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