This paper presents a context-sensitive and path-sensitive algorithm for detecting null pointer dereferences (NPD).Our algorithm tracks the flow of values from the points where a null pointer might be produced to dereference points via value dependence graph that captures def-use relations and combines interval analysis results.Edges in the graph are annotated with guards that describe branch conditions in the program.In the meantime

for reducing the false warnings we propose an innovative demand-driven must-alias algorithm using this graph.Our implemented tool detects more than 70 points which might produce null pointer dereferences in ten SPEC 2000 benchmarks while keeping the false positive rate around 6%

which is excellent experimental results.