Diffing a plurality of subject replayable traces against a plurality comparison replayable traces includes identifying first mappings among sections of consecutive instructions recorded in the subject traces, identifying distinct subject sections within the subject traces, identifying second mappings among sections of consecutive instructions recorded in the comparison traces, and identifying a plurality of distinct comparison sections within the comparison traces. Each distinct subject section is compared against distinct comparison section(s) to determine a comparison status of each distinct subject section, including whether each distinct subject section is equal to a corresponding distinct comparison section, or different than the distinct comparison sections. The comparison status of a distinct subject section with respect a corresponding distinct comparison section is applied to each comparison section to which the distinct comparison section is mapped in the second mappings, and to each subject section to which the subject section is mapped in the first mappings.