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//===-- llvm/CodeGen/MachineCodeEmitter.h - Code emission -------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file 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
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