Hello,
this patch adds an attribute to let the compiler know that a function
never returns NULL. I saw some ECF_* flags, but the attribute seems
sufficient. I considered using nonnull(0), but then it would have been
confusing that the version of nonnull without arguments applies only to
parameters and not the return value.
2013-10-08 Marc Glisse <marc.gli...@inria.fr>
PR tree-optimization/20318
gcc/c-family/
* c-common.c (handle_returns_nonnull_attribute): New function.
(c_common_attribute_table): Add returns_nonnull.
gcc/
* doc/extend.texi (returns_nonnull): New function attribute.
* fold-const.c (tree_expr_nonzero_warnv_p): Look for returns_nonnull
attribute.
* tree-vrp.c (gimple_stmt_nonzero_warnv_p): Likewise.
(stmt_interesting_for_vrp): Accept all GIMPLE_CALL.
gcc/testsuite/
* c-c++-common/pr20318.c: New file.
* gcc.dg/tree-ssa/pr20318.c: New file.
--
Marc GlisseIndex: c-family/c-common.c
===================================================================
--- c-family/c-common.c (revision 203241)
+++ c-family/c-common.c (working copy)
@@ -364,20 +364,21 @@ static tree handle_warn_unused_result_at
bool *);
static tree handle_sentinel_attribute (tree *, tree, tree, int, bool *);
static tree handle_type_generic_attribute (tree *, tree, tree, int, bool *);
static tree handle_alloc_size_attribute (tree *, tree, tree, int, bool *);
static tree handle_target_attribute (tree *, tree, tree, int, bool *);
static tree handle_optimize_attribute (tree *, tree, tree, int, bool *);
static tree ignore_attribute (tree *, tree, tree, int, bool *);
static tree handle_no_split_stack_attribute (tree *, tree, tree, int, bool *);
static tree handle_fnspec_attribute (tree *, tree, tree, int, bool *);
static tree handle_warn_unused_attribute (tree *, tree, tree, int, bool *);
+static tree handle_returns_nonnull_attribute (tree *, tree, tree, int, bool *);
static void check_function_nonnull (tree, int, tree *);
static void check_nonnull_arg (void *, tree, unsigned HOST_WIDE_INT);
static bool nonnull_check_p (tree, unsigned HOST_WIDE_INT);
static bool get_nonnull_operand (tree, unsigned HOST_WIDE_INT *);
static int resort_field_decl_cmp (const void *, const void *);
/* Reserved words. The third field is a mask: keywords are disabled
if they match the mask.
@@ -740,20 +741,22 @@ const struct attribute_spec c_common_att
{ "*tm regparm", 0, 0, false, true, true,
ignore_attribute, false },
{ "no_split_stack", 0, 0, true, false, false,
handle_no_split_stack_attribute, false },
/* For internal use (marking of builtins and runtime functions) only.
The name contains space to prevent its usage in source code. */
{ "fn spec", 1, 1, false, true, true,
handle_fnspec_attribute, false },
{ "warn_unused", 0, 0, false, false, false,
handle_warn_unused_attribute, false },
+ { "returns_nonnull", 0, 0, false, true, true,
+ handle_returns_nonnull_attribute, false },
{ NULL, 0, 0, false, false, false, NULL, false }
};
/* Give the specifications for the format attributes, used by C and all
descendants. */
const struct attribute_spec c_common_format_attribute_table[] =
{
/* { name, min_len, max_len, decl_req, type_req, fn_type_req, handler,
affects_type_identity } */
@@ -9041,20 +9044,37 @@ handle_no_split_stack_attribute (tree *n
}
else if (DECL_INITIAL (decl))
{
error_at (DECL_SOURCE_LOCATION (decl),
"can%'t set %qE attribute after definition", name);
*no_add_attrs = true;
}
return NULL_TREE;
}
+
+/* Handle a "returns_nonnull" attribute; arguments as in
+ struct attribute_spec.handler. */
+
+static tree
+handle_returns_nonnull_attribute (tree *node, tree, tree, int,
+ bool *no_add_attrs)
+{
+ // Even without a prototype we still have a return type we can check.
+ if (TREE_CODE (TREE_TYPE (*node)) != POINTER_TYPE)
+ {
+ error ("returns_nonnull attribute on a function not returning a
pointer");
+ *no_add_attrs = true;
+ }
+ return NULL_TREE;
+}
+
/* Check for valid arguments being passed to a function with FNTYPE.
There are NARGS arguments in the array ARGARRAY. */
void
check_function_arguments (const_tree fntype, int nargs, tree *argarray)
{
/* Check for null being passed in a pointer argument that must be
non-null. We also need to do this if format checking is enabled. */
if (warn_nonnull)
Index: doc/extend.texi
===================================================================
--- doc/extend.texi (revision 203241)
+++ doc/extend.texi (working copy)
@@ -2126,21 +2126,22 @@ attributes when making a declaration. T
attribute specification inside double parentheses. The following
attributes are currently defined for functions on all targets:
@code{aligned}, @code{alloc_size}, @code{noreturn},
@code{returns_twice}, @code{noinline}, @code{noclone},
@code{always_inline}, @code{flatten}, @code{pure}, @code{const},
@code{nothrow}, @code{sentinel}, @code{format}, @code{format_arg},
@code{no_instrument_function}, @code{no_split_stack},
@code{section}, @code{constructor},
@code{destructor}, @code{used}, @code{unused}, @code{deprecated},
@code{weak}, @code{malloc}, @code{alias}, @code{ifunc},
-@code{warn_unused_result}, @code{nonnull}, @code{gnu_inline},
+@code{warn_unused_result}, @code{nonnull},
+@code{returns_nonnull}, @code{gnu_inline},
@code{externally_visible}, @code{hot}, @code{cold}, @code{artificial},
@code{no_sanitize_address}, @code{no_address_safety_analysis},
@code{no_sanitize_undefined},
@code{error} and @code{warning}.
Several other attributes are defined for functions on particular
target systems. Other attributes, including @code{section} are
supported for variables declarations (@pxref{Variable Attributes})
and for types (@pxref{Type Attributes}).
GCC plugins may provide their own attributes.
@@ -3302,20 +3303,34 @@ on the knowledge that certain function a
If no argument index list is given to the @code{nonnull} attribute,
all pointer arguments are marked as non-null. To illustrate, the
following declaration is equivalent to the previous example:
@smallexample
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull));
@end smallexample
+@item returns_nonnull (@var{arg-index}, @dots{})
+@cindex @code{returns_nonnull} function attribute
+The @code{returns_nonnull} attribute specifies that the function
+return value should be a non-null pointer. For instance, the declaration:
+
+@smallexample
+extern void *
+mymalloc (size_t len) __attribute__((returns_nonnull));
+@end smallexample
+
+@noindent
+lets the compiler optimize callers based on the knowledge
+that the return value will never be null.
+
@item noreturn
@cindex @code{noreturn} function attribute
A few standard library functions, such as @code{abort} and @code{exit},
cannot return. GCC knows this automatically. Some programs define
their own functions that never return. You can declare them
@code{noreturn} to tell the compiler this fact. For example,
@smallexample
@group
void fatal () __attribute__ ((noreturn));
Index: fold-const.c
===================================================================
--- fold-const.c (revision 203241)
+++ fold-const.c (working copy)
@@ -16222,20 +16222,24 @@ tree_expr_nonzero_warnv_p (tree t, bool
strict_overflow_p);
case CALL_EXPR:
{
tree fndecl = get_callee_fndecl (t);
if (!fndecl) return false;
if (flag_delete_null_pointer_checks && !flag_check_new
&& DECL_IS_OPERATOR_NEW (fndecl)
&& !TREE_NOTHROW (fndecl))
return true;
+ if (flag_delete_null_pointer_checks
+ && lookup_attribute ("returns_nonnull",
+ TYPE_ATTRIBUTES (TREE_TYPE (fndecl))))
+ return true;
return alloca_call_p (t);
}
default:
break;
}
return false;
}
/* Return true when T is an address and is known to be nonzero.
Index: testsuite/c-c++-common/pr20318.c
===================================================================
--- testsuite/c-c++-common/pr20318.c (revision 0)
+++ testsuite/c-c++-common/pr20318.c (working copy)
@@ -0,0 +1,3 @@
+/* { dg-do compile } */
+
+extern int f() __attribute__((returns_nonnull)); /* { dg-error "not returning
a pointer" } */
Property changes on: testsuite/c-c++-common/pr20318.c
___________________________________________________________________
Added: svn:eol-style
## -0,0 +1 ##
+native
\ No newline at end of property
Added: svn:keywords
## -0,0 +1 ##
+Author Date Id Revision URL
\ No newline at end of property
Index: testsuite/gcc.dg/tree-ssa/pr20318.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/pr20318.c (revision 0)
+++ testsuite/gcc.dg/tree-ssa/pr20318.c (working copy)
@@ -0,0 +1,19 @@
+/* { dg-do compile { target { ! keeps_null_pointer_checks } } } */
+/* { dg-options "-O2 -fdump-tree-original -fdump-tree-vrp1" } */
+
+extern int* f(int) __attribute__((returns_nonnull));
+extern void eliminate ();
+void g () {
+ if (f (2) == 0)
+ eliminate ();
+}
+void h () {
+ int *p = f (2);
+ if (p == 0)
+ eliminate ();
+}
+
+/* { dg-final { scan-tree-dump-times "== 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "Folding predicate\[^\\n\]*to 0" 1 "vrp1"
} } */
+/* { dg-final { cleanup-tree-dump "original" } } */
+/* { dg-final { cleanup-tree-dump "vrp1" } } */
Property changes on: testsuite/gcc.dg/tree-ssa/pr20318.c
___________________________________________________________________
Added: svn:keywords
## -0,0 +1 ##
+Author Date Id Revision URL
\ No newline at end of property
Added: svn:eol-style
## -0,0 +1 ##
+native
\ No newline at end of property
Index: tree-vrp.c
===================================================================
--- tree-vrp.c (revision 203241)
+++ tree-vrp.c (working copy)
@@ -1031,40 +1031,44 @@ gimple_assign_nonzero_warnv_p (gimple st
case GIMPLE_SINGLE_RHS:
return tree_single_nonzero_warnv_p (gimple_assign_rhs1 (stmt),
strict_overflow_p);
case GIMPLE_INVALID_RHS:
gcc_unreachable ();
default:
gcc_unreachable ();
}
}
-/* Return true if STMT is know to to compute a non-zero value.
+/* Return true if STMT is known to compute a non-zero value.
If the return value is based on the assumption that signed overflow is
undefined, set *STRICT_OVERFLOW_P to true; otherwise, don't change
*STRICT_OVERFLOW_P.*/
static bool
gimple_stmt_nonzero_warnv_p (gimple stmt, bool *strict_overflow_p)
{
switch (gimple_code (stmt))
{
case GIMPLE_ASSIGN:
return gimple_assign_nonzero_warnv_p (stmt, strict_overflow_p);
case GIMPLE_CALL:
{
tree fndecl = gimple_call_fndecl (stmt);
if (!fndecl) return false;
if (flag_delete_null_pointer_checks && !flag_check_new
&& DECL_IS_OPERATOR_NEW (fndecl)
&& !TREE_NOTHROW (fndecl))
return true;
+ if (flag_delete_null_pointer_checks &&
+ lookup_attribute ("returns_nonnull",
+ TYPE_ATTRIBUTES (gimple_call_fntype (stmt))))
+ return true;
return gimple_alloca_call_p (stmt);
}
default:
gcc_unreachable ();
}
}
/* Like tree_expr_nonzero_warnv_p, but this function uses value ranges
obtained so far. */
@@ -6489,24 +6493,21 @@ stmt_interesting_for_vrp (gimple stmt)
else if (is_gimple_assign (stmt) || is_gimple_call (stmt))
{
tree lhs = gimple_get_lhs (stmt);
/* In general, assignments with virtual operands are not useful
for deriving ranges, with the obvious exception of calls to
builtin functions. */
if (lhs && TREE_CODE (lhs) == SSA_NAME
&& (INTEGRAL_TYPE_P (TREE_TYPE (lhs))
|| POINTER_TYPE_P (TREE_TYPE (lhs)))
- && ((is_gimple_call (stmt)
- && gimple_call_fndecl (stmt) != NULL_TREE
- && (DECL_BUILT_IN (gimple_call_fndecl (stmt))
- || DECL_IS_OPERATOR_NEW (gimple_call_fndecl (stmt))))
+ && (is_gimple_call (stmt)
|| !gimple_vuse (stmt)))
return true;
}
else if (gimple_code (stmt) == GIMPLE_COND
|| gimple_code (stmt) == GIMPLE_SWITCH)
return true;
return false;
}
