https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113973
Bug ID: 113973
Summary: Pleas issue a warning when using plain character
values in bitwise operations
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc-bugzilla at mkarcher dot dialup.fu-berlin.de
Target Milestone: ---
This example program compiles without any kind of warning in gcc:
static char x = 0xD8;
int main(void)
{
return 0x1200 | x;
}
The value returned from main is 0xFFFFFFD8 on architectures with 32-bit int and
signed characters by default. After just fixing a bug that was caused by an
unexpected sign expansion when building an int from individual bytes, I'd
rather have a warning if
1) A variable of type char is promoted to int.
2) The int value is used in an bitwise expression
3) More than 8 bits of the results are actually used
4) More than 8 bits may be non-zero
Because of condition 3, this will yiels no warning on "char y = x | 0x40;" (top
bits truncated, so condition 3 fails) and no warning on "int y = x & 0x40;"
(all high bits are guaranteed to be zero, so condition 4 fails).
The real-world bug that motivates this enhancement proposal is
https://github.com/hfst/hfst-ospell/issues/43
