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[C] Synthesize nonnull attribute for parameters declared with static

Message ID cc6f18335ec6dd5d87e06e3b77fee1e55b36529f.camel@gwdg.de
State New
Headers show
Series [C] Synthesize nonnull attribute for parameters declared with static | expand

Commit Message

Martin Uecker July 26, 2023, 4:06 p.m. UTC 
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.


+
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Patch

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" } */
+}