd) {
181 *((uint32_t*)CurBufferPtr) = Value;
184 CurBufferPtr = BufferEnd;
188 /// emitInt64 - Emit a int64 directive.
189 void emitInt64(uint64_t Value) {
190 if (CurBufferPtr+8 <= BufferEnd) {
191 *((uint64_t*)CurBufferPtr) = Value;
194 CurBufferPtr = BufferEnd;
198 /// emitAt - Emit Value in Addr
199 void emitAt(uintptr_t *Addr, uintptr_t Value) {
200 if (Addr >= (uintptr_t*)BufferBegin && Addr < (uintptr_t*)BufferEnd)
204 /// emitLabel - Emits a label
205 virtual void emitLabel(uint64_t LabelID) = 0;
207 /// allocateSpace - Allocate a block of space in the current output buffer,
208 /// returning null (and setting conditions to indicate buffer overflow) on
209 /// failure. Alignment is the alignment in bytes of the buffer desired.
210 void *allocateSpace(intptr_t Size, unsigned Alignment) {
211 emitAlignment(Alignment);
212 void *Result = CurBufferPtr;
214 // Allocate the space.
215 CurBufferPtr += Size;
217 // Check for buffer overflow.
218 if (CurBufferPtr >= BufferEnd) {
219 CurBufferPtr = BufferEnd;
225 /// StartMachineBasicBlock - This should be called by the target when a new
226 /// basic block is about to be emitted. This way the MCE knows where the
227 /// start of the block is, and can implement getMachineBasicBlockAddress.
228 virtual void StartMachineBasicBlock(MachineBasicBlock *MBB) = 0;
230 /// getCurrentPCValue - This returns the address that the next emitted byte
231 /// will be output to.
233 virtual intptr_t getCurrentPCValue() const {
234 return (intptr_t)CurBufferPtr;
237 /// getCurrentPCOffset - Return the offset from the start of the emitted
238 /// buffer that we are currently writing to.
239 intptr_t getCurrentPCOffset() const {
240 return CurBufferPtr-BufferBegin;
243 /// addRelocation - Whenever a relocatable address is needed, it should be
244 /// noted with this interface.
245 virtual void addRelocation(const MachineRelocation &MR) = 0;
248 /// FIXME: These should all be handled with relocations!
250 /// getConstantPoolEntryAddress - Return the address of the 'Index' entry in
251 /// the constant pool that was last emitted with the emitConstantPool method.
253 virtual intptr_t getConstantPoolEntryAddress(unsigned Index) const = 0;
255 /// getJumpTableEntryAddress - Return the address of the jump table with index
256 /// 'Index' in the function that last called initJumpTableInfo.
258 virtual intptr_t getJumpTableEntryAddress(unsigned Index) const = 0;
260 /// getMachineBasicBlockAddress - Return the address of the specified
261 /// MachineBasicBlock, only usable after the label for the MBB has been
264 virtual intptr_t getMachineBasicBlockAddress(MachineBasicBlock *MBB) const= 0;
266 /// getLabelAddress - Return the address of the specified LabelID, only usable
267 /// after the LabelID has been emitted.
269 virtual intptr_t getLabelAddress(uint64_t LabelID) const = 0;
271 /// Specifies the MachineModuleInfo object. This is used for exception handling
273 virtual void setModuleInfo(MachineModuleInfo* Info) = 0;
276 } // End llvm namespace