On Wed, Aug 03, 2011 at 02:31:17PM +0200, Jakub Jelinek wrote:
> 2011-08-03 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/49905
> * decl.c (cxx_init_decl_processing): Add alloc_size (1) attribute
> for operator new and operator new [].
Unfortunately the patch caused a bunch of regressions, apparently
attribs.c initializes itself only on the call to decl_attributes, if there
was none, the hash table wasn't initialized and type hashing would crash
when seeing a type with TYPE_ATTRIBUTES.
This version passed bootstrap/regtest on i686-linux.
As for the properties which the middle-end would like to assume or not
from the operator new/operator new[]:
1) for alloc_size it is whether the returned pointer has exactly the
requested bytes defined, i.e. can't return a buffer where only fewer bytes
are valid and it is invalid to access bytes beyond those that were requested
2) aliasing - is the returned buffer guaranteed not to alias any other
object the program may validly access?
3) side-effects - currently for malloc we assume it has no visible
side-effects other than allocating the memory (i.e. malloc internals are
treated as black box), I guess for user supplied operator new/operator
new[] we shouldn't assume it doesn't have other side-effects (thus e.g. we
shouldn't optimize it away, etc.)
Richard, any other properties we are interested in?
2011-08-03 Jakub Jelinek <ja...@redhat.com>
PR middle-end/49905
* tree.h (init_attributes): New prototype.
* attribs.c (init_attributes): No longer static.
* decl.c (cxx_init_decl_processing): Add alloc_size (1) attribute
for operator new and operator new []. Call init_attributes.
* g++.dg/ext/builtin-object-size3.C: New test.
--- gcc/tree.h.jj 2011-08-02 18:08:11.000000000 +0200
+++ gcc/tree.h 2011-08-03 18:41:07.691420159 +0200
@@ -5547,6 +5547,8 @@ extern bool must_pass_in_stack_var_size_
extern const struct attribute_spec *lookup_attribute_spec (const_tree);
+extern void init_attributes (void);
+
/* Process the attributes listed in ATTRIBUTES and install them in *NODE,
which is either a DECL (including a TYPE_DECL) or a TYPE. If a DECL,
it should be modified in place; if a TYPE, a copy should be created
--- gcc/attribs.c.jj 2011-06-22 12:32:22.000000000 +0200
+++ gcc/attribs.c 2011-08-03 17:57:43.977558394 +0200
@@ -34,8 +34,6 @@ along with GCC; see the file COPYING3.
#include "hashtab.h"
#include "plugin.h"
-static void init_attributes (void);
-
/* Table of the tables of attributes (common, language, format, machine)
searched. */
static const struct attribute_spec *attribute_tables[4];
@@ -107,12 +105,15 @@ eq_attr (const void *p, const void *q)
/* Initialize attribute tables, and make some sanity checks
if --enable-checking. */
-static void
+void
init_attributes (void)
{
size_t i;
int k;
+ if (attributes_initialized)
+ return;
+
attribute_tables[0] = lang_hooks.common_attribute_table;
attribute_tables[1] = lang_hooks.attribute_table;
attribute_tables[2] = lang_hooks.format_attribute_table;
--- gcc/cp/decl.c.jj 2011-07-22 22:00:43.970484172 +0200
+++ gcc/cp/decl.c 2011-08-03 17:59:51.130796523 +0200
@@ -3629,6 +3629,7 @@ cxx_init_decl_processing (void)
current_lang_name = lang_name_cplusplus;
{
+ tree newattrs;
tree newtype, deltype;
tree ptr_ftype_sizetype;
tree new_eh_spec;
@@ -3656,7 +3657,13 @@ cxx_init_decl_processing (void)
else
new_eh_spec = noexcept_false_spec;
- newtype = build_exception_variant (ptr_ftype_sizetype, new_eh_spec);
+ /* Ensure attribs.c is initialized. */
+ init_attributes ();
+ newattrs
+ = build_tree_list (get_identifier ("alloc_size"),
+ build_tree_list (NULL_TREE, integer_one_node));
+ newtype = cp_build_type_attribute_variant (ptr_ftype_sizetype, newattrs);
+ newtype = build_exception_variant (newtype, new_eh_spec);
deltype = build_exception_variant (void_ftype_ptr, empty_except_spec);
push_cp_library_fn (NEW_EXPR, newtype);
push_cp_library_fn (VEC_NEW_EXPR, newtype);
--- gcc/testsuite/g++.dg/ext/builtin-object-size3.C.jj 2011-08-03
16:08:07.732671633 +0200
+++ gcc/testsuite/g++.dg/ext/builtin-object-size3.C 2011-08-03
16:08:07.732671633 +0200
@@ -0,0 +1,26 @@
+// { dg-do compile }
+// { dg-options "-O2" }
+
+void baz (int *, int *);
+
+#define MEMCPY(d,s,l) __builtin___memcpy_chk (d, s, l, __builtin_object_size
(d, 0))
+
+int
+foo ()
+{
+ int *p = new int;
+ int *q = new int[4];
+ MEMCPY (p, "abcdefghijklmnopqrstuvwxyz", sizeof (int));
+ MEMCPY (q, "abcdefghijklmnopqrstuvwxyz", 4 * sizeof (int));
+ baz (p, q);
+}
+
+int
+bar ()
+{
+ int *p = new int;
+ int *q = new int[4];
+ MEMCPY (p, "abcdefghijklmnopqrstuvwxyz", sizeof (int) + 1); // {
dg-warning "will always overflow destination buffer" }
+ MEMCPY (q, "abcdefghijklmnopqrstuvwxyz", 4 * sizeof (int) + 1); // {
dg-warning "will always overflow destination buffer" }
+ baz (p, q);
+}
Jakub
