https://bugs.llvm.org/show_bug.cgi?id=38856
Bug ID: 38856
Summary: -Wconditional-uninitialized false positive on struct
array field
Product: clang
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Static Analyzer
Assignee: dcough...@apple.com
Reporter: evan.j.pre...@gmail.com
CC: llvm-bugs@lists.llvm.org
Created attachment 20850
--> https://bugs.llvm.org/attachment.cgi?id=20850&action=edit
test.c
I have attached a case highlighting some strange behavior regarding
-Wconditional-uninitialized.
----- test.c -----
#include <stdio.h>
typedef struct { int x[2]; } test_t;
test_t foo_1(void);
test_t foo_2(void);
test_t foo_3(void);
test_t foo_1() {
test_t t;
for(int i = 0; i < 2; i++) t.x[i] = 0;
return t;
}
test_t foo_2() {
test_t t;
t.x[0] = 0;
for(int i = 0; i < 2; i++) t.x[i] = 0;
return t;
}
test_t foo_3() {
test_t t;
t.x[0] = 0;
return t;
}
int main() {
test_t t;
t = foo_1();
printf("%i %i\n", t.x[0], t.x[1]);
t = foo_2();
printf("%i %i\n", t.x[0], t.x[1]);
t = foo_3();
printf("%i %i\n", t.x[0], t.x[1]);
}
------------------
Compilation gives:
------------------
$ clang -Weverything test.c
test.c:12:12: warning: variable 't' may be uninitialized when used here
[-Wconditional-uninitialized]
return t;
^
test.c:10:5: note: variable 't' is declared here
test_t t;
^
1 warning generated.
------------------
although both elements of the array in the struct test_t have been assigned in
foo_1() where the warning is coming from. Manual assignment of the elements
without a loop gives no warnings. Strangely, if the first element is set as in
foo_2() followed by the loop, there is no warning.
This is fine if false positives from -Wconditional-uninitialized are considered
to be acceptable. However, in foo_3(), only the first element of the array is
set and there are no warnings; the second element is actually uninitialized.
This seems like it shouldn't happen. Is this valid/wontfix behavior or a real
problem?
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