https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124017
Bug ID: 124017
Summary: Incomplete/Misleading diagnostic locations for
multiple undefined labels in goto statements
Product: gcc
Version: 15.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: 220246428 at seu dot edu.cn
Target Milestone: ---
When a function contains multiple goto statements pointing to the same
undefined label, GCC fails to provide a diagnostic message for each occurrence.
Instead, it only reports the error at the last occurrence or a significantly
offset position, effectively suppressing the location information of earlier
violations. However, Clang precisely reports the location and type of the
misalignment whenever an error occurs.
Minimal Reproducible Example
/* test_goto.c */
void test_function(int logic_gate) {
if (logic_gate > 10) {
goto lbl_missing; /* Violation 1: Line 4 */
}
int x = 0;
if (logic_gate < 5) {
goto lbl_missing; /* Violation 2: Line 9 */
}
x++;
goto lbl_missing; /* Violation 3: Line 13 */
}
Steps to reproduce: gcc -c test_goto.c
Actual Results:
test_goto.c: In function 'test_function':
test_goto.c:13:5: error: label 'lbl_missing' used but not defined
13 | goto lbl_missing;
| ^~~~
(Note: Lines 4 and 9 are completely ignored in the error report.)
While GCC does produce a diagnostic, its failure to identify the earlier goto
statements as constraint violations at their respective coordinates makes the
diagnostic information incomplete. In large, machine-generated, or complex
files (like the attached case), this behavior forces a "trial-and-error"
debugging process where the developer fixes one line only to have the compiler
"discover" the previous one in a subsequent pass.
The complete large file is attached. The same error appears at lines 772, 808,
and 923, yet GCC reports only an error at line 923.
