https://bugs.llvm.org/show_bug.cgi?id=51865
Bug ID: 51865
Summary: Variable is incorrectly marked as "set but not used"
when used with the __cleanup__() attribute
Product: clang
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Frontend
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected]
Hello,
Yesterday I came across a possible issue in clang-13 when trying to rebuild[0]
the systemd codebase with one of the nightly[1] LLVM builds. After minimizing
the reproducer, the issue stems from a fact that clang incorrectly marks a
variable as "set but not used" if the variable is used only from the
__cleanup__() function:
Reproducer:
#include <stdio.h>
static void my_cleanup(char **test) {
if (test)
printf("my_cleanup: %s\n", *test);
}
int main(void) {
__attribute__((__cleanup__(my_cleanup))) char *x = NULL;
puts("Hello");
x = "test";
puts("World");
return 0;
}
Expected behavior (clang-12):
# clang --version
clang version 12.0.1 (Fedora 12.0.1-1.fc34)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /bin
# clang -Wall -Wextra -Werror -o test test.c
Unexpected behavior (clang-13):
# clang-13 --version
Ubuntu clang version
13.0.0-++20210914062619+f6b09e394a5f-1~exp1~20210914043438.103
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
# clang-13 -Wall -Wextra -Werror -o test test.c
test.c:9:52: error: variable 'x' set but not used
[-Werror,-Wunused-but-set-variable]
__attribute__((__cleanup__(my_cleanup))) char *x = NULL;
^
1 error generated.
[0] https://github.com/systemd/systemd/pull/20738
[1] https://apt.llvm.org/
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