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Avoid clobbering primary virtual base when not in charge.

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* decl.c (build_clobber_this): Factor out of
	start_preparsed_function and begin_destructor_body.  Handle
	virtual bases better.

From-SVN: r234334
This commit is contained in:
Jason Merrill 2016-03-18 11:31:29 -04:00 committed by Jason Merrill
parent eb0dbdc723
commit bf08acdaa5
3 changed files with 44 additions and 24 deletions
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4
gcc/cp/ChangeLog
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@ -1,5 +1,9 @@
2016-03-18 Jason Merrill <jason@redhat.com>
* decl.c (build_clobber_this): Factor out of
start_preparsed_function and begin_destructor_body. Handle
virtual bases better.
* class.c (build_if_in_charge): Split out from build_base_path.
* init.c (expand_virtual_init, expand_default_init): Use it.
* call.c (build_special_member_call): Use it.

2
gcc/cp/cp-tree.h
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@ -1988,7 +1988,7 @@ struct GTY(()) lang_type {
#define CLASSTYPE_VBASECLASSES(NODE) (LANG_TYPE_CLASS_CHECK (NODE)->vbases)
/* The type corresponding to NODE when NODE is used as a base class,
i.e., NODE without virtual base classes. */
i.e., NODE without virtual base classes or tail padding. */
#define CLASSTYPE_AS_BASE(NODE) (LANG_TYPE_CLASS_CHECK (NODE)->as_base)

62
gcc/cp/decl.c
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@ -13712,6 +13712,43 @@ implicit_default_ctor_p (tree fn)
&& sufficient_parms_p (FUNCTION_FIRST_USER_PARMTYPE (fn)));
}
/* Clobber the contents of *this to let the back end know that the object
storage is dead when we enter the constructor or leave the destructor. */
static tree
build_clobber_this ()
{
/* Clobbering an empty base is pointless, and harmful if its one byte
TYPE_SIZE overlays real data. */
if (is_empty_class (current_class_type))
return void_node;
/* If we have virtual bases, clobber the whole object, but only if we're in
charge. If we don't have virtual bases, clobber the as-base type so we
don't mess with tail padding. */
bool vbases = CLASSTYPE_VBASECLASSES (current_class_type);
tree ctype = current_class_type;
if (!vbases)
ctype = CLASSTYPE_AS_BASE (ctype);
tree clobber = build_constructor (ctype, NULL);
TREE_THIS_VOLATILE (clobber) = true;
tree thisref = current_class_ref;
if (ctype != current_class_type)
{
thisref = build_nop (build_reference_type (ctype), current_class_ptr);
thisref = convert_from_reference (thisref);
}
tree exprstmt = build2 (MODIFY_EXPR, void_type_node, thisref, clobber);
if (vbases)
exprstmt = build_if_in_charge (exprstmt);
return exprstmt;
}
/* Create the FUNCTION_DECL for a function definition.
DECLSPECS and DECLARATOR are the parts of the declaration;
they describe the function's name and the type it returns,
@ -14127,17 +14164,7 @@ start_preparsed_function (tree decl1, tree attrs, int flags)
because part of the initialization might happen before we enter the
constructor, via AGGR_INIT_ZERO_FIRST (c++/68006). */
&& !implicit_default_ctor_p (decl1))
{
/* Insert a clobber to let the back end know that the object storage
is dead when we enter the constructor. */
tree btype = CLASSTYPE_AS_BASE (current_class_type);
tree clobber = build_constructor (btype, NULL);
TREE_THIS_VOLATILE (clobber) = true;
tree bref = build_nop (build_reference_type (btype), current_class_ptr);
bref = convert_from_reference (bref);
tree exprstmt = build2 (MODIFY_EXPR, btype, bref, clobber);
finish_expr_stmt (exprstmt);
}
finish_expr_stmt (build_clobber_this ());
if (!processing_template_decl
&& DECL_CONSTRUCTOR_P (decl1)
@ -14357,18 +14384,7 @@ begin_destructor_body (void)
if (flag_lifetime_dse
/* Clobbering an empty base is harmful if it overlays real data. */
&& !is_empty_class (current_class_type))
{
/* Insert a cleanup to let the back end know that the object is dead
when we exit the destructor, either normally or via exception. */
tree btype = CLASSTYPE_AS_BASE (current_class_type);
tree clobber = build_constructor (btype, NULL);
TREE_THIS_VOLATILE (clobber) = true;
tree bref = build_nop (build_reference_type (btype),
current_class_ptr);
bref = convert_from_reference (bref);
tree exprstmt = build2 (MODIFY_EXPR, btype, bref, clobber);
finish_decl_cleanup (NULL_TREE, exprstmt);
}
finish_decl_cleanup (NULL_TREE, build_clobber_this ());
/* And insert cleanups for our bases and members so that they
will be properly destroyed if we throw. */