https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104205
Bug ID: 104205
Summary: Signed overflow in case label reports confusing
warning with -Wpedantic
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: stephen.wassell at sophos dot com
Target Milestone: ---
When compiling the following code with "gcc -Wpedantic":
int convert(int err)
{
switch (err)
{
case 1 << 31: // signed overflow - undefined behaviour
return 0;
default:
return 1;
}
}
int main()
{
return convert(1 << 31);
}
It reports a confusingly worded warning since version 6. It should say
something about undefined behaviour instead. Should there also be a warning for
the other use of 1 << 31?
<source>: In function 'convert':
<source>:5:9: warning: case label is not an integer constant expression
[-Wpedantic]
5 | case 1 << 31:
| ^~~~
Seen on gcc (Ubuntu 11.2.0-7ubuntu2) 11.2.0 x64, and multiple versions on
Compiler Explorer.
https://godbolt.org/z/4Tr1qxaqv
