Extend nonnull_if_nonzero attribute [PR120520]

Extend nonnull_if_nonzero attribute [PR120520]

C2Y voted in the
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3466.pdf
paper, which clarifies some of the conditional nonnull cases.
For strncat/__strncat_chk no changes are necessary, we already
use __attribute__((nonnull (1), nonnull_if_nonzero (2, 3))) attributes
on the builtin and glibc can do the same too, meaning that first
argument must be nonnull always and second must be nonnull if
the third one is nonzero.

The problem is with the fread/fwrite changes, where the paper adds:
 If size or nmemb is zero,
+ptr may be a null pointer,
 fread returns zero and the contents of the array and the state of
 the stream remain unchanged.
and ditto for fwrite, so the two argument nonnull_if_nonzero attribute
isn't usable to express that, because whether the pointer can be null
depends on 2 integral arguments rather than one.

The following patch extends the nonnull_if_nonzero attribute, so that
instead of requiring 2 arguments it allows 2 or 3, the first one
is still the pointer argument index which sometimes must not be null
and the other one or two are integral arguments, if there are 2, the
invalid case is only if pointer is null and both the integral arguments
are nonzero.

2025-06-30  Jakub Jelinek  <jakub@redhat.com>

	PR c/120520
	PR c/117023
gcc/
	* builtin-attrs.def (DEF_LIST_INT_INT_INT): Define it and
	use for 1,2,3.
	(ATTR_NONNULL_IF123_LIST): New DEF_ATTR_TREE_LIST.
	(ATTR_NONNULL_4_IF123_LIST): Likewise.
	* builtins.def (BUILT_IN_FWRITE): Use ATTR_NONNULL_4_IF123_LIST
	instead of ATTR_NONNULL_LIST.
	(BUILT_IN_FWRITE_UNLOCKED): Likewise.
	* gimple.h (infer_nonnull_range_by_attribute): Add another optional
	tree * argument defaulted to NULL.
	* gimple.cc (infer_nonnull_range_by_attribute): Add OP3 argument,
	handle 3 argument nonnull_if_nonzero attribute.
	* builtins.cc (validate_arglist): Handle 3 argument nonnull_if_nonzero
	attribute.
	* tree-ssa-ccp.cc (pass_post_ipa_warn::execute): Likewise.
	* ubsan.cc (instrument_nonnull_arg): Adjust
	infer_nonnull_range_by_attribute caller, handle 3 argument
	nonnull_if_nonzero attribute.
	* gimple-range-infer.cc (gimple_infer_range::gimple_infer_range):
	Handle 3 argument nonnull_if_nonzero attribute.
	* doc/extend.texi (nonnull_if_nonzero): Document 3 argument version
	of the attribute.
gcc/c-family/
	* c-attribs.cc (c_common_gnu_attributes): Allow 2 or 3 arguments for
	nonnull_if_nonzero attribute instead of only 2.
	(handle_nonnull_if_nonzero_attribute): Handle 3 argument
	nonnull_if_nonzero.
	* c-common.cc (struct nonnull_arg_ctx): Rename other member to other1,
	add other2 member.
	(check_function_nonnull): Clear a if nonnull attribute has an
	argument.  Adjust for nonnull_arg_ctx changes.  Handle 3 argument
	nonnull_if_nonzero attribute.
	(check_nonnull_arg): Adjust for nonnull_arg_ctx changes, emit different
	diagnostics for 3 argument nonnull_if_nonzero attributes.
	(check_function_arguments): Adjust ctx var initialization.
gcc/analyzer/
	* sm-malloc.cc (malloc_state_machine::on_stmt): Handle 3 argument
	nonnull_if_nonzero attribute.
gcc/testsuite/
	* gcc.dg/nonnull-9.c: Tweak for 3 argument nonnull_if_nonzero
	attribute support, add further tests.
	* gcc.dg/nonnull-12.c: New test.
	* gcc.dg/nonnull-13.c: New test.
	* gcc.dg/nonnull-14.c: New test.
	* c-c++-common/ubsan/nonnull-8.c: New test.
	* c-c++-common/ubsan/nonnull-9.c: New test.