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Re: [RFC][PATCH] Extend DCE to remove unnecessary new/delete-pairs
On Wed, Nov 22, 2017 at 1:47 PM, Nathan Sidwell <nathan@acm.org> wrote:
> On 11/21/2017 06:14 AM, Dominik Inführ wrote:
>>
>> Hi,
>>
>> this patch tries to extend tree-ssa-dce.c to remove unnecessary
>> new/delete-pairs (it already does that for malloc/free). Clang does it too
>> and it seems to be allowed by
>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3664.html. I’ve
>> bootstrapped/regtested on aarch64-linux and x86_64-linux.
>
>
> nice.
>
>> --- a/gcc/tree-core.h
>> +++ b/gcc/tree-core.h
>> @@ -1787,7 +1787,9 @@ struct GTY(()) tree_function_decl {
>> unsigned has_debug_args_flag : 1;
>> unsigned tm_clone_flag : 1;
>> unsigned versioned_function : 1;
>> - /* No bits left. */
>> +
>> + unsigned operator_delete_flag : 1;
>> + /* 31 bits left. */
>> };
>
>
> that's unpleasant. We have DECL_IS_{MALLOC,OPERATOR_{NEW,DELETE}} flags,
> which are all mutually exclusive. If only there was a way to encode a
> 4-valued enumeration in fewer than 3 bits ... :) (not sure why we don't
> have DECL_IS_FREE, and as we don't, why is DECL_IS_OPERATOR_DELETE needed?
>
> (we also have DECL_IS_{CON,DE}STRUCTOR flags, which I think are also
> mutually exclusive with the above. So that's 5 or (6 if we add
> DECL_IS_FREE), that could be encoded in 3 bits.
>
> There may be even more mutually exclusive flags,
> DECL_STATIC_{CON,DE}STRUCTOR may be candiates?
Yes, there's room for cleanup (as I noted). And ok, if we don't want
to regress 32bit hosts we can put
a new flag in decl_common indeed.
So please do that.
Anything else can be done as followup and need not be done as part of
this patch. An enum for
this would work I guess.
Richard.
>
> nathan
>
> --
> Nathan Sidwell