dicthelpers.diff: compare against default for missing values This is not only a bit faster, but also aligns with callers' expectations better since we can legitimately have manifestdict's _flags set to '' instead of unset. hg perfmergecalculate -r . before: ! wall 0.139582 comb 0.140000 user 0.140000 sys 0.000000 (best of 59) after: ! wall 0.126154 comb 0.120000 user 0.120000 sys 0.000000 (best of 74) hg perfmergecalculate -r .^ before: ! wall 0.236333 comb 0.240000 user 0.240000 sys 0.000000 (best of 36) after: ! wall 0.212265 comb 0.210000 user 0.210000 sys 0.000000 (best of 45)