https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108767
Bug ID: 108767
Summary: O2 optimization has side effects on static analysis.
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: analyzer
Assignee: dmalcolm at gcc dot gnu.org
Reporter: geoffreydgr at icloud dot com
Target Milestone: ---
Hi, David. I found a problem through the following case that the optimization
`-O2` has side effects on static analysis. GCC static analzyer falsely gives a
NPD warning under the optimization `-O2`.
Input:
```c
#include "stdio.h"
extern void __analyzer_describe ();
extern void __analyzer_eval ();
extern void __analyzer_dump ();
int main()
{
int b = 1;
int e = 2;
int f = 3;
int *g[] = {&e, &e};
int *h = &b;
int *j = &f;
for (int d = 0; d <= 1; d++)
{
*j = (*h && (h = g[d]));
// __analyzer_dump ();
__analyzer_eval(h==0);
// __analyzer_describe(0,h);
}
printf("NPD_FLAG %d\n", *j);
}
```
options: -O2 -fanalyzer
Output:
```
<source>: In function 'main':
<source>:19:9: warning: FALSE
19 | __analyzer_eval(h==0);
| ^~~~~~~~~~~~~~~~~~~~~
<source>:19:9: warning: UNKNOWN
<source>:19:9: warning: TRUE
<source>:19:9: warning: TRUE
<source>:19:9: warning: UNKNOWN
<source>:19:9: warning: TRUE
<source>:19:9: warning: TRUE
<source>:19:9: warning: UNKNOWN
<source>:17:15: warning: dereference of NULL 'h' [CWE-476]
[-Wanalyzer-null-dereference]
17 | *j = (*h && (h = g[d]));
| ^~
'main': events 1-9
|
| 15 | for (int d = 0; d <= 1; d++)
| | ~~^~~~
| | |
| | (1) following 'true' branch (when 'd !=
2')...
| | (5) following 'true' branch (when 'd !=
2')...
| | (7) following 'true' branch (when 'd !=
2')...
| 16 | {
| 17 | *j = (*h && (h = g[d]));
| | ~~~~~~~~~~~~~~~~~~~~~~~
| | | | | |
| | | | | (3) following 'true' branch...
| | | | (9) dereference of NULL 'h'
| | | (4) ...to here
| | (2) ...to here
| | (6) ...to here
| | (8) ...to here
|
Compiler returned: 0
```
options : -O1 -fanalyzer
Output:
```
<source>: In function 'main':
<source>:19:9: warning: FALSE
19 | __analyzer_eval(h==0);
| ^~~~~~~~~~~~~~~~~~~~~
<source>:19:9: warning: UNKNOWN
Compiler returned: 0
```
-O2: https://godbolt.org/z/GeTaeGMaf
-O1: https://godbolt.org/z/adnY8aa3K
