# [PATCH 0/3] scan-build fixes 13 messages from 2019-09-25 to 2019-09-29. Participants: Alex Henrie, Derrick Stolee, Johannes Schindelin, Jeff King. Thread: https://gitlist.dev/t/51912 ## Alex Henrie, 2019-09-25 02:01 Subject: [PATCH 0/3] scan-build fixes Message-ID: <20190925020158.751492-1-alexhenrie24@gmail.com> URL: https://gitlist.dev/e/20190925020158.751492-1-alexhenrie24%40gmail.com ``` These patches fix a few problems identified by scan-build [1]. None of them affect behavior, but they do make the code easier to follow and ensure that the compiler is able to optimize it to the fullest. -Alex [1] https://clang-analyzer.llvm.org/scan-build.html Alex Henrie (3): commit-graph: remove a duplicate assignment diffcore-break: use a goto instead of a redundant if statement wrapper: use a loop instead of repetitive statements commit-graph.c | 1 - diffcore-break.c | 15 +++++++-------- wrapper.c | 11 +++++------ 3 files changed, 12 insertions(+), 15 deletions(-) -- 2.23.0 ``` ## Alex Henrie, 2019-09-25 02:01 Subject: [PATCH 1/3] commit-graph: remove a duplicate assignment Message-ID: <20190925020158.751492-2-alexhenrie24@gmail.com> URL: https://gitlist.dev/e/20190925020158.751492-2-alexhenrie24%40gmail.com In-Reply-To: <20190925020158.751492-1-alexhenrie24@gmail.com> ``` Signed-off-by: Alex Henrie --- commit-graph.c | 1 - 1 file changed, 1 deletion(-) diff --git a/commit-graph.c b/commit-graph.c index 9b02d2c426..659f4bb4f4 100644 --- a/commit-graph.c +++ b/commit-graph.c @@ -1534,7 +1534,6 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx) size_mult = ctx->split_opts->size_multiple; } - g = ctx->r->objects->commit_graph; ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1; while (g && (g->num_commits <= size_mult * num_commits || -- 2.23.0 ``` ## Alex Henrie, 2019-09-25 02:01 Subject: [PATCH 2/3] diffcore-break: use a goto instead of a redundant if statement Message-ID: <20190925020158.751492-3-alexhenrie24@gmail.com> URL: https://gitlist.dev/e/20190925020158.751492-3-alexhenrie24%40gmail.com In-Reply-To: <20190925020158.751492-1-alexhenrie24@gmail.com> ``` Signed-off-by: Alex Henrie --- diffcore-break.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/diffcore-break.c b/diffcore-break.c index 875aefd3fe..f6ab74141b 100644 --- a/diffcore-break.c +++ b/diffcore-break.c @@ -286,18 +286,17 @@ void diffcore_merge_broken(void) /* Peer survived. Merge them */ merge_broken(p, pp, &outq); q->queue[j] = NULL; - break; + goto done; } } - if (q->nr <= j) - /* The peer did not survive, so we keep - * it in the output. - */ - diff_q(&outq, p); + /* The peer did not survive, so we keep + * it in the output. + */ } - else - diff_q(&outq, p); + diff_q(&outq, p); } + +done: free(q->queue); *q = outq; -- 2.23.0 ``` ## Alex Henrie, 2019-09-25 02:01 Subject: [PATCH 3/3] wrapper: use a loop instead of repetitive statements Message-ID: <20190925020158.751492-4-alexhenrie24@gmail.com> URL: https://gitlist.dev/e/20190925020158.751492-4-alexhenrie24%40gmail.com In-Reply-To: <20190925020158.751492-1-alexhenrie24@gmail.com> ``` Signed-off-by: Alex Henrie --- wrapper.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/wrapper.c b/wrapper.c index c55d7722d7..c23ac6adcd 100644 --- a/wrapper.c +++ b/wrapper.c @@ -469,13 +469,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) filename_template = &pattern[len - 6 - suffix_len]; for (count = 0; count < TMP_MAX; ++count) { uint64_t v = value; + int i; /* Fill in the random bits. */ - filename_template[0] = letters[v % num_letters]; v /= num_letters; - filename_template[1] = letters[v % num_letters]; v /= num_letters; - filename_template[2] = letters[v % num_letters]; v /= num_letters; - filename_template[3] = letters[v % num_letters]; v /= num_letters; - filename_template[4] = letters[v % num_letters]; v /= num_letters; - filename_template[5] = letters[v % num_letters]; v /= num_letters; + for (i = 0; i < 6; i++) { + filename_template[i] = letters[v % num_letters]; + v /= num_letters; + } fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode); if (fd >= 0) -- 2.23.0 ``` ## Derrick Stolee, 2019-09-26 13:02 Subject: Re: [PATCH 1/3] commit-graph: remove a duplicate assignment Message-ID: <8307cccf-e115-c720-6670-2ab537066a01@gmail.com> URL: https://gitlist.dev/e/8307cccf-e115-c720-6670-2ab537066a01%40gmail.com In-Reply-To: <20190925020158.751492-2-alexhenrie24@gmail.com> ``` On 9/24/2019 10:01 PM, Alex Henrie wrote: > Signed-off-by: Alex Henrie > --- > commit-graph.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/commit-graph.c b/commit-graph.c > index 9b02d2c426..659f4bb4f4 100644 > --- a/commit-graph.c > +++ b/commit-graph.c > @@ -1534,7 +1534,6 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx) > size_mult = ctx->split_opts->size_multiple; > } > > - g = ctx->r->objects->commit_graph; > ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1; > > while (g && (g->num_commits <= size_mult * num_commits || Could we instead remove the assignment during the declaration? It is easier to know the while loop will work if the assignment is closer to the loop. Thanks, -Stolee ``` ## Derrick Stolee, 2019-09-26 13:12 Subject: Re: [PATCH 2/3] diffcore-break: use a goto instead of a redundant if statement Message-ID: <5382f6cc-d699-0c99-6d61-60cae45f27c2@gmail.com> URL: https://gitlist.dev/e/5382f6cc-d699-0c99-6d61-60cae45f27c2%40gmail.com In-Reply-To: <20190925020158.751492-3-alexhenrie24@gmail.com> ``` On 9/24/2019 10:01 PM, Alex Henrie wrote: > Signed-off-by: Alex Henrie > --- > diffcore-break.c | 15 +++++++-------- > 1 file changed, 7 insertions(+), 8 deletions(-) > > diff --git a/diffcore-break.c b/diffcore-break.c > index 875aefd3fe..f6ab74141b 100644 > --- a/diffcore-break.c > +++ b/diffcore-break.c > @@ -286,18 +286,17 @@ void diffcore_merge_broken(void) > /* Peer survived. Merge them */ > merge_broken(p, pp, &outq); > q->queue[j] = NULL; > - break; > + goto done; > } > } > - if (q->nr <= j) > - /* The peer did not survive, so we keep > - * it in the output. > - */ > - diff_q(&outq, p); > + /* The peer did not survive, so we keep > + * it in the output. > + */ > } > - else > - diff_q(&outq, p); > + diff_q(&outq, p); > } > + > +done: > free(q->queue); > *q = outq; This took a little more context to check. The "if (q->nr <= j)" condition essentially means "did the for loop above end via the sentinel, not a break?" This means that the diff_q() call is run if the for loop finishes normally OR if we hit the visible "else" call. There is some subtlety with the if / else if / else conditions. The 'if' condition has a 'continue' which avoids the diff_q in its new position. Something like the two paragraphs above would be good to add to the commit message so we can more easily read this patch in the future. Here is the full method context (in master) to help others: void diffcore_merge_broken(void) { struct diff_queue_struct *q = &diff_queued_diff; struct diff_queue_struct outq; int i, j; DIFF_QUEUE_CLEAR(&outq); for (i = 0; i < q->nr; i++) { struct diff_filepair *p = q->queue[i]; if (!p) /* we already merged this with its peer */ continue; else if (p->broken_pair && !strcmp(p->one->path, p->two->path)) { /* If the peer also survived rename/copy, then * we merge them back together. */ for (j = i + 1; j < q->nr; j++) { struct diff_filepair *pp = q->queue[j]; if (pp->broken_pair && !strcmp(pp->one->path, pp->two->path) && !strcmp(p->one->path, pp->two->path)) { /* Peer survived. Merge them */ merge_broken(p, pp, &outq); q->queue[j] = NULL; break; } } if (q->nr <= j) /* The peer did not survive, so we keep * it in the output. */ diff_q(&outq, p); } else diff_q(&outq, p); } free(q->queue); *q = outq; return; } ``` ## Derrick Stolee, 2019-09-26 13:13 Subject: Re: [PATCH 3/3] wrapper: use a loop instead of repetitive statements Message-ID: <03e509db-942e-4538-4729-4e345df82a7e@gmail.com> URL: https://gitlist.dev/e/03e509db-942e-4538-4729-4e345df82a7e%40gmail.com In-Reply-To: <20190925020158.751492-4-alexhenrie24@gmail.com> ``` On 9/24/2019 10:01 PM, Alex Henrie wrote: > Signed-off-by: Alex Henrie > --- > wrapper.c | 11 +++++------ > 1 file changed, 5 insertions(+), 6 deletions(-) > > diff --git a/wrapper.c b/wrapper.c > index c55d7722d7..c23ac6adcd 100644 > --- a/wrapper.c > +++ b/wrapper.c > @@ -469,13 +469,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) > filename_template = &pattern[len - 6 - suffix_len]; > for (count = 0; count < TMP_MAX; ++count) { > uint64_t v = value; > + int i; > /* Fill in the random bits. */ > - filename_template[0] = letters[v % num_letters]; v /= num_letters; > - filename_template[1] = letters[v % num_letters]; v /= num_letters; > - filename_template[2] = letters[v % num_letters]; v /= num_letters; > - filename_template[3] = letters[v % num_letters]; v /= num_letters; > - filename_template[4] = letters[v % num_letters]; v /= num_letters; > - filename_template[5] = letters[v % num_letters]; v /= num_letters; > + for (i = 0; i < 6; i++) { > + filename_template[i] = letters[v % num_letters]; > + v /= num_letters; > + } > > fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode); > if (fd >= 0) > This change is clear. Thanks, -Stolee ``` ## Alex Henrie, 2019-09-26 18:05 Subject: Re: [PATCH 1/3] commit-graph: remove a duplicate assignment Message-ID: URL: https://gitlist.dev/e/CAMMLpeTxGiGrgYcC8jbtV-vAeEKMGZD7YRK397mwwpQdHig4KA%40mail.gmail.com In-Reply-To: <8307cccf-e115-c720-6670-2ab537066a01@gmail.com> ``` On Thu, Sep 26, 2019 at 7:02 AM Derrick Stolee wrote: > > Could we instead remove the assignment during the declaration? It is > easier to know the while loop will work if the assignment is closer > to the loop. Sure, that's fine. I'll send a v2 with that change. -Alex ``` ## Johannes Schindelin, 2019-09-26 20:14 Subject: Re: [PATCH 3/3] wrapper: use a loop instead of repetitive statements Message-ID: URL: https://gitlist.dev/e/nycvar.QRO.7.76.6.1909262155020.15067%40tvgsbejvaqbjf.bet In-Reply-To: <03e509db-942e-4538-4729-4e345df82a7e@gmail.com> ``` Hi, On Thu, 26 Sep 2019, Derrick Stolee wrote: > On 9/24/2019 10:01 PM, Alex Henrie wrote: > > Signed-off-by: Alex Henrie > > --- > > wrapper.c | 11 +++++------ > > 1 file changed, 5 insertions(+), 6 deletions(-) > > > > diff --git a/wrapper.c b/wrapper.c > > index c55d7722d7..c23ac6adcd 100644 > > --- a/wrapper.c > > +++ b/wrapper.c > > @@ -469,13 +469,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) > > filename_template = &pattern[len - 6 - suffix_len]; > > for (count = 0; count < TMP_MAX; ++count) { > > uint64_t v = value; > > + int i; > > /* Fill in the random bits. */ > > - filename_template[0] = letters[v % num_letters]; v /= num_letters; > > - filename_template[1] = letters[v % num_letters]; v /= num_letters; > > - filename_template[2] = letters[v % num_letters]; v /= num_letters; > > - filename_template[3] = letters[v % num_letters]; v /= num_letters; > > - filename_template[4] = letters[v % num_letters]; v /= num_letters; > > - filename_template[5] = letters[v % num_letters]; v /= num_letters; > > + for (i = 0; i < 6; i++) { > > + filename_template[i] = letters[v % num_letters]; > > + v /= num_letters; > > + } > > > > fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode); > > if (fd >= 0) > > > > This change is clear. Not so fast. This looks like it was intended to help compilers that cannot unroll loops all that easily, and just because current clang can does not mean that we should put people at a deliberate disadvantage when they are stuck with a C compiler that cannot optimize the post-image of this diff. Let's first see whether my gut feeling has any merit. This part of the code entered Git's tree in 0620b39b3b7 (compat: add a mkstemps() compatibility function, 2009-05-31), and it was clearly copy-edited from libiberty. It entered libiberty in https://github.com/gcc-mirror/gcc/commit/119735e34916. That commit claims that it was copy-edited from glibc, and edited it was, as it inlined the `__gen_tempname()` function. Sadly, the commit message of the patch that introduced this pattern into glibc is pretty much not helpful at all here: https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=a7ab2023fcdd5c90c9f664cbaed8ef90dd38e818 (it only talks about using a random-name generator that is already used elsewhere.) In short: sadly, this history excursion did not reveal anything to back up my intuition that your change would revert a change that might be crucial on older platforms. However, I think that this patch should at least be accompanied by a commit message that suggests that some thought was put into it, and that concerns like mine were considered carefully. I mean, if there is _any_ performance-critical code path hitting this unrolled loop, we may want to keep it unrolled. Ciao, Johannes ``` ## Jeff King, 2019-09-27 02:45 Subject: Re: [PATCH 3/3] wrapper: use a loop instead of repetitive statements Message-ID: <20190927024502.GC23736@sigill.intra.peff.net> URL: https://gitlist.dev/e/20190927024502.GC23736%40sigill.intra.peff.net In-Reply-To: <20190925020158.751492-4-alexhenrie24@gmail.com> ``` On Tue, Sep 24, 2019 at 08:01:58PM -0600, Alex Henrie wrote: > diff --git a/wrapper.c b/wrapper.c > index c55d7722d7..c23ac6adcd 100644 > --- a/wrapper.c > +++ b/wrapper.c > @@ -469,13 +469,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) > filename_template = &pattern[len - 6 - suffix_len]; > for (count = 0; count < TMP_MAX; ++count) { > uint64_t v = value; > + int i; > /* Fill in the random bits. */ > - filename_template[0] = letters[v % num_letters]; v /= num_letters; > - filename_template[1] = letters[v % num_letters]; v /= num_letters; > - filename_template[2] = letters[v % num_letters]; v /= num_letters; > - filename_template[3] = letters[v % num_letters]; v /= num_letters; > - filename_template[4] = letters[v % num_letters]; v /= num_letters; > - filename_template[5] = letters[v % num_letters]; v /= num_letters; > + for (i = 0; i < 6; i++) { > + filename_template[i] = letters[v % num_letters]; > + v /= num_letters; > + } I'm not sure the readability is changed much either way. But it does enable this additional cleanup on top: -- >8 -- Subject: git_mkstemps_mode(): replace magic numbers with computed value The magic number "6" appears several times in the function, and is related to the size of the "XXXXXX" string we expect to find in the template. Let's pull that "XXXXXX" into a constant array, whose size we can get at compile time with ARRAY_SIZE(). Note that we probably can't just change this value, since callers will be feeding us a certain number of X's, but it hopefully makes the function itself easier to follow. While we're here, let's do the same with the "letters" array (which we _could_ modify if we wanted to include more characters). Signed-off-by: Jeff King --- wrapper.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/wrapper.c b/wrapper.c index c23ac6adcd..e1eaef2e16 100644 --- a/wrapper.c +++ b/wrapper.c @@ -441,7 +441,9 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) "abcdefghijklmnopqrstuvwxyz" "ABCDEFGHIJKLMNOPQRSTUVWXYZ" "0123456789"; - static const int num_letters = 62; + static const int num_letters = ARRAY_SIZE(letters) - 1; + static const char x_pattern[] = "XXXXXX"; + static const int num_x = ARRAY_SIZE(x_pattern) - 1; uint64_t value; struct timeval tv; char *filename_template; @@ -450,12 +452,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) len = strlen(pattern); - if (len < 6 + suffix_len) { + if (len < num_x + suffix_len) { errno = EINVAL; return -1; } - if (strncmp(&pattern[len - 6 - suffix_len], "XXXXXX", 6)) { + if (strncmp(&pattern[len - num_x - suffix_len], x_pattern, num_x)) { errno = EINVAL; return -1; } @@ -466,12 +468,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) */ gettimeofday(&tv, NULL); value = ((uint64_t)tv.tv_usec << 16) ^ tv.tv_sec ^ getpid(); - filename_template = &pattern[len - 6 - suffix_len]; + filename_template = &pattern[len - num_x - suffix_len]; for (count = 0; count < TMP_MAX; ++count) { uint64_t v = value; int i; /* Fill in the random bits. */ - for (i = 0; i < 6; i++) { + for (i = 0; i < num_x; i++) { filename_template[i] = letters[v % num_letters]; v /= num_letters; } -- 2.23.0.765.g1fc3e247e7 ``` ## Jeff King, 2019-09-27 02:50 Subject: Re: [PATCH 3/3] wrapper: use a loop instead of repetitive statements Message-ID: <20190927025000.GD23736@sigill.intra.peff.net> URL: https://gitlist.dev/e/20190927025000.GD23736%40sigill.intra.peff.net In-Reply-To: ``` On Thu, Sep 26, 2019 at 10:14:17PM +0200, Johannes Schindelin wrote: > I mean, if there is _any_ performance-critical code path hitting this > unrolled loop, we may want to keep it unrolled. The loop in question is maybe a few dozen instructions, and then it immediately makes an open() syscall, which is probably multiple orders of magnitude more expensive. So I'd be very surprised if it was a problem no matter what the generated code looks like. But... > However, I think that this patch should at least be accompanied by a > commit message that suggests that some thought was put into it, and that > concerns like mine were considered carefully. ...this I would definitely agree with. -Peff ``` ## Derrick Stolee, 2019-09-27 11:48 Subject: Re: [PATCH 3/3] wrapper: use a loop instead of repetitive statements Message-ID: URL: https://gitlist.dev/e/d26869f8-9373-51a1-a146-7367aeeb2e85%40gmail.com In-Reply-To: <20190927024502.GC23736@sigill.intra.peff.net> ``` On 9/26/2019 10:45 PM, Jeff King wrote: > On Tue, Sep 24, 2019 at 08:01:58PM -0600, Alex Henrie wrote: > >> diff --git a/wrapper.c b/wrapper.c >> index c55d7722d7..c23ac6adcd 100644 >> --- a/wrapper.c >> +++ b/wrapper.c >> @@ -469,13 +469,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) >> filename_template = &pattern[len - 6 - suffix_len]; >> for (count = 0; count < TMP_MAX; ++count) { >> uint64_t v = value; >> + int i; >> /* Fill in the random bits. */ >> - filename_template[0] = letters[v % num_letters]; v /= num_letters; >> - filename_template[1] = letters[v % num_letters]; v /= num_letters; >> - filename_template[2] = letters[v % num_letters]; v /= num_letters; >> - filename_template[3] = letters[v % num_letters]; v /= num_letters; >> - filename_template[4] = letters[v % num_letters]; v /= num_letters; >> - filename_template[5] = letters[v % num_letters]; v /= num_letters; >> + for (i = 0; i < 6; i++) { >> + filename_template[i] = letters[v % num_letters]; >> + v /= num_letters; >> + } > > I'm not sure the readability is changed much either way. But it does > enable this additional cleanup on top: > > -- >8 -- > Subject: git_mkstemps_mode(): replace magic numbers with computed value > > The magic number "6" appears several times in the function, and is > related to the size of the "XXXXXX" string we expect to find in the > template. Let's pull that "XXXXXX" into a constant array, whose size we > can get at compile time with ARRAY_SIZE(). Removing magic numbers is always a good change. Thanks! > Note that we probably can't just change this value, since callers will > be feeding us a certain number of X's, but it hopefully makes the > function itself easier to follow. > > While we're here, let's do the same with the "letters" array (which we > _could_ modify if we wanted to include more characters). > > Signed-off-by: Jeff King > --- > wrapper.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/wrapper.c b/wrapper.c > index c23ac6adcd..e1eaef2e16 100644 > --- a/wrapper.c > +++ b/wrapper.c > @@ -441,7 +441,9 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) > "abcdefghijklmnopqrstuvwxyz" > "ABCDEFGHIJKLMNOPQRSTUVWXYZ" > "0123456789"; > - static const int num_letters = 62; > + static const int num_letters = ARRAY_SIZE(letters) - 1; > + static const char x_pattern[] = "XXXXXX"; > + static const int num_x = ARRAY_SIZE(x_pattern) - 1; > uint64_t value; > struct timeval tv; > char *filename_template; > @@ -450,12 +452,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) > > len = strlen(pattern); > > - if (len < 6 + suffix_len) { > + if (len < num_x + suffix_len) { > errno = EINVAL; > return -1; > } > > - if (strncmp(&pattern[len - 6 - suffix_len], "XXXXXX", 6)) { > + if (strncmp(&pattern[len - num_x - suffix_len], x_pattern, num_x)) { > errno = EINVAL; > return -1; > } > @@ -466,12 +468,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode) > */ > gettimeofday(&tv, NULL); > value = ((uint64_t)tv.tv_usec << 16) ^ tv.tv_sec ^ getpid(); > - filename_template = &pattern[len - 6 - suffix_len]; > + filename_template = &pattern[len - num_x - suffix_len]; > for (count = 0; count < TMP_MAX; ++count) { > uint64_t v = value; > int i; > /* Fill in the random bits. */ > - for (i = 0; i < 6; i++) { > + for (i = 0; i < num_x; i++) { > filename_template[i] = letters[v % num_letters]; > v /= num_letters; > } > ``` ## Alex Henrie, 2019-09-29 00:51 Subject: Re: [PATCH 3/3] wrapper: use a loop instead of repetitive statements Message-ID: URL: https://gitlist.dev/e/CAMMLpeRva%2BsVxhTE14prMFvZnJhouQO%2BvDYeze9ZRao-dAfsFA%40mail.gmail.com In-Reply-To: <20190927025000.GD23736@sigill.intra.peff.net> ``` On Thu, Sep 26, 2019 at 8:50 PM Jeff King wrote: > > On Thu, Sep 26, 2019 at 10:14:17PM +0200, Johannes Schindelin wrote: > > > However, I think that this patch should at least be accompanied by a > > commit message that suggests that some thought was put into it, and that > > concerns like mine were considered carefully. > > ...this I would definitely agree with. Thanks for the feedback everyone. I am not used to projects requiring detailed commit messages for small changes. I will send a v3 of the three patches with the additional explanations you requested. -Alex ```