String: Add support for __memcmpeq() ABI on all targets

No bug.

This commit adds support for __memcmpeq() as a new ABI for all
targets. In this commit __memcmpeq() is implemented only as an alias
to the corresponding targets memcmp() implementation. __memcmpeq() is
added as a new symbol starting with GLIBC_2.35 and defined in string.h
with comments explaining its behavior. Basic tests that it is callable
and works where added in string/tester.c

As discussed in the proposal "Add new ABI '__memcmpeq()' to libc"
__memcmpeq() is essentially a reserved namespace for bcmp(). The means
is shares the same specifications as memcmp() except the return value
for non-equal byte sequences is any non-zero value. This is less
strict than memcmp()'s return value specification and can be better
optimized when a boolean return is all that is needed.

__memcmpeq() is meant to only be called by compilers if they can prove
that the return value of a memcmp() call is only used for its boolean
value.

All tests in string/tester.c passed. As well build succeeds on
x86_64-linux-gnu target.

1 files changed, 1 insertions, 0 deletions

diff --git a/sysdeps/s390/memcmp.c b/sysdeps/s390/memcmp.c
index 0b4e9da717..52c20af772 100644
--- a/sysdeps/s390/memcmp.c
+++ b/sysdeps/s390/memcmp.c
@@ -46,4 +46,5 @@ s390_libc_ifunc_expr (__redirect_memcmp, memcmp,
 		      })
 		      )
 weak_alias (memcmp, bcmp);
+strong_alias (memcmp, __memcmpeq)
 #endif