Detect Copy-Paste Bugs
Pattern Miner can help you identify copy-paste bugs in your code base. When developers want to implement code that is mostly similar to existing code, but need to make minor modifications to fit the code into the new context, they often use copy-paste to save time. It is easy to introduce bugs during this process. For example, when you copy-paste a code segment from one place to another, you may often need to modify one variable name (e.g., variable i), to another (e.g., variable j). If you modify the segment in most instances, but forget to modify consistently within the replicated block, you can introduce a bug.
Here's an example from the Linux kernel: the loop in lines 111-118 was copied from lines 92-99. In the new copy-pasted segment (lines 111-118), the variable prom_phys_total is replaced with prom_prom_taken in all cases except in line 117 (shown in bold font). As a result, the pointer prom_prom_taken[iter].theres_more incorrectly points to the element of prom_phys_total instead of prom_prom_taken.
It's very difficult to detect copy-paste errors — since they are semantic errors, you cannot detect them visually or by using static or dynamic analysis tools. What makes it yet more challenging is that in many cases, the copy-paste code is slightly modified by the addition or deletion of statements.
Pattern Miner can help you detect these hard-to-find bugs. Pattern Miner efficiently detects similar code patterns that appear multiple times. It then flags code segments with multiple copies that have inconsistent changes between the copies, which indicate potential bugs.
