jsrinlineradapter.java

asm的源码包 并且包含英文的文档

     * @param instant TODO.
     * @param workList TODO.
     * @param newInstructions TODO.
     * @param newTryCatchBlocks TODO.
     */
    private void emitSubroutine(
        final Instantiation instant,
        final List worklist,
        final InsnList newInstructions,
        final List newTryCatchBlocks,
        final List newLocalVariables)
    {
        LabelNode duplbl = null;

        if (LOGGING) {
            log("--------------------------------------------------------");
            log("Emitting instantiation of subroutine " + instant.subroutine);
        }

        // Emit the relevant instructions for this instantiation, translating
        // labels and jump targets as we go:
        for (int i = 0, c = instructions.size(); i < c; i++) {
            AbstractInsnNode insn = instructions.get(i);
            Instantiation owner = instant.findOwner(i);

            // Always remap labels:
            if (insn.getType() == AbstractInsnNode.LABEL) {
                // Translate labels into their renamed equivalents.
                // Avoid adding the same label more than once. Note
                // that because we own this instruction the gotoTable
                // and the rangeTable will always agree.
                LabelNode ilbl = (LabelNode) insn;
                LabelNode remap = instant.rangeLabel(ilbl);
                if (LOGGING) {
                    log("Translating lbl #" + i + ":" + ilbl + " to " + remap);
                }
                if (remap != duplbl) {
                    newInstructions.add(remap);
                    duplbl = remap;
                }
                continue;
            }

            // We don't want to emit instructions that were already
            // emitted by a subroutine higher on the stack. Note that
            // it is still possible for a given instruction to be
            // emitted twice because it may belong to two subroutines
            // that do not invoke each other.
            if (owner != instant) {
                continue;
            }

            if (LOGGING) {
                log("Emitting inst #" + i);
            }

            if (insn.getOpcode() == RET) {
                // Translate RET instruction(s) to a jump to the return label
                // for the appropriate instantiation. The problem is that the
                // subroutine may "fall through" to the ret of a parent
                // subroutine; therefore, to find the appropriate ret label we
                // find the lowest subroutine on the stack that claims to own
                // this instruction. See the class javadoc comment for an
                // explanation on why this technique is safe (note: it is only
                // safe if the input is verifiable).
                LabelNode retlabel = null;
                for (Instantiation p = instant; p != null; p = p.previous) {
                    if (p.subroutine.ownsInstruction(i)) {
                        retlabel = p.returnLabel;
                    }
                }
                if (retlabel == null) {
                    // This is only possible if the mainSubroutine owns a RET
                    // instruction, which should never happen for verifiable
                    // code.
                    throw new RuntimeException("Instruction #" + i
                            + " is a RET not owned by any subroutine");
                }
                newInstructions.add(new JumpInsnNode(GOTO, retlabel));
            } else if (insn.getOpcode() == JSR) {
                LabelNode lbl = ((JumpInsnNode) insn).label;
                Subroutine sub = (Subroutine) subroutineHeads.get(lbl);
                Instantiation newinst = new Instantiation(instant, sub);
                LabelNode startlbl = newinst.gotoLabel(lbl);

                if (LOGGING) {
                    log(" Creating instantiation of subr " + sub);
                }

                // Rather than JSRing, we will jump to the inline version and
                // push NULL for what was once the return value. This hack
                // allows us to avoid doing any sort of data flow analysis to
                // figure out which instructions manipulate the old return value
                // pointer which is now known to be unneeded.
                newInstructions.add(new InsnNode(ACONST_NULL));
                newInstructions.add(new JumpInsnNode(GOTO, startlbl));
                newInstructions.add(newinst.returnLabel);

                // Insert this new instantiation into the queue to be emitted
                // later.
                worklist.add(newinst);
            } else {
                newInstructions.add(insn.clone(instant));
            }
        }

        // Emit try/catch blocks that are relevant to this method.
        for (Iterator it = tryCatchBlocks.iterator(); it.hasNext();) {
            TryCatchBlockNode trycatch = (TryCatchBlockNode) it.next();

            if (LOGGING) {
                log("try catch block original labels=" + trycatch.start + "-"
                        + trycatch.end + "->" + trycatch.handler);
            }

            final LabelNode start = instant.rangeLabel(trycatch.start);
            final LabelNode end = instant.rangeLabel(trycatch.end);

            // Ignore empty try/catch regions
            if (start == end) {
                if (LOGGING) {
                    log(" try catch block empty in this subroutine");
                }
                continue;
            }

            final LabelNode handler = instant.gotoLabel(trycatch.handler);

            if (LOGGING) {
                log(" try catch block new labels=" + start + "-" + end + "->"
                        + handler);
            }

            if (start == null || end == null || handler == null) {
                throw new RuntimeException("Internal error!");
            }

            newTryCatchBlocks.add(new TryCatchBlockNode(start,
                    end,
                    handler,
                    trycatch.type));
        }

        for (Iterator it = localVariables.iterator(); it.hasNext();) {
            LocalVariableNode lvnode = (LocalVariableNode) it.next();
            if (LOGGING) {
                log("local var " + lvnode.name);
            }
            final LabelNode start = instant.rangeLabel(lvnode.start);
            final LabelNode end = instant.rangeLabel(lvnode.end);
            if (start == end) {
                if (LOGGING) {
                    log("  local variable empty in this sub");
                }
                continue;
            }
            newLocalVariables.add(new LocalVariableNode(lvnode.name,
                    lvnode.desc,
                    lvnode.signature,
                    start,
                    end,
                    lvnode.index));
        }
    }

    private void log(final String str) {
        System.err.println(str);
    }

    protected static class Subroutine {

        public final BitSet instructions = new BitSet();

        public void addInstruction(final int idx) {
            instructions.set(idx);
        }

        public boolean ownsInstruction(final int idx) {
            return instructions.get(idx);
        }

        public String toString() {
            return "Subroutine: " + instructions;
        }
    }

    /**
     * A class that represents an instantiation of a subroutine. Each
     * instantiation has an associate "stack" --- which is a listing of those
     * instantiations that were active when this particular instance of this
     * subroutine was invoked. Each instantiation also has a map from the
     * original labels of the program to the labels appropriate for this
     * instantiation, and finally a label to return to.
     */
    private class Instantiation extends AbstractMap {

        /**
         * Previous instantiations; the stack must be statically predictable to
         * be inlinable.
         */
        final Instantiation previous;

        /**
         * The subroutine this is an instantiation of.
         */
        public final Subroutine subroutine;

        /**
         * This table maps Labels from the original source to Labels pointing at
         * code specific to this instantiation, for use in remapping try/catch
         * blocks,as well as gotos.
         * 
         * Note that in the presence of dual citizens instructions, that is,
         * instructions which belong to more than one subroutine due to the
         * merging of control flow without a RET instruction, we will map the
         * target label of a GOTO to the label used by the instantiation lowest
         * on the stack. This avoids code duplication during inlining in most
         * cases.
         * 
         * @see #findOwner(int)
         */
        public final Map rangeTable = new HashMap();

        /**
         * All returns for this instantiation will be mapped to this label
         */
        public final LabelNode returnLabel;

        public Instantiation(final Instantiation prev, final Subroutine sub) {
            previous = prev;
            subroutine = sub;
            for (Instantiation p = prev; p != null; p = p.previous) {
                if (p.subroutine == sub) {
                    throw new RuntimeException("Recursive invocation of " + sub);
                }
            }

            // Determine the label to return to when this subroutine terminates
            // via RET: note that the main subroutine never terminates via RET.
            if (prev != null) {
                returnLabel = new LabelNode();
            } else {
                returnLabel = null;
            }

            // Each instantiation will remap the labels from the code above to
            // refer to its particular copy of its own instructions. Note that
            // we collapse labels which point at the same instruction into one:
            // this is fairly common as we are often ignoring large chunks of
            // instructions, so what were previously distinct labels become
            // duplicates.
            LabelNode duplbl = null;
            for (int i = 0, c = instructions.size(); i < c; i++) {
                AbstractInsnNode insn = instructions.get(i);

                if (insn.getType() == AbstractInsnNode.LABEL) {
                    LabelNode ilbl = (LabelNode) insn;

                    if (duplbl == null) {
                        // if we already have a label pointing at this spot,
                        // don't recreate it.
                        duplbl = new LabelNode();
                    }

                    // Add an entry in the rangeTable for every label
                    // in the original code which points at the next
                    // instruction of our own to be emitted.
                    rangeTable.put(ilbl, duplbl);
                } else if (findOwner(i) == this) {
                    // We will emit this instruction, so clear the 'duplbl' flag
                    // since the next Label will refer to a distinct
                    // instruction.
                    duplbl = null;
                }
            }
        }

        /**
         * Returns the "owner" of a particular instruction relative to this
         * instantiation: the owner referes to the Instantiation which will emit
         * the version of this instruction that we will execute.
         * 
         * Typically, the return value is either <code>this</code> or
         * <code>null</code>. <code>this</code> indicates that this
         * instantiation will generate the version of this instruction that we
         * will execute, and <code>null</code> indicates that this
         * instantiation never executes the given instruction.
         * 
         * Sometimes, however, an instruction can belong to multiple
         * subroutines; this is called a "dual citizen" instruction (though it
         * may belong to more than 2 subroutines), and occurs when multiple
         * subroutines branch to common points of control. In this case, the
         * owner is the subroutine that appears lowest on the stack, and which
         * also owns the instruction in question.
         * 
         * @param i the index of the instruction in the original code
         * @return the "owner" of a particular instruction relative to this
         *         instantiation.
         */
        public Instantiation findOwner(final int i) {
            if (!subroutine.ownsInstruction(i)) {
                return null;
            }
            if (!dualCitizens.get(i)) {
                return this;
            }
            Instantiation own = this;
            for (Instantiation p = previous; p != null; p = p.previous) {
                if (p.subroutine.ownsInstruction(i)) {
                    own = p;
                }
            }
            return own;
        }

        /**
         * Looks up the label <code>l</code> in the <code>gotoTable</code>,
         * thus translating it from a Label in the original code, to a Label in
         * the inlined code that is appropriate for use by an instruction that
         * branched to the original label.
         * 
         * @param l The label we will be translating
         * @return a label for use by a branch instruction in the inlined code
         * @see #gotoTable
         */
        public LabelNode gotoLabel(final LabelNode l) {
            // owner should never be null, because owner is only null
            // if an instruction cannot be reached from this subroutine
            Instantiation owner = findOwner(instructions.indexOf(l));
            return (LabelNode) owner.rangeTable.get(l);
        }

        /**
         * Looks up the label <code>l</code> in the <code>rangeTable</code>,
         * thus translating it from a Label in the original code, to a Label in
         * the inlined code that is appropriate for use by an try/catch or
         * variable use annotation.
         * 
         * @param l The label we will be translating
         * @return a label for use by a try/catch or variable annotation in the
         *         original code
         * @see #rangeTable
         */
        public LabelNode rangeLabel(final LabelNode l) {
            return (LabelNode) rangeTable.get(l);
        }

        // AbstractMap implementation

        public Set entrySet() {
            return null;
        }

        public Object get(final Object o) {
            return gotoLabel((LabelNode) o);
        }
    }
}