http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55715
Bug #: 55715
Summary: bogus overflow warning for #if A-B when A<0 &
B==minimum integer
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: preprocessor
AssignedTo: [email protected]
ReportedBy: [email protected]
Consider this C program:
#if 9223372036854775807 < 0
#endif
#if -1 - 9223372036854775807 < 0
#endif
#if -1 - (-1 - 9223372036854775807) < 0
#endif
When compiled with GCC (x86-64), GCC 4.7.2 warns:
t.c:5:37: warning: integer overflow in preprocessor expression [enabled by
default]
The warning is incorrect, since there is no overflow in this program.
Evidently GCC's preprocessor computes A-B by first negating B, and then adding
the result to A. This causes GCC to incorrectly report overflow when B is the
minimum possible integer and A is negative, because in this case -B overflows
even though A-B does not overflow.
