[Bug c/108660] New: Wrong location for first statement of for loop (-Wunused-value)

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108660

            Bug ID: 108660
           Summary: Wrong location for first statement of for loop
                    (-Wunused-value)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
void t1(int t)
{
  for (t; t < 10; t++)
    ;
}
```
This should warn about a statement with no effect and GCC does but the location
marker is incorrect. The C front-end underlines the for keyword rather than the
expression `t`.
```
<source>: In function 't1':
<source>:3:3: warning: statement with no effect [-Wunused-value]
    3 |   for (t; t < 10; t++)
      |   ^~~
```


Note the C++ front-end gets it correct:
```
<source>: In function 'void t1(int)':
<source>:3:8: warning: statement has no effect [-Wunused-value]
    3 |   for (t; t < 10; t++)
      |        ^
```