Hi,
After some more study on __builtin_clear_padding and the corresponding testing
cases.
And also considered both Richard Biener and Richard Sandiford’s previous
suggestion to use
__builtin_clear_padding. I have the following thought on the paddings
initialization:
****** We can insert a call to __builtin_clear_padding (&decl, 0) to all the
variables that need to be
Auto-initialized during gimplification phase. This include two places:
A. If the auto-variable does not have an explicit initializer, and we need
to add a call to .DEFERRED_INIT.
We always add a call to __builtin_clear_padding following this
.DEFERRED_INIT call.
structure_type temp;
temp = .DEFERRED_INIT ();
__builtin_clear_padding (&temp, 0);
NOTE:
****** If temp has a type without paddings, then __builtin_clear_padding
will be lowered to a gimple_nop automatically.
****** regardless with zero or pattern init, the paddings will be always
initialized to ZEROes, which is compatible with CLANG.
B. If the auto-variable does HAVE an explicit initializer, then we will add
the call to __builtin_clear_padding
In the beginning of “gimplify_init_constructor”.
structure_type temp = {…..};
__builtin_clear_padding (&temp, 0);
Expand_the_constructor;
NOTE:
****** if temp has a type without padding, the call to
__builtin_clear_padding will be lowed to gimple_nop;
****** padding will be always initialized to ZEROes.
******the major benefit with this approach are:
1. Padding initialization will be compatible with CLANG;
2. Implemenation will be much more simple and consistent;
My questions:
1. What do you think of this approach?
2. During implementation, if I want to add the following routine:
/* Generate padding initialization for automatic vairable DECL.
C guarantees that brace-init with fewer initializers than members
aggregate will initialize the rest of the aggregate as-if it were
static initialization. In turn static initialization guarantees
that padding is initialized to zero. So, we always initialize paddings
to zeroes regardless INIT_TYPE.
To do the padding initialization, we insert a call to
__BUILTIN_CLEAR_PADDING (&decl, 0).
*/
static void
gimple_add_padding_init_for_auto_var (tree decl, gimple_seq *seq_p)
{
?????? how to build a addr_of_decl tree node???
tree addr_of_decl = ….
gimple *call = gimple_build_call (builtin_decl_implicit
(BUILT_IN_CLEAR_PADDING),
2, addr_of_decl, build_zero_cst (TREE_TYPE
(decl));
gimplify_seq_add_stmt (seq_p, call);
}
I need help on how to build “addr_of_decl” in the above routine.
Thanks a lot for your help.
Qing
