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Re: [PATCH] PR c++/PR48035
On Fri, Mar 11, 2011 at 09:56:59AM -0500, Jason Merrill wrote:
> On 03/11/2011 03:01 AM, Jakub Jelinek wrote:
> >Do we need to redo parts of class.c anyway? From what I understand, the
> >problematic vtbl pointers are at the end of the base types and DECL_SIZE
> >is set to the CLASSTYPE_AS_BASE type size, thus those pointers ought to
> >be at or beyond the containing field's size.
> >So, can't we simply skip subfields whose bit_position is equal or larger
> >to containing field's size? Something like (works on the testcase from this
> >PR, otherwise untested):
>
> Sure, that should work. I had been thinking of stopping when we run
> out of fields in CLASSTYPE_AS_BASE, but your approach seems simpler.
It worked, here is what I've bootstrapped/regtested on x86_64-linux and
i686-linux. Is that ok then?
> >Or, in the simplify_aggr_init case where the created tree is handed
> >immediately to the gimplifier, there is IMHO no point in initializing
> >all fields to zero when the gimplifier throws that immediately away again.
>
> Unfortunately, pointers to data members make this not good enough:
> zero-initializing one means setting the bits to -1. Though I
> suppose we could keep track of whether or not a class has a pointer
> to data member field somewhere (and therefore need to do this the
> hard way) and if not, just use an empty CONSTRUCTOR.
Np, we'd need to call a recursive function then to tell us if there
is a pointer to data member then.
2011-03-11 Jakub Jelinek <jakub@redhat.com>
PR c++/48035
* init.c (build_zero_init_1): Extracted from build_zero_init.
Add FIELD_SIZE argument, if non-NULL and field bit_position
as not smaller than that, don't add that field's initializer.
Pass DECL_SIZE as last argument to build_zero_init_1
for DECL_FIELD_IS_BASE fields.
(build_zero_init): Use build_zero_init_1.
* g++.dg/inherit/virtual8.C: New test.
--- gcc/cp/init.c.jj 2011-03-11 08:06:36.000000000 +0100
+++ gcc/cp/init.c 2011-03-11 08:40:29.321401994 +0100
@@ -140,10 +140,13 @@ initialize_vtbl_ptrs (tree addr)
is the number of elements in the array. If STATIC_STORAGE_P is
TRUE, initializers are only generated for entities for which
zero-initialization does not simply mean filling the storage with
- zero bytes. */
+ zero bytes. FIELD_SIZE, if non-NULL, is the bit size of the field,
+ subfields with bit positions at or above that bit size shouldn't
+ be added. */
-tree
-build_zero_init (tree type, tree nelts, bool static_storage_p)
+static tree
+build_zero_init_1 (tree type, tree nelts, bool static_storage_p,
+ tree field_size)
{
tree init = NULL_TREE;
@@ -188,15 +191,32 @@ build_zero_init (tree type, tree nelts,
if (TREE_CODE (field) != FIELD_DECL)
continue;
+ /* Don't add virtual bases for base classes if they are beyond
+ the size of the current field, that means it is present
+ somewhere else in the object. */
+ if (field_size)
+ {
+ tree bitpos = bit_position (field);
+ if (TREE_CODE (bitpos) == INTEGER_CST
+ && !tree_int_cst_lt (bitpos, field_size))
+ continue;
+ }
+
/* Note that for class types there will be FIELD_DECLs
corresponding to base classes as well. Thus, iterating
over TYPE_FIELDs will result in correct initialization of
all of the subobjects. */
if (!static_storage_p || !zero_init_p (TREE_TYPE (field)))
{
- tree value = build_zero_init (TREE_TYPE (field),
- /*nelts=*/NULL_TREE,
- static_storage_p);
+ tree new_field_size
+ = (DECL_FIELD_IS_BASE (field)
+ && DECL_SIZE (field)
+ && TREE_CODE (DECL_SIZE (field)) == INTEGER_CST)
+ ? DECL_SIZE (field) : NULL_TREE;
+ tree value = build_zero_init_1 (TREE_TYPE (field),
+ /*nelts=*/NULL_TREE,
+ static_storage_p,
+ new_field_size);
if (value)
CONSTRUCTOR_APPEND_ELT(v, field, value);
}
@@ -244,9 +264,9 @@ build_zero_init (tree type, tree nelts,
ce->index = build2 (RANGE_EXPR, sizetype, size_zero_node,
max_index);
- ce->value = build_zero_init (TREE_TYPE (type),
- /*nelts=*/NULL_TREE,
- static_storage_p);
+ ce->value = build_zero_init_1 (TREE_TYPE (type),
+ /*nelts=*/NULL_TREE,
+ static_storage_p, NULL_TREE);
}
/* Build a constructor to contain the initializations. */
@@ -264,6 +284,24 @@ build_zero_init (tree type, tree nelts,
return init;
}
+/* Return an expression for the zero-initialization of an object with
+ type T. This expression will either be a constant (in the case
+ that T is a scalar), or a CONSTRUCTOR (in the case that T is an
+ aggregate), or NULL (in the case that T does not require
+ initialization). In either case, the value can be used as
+ DECL_INITIAL for a decl of the indicated TYPE; it is a valid static
+ initializer. If NELTS is non-NULL, and TYPE is an ARRAY_TYPE, NELTS
+ is the number of elements in the array. If STATIC_STORAGE_P is
+ TRUE, initializers are only generated for entities for which
+ zero-initialization does not simply mean filling the storage with
+ zero bytes. */
+
+tree
+build_zero_init (tree type, tree nelts, bool static_storage_p)
+{
+ return build_zero_init_1 (type, nelts, static_storage_p, NULL_TREE);
+}
+
/* Return a suitable initializer for value-initializing an object of type
TYPE, as described in [dcl.init]. */
--- gcc/testsuite/g++.dg/inherit/virtual8.C
+++ gcc/testsuite/g++.dg/inherit/virtual8.C
@@ -0,0 +1,48 @@
+// PR c++/48035
+// { dg-do run }
+
+#include <new>
+#include <cstring>
+#include <cstdlib>
+
+struct A
+{
+ virtual void foo (void) {}
+ virtual ~A () {}
+};
+
+struct B : public A
+{
+ virtual ~B () {}
+};
+
+struct C
+{
+ virtual ~C () {}
+ int c;
+};
+
+struct D : public virtual B, public C
+{
+ virtual ~D () {}
+};
+
+struct E : public virtual D
+{
+ virtual ~E () {}
+};
+
+int
+main ()
+{
+ char *v = new char[sizeof (E) + 16];
+ memset (v, 0x55, sizeof (E) + 16);
+ E *e = new (v) E ();
+ e->~E ();
+
+ for (unsigned i = sizeof (E); i < sizeof (E) + 16; ++i)
+ if (v[i] != 0x55)
+ abort ();
+
+ delete[] v;
+}
Jakub