methodwriter.java

asm的源码包 并且包含英文的文档

        int source = code.length;
        code.putByte(Opcodes.TABLESWITCH);
        code.length += (4 - code.length % 4) % 4;
        dflt.put(this, code, source, true);
        code.putInt(min).putInt(max);
        for (int i = 0; i < labels.length; ++i) {
            labels[i].put(this, code, source, true);
        }
        // updates currentBlock
        visitSwitchInsn(dflt, labels);
    }

    public void visitLookupSwitchInsn(
        final Label dflt,
        final int keys[],
        final Label labels[])
    {
        // adds the instruction to the bytecode of the method
        int source = code.length;
        code.putByte(Opcodes.LOOKUPSWITCH);
        code.length += (4 - code.length % 4) % 4;
        dflt.put(this, code, source, true);
        code.putInt(labels.length);
        for (int i = 0; i < labels.length; ++i) {
            code.putInt(keys[i]);
            labels[i].put(this, code, source, true);
        }
        // updates currentBlock
        visitSwitchInsn(dflt, labels);
    }

    private void visitSwitchInsn(final Label dflt, final Label[] labels) {
        // Label currentBlock = this.currentBlock;
        if (currentBlock != null) {
            if (compute == FRAMES) {
                currentBlock.frame.execute(Opcodes.LOOKUPSWITCH, 0, null, null);
                // adds current block successors
                addSuccessor(Edge.NORMAL, dflt);
                dflt.getFirst().status |= Label.TARGET;
                for (int i = 0; i < labels.length; ++i) {
                    addSuccessor(Edge.NORMAL, labels[i]);
                    labels[i].getFirst().status |= Label.TARGET;
                }
            } else {
                // updates current stack size (max stack size unchanged)
                --stackSize;
                // adds current block successors
                addSuccessor(stackSize, dflt);
                for (int i = 0; i < labels.length; ++i) {
                    addSuccessor(stackSize, labels[i]);
                }
            }
            // ends current block
            noSuccessor();
        }
    }

    public void visitMultiANewArrayInsn(final String desc, final int dims) {
        Item i = cw.newClassItem(desc);
        // Label currentBlock = this.currentBlock;
        if (currentBlock != null) {
            if (compute == FRAMES) {
                currentBlock.frame.execute(Opcodes.MULTIANEWARRAY, dims, cw, i);
            } else {
                // updates current stack size (max stack size unchanged because
                // stack size variation always negative or null)
                stackSize += 1 - dims;
            }
        }
        // adds the instruction to the bytecode of the method
        code.put12(Opcodes.MULTIANEWARRAY, i.index).putByte(dims);
    }

    public void visitTryCatchBlock(
        final Label start,
        final Label end,
        final Label handler,
        final String type)
    {
        ++handlerCount;
        Handler h = new Handler();
        h.start = start;
        h.end = end;
        h.handler = handler;
        h.desc = type;
        h.type = type != null ? cw.newClass(type) : 0;
        if (lastHandler == null) {
            firstHandler = h;
        } else {
            lastHandler.next = h;
        }
        lastHandler = h;
    }

    public void visitLocalVariable(
        final String name,
        final String desc,
        final String signature,
        final Label start,
        final Label end,
        final int index)
    {
        if (signature != null) {
            if (localVarType == null) {
                localVarType = new ByteVector();
            }
            ++localVarTypeCount;
            localVarType.putShort(start.position)
                    .putShort(end.position - start.position)
                    .putShort(cw.newUTF8(name))
                    .putShort(cw.newUTF8(signature))
                    .putShort(index);
        }
        if (localVar == null) {
            localVar = new ByteVector();
        }
        ++localVarCount;
        localVar.putShort(start.position)
                .putShort(end.position - start.position)
                .putShort(cw.newUTF8(name))
                .putShort(cw.newUTF8(desc))
                .putShort(index);
        if (compute != NOTHING) {
            // updates max locals
            char c = desc.charAt(0);
            int n = index + (c == 'J' || c == 'D' ? 2 : 1);
            if (n > maxLocals) {
                maxLocals = n;
            }
        }
    }

    public void visitLineNumber(final int line, final Label start) {
        if (lineNumber == null) {
            lineNumber = new ByteVector();
        }
        ++lineNumberCount;
        lineNumber.putShort(start.position);
        lineNumber.putShort(line);
    }

    public void visitMaxs(final int maxStack, final int maxLocals) {
        if (compute == FRAMES) {
            // completes the control flow graph with exception handler blocks
            Handler handler = firstHandler;
            while (handler != null) {
                Label l = handler.start.getFirst();
                Label h = handler.handler.getFirst();
                Label e = handler.end.getFirst();
                // computes the kind of the edges to 'h'
                String t = handler.desc == null
                        ? "java/lang/Throwable"
                        : handler.desc;
                int kind = Frame.OBJECT | cw.addType(t);
                // h is an exception handler
                h.status |= Label.TARGET;
                // adds 'h' as a successor of labels between 'start' and 'end'
                while (l != e) {
                    // creates an edge to 'h'
                    Edge b = new Edge();
                    b.info = kind;
                    b.successor = h;
                    // adds it to the successors of 'l'
                    b.next = l.successors;
                    l.successors = b;
                    // goes to the next label
                    l = l.successor;
                }
                handler = handler.next;
            }

            // creates and visits the first (implicit) frame
            Frame f = labels.frame;
            Type[] args = Type.getArgumentTypes(descriptor);
            f.initInputFrame(cw, access, args, this.maxLocals);
            visitFrame(f);

            /*
             * fix point algorithm: mark the first basic block as 'changed'
             * (i.e. put it in the 'changed' list) and, while there are changed
             * basic blocks, choose one, mark it as unchanged, and update its
             * successors (which can be changed in the process).
             */
            int max = 0;
            Label changed = labels;
            while (changed != null) {
                // removes a basic block from the list of changed basic blocks
                Label l = changed;
                changed = changed.next;
                l.next = null;
                f = l.frame;
                // a reacheable jump target must be stored in the stack map
                if ((l.status & Label.TARGET) != 0) {
                    l.status |= Label.STORE;
                }
                // all visited labels are reacheable, by definition
                l.status |= Label.REACHABLE;
                // updates the (absolute) maximum stack size
                int blockMax = f.inputStack.length + l.outputStackMax;
                if (blockMax > max) {
                    max = blockMax;
                }
                // updates the successors of the current basic block
                Edge e = l.successors;
                while (e != null) {
                    Label n = e.successor.getFirst();
                    boolean change = f.merge(cw, n.frame, e.info);
                    if (change && n.next == null) {
                        // if n has changed and is not already in the 'changed'
                        // list, adds it to this list
                        n.next = changed;
                        changed = n;
                    }
                    e = e.next;
                }
            }
            this.maxStack = max;

            // visits all the frames that must be stored in the stack map
            Label l = labels;
            while (l != null) {
                f = l.frame;
                if ((l.status & Label.STORE) != 0) {
                    visitFrame(f);
                }
                if ((l.status & Label.REACHABLE) == 0) {
                    // finds start and end of dead basic block
                    Label k = l.successor;
                    int start = l.position;
                    int end = (k == null ? code.length : k.position) - 1;
                    // if non empty basic block
                    if (end >= start) {
                        // replaces instructions with NOP ... NOP ATHROW
                        for (int i = start; i < end; ++i) {
                            code.data[i] = Opcodes.NOP;
                        }
                        code.data[end] = (byte) Opcodes.ATHROW;
                        // emits a frame for this unreachable block
                        startFrame(start, 0, 1);
                        frame[frameIndex++] = Frame.OBJECT
                                | cw.addType("java/lang/Throwable");
                        endFrame();
                    }
                }
                l = l.successor;
            }
        } else if (compute == MAXS) {
            // completes the control flow graph with exception handler blocks
            Handler handler = firstHandler;
            while (handler != null) {
                Label l = handler.start;
                Label h = handler.handler;
                Label e = handler.end;
                // adds 'h' as a successor of labels between 'start' and 'end'
                while (l != e) {
                    // creates an edge to 'h'
                    Edge b = new Edge();
                    b.info = Edge.EXCEPTION;
                    b.successor = h;
                    // adds it to the successors of 'l'
                    if ((l.status & Label.JSR) != 0) {
                        // if l is a JSR block, adds b after the first two edges
                        // to preserve the hypothesis about JSR block successors
                        // order (see {@link #visitJumpInsn})
                        b.next = l.successors.next.next;
                        l.successors.next.next = b;
                    } else {
                        b.next = l.successors;
                        l.successors = b;
                    }
                    // goes to the next label
                    l = l.successor;
                }
                handler = handler.next;
            }

            if (jsr) {
                // completes the control flow graph with the RET successors
                /*
                 * first step: finds the subroutines. This step determines, for
                 * each basic block, to which subroutine(s) it belongs, and
                 * stores this set as a bit set in the {@link Label#status}
                 * field. Subroutines are numbered with powers of two, from
                 * 0x1000 to 0x80000000 (so there must be at most 20 subroutines
                 * in a method).
                 */
                // finds the basic blocks that belong to the "main" subroutine
                int id = 0x1000;
                findSubroutine(labels, id);
                // finds the basic blocks that belong to the real subroutines
                Label l = labels;
                while (l != null) {
                    if ((l.status & Label.JSR) != 0) {
                        // the subroutine is defined by l's TARGET, not by l
                        Label subroutine = l.successors.next.successor;
                        // if this subroutine does not have an id yet...
                        if ((subroutine.status & ~0xFFF) == 0) {
                            // ...assigns it a new id and finds its basic blocks
                            id = id << 1;
                            findSubroutine(subroutine, id);
                        }
                    }
                    l = l.successor;
                }
                // second step: finds the successors of RET blocks
                findSubroutineSuccessors(0x1000, new Label[10], 0);
            }

            /*
             * control flow analysis algorithm: while the block stack is not
             * empty, pop a block from this stack, update the max stack size,
             * compute the true (non relative) begin stack size of the
             * successors of this block, and push these successors onto the
             * stack (unless they have already been pushed onto the stack).
             * Note: by hypothesis, the {@link Label#inputStackTop} of the
             * blocks in the block stack are the true (non relative) beginning
             * stack sizes of these blocks.
             */
            int max = 0;
            Label stack = labels;
            while (stack != null) {
                // pops a block from the stack
                Label l = stack;
                stack = stack.next;
                // computes the true (non relative) max stack size of this block
                int start = l.inputStackTop;
                int blockMax = start + l.outputStackMax;
                // updates the global max stack size
                if (blockMax > max) {
                    max = blockMax;
                }
                // analyses the successors of the block
                Edge b = l.successors;
                if ((l.status & Label.JSR) != 0) {
                    // ignores the first edge of JSR blocks (virtual successor)
                    b = b.next;
                }
                while (b != null) {
                    l = b.successor;
                    // if this successor has not already been pushed...
                    if ((l.status & Label.PUSHED) == 0) {
                        // computes its true beginning stack size...
                        l.inputStackTop = b.info == Edge.EXCEPTION ? 1 : start
                                + b.info;
                        // ...and pushes it onto the stack
                        l.status |= Label.PUSHED;