Use nonnull_if_nonzero attribute rather than nonnull on various builtins [PR117023]

Use nonnull_if_nonzero attribute rather than nonnull on various builtins [PR117023]

On top of the
https://gcc.gnu.org/pipermail/gcc-patches/2024-November/668554.html
https://gcc.gnu.org/pipermail/gcc-patches/2024-November/668699.html
https://gcc.gnu.org/pipermail/gcc-patches/2024-November/668700.html
patches the following patch adds nonnull_if_nonzero attribute(s) to
various builtins instead of or in addition to nonnull attribute.

The patch adjusts builtins (when we have them) corresponding to the APIs
mentioned in the C2Y N3322 paper:
1) strndup and memset get one nonnull_if_nonzero attribute instead of
   nonnull
2) memcpy, memmove, strncpy, memcmp, strncmp get two nonnull_if_nonzero
   attributes instead of nonnull
3) strncat has nonnull without argument changed to nonnull (1) and
   gets one nonnull_if_nonzero for the src argument (maybe it needs
   to be clarified in C2Y, but I really think first argument to strncat
   and wcsncat shouldn't be NULL even for n == 0, because NULL doesn't
   point to NULL terminated string and one can't append anything to it;
   and various implementations in the wild including glibc will crash
   with NULL first argument (x86_64 avx+ doesn't though)

Such changes are done also to the _chk suffixed counterparts of the
builtins.

Furthermore I've changed a couple of builtins for POSIX functions which
aren't covered by ISO C, but I'd expect if/when POSIX incorporates C2Y
it would do the same changes.  In particular

4) strnlen gets one nonnull_if_nonzero instead of nonnull
5) mempcpy and stpncpy get two nonnull_if_nonzero instead of nonnull
   and lose returns_nonnull attribute; this is kind of unfortunate
   but I think in the spirit of N3322 mempcpy (NULL, src, 0) should
   return NULL (i.e. dest + n aka NULL + 0, now valid) and it is hard to
   express returns non-NULL if first argument is non-NULL or third argument
   is non-zero

I'm not really sure about fread/fwrite, N3322 doesn't mention those,
can the first argument be NULL if third argument is 0?  What about
if second argument is 0?  Can the fourth argument be NULL in such cases?

And of course, when not using builtins the glibc headers will affect stuff
too, so we'll need to wait for N3322 implementation there too (possibly
by dropping the nonnull attributes and perhaps conditionally replacing them
with this new one if the compiler supports them).

2025-02-24  Jakub Jelinek  <jakub@redhat.com>

	PR c/117023
gcc/
	* builtin-attrs.def (ATTR_NONNULL_IF_NONZERO): New DEF_ATTR_IDENT.
	(ATTR_NOTHROW_NONNULL_IF12_LEAF, ATTR_NOTHROW_NONNULL_IF13_LEAF,
	ATTR_NOTHROW_NONNULL_IF123_LEAF, ATTR_NOTHROW_NONNULL_IF23_LEAF,
	ATTR_NOTHROW_NONNULL_1_IF23_LEAF, ATTR_PURE_NOTHROW_NONNULL_IF12_LEAF,
	ATTR_PURE_NOTHROW_NONNULL_IF13_LEAF,
	ATTR_PURE_NOTHROW_NONNULL_IF123_LEAF,
	ATTR_WARN_UNUSED_RESULT_NOTHROW_NONNULL_IF12_LEAF,
	ATTR_MALLOC_WARN_UNUSED_RESULT_NOTHROW_NONNULL_IF12_LEAF): New
	DEF_ATTR_TREE_LIST.
	* builtins.def (BUILT_IN_STRNDUP): Use
	ATTR_MALLOC_WARN_UNUSED_RESULT_NOTHROW_NONNULL_IF12_LEAF instead of
	ATTR_MALLOC_WARN_UNUSED_RESULT_NOTHROW_NONNULL_LEAF.
	(BUILT_IN_STRNCAT, BUILT_IN_STRNCAT_CHK): Use
	ATTR_NOTHROW_NONNULL_1_IF23_LEAF instead of ATTR_NOTHROW_NONNULL_LEAF.
	(BUILT_IN_BCOPY, BUILT_IN_MEMCPY, BUILT_IN_MEMCPY_CHK,
	BUILT_IN_MEMMOVE, BUILT_IN_MEMMOVE_CHK,  BUILT_IN_STRNCPY,
	BUILT_IN_STRNCPY_CHK): Use ATTR_NOTHROW_NONNULL_IF123_LEAF instead of
	ATTR_NOTHROW_NONNULL_LEAF.
	(BUILT_IN_MEMPCPY, BUILT_IN_MEMPCPY_CHK, BUILT_IN_STPNCPY,
	BUILT_IN_STPNCPY_CHK): Use ATTR_NOTHROW_NONNULL_IF123_LEAF instead of
	ATTR_RETNONNULL_NOTHROW_LEAF.
	(BUILT_IN_BZERO, BUILT_IN_MEMSET, BUILT_IN_MEMSET_CHK): Use
	ATTR_NOTHROW_NONNULL_IF13_LEAF instead of ATTR_NOTHROW_NONNULL_LEAF.
	(BUILT_IN_BCMP, BUILT_IN_MEMCMP, BUILT_IN_STRNCASECMP,
	BUILT_IN_STRNCMP): Use ATTR_PURE_NOTHROW_NONNULL_IF123_LEAF instead of
	ATTR_PURE_NOTHROW_NONNULL_LEAF.
	(BUILT_IN_STRNLEN): Use ATTR_PURE_NOTHROW_NONNULL_IF12_LEAF instead of
	ATTR_PURE_NOTHROW_NONNULL_LEAF.
	(BUILT_IN_MEMCHR): Use ATTR_PURE_NOTHROW_NONNULL_IF13_LEAF instead of
	ATTR_PURE_NOTHROW_NONNULL_LEAF.
gcc/testsuite/
	* gcc.dg/builtins-nonnull.c (test_memfuncs, test_memfuncs_chk,
	test_strfuncs, test_strfuncs_chk): Add if (n == 0) return; at the
	start of the functions.
	* gcc.dg/Wnonnull-2.c: Copy __builtin_* call statements where
	appropriate 3 times, once with 0 length, once with n and once with
	non-zero constant and expect warning only in the third case.
	Formatting fixes.
	* gcc.dg/Wnonnull-3.c: Copy __builtin_* call statements where
	appropriate 3 times, once with 0 length, once with n and once with
	n guarded with n != 0 and expect warning only in the third case.
	Formatting fixes.
	* gcc.dg/nonnull-3.c (foo): Use 16 instead of 0 in the calls added
	for PR80936.
	* gcc.dg/nonnull-11.c: New test.
	* c-c++-common/ubsan/nonnull-1.c: Don't expect runtime diagnostics
	for the __builtin_memcpy call.
	* gcc.dg/tree-ssa/pr78154.c (f): Add dn argument and return early
	if it is NULL.  Duplicate cases of builtins which have the first
	argument changed from nonnull to nonnull_if_nonzero except stpncpy,
	once with dn as first argument instead of d and once with constant
	non-zero count rather than n.  Disable the stpncpy non-null check.
	* gcc.dg/Wbuiltin-declaration-mismatch-14.c (test_builtin_calls):
	Triplicate the strncmp calls, once with 1 last argument and expect
	warning, once with n last argument and don't expect warning and
	once with 0 last argument and don't expect warning.
	* gcc.dg/Wbuiltin-declaration-mismatch-15.c (test_builtin_calls_fe):
	Likewise.