C programmers increasingly use static to indicate that pointer parameters are non-null. Clang can exploit this for warnings and optimizations. GCC has some warnings but not all warnings it has for nonnull. Below is a patch to add a nonnull attribute automatically for such arguments and to remove the special and more limited nonnull warnings for static. This patch found some misplaced annotations in one of my projects via -Wnonnull-compare which clang does not seem to have, so I think this could be useful. Parameters declared with `static` are nonnull. We synthesize an artifical nonnull attribute for such parameters to get the same warnings and optimizations. Bootstrapped and regression tested on x86. gcc/c-family/: * c-attribs.cc (build_attr_access_from_parms): Synthesize nonnull attribute for parameters declared with `static`. gcc/: * gimple-ssa-warn-access.cc (pass_waccess::maybe_check_access_sizes): remove warning for parameters declared with `static`. gcc/testsuite/: * gcc.dg/Wnonnull-8.c: Adapt test. * gcc.dg/Wnonnull-9.c: New test. diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc index e2792ca6898..ae7ffeb1f65 100644 --- a/gcc/c-family/c-attribs.cc +++ b/gcc/c-family/c-attribs.cc @@ -5280,6 +5280,7 @@ build_attr_access_from_parms (tree parms, bool skip_voidptr) arg2pos.put (arg, argpos); } + tree nnlist = NULL_TREE; argpos = 0; for (tree arg = parms; arg; arg = TREE_CHAIN (arg), ++argpos) { @@ -5313,6 +5314,11 @@ build_attr_access_from_parms (tree parms, bool skip_voidptr) tree str = TREE_VALUE (argspec); const char *s = TREE_STRING_POINTER (str); + /* Collect the list of nonnull arguments which use "[static ..]". */ + if (s != NULL && s[0] == '[' && s[1] == 's') + nnlist = tree_cons (NULL_TREE, build_int_cst (integer_type_node, + argpos + 1), nnlist); + /* Create the attribute access string from the arg spec string, optionally followed by position of the VLA bound argument if it is one. */ @@ -5380,6 +5386,10 @@ build_attr_access_from_parms (tree parms, bool skip_voidptr) if (!spec.length ()) return NULL_TREE; + /* If we have nonnull arguments, synthesize an attribute. */ + if (nnlist != NULL_TREE) + nnlist = build_tree_list (get_identifier ("nonnull"), nnlist); + /* Attribute access takes a two or three arguments. Wrap VBLIST in another list in case it has more nodes than would otherwise fit. */ vblist = build_tree_list (NULL_TREE, vblist); @@ -5390,7 +5400,7 @@ build_attr_access_from_parms (tree parms, bool skip_voidptr) tree str = build_string (spec.length (), spec.c_str ()); tree attrargs = tree_cons (NULL_TREE, str, vblist); tree name = get_identifier ("access"); - return build_tree_list (name, attrargs); + return tree_cons (name, attrargs, nnlist); } /* Handle a "nothrow" attribute; arguments as in diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn- access.cc index ac07a6f9b95..b1cd088886c 100644 --- a/gcc/gimple-ssa-warn-access.cc +++ b/gcc/gimple-ssa-warn-access.cc @@ -3504,16 +3504,6 @@ pass_waccess::maybe_check_access_sizes (rdwr_map *rwm, tree fndecl, tree fntype, ptridx + 1, sizidx + 1, sizstr)) arg_warned = OPT_Wnonnull; } - else if (access_size && access.second.static_p) - { - /* Warn about null pointers for [static N] array arguments - but do not warn for ordinary (i.e., nonstatic) arrays. */ - if (warning_at (loc, OPT_Wnonnull, - "argument %i to %<%T[static %E]%> " - "is null where non-null expected", - ptridx + 1, argtype, access_nelts)) - arg_warned = OPT_Wnonnull; - } if (arg_warned != no_warning) { diff --git a/gcc/testsuite/gcc.dg/Wnonnull-8.c b/gcc/testsuite/gcc.dg/Wnonnull-8.c index 02871a76689..b24fd67cebc 100644 --- a/gcc/testsuite/gcc.dg/Wnonnull-8.c +++ b/gcc/testsuite/gcc.dg/Wnonnull-8.c @@ -10,5 +10,5 @@ foo (int a[static 7]) int main () { - foo ((int *) 0); /* { dg-warning "argument 1 to 'int\\\[static 7\\\]' is null where non-null expected" } */ + foo ((int *) 0); /* { dg-warning "argument 1 null where non-null expected" } */ } diff --git a/gcc/testsuite/gcc.dg/Wnonnull-9.c b/gcc/testsuite/gcc.dg/Wnonnull-9.c new file mode 100644 index 00000000000..1c57eefd2ae --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wnonnull-9.c @@ -0,0 +1,17 @@ +/* { dg-do compile } */ +/* { dg-options "-Wall" } */ + + +void +foo (int a[static 1]) +{ + if ((void*)0 == a) /* { dg-warning "argument" "compared to NULL" } */ + return; +} + +int +main () +{ + foo ((void*)0); /* { dg-warning "argument 1 null where non-null expected" } */ +} +