| Issue |
76546
|
| Summary |
False positives for -Wunsequenced
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Halalaluyafail3
|
Clang interprets the evaluation of initializers as being unsequenced, which is incorrect.
For example the code here https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1729.htm in point B:
```c
#include <stdio.h>
#define ONE_INIT '0' + i++ % 3
#define INITIALIZERS [2] = ONE_INIT, [1] = ONE_INIT, [0] = ONE_INIT
int main()
{
int i = 0;
char x[4] = { INITIALIZERS }; // case 1
puts(x);
puts((char [4]){ INITIALIZERS }); // case 2
puts((char [4]){ INITIALIZERS } + i % 2); // case 3
}
```
A warning is generated for case 3, which is correct; but no `-Wunsequenced` warnings should be generated for cases 1 or 2 which have defined behavior.
I found issue #32412 which references the same problem, and the conclusion reached there doesn't really make much sense.
> The evaluations of the initialization list expressions are indeterminately sequenced with respect to
> one another and thus the order in which any side effects occur is unspecified.
Section 6.7.9 "Initialization" Paragraph 23 ISO 9899:2018
> Evaluations A and B are indeterminately sequenced when A is
> sequenced either before or after B, but it is unspecified which.
Section 5.1.2.3 "Program execution" Paragraph 3 ISO 9899:2018
The evaluations of each initializer are sequenced and are in unspecified order, but this doesn't mean that they are unsequenced.
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