public static int getMaxStack()

in src/main/java/org/apache/bcel/generic/MethodGen.java [139:204]
52 lines of code
18 McCabe index (conditional complexity)

    public static int getMaxStack(final ConstantPoolGen cp, final InstructionList il, final CodeExceptionGen[] et) {
        final BranchStack branchTargets = new BranchStack();
        /*
         * Initially, populate the branch stack with the exception handlers, because these aren't (necessarily) branched to
         * explicitly. in each case, the stack will have depth 1, containing the exception object.
         */
        for (final CodeExceptionGen element : et) {
            final InstructionHandle handlerPc = element.getHandlerPC();
            if (handlerPc != null) {
                branchTargets.push(handlerPc, 1);
            }
        }
        int stackDepth = 0;
        int maxStackDepth = 0;
        InstructionHandle ih = il.getStart();
        while (ih != null) {
            final Instruction instruction = ih.getInstruction();
            final short opcode = instruction.getOpcode();
            final int delta = instruction.produceStack(cp) - instruction.consumeStack(cp);
            stackDepth += delta;
            if (stackDepth > maxStackDepth) {
                maxStackDepth = stackDepth;
            }
            // choose the next instruction based on whether current is a branch.
            if (instruction instanceof BranchInstruction) {
                final BranchInstruction branch = (BranchInstruction) instruction;
                if (instruction instanceof Select) {
                    // explore all of the select's targets. the default target is handled below.
                    final Select select = (Select) branch;
                    final InstructionHandle[] targets = select.getTargets();
                    for (final InstructionHandle target : targets) {
                        branchTargets.push(target, stackDepth);
                    }
                    // nothing to fall through to.
                    ih = null;
                } else if (!(branch instanceof IfInstruction)) {
                    // if an instruction that comes back to following PC,
                    // push next instruction, with stack depth reduced by 1.
                    if (opcode == Const.JSR || opcode == Const.JSR_W) {
                        branchTargets.push(ih.getNext(), stackDepth - 1);
                    }
                    ih = null;
                }
                // for all branches, the target of the branch is pushed on the branch stack.
                // conditional branches have a fall through case, selects don't, and
                // jsr/jsr_w return to the next instruction.
                branchTargets.push(branch.getTarget(), stackDepth);
            } else // check for instructions that terminate the method.
            if (opcode == Const.ATHROW || opcode == Const.RET || opcode >= Const.IRETURN && opcode <= Const.RETURN) {
                ih = null;
            }
            // normal case, go to the next instruction.
            if (ih != null) {
                ih = ih.getNext();
            }
            // if we have no more instructions, see if there are any deferred branches to explore.
            if (ih == null) {
                final BranchTarget bt = branchTargets.pop();
                if (bt != null) {
                    ih = bt.target;
                    stackDepth = bt.stackDepth;
                }
            }
        }
        return maxStackDepth;
    }