[Bug middle-end/102887] New: wrong warning location with macro expansion

[Bug middle-end/102887] New: wrong warning location with macro expansion

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102887

            Bug ID: 102887
           Summary: wrong warning location with macro expansion
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

As noted here:
https://gcc.gnu.org/pipermail/gcc-patches/2021-October/582316.html
in a -Wuninitialized warning for the use of a variable in the expansion of a
macro the warning points to the macro definition and not to the point of its
expansion as in other warnings such as -Warray-bounds.  The test case below
shows the difference.  Pointing also to the point of the macro's expansion is
important in large functions.

$ cat t.C && gcc -O2 -S -Wall -Wextra t.C
#define X(x) x ? x + 1 : 2   // warning here (not helpful)

int f (int i, int j)
{
  int x;                     // note here (good)
  if (i < 0)
    x = i + 1;
  if (j < 0)
    return X (x);
  return -1;
}

#define A(i) a[i]            // note here (good)
extern int a[4];             // note here (good)

int g (int i)
{
  if (i < 0)
    return A (7);            // warning here (helpful)
  return -1;
}
t.C: In function ‘int f(int, int)’:
t.C:1:16: warning: ‘x’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
    1 | #define X(x) x ? x + 1 : 2   // warning here (not helpful)
      |                ^
t.C:5:7: note: ‘x’ was declared here
    5 |   int x;                     // note here (good)
      |       ^
t.C: In function ‘int g(int)’:
t.C:13:17: warning: array subscript 7 is above array bounds of ‘int [4]’
[-Warray-bounds]
   13 | #define A(i) a[i]            // note here (good)
      |              ~~~^
t.C:19:12: note: in expansion of macro ‘A’
   19 |     return A (7);            // warning here (helpful)
      |            ^
t.C:14:12: note: while referencing ‘a’
   14 | extern int a[4];             // note here (good)
      |            ^

[Bug middle-end/102887] wrong warning location with macro expansion

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102887

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
   Last reconfirmed|                            |2021-10-21
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
             Blocks|                            |24639


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639
[Bug 24639] [meta-bug] bug to track all Wuninitialized issues