On Wed, 10 Aug 2011, Richard Guenther wrote:
>
> Nothing in the middle-end happens conditional on
> can_trust_pointer_alignment anymore - we can always "trust" pointer
> alignment, that function and its comment is somewhat gross.
> In fact we can now track alignment properly via CCP and thus
> the hack in cfgexpand.c:expand_call_stmt should not be neccessary
> anymore.
>
> Now, looking at the use of can_trust_pointer_alignment in build_over_call
> and especially its comment:
>
> if (!can_trust_pointer_alignment ())
> {
> /* If we can't be sure about pointer alignment, a call
> to __builtin_memcpy is expanded as a call to memcpy, which
> is invalid with identical args. Otherwise it is
> expanded as a block move, which should be safe. */
> arg0 = save_expr (arg0);
> arg1 = save_expr (arg1);
> test = build2 (EQ_EXPR, boolean_type_node, arg0, arg1);
> }
>
> "Otherwise it is expanded as a block move" is certainly not true.
> Whether it is expanded as block move depends on optimization setting,
> target costs and, well, a way to do block moves (we fall back to
> memcpy after all).
>
> So the patch changes the above to if (!optimize), but I'd argue
> we can as well either remove the conditional or emit it unconditional.
> Dependent on whether we believe a memcpy implementation exists in
> the wild that asserts that src != dst.
The following patch changes us to unconditionally call memcpy, like
the backend may decide to do for the
tree_int_cst_equal (TYPE_SIZE (type), TYPE_SIZE (as_base))
MODIFY_EXPR case.
Bootstrapped and tested on x86_64-unknown-linux-gnu.
Ok?
Thanks,
Richard.
2011-08-10 Richard Guenther <rguent...@suse.de>
* tree.h (can_trust_pointer_alignment): Remove.
* builtins.c (can_trust_pointer_alignment): Remove.
cp/
* call.c (build_over_call): Call memcpy unconditionally.
Index: trunk/gcc/builtins.c
===================================================================
*** trunk.orig/gcc/builtins.c 2011-08-10 14:25:04.000000000 +0200
--- trunk/gcc/builtins.c 2011-08-10 14:25:53.000000000 +0200
*************** get_object_alignment (tree exp)
*** 453,468 ****
return align;
}
- /* Returns true iff we can trust that alignment information has been
- calculated properly. */
-
- bool
- can_trust_pointer_alignment (void)
- {
- /* We rely on TER to compute accurate alignment information. */
- return (optimize && flag_tree_ter);
- }
-
/* Return the alignment in bits of EXP, a pointer valued expression.
The alignment returned is, by default, the alignment of the thing that
EXP points to. If it is not a POINTER_TYPE, 0 is returned.
--- 453,458 ----
Index: trunk/gcc/cp/call.c
===================================================================
*** trunk.orig/gcc/cp/call.c 2011-08-10 14:19:23.000000000 +0200
--- trunk/gcc/cp/call.c 2011-08-10 14:26:58.000000000 +0200
*************** build_over_call (struct z_candidate *can
*** 6767,6799 ****
else
{
/* We must only copy the non-tail padding parts.
! Use __builtin_memcpy for the bitwise copy.
! FIXME fix 22488 so we can go back to using MODIFY_EXPR
! instead of an explicit call to memcpy. */
!
tree arg0, arg1, arg2, t;
- tree test = NULL_TREE;
arg2 = TYPE_SIZE_UNIT (as_base);
arg1 = arg;
arg0 = cp_build_addr_expr (to, complain);
- if (!can_trust_pointer_alignment ())
- {
- /* If we can't be sure about pointer alignment, a call
- to __builtin_memcpy is expanded as a call to memcpy, which
- is invalid with identical args. Otherwise it is
- expanded as a block move, which should be safe. */
- arg0 = save_expr (arg0);
- arg1 = save_expr (arg1);
- test = build2 (EQ_EXPR, boolean_type_node, arg0, arg1);
- }
t = implicit_built_in_decls[BUILT_IN_MEMCPY];
t = build_call_n (t, 3, arg0, arg1, arg2);
t = convert (TREE_TYPE (arg0), t);
- if (test)
- t = build3 (COND_EXPR, TREE_TYPE (t), test, arg0, t);
val = cp_build_indirect_ref (t, RO_NULL, complain);
TREE_NO_WARNING (val) = 1;
}
--- 6767,6783 ----
else
{
/* We must only copy the non-tail padding parts.
! Use __builtin_memcpy for the bitwise copy. */
tree arg0, arg1, arg2, t;
arg2 = TYPE_SIZE_UNIT (as_base);
arg1 = arg;
arg0 = cp_build_addr_expr (to, complain);
t = implicit_built_in_decls[BUILT_IN_MEMCPY];
t = build_call_n (t, 3, arg0, arg1, arg2);
t = convert (TREE_TYPE (arg0), t);
val = cp_build_indirect_ref (t, RO_NULL, complain);
TREE_NO_WARNING (val) = 1;
}
Index: trunk/gcc/tree.h
===================================================================
*** trunk.orig/gcc/tree.h 2011-08-10 14:25:04.000000000 +0200
--- trunk/gcc/tree.h 2011-08-10 14:25:37.000000000 +0200
*************** extern tree build_va_arg_indirect_ref (t
*** 5358,5364 ****
extern tree build_string_literal (int, const char *);
extern bool validate_arglist (const_tree, ...);
extern rtx builtin_memset_read_str (void *, HOST_WIDE_INT, enum machine_mode);
- extern bool can_trust_pointer_alignment (void);
extern bool is_builtin_name (const char *);
extern bool is_builtin_fn (tree);
extern unsigned int get_object_alignment_1 (tree, unsigned HOST_WIDE_INT *);
--- 5358,5363 ----
