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//===-- WriteInst.cpp - Functions for writing instructions -------*- C++ -*--=//
//
// This file implements the routines for encoding instruction opcodes to a
// bytecode stream.
//
// Note that the performance of this library is not terribly important, because
// it shouldn't be used by JIT type applications... so it is not a huge focus
// at least. :)
//
//===----------------------------------------------------------------------===//
#include "WriterInternals.h"
#include "llvm/Module.h"
#include "llvm/Method.h"
#include "llvm/BasicBlock.h"
#include "llvm/Instruction.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Tools/DataTypes.h"
#include <algorithm>
typedef unsigned char uchar;
// outputInstructionFormat0 - Output those wierd instructions that have a large
// number of operands or have large operands themselves...
//
// Format: [opcode] [type] [numargs] [arg0] [arg1] ... [arg<numargs-1>]
//
static void outputInstructionFormat0(const Instruction *I,
const SlotCalculator &Table,
unsigned Type, vector<uchar> &Out) {
// Opcode must have top two bits clear...
output_vbr(I->getInstType(), Out); // Instruction Opcode ID
output_vbr(Type, Out); // Result type
unsigned NumArgs; // Count the number of arguments to the instruction
for (NumArgs = 0; I->getOperand(NumArgs); NumArgs++) /*empty*/;
output_vbr(NumArgs, Out);
for (unsigned i = 0; const Value *N = I->getOperand(i); i++) {
assert(i < NumArgs && "Count of arguments failed!");
int Slot = Table.getValSlot(N);
output_vbr((unsigned)Slot, Out);
}
align32(Out); // We must maintain correct alignment!
}
// outputInstructionFormat1 - Output one operand instructions, knowing that no
// operand index is >= 2^12.
//
static void outputInstructionFormat1(const Instruction *I,
const SlotCalculator &Table, int *Slots,
unsigned Type, vector<uchar> &Out) {
unsigned IType = I->getInstType(); // Instruction Opcode ID
// bits Instruction format:
// --------------------------
// 31-30: Opcode type, fixed to 1.
// 29-24: Opcode
// 23-12: Resulting type plane
// 11- 0: Operand #1 (if set to (2^12-1), then zero operands)
//
unsigned Opcode = (1 << 30) | (IType << 24) | (Type << 12) | Slots[0];
// cerr << "1 " << IType << " " << Type << " " << Slots[0] << endl;
output(Opcode, Out);
}
// outputInstructionFormat2 - Output two operand instructions, knowing that no
// operand index is >= 2^8.
//
static void outputInstructionFormat2(const Instruction *I,
const SlotCalculator &Table, int *Slots,
unsigned Type, vector<uchar> &Out) {
unsigned IType = I->getInstType(); // Instruction Opcode ID
// bits Instruction format:
// --------------------------
// 31-30: Opcode type, fixed to 2.
// 29-24: Opcode
// 23-16: Resulting type plane
// 15- 8: Operand #1
// 7- 0: Operand #2
//
unsigned Opcode = (2 << 30) | (IType << 24) | (Type << 16) |
(Slots[0] << 8) | (Slots[1] << 0);
// cerr << "2 " << IType << " " << Type << " " << Slots[0] << " "
// << Slots[1] << endl;
output(Opcode, Out);
}
// outputInstructionFormat3 - Output three operand instructions, knowing that no
// operand index is >= 2^6.
//
static void outputInstructionFormat3(const Instruction *I,
const SlotCalculator &Table, int *Slots,
unsigned Type, vector<uchar> &Out) {
unsigned IType = I->getInstType(); // Instruction Opcode ID
// bits Instruction format:
// --------------------------
// 31-30: Opcode type, fixed to 3
// 29-24: Opcode
// 23-18: Resulting type plane
// 17-12: Operand #1
// 11- 6: Operand #2
// 5- 0: Operand #3
//
unsigned Opcode = (3 << 30) | (IType << 24) | (Type << 18) |
(Slots[0] << 12) | (Slots[1] << 6) | (Slots[2] << 0);
// cerr << "3 " << IType << " " << Type << " " << Slots[0] << " "
// << Slots[1] << " " << Slots[2] << endl;
output(Opcode, Out);
}
bool BytecodeWriter::processInstruction(const Instruction *I) {
assert(I->getInstType() < 64 && "Opcode too big???");
unsigned NumOperands = 0;
int MaxOpSlot = 0;
int Slots[3]; Slots[0] = (1 << 12)-1;
const Value *Def;
while ((Def = I->getOperand(NumOperands))) {
int slot = Table.getValSlot(Def);
assert(slot != -1 && "Broken bytecode!");
if (slot > MaxOpSlot) MaxOpSlot = slot;
if (NumOperands < 3) Slots[NumOperands] = slot;
NumOperands++;
}
// Figure out which type to encode with the instruction. Typically we want
// the type of the first parameter, as opposed to the type of the instruction
// (for example, with setcc, we always know it returns bool, but the type of
// the first param is actually interesting). But if we have no arguments
// we take the type of the instruction itself.
//
const Type *Ty;
if (NumOperands)
Ty = I->getOperand(0)->getType();
else
Ty = I->getType();
unsigned Type;
int Slot = Table.getValSlot(Ty);
assert(Slot != -1 && "Type not available!!?!");
Type = (unsigned)Slot;
// Decide which instruction encoding to use. This is determined primarily by
// the number of operands, and secondarily by whether or not the max operand
// will fit into the instruction encoding. More operands == fewer bits per
// operand.
//
switch (NumOperands) {
case 0:
case 1:
if (MaxOpSlot < (1 << 12)-1) { // -1 because we use 4095 to indicate 0 ops
outputInstructionFormat1(I, Table, Slots, Type, Out);
return false;
}
break;
case 2:
if (MaxOpSlot < (1 << 8)) {
outputInstructionFormat2(I, Table, Slots, Type, Out);
return false;
}
break;
case 3:
if (MaxOpSlot < (1 << 6)) {
outputInstructionFormat3(I, Table, Slots, Type, Out);
return false;
}
break;
}
outputInstructionFormat0(I, Table, Type, Out);
return false;
}
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