https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104711
Bug ID: 104711
Summary: Unnecessary -Wshift-negative-value warning
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: arnd at linaro dot org
Target Milestone: ---
During the discussion of increasing the C standard version of the Linux kernel
fro m gnu89 to gnu99 or higher, it turned out that gcc warns about code that
shifts negative signed integers [2].
This is undefined behavior in standard C99, but defined as a GNU extension in
GCC.[3]. This warning is enabled by default at the -Wextra level for C99/GNU99
or higher, but disabled for C89/GNU89. In clang, the warning is enabled by
default at the -Wall level but in turn disabled when building with -fwrapv or
-fno-strict-overflow (as the Linux kernel does).
It would be nice if future compiler releases could either demote the warning
from being enabled at -Wextra to -Wpedantic, or follow clang and disable it
when used with -fwrapv/-fno-strict-overflow.
[1] https://lore.kernel.org/lkml/20220227010956.gw...@gate.crashing.org/
[2] https://www.godbolt.org/z/s1TzxrGz4
[3] https://gcc.gnu.org/onlinedocs/gcc-11.2.0/gcc/Integers-implementation.html
