From: Derrick Stolee Date: Mon, 01 Oct 2018 19:26:00 GMT Subject: Re: [PATCH 15/16] commit-reach: make can_all_from_reach... linear Message-ID: In-Reply-To: On 10/1/2018 3:16 PM, René Scharfe wrote: > Am 28.06.2018 um 14:31 schrieb Derrick Stolee via GitGitGadget: >> diff --git a/commit-reach.c b/commit-reach.c >> index c58e50fbb..ac132c8e4 100644 >> --- a/commit-reach.c >> +++ b/commit-reach.c >> @@ -513,65 +513,88 @@ int commit_contains(struct ref_filter *filter, struct commit *commit, >> return is_descendant_of(commit, list); >> } >> >> -int reachable(struct commit *from, int with_flag, int assign_flag, >> - time_t min_commit_date) >> +static int compare_commits_by_gen(const void *_a, const void *_b) >> { >> - struct prio_queue work = { compare_commits_by_commit_date }; >> + const struct commit *a = (const struct commit *)_a; >> + const struct commit *b = (const struct commit *)_b; > This cast is bogus. QSORT gets handed a struct commit **, i.e. an array > of pointers, and qsort(1) passes references to those pointers to the > compare function, and not the pointer values. Good catch! I'm disappointed that we couldn't use type-checking here, as it is quite difficult to discover that the types are wrong here. > As a result it's unlikely that the array is sorted in the intended > order. Given that, a silly question: Is sorting even necessary here? The reason to sort is to hopefully minimize the amount we walk by exploring the "lower" commits first. This is a performance-only thing, not a correctness issue (which is why the bug exists). Even then, it is just a heuristic. > Anyway, the patch below should fix it. > > -- >8 -- > Subject: [PATCH] commit-reach: fix cast in compare_commits_by_gen() > > The elements of the array to be sorted are commit pointers, so the > comparison function gets handed references to these pointers, not > pointers to commit objects. Cast to the right type and dereference > once to correctly get the commit reference. > > Found using Clang's ASan and t5500. > > Signed-off-by: Rene Scharfe > --- > Has this patch a performance impact? > > commit-reach.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/commit-reach.c b/commit-reach.c > index 00e5ceee6f..2f5e592d16 100644 > --- a/commit-reach.c > +++ b/commit-reach.c > @@ -529,8 +529,8 @@ int commit_contains(struct ref_filter *filter, struct commit *commit, > > static int compare_commits_by_gen(const void *_a, const void *_b) > { > - const struct commit *a = (const struct commit *)_a; > - const struct commit *b = (const struct commit *)_b; > + const struct commit *a = *(const struct commit * const *)_a; > + const struct commit *b = *(const struct commit * const *)_b; I would expect s/* const */**/ here, but I'm guessing your formulation is a bit extra careful about types. Thanks! Reviewed-by: Derrick Stolee