The unsafe language features of C, such as low-level control of memory, often lead to memory errors, which can result in silent data corruption, security vulnerabilities, and program crashes. Dynamic analysis tools, which are widely used to detect memory errors at runtime, usually perform instrumentation at the IR-level or binary-level. However, their underlying non-source-level instrumentation techniques have three inherent limitations: optimization sensitivity, platform-dependence and DO-178C non-compliance. Due to optimization sensitivity, these tools are used to trade either performance for effectiveness by compiling the program at -O0 or effectiveness for performance by compiling the program at a higher optimization level, say, -O3. In this paper, we overcome these three limitations by proposing a new source-level instrumentation technique and implementing it in a tool, called SouLI, in a pointer-based instrumentation framework. Validation against a set of 86 microbenchmarks (with ground truth) and a set of 10 MiBench benchmarks shows that SouLI outperforms state-of-the-art tools, SoCets, ASan and Valgrind, in terms of both effectiveness and performance considered together.