程序包 proguard.analysis

类 DominatorCalculator

  • 所有已实现的接口:
    AttributeVisitor
    public class DominatorCalculator
extends java.lang.Object
implements AttributeVisitor
    Calculate the dominator tree of any method, making it possible to determine which instructions are guaranteed to be executed before others.

    This is useful for applications like the CallResolver that would like to know whether an instruction, e.g. a method call, is always guaranteed to be executed assuming the containing method is invoked, or if its execution requires specific branches in the method to be taken.

    In principle, dominator analysis is based on a simple equation:

    1. The entry node dominates only itself
    2. Any other node's dominator set is calculated by forming the intersection of the dominator sets of all its control flow predecessors. Afterwards, the node itself is also added to its dominator set.
    Like this, the dominator information is propagated through the control flow graph one by one, potentially requiring several iterations until the solution is stable, as the dominator sets of some predecessors might still be uninitialized when used.

    The implementation here is based on an algorithm that solves the underlying dataflow equation using optimized BitSet objects instead of normal sets.

    • 字段详细资料

      • EXIT_NODE_OFFSET

        public static final int EXIT_NODE_OFFSET
        Virtual instruction offset modelling the method exit, i.e. all return instructions.
        另请参阅:
        常量字段值

      • ENTRY_NODE_OFFSET

        public static final int ENTRY_NODE_OFFSET
        Virtual instruction offset modelling the method entry. This is needed such that the method entry is guaranteed to have no incoming control flow edges, as this would prevent the algorithm from converging properly without complicated alternative measures.
        另请参阅:
        常量字段值

    • 构造器详细资料

      • DominatorCalculator

        public DominatorCalculator()
        Creates a new DominatorCalculator. The default behavior is to ignore exceptions.

      • DominatorCalculator

        public DominatorCalculator​(boolean ignoreExceptions)
        Creates a new DominatorCalculator.
        参数:
        ignoreExceptions - If false, exceptions will be taken into account in the analysis.

    • 方法详细资料

      • dominates

        @Deprecated
public boolean dominates​(int dominator,
                         int inferior)
        已过时。
        Callers should use maybeDominates(int, int) to handle an optional value instead of an exception.
        Check if one instruction dominates another one. If this is the case, the dominating instruction is guaranteed to be executed before the inferior instruction. Should you wish to check whether an instruction is guaranteed to be executed once the containing method is invoked, you can use the virtual inferior EXIT_NODE_OFFSET as a collection for all return instructions.
        参数:
        dominator - The potentially dominating instruction's offset
        inferior - The potentially dominated instruction's offset
        返回:
        true if the potential dominator is indeed guaranteed to be executed before the inferior

      • maybeDominates

        public java.util.Optional<java.lang.Boolean> maybeDominates​(int dominator,
                                                            int inferior)
        Check if one instruction dominates another one. If this is the case, the dominating instruction is guaranteed to be executed before the inferior instruction. Should you wish to check whether an instruction is guaranteed to be executed once the containing method is invoked, you can use the virtual inferior EXIT_NODE_OFFSET as a collection for all return instructions.
        参数:
        dominator - The potentially dominating instruction's offset
        inferior - The potentially dominated instruction's offset
        返回:
        Optional.true if the potential dominator is indeed guaranteed to be executed before the inferior, Optional.false if not and Optional.empty when no dominator information is known.