methodwriter.java

asm的源码包 并且包含英文的文档

            if (n > maxLocals) {
                maxLocals = n;
            }
        }
        // adds the instruction to the bytecode of the method
        if (var < 4 && opcode != Opcodes.RET) {
            int opt;
            if (opcode < Opcodes.ISTORE) {
                /* ILOAD_0 */
                opt = 26 + ((opcode - Opcodes.ILOAD) << 2) + var;
            } else {
                /* ISTORE_0 */
                opt = 59 + ((opcode - Opcodes.ISTORE) << 2) + var;
            }
            code.putByte(opt);
        } else if (var >= 256) {
            code.putByte(196 /* WIDE */).put12(opcode, var);
        } else {
            code.put11(opcode, var);
        }
        if (opcode >= Opcodes.ISTORE && compute == FRAMES && handlerCount > 0) {
            visitLabel(new Label());
        }
    }

    public void visitTypeInsn(final int opcode, final String desc) {
        Item i = cw.newClassItem(desc);
        // Label currentBlock = this.currentBlock;
        if (currentBlock != null) {
            if (compute == FRAMES) {
                currentBlock.frame.execute(opcode, code.length, cw, i);
            } else if (opcode == Opcodes.NEW) {
                // updates current and max stack sizes only if opcode == NEW
                // (no stack change for ANEWARRAY, CHECKCAST, INSTANCEOF)
                int size = stackSize + 1;
                if (size > maxStackSize) {
                    maxStackSize = size;
                }
                stackSize = size;
            }
        }
        // adds the instruction to the bytecode of the method
        code.put12(opcode, i.index);
    }

    public void visitFieldInsn(
        final int opcode,
        final String owner,
        final String name,
        final String desc)
    {
        Item i = cw.newFieldItem(owner, name, desc);
        // Label currentBlock = this.currentBlock;
        if (currentBlock != null) {
            if (compute == FRAMES) {
                currentBlock.frame.execute(opcode, 0, cw, i);
            } else {
                int size;
                // computes the stack size variation
                char c = desc.charAt(0);
                switch (opcode) {
                    case Opcodes.GETSTATIC:
                        size = stackSize + (c == 'D' || c == 'J' ? 2 : 1);
                        break;
                    case Opcodes.PUTSTATIC:
                        size = stackSize + (c == 'D' || c == 'J' ? -2 : -1);
                        break;
                    case Opcodes.GETFIELD:
                        size = stackSize + (c == 'D' || c == 'J' ? 1 : 0);
                        break;
                    // case Constants.PUTFIELD:
                    default:
                        size = stackSize + (c == 'D' || c == 'J' ? -3 : -2);
                        break;
                }
                // updates current and max stack sizes
                if (size > maxStackSize) {
                    maxStackSize = size;
                }
                stackSize = size;
            }
        }
        // adds the instruction to the bytecode of the method
        code.put12(opcode, i.index);
    }

    public void visitMethodInsn(
        final int opcode,
        final String owner,
        final String name,
        final String desc)
    {
        boolean itf = opcode == Opcodes.INVOKEINTERFACE;
        Item i = cw.newMethodItem(owner, name, desc, itf);
        int argSize = i.intVal;
        // Label currentBlock = this.currentBlock;
        if (currentBlock != null) {
            if (compute == FRAMES) {
                currentBlock.frame.execute(opcode, 0, cw, i);
            } else {
                /*
                 * computes the stack size variation. In order not to recompute
                 * several times this variation for the same Item, we use the
                 * intVal field of this item to store this variation, once it
                 * has been computed. More precisely this intVal field stores
                 * the sizes of the arguments and of the return value
                 * corresponding to desc.
                 */
                if (argSize == 0) {
                    // the above sizes have not been computed yet,
                    // so we compute them...
                    argSize = getArgumentsAndReturnSizes(desc);
                    // ... and we save them in order
                    // not to recompute them in the future
                    i.intVal = argSize;
                }
                int size;
                if (opcode == Opcodes.INVOKESTATIC) {
                    size = stackSize - (argSize >> 2) + (argSize & 0x03) + 1;
                } else {
                    size = stackSize - (argSize >> 2) + (argSize & 0x03);
                }
                // updates current and max stack sizes
                if (size > maxStackSize) {
                    maxStackSize = size;
                }
                stackSize = size;
            }
        }
        // adds the instruction to the bytecode of the method
        if (itf) {
            if (argSize == 0) {
                argSize = getArgumentsAndReturnSizes(desc);
                i.intVal = argSize;
            }
            code.put12(Opcodes.INVOKEINTERFACE, i.index).put11(argSize >> 2, 0);
        } else {
            code.put12(opcode, i.index);
        }
    }

    public void visitJumpInsn(final int opcode, final Label label) {
        Label nextInsn = null;
        // Label currentBlock = this.currentBlock;
        if (currentBlock != null) {
            if (compute == FRAMES) {
                currentBlock.frame.execute(opcode, 0, null, null);
                // 'label' is the target of a jump instruction
                label.getFirst().status |= Label.TARGET;
                // adds 'label' as a successor of this basic block
                addSuccessor(Edge.NORMAL, label);
                if (opcode != Opcodes.GOTO) {
                    // creates a Label for the next basic block
                    nextInsn = new Label();
                }
            } else {
                if (opcode == Opcodes.JSR) {
                    jsr = true;
                    currentBlock.status |= Label.JSR;
                    addSuccessor(stackSize + 1, label);
                    // creates a Label for the next basic block
                    nextInsn = new Label();
                    /*
                     * note that, by construction in this method, a JSR block
                     * has at least two successors in the control flow graph:
                     * the first one leads the next instruction after the JSR,
                     * while the second one leads to the JSR target.
                     */
                } else {
                    // updates current stack size (max stack size unchanged
                    // because stack size variation always negative in this
                    // case)
                    stackSize += Frame.SIZE[opcode];
                    addSuccessor(stackSize, label);
                }
            }
        }
        // adds the instruction to the bytecode of the method
        if ((label.status & Label.RESOLVED) != 0
                && label.position - code.length < Short.MIN_VALUE)
        {
            /*
             * case of a backward jump with an offset < -32768. In this case we
             * automatically replace GOTO with GOTO_W, JSR with JSR_W and IFxxx
             * <l> with IFNOTxxx <l'> GOTO_W <l>, where IFNOTxxx is the
             * "opposite" opcode of IFxxx (i.e., IFNE for IFEQ) and where <l'>
             * designates the instruction just after the GOTO_W.
             */
            if (opcode == Opcodes.GOTO) {
                code.putByte(200); // GOTO_W
            } else if (opcode == Opcodes.JSR) {
                code.putByte(201); // JSR_W
            } else {
                // if the IF instruction is transformed into IFNOT GOTO_W the
                // next instruction becomes the target of the IFNOT instruction
                if (nextInsn != null) {
                    nextInsn.status |= Label.TARGET;
                }
                code.putByte(opcode <= 166
                        ? ((opcode + 1) ^ 1) - 1
                        : opcode ^ 1);
                code.putShort(8); // jump offset
                code.putByte(200); // GOTO_W
            }
            label.put(this, code, code.length - 1, true);
        } else {
            /*
             * case of a backward jump with an offset >= -32768, or of a forward
             * jump with, of course, an unknown offset. In these cases we store
             * the offset in 2 bytes (which will be increased in
             * resizeInstructions, if needed).
             */
            code.putByte(opcode);
            label.put(this, code, code.length - 1, false);
        }
        if (currentBlock != null) {
            if (nextInsn != null) {
                // if the jump instruction is not a GOTO, the next instruction
                // is also a successor of this instruction. Calling visitLabel
                // adds the label of this next instruction as a successor of the
                // current block, and starts a new basic block
                visitLabel(nextInsn);
            }
            if (opcode == Opcodes.GOTO) {
                noSuccessor();
            }
        }
    }

    public void visitLabel(final Label label) {
        // resolves previous forward references to label, if any
        resize |= label.resolve(this, code.length, code.data);
        // updates currentBlock
        if ((label.status & Label.DEBUG) != 0) {
            return;
        }
        if (compute == FRAMES) {
            if (currentBlock != null) {
                if (label.position == currentBlock.position) {
                    // successive labels, do not start a new basic block
                    currentBlock.status |= (label.status & Label.TARGET);
                    label.frame = currentBlock.frame;
                    return;
                }
                // ends current block (with one new successor)
                addSuccessor(Edge.NORMAL, label);
            }
            // begins a new current block
            currentBlock = label;
            if (label.frame == null) {
                label.frame = new Frame();
                label.frame.owner = label;
            }
            // updates the basic block list
            if (previousBlock != null) {
                if (label.position == previousBlock.position) {
                    previousBlock.status |= (label.status & Label.TARGET);
                    label.frame = previousBlock.frame;
                    currentBlock = previousBlock;
                    return;
                }
                previousBlock.successor = label;
            }
            previousBlock = label;
        } else if (compute == MAXS) {
            if (currentBlock != null) {
                // ends current block (with one new successor)
                currentBlock.outputStackMax = maxStackSize;
                addSuccessor(stackSize, label);
            }
            // begins a new current block
            currentBlock = label;
            // resets the relative current and max stack sizes
            stackSize = 0;
            maxStackSize = 0;
            // updates the basic block list
            if (previousBlock != null) {
                previousBlock.successor = label;
            }
            previousBlock = label;
        }
    }

    public void visitLdcInsn(final Object cst) {
        Item i = cw.newConstItem(cst);
        // Label currentBlock = this.currentBlock;
        if (currentBlock != null) {
            if (compute == FRAMES) {
                currentBlock.frame.execute(Opcodes.LDC, 0, cw, i);
            } else {
                int size;
                // computes the stack size variation
                if (i.type == ClassWriter.LONG || i.type == ClassWriter.DOUBLE)
                {
                    size = stackSize + 2;
                } else {
                    size = stackSize + 1;
                }
                // updates current and max stack sizes
                if (size > maxStackSize) {
                    maxStackSize = size;
                }
                stackSize = size;
            }
        }
        // adds the instruction to the bytecode of the method
        int index = i.index;
        if (i.type == ClassWriter.LONG || i.type == ClassWriter.DOUBLE) {
            code.put12(20 /* LDC2_W */, index);
        } else if (index >= 256) {
            code.put12(19 /* LDC_W */, index);
        } else {
            code.put11(Opcodes.LDC, index);
        }
    }

    public void visitIincInsn(final int var, final int increment) {
        if (currentBlock != null) {
            if (compute == FRAMES) {
                currentBlock.frame.execute(Opcodes.IINC, var, null, null);
            }
        }
        if (compute != NOTHING) {
            // updates max locals
            int n = var + 1;
            if (n > maxLocals) {
                maxLocals = n;
            }
        }
        // adds the instruction to the bytecode of the method
        if ((var > 255) || (increment > 127) || (increment < -128)) {
            code.putByte(196 /* WIDE */)
                    .put12(Opcodes.IINC, var)
                    .putShort(increment);
        } else {
            code.putByte(Opcodes.IINC).put11(var, increment);
        }
    }

    public void visitTableSwitchInsn(
        final int min,
        final int max,
        final Label dflt,
        final Label labels[])
    {
        // adds the instruction to the bytecode of the method