https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87038
--- Comment #19 from Harald van Dijk <harald at gigawatt dot nl> ---
(In reply to Segher Boessenkool from comment #18)
> (In reply to Harald van Dijk from comment #15)
> > (In reply to Segher Boessenkool from comment #10)
> > > The initialisation (the call to f1) could have a side effect, but the
> > > a==1 case skips that. GCC is right to warn here in my opinion.
>
> > And warnings that are likely to trigger on
> > perfectly valid code that behaves exactly as the author intended shouldn't
> > be included in -Wall, per your own comment.
>
> No, that is not what I said. *All* warnings are likely to trigger on valid
> code, after all. I said "frequent false positives".
Please re-read what I said. I didn't just say valid code, I said valid code
that behaves exactly as the author intended, or in other words code where the
fact that the initialisation is skipped over does not point to any problem, or
in other words a false positive.
I'm only at the start of a rebuild to see how commonly this warning will be
triggered, but I have found more false positives already almost immediately:
alsa-lib-1.1.7:
setup.c: In function 'snd_config_get_ctl_elem_value':
setup.c:361:5: error: jump skips variable initialization
[-Werror=jump-misses-init]
goto _bad_content;
^~~~
setup.c:313:4: note: label '_bad_content' defined here
_bad_content:
^~~~~~~~~~~~
setup.c:311:17: note: 'idx' declared here
unsigned int idx = 0;
^~~
(and more)
anjuta-3.28.0:
jsparse.c: In function 'print_node':
jsparse.c:49:4: error: switch jumps over variable initialization
[-Werror=jump-misses-init]
case TOK_RC:
^~~~
jsparse.c:32:4: note: switch starts here
switch ((JSTokenType)node->pn_type)
^~~~~~
jsparse.c:43:9: note: 'k' declared here
int k = 0;
^
(and more)
at-spi2-core-2.30.0:
../at-spi2-core-2.30.0/dbind/dbind-any.c: In function 'dbind_any_demarshal':
../at-spi2-core-2.30.0/dbind/dbind-any.c:642:5: error: switch jumps over
variable initialization [-Werror=jump-misses-init]
case DBUS_TYPE_VARIANT:
^~~~
../at-spi2-core-2.30.0/dbind/dbind-any.c:541:5: note: switch starts here
switch (**type) {
^~~~~~
../at-spi2-core-2.30.0/dbind/dbind-any.c:618:21: note: 'offset' declared here
int offset = 0, stralign;
^~~~~~
(and more)
busybox-1.29.3:
archival/bbunzip.c: In function 'bbunpack':
archival/bbunzip.c:68:6: error: jump skips variable initialization
[-Werror=jump-misses-init]
goto free_name;
^~~~
archival/bbunzip.c:183:2: note: label 'free_name' defined here
free_name:
^~~~~~~~~
archival/bbunzip.c:139:10: note: 'del' declared here
char *del = new_name;
^~~
In file included from archival/bzip2.c:101:
archival/libarchive/bz/compress.c: In function 'generateMTFValues':
archival/libarchive/bz/compress.c:286:3: error: jump skips variable
initialization [-Werror=jump-misses-init]
goto process_zPend; /* "process it and come back here" */
^~~~
archival/libarchive/bz/compress.c:251:2: note: label 'process_zPend' defined
here
process_zPend:
^~~~~~~~~~~~~
archival/libarchive/bz/compress.c:235:11: note: 'll_i' declared here
uint8_t ll_i = ll_i; /* gcc 4.3.1 thinks it may be used w/o init */
^~~~
cargo-vendor-0.1.15:
/h/cargo-vendor-src-0.1.15/vendor/libssh2-sys/libssh2/src/packet.c: In function
'_libssh2_packet_add':
/h/cargo-vendor-src-0.1.15/vendor/libssh2-sys/libssh2/src/packet.c:454:9:
error: jump skips variable initialization [-Werror=jump-misses-init]
goto libssh2_packet_add_jump_point5;
^~~~
/h/cargo-vendor-src-0.1.15/vendor/libssh2-sys/libssh2/src/packet.c:588:19:
note: label 'libssh2_packet_add_jump_point5' defined here
libssh2_packet_add_jump_point5:
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/h/cargo-vendor-src-0.1.15/vendor/libssh2-sys/libssh2/src/packet.c:574:31:
note: 'want_reply' declared here
unsigned char want_reply=0;
^~~~~~~~~~
(and more)
chromium-71.0.3578.10:
../../third_party/angle/third_party/vulkan-loader/src/loader/trampoline.c: In
function 'vkEnumeratePhysicalDevices':
../../third_party/angle/third_party/vulkan-loader/src/loader/trampoline.c:658:9:
error: jump skips variable initialization [-Werror=jump-misses-init]
goto out;
^~~~
../../third_party/angle/third_party/vulkan-loader/src/loader/trampoline.c:696:1:
note: label 'out' defined here
out:
^~~
../../third_party/angle/third_party/vulkan-loader/src/loader/trampoline.c:671:14:
note: 'setup_res' declared here
VkResult setup_res = setupLoaderTrampPhysDevs(instance);
^~~~~~~~~
(and more)
efivar-36:
efivarfs.c: In function 'efivarfs_get_variable_size':
efivarfs.c:182:3: error: jump skips variable initialization
[-Werror=jump-misses-init]
goto err;
^~~~
efivarfs.c:195:1: note: label 'err' defined here
err:
^~~
efivarfs.c:185:14: note: 'statbuf' declared here
struct stat statbuf = { 0, };
^~~~~~~
firefox-63.0b13:
1:45.56 In file included from
/h/firefox-63.0/third_party/prio/prio/client.c:21:
1:45.56 /h/firefox-63.0/third_party/prio/prio/client.c: In function
'share_polynomials':
1:45.56 /h/firefox-63.0/third_party/prio/prio/util.h:31:7: error: jump skips
variable initialization [-Werror=jump-misses-init]
1:45.56 goto cleanup;\
1:45.56 ^~~~
1:45.56 /h/firefox-63.0/third_party/prio/prio/client.c:98:3: note: in
expansion of macro 'P_CHECKA'
1:45.56 P_CHECKA (points_g = MPArray_dup (points_f));
1:45.56 ^~~~~~~~
1:45.56 /h/firefox-63.0/third_party/prio/prio/client.c:143:1: note: label
'cleanup' defined here
1:45.56 cleanup:
1:45.56 ^~~~~~~
1:45.56 /h/firefox-63.0/third_party/prio/prio/client.c:136:7: note: 'j'
declared here
1:45.56 int j = 0;
1:45.56 ^
(and more)
ksh-93v:
/h/ast-93v/src/lib/libast/path/pathopen.c: In function 'pathopen':
/h/ast-93v/src/lib/libast/path/pathopen.c:248:5: error: jump skips variable
initialization [-Werror=jump-misses-init]
goto adjust;
^~~~
/h/ast-93v/src/lib/libast/path/pathopen.c:358:3: note: label 'adjust' defined
here
adjust:
^~~~~~
/h/ast-93v/src/lib/libast/path/pathopen.c:255:10: note: 'server' declared here
int server = (oflags&(O_CREAT|O_NOCTTY)) == (O_CREAT|O_NOCTTY);
^~~~~~
cc1: some warnings being treated as errors
I've inspected all of these, and I'm convinced they are all false positives so
far. In almost all cases, the initialisation has no side effects. In the one
exception to that, the side effect is unwanted when the initialisation is
skipped. In all these cases, after the label being jumped to, as far as I can
tell the variable is not used any more. There is no point in warning about any
of this. In one of those cases, the variable is *only* initialised to suppress
another GCC false positive!
