> On Nov 24, 2020, at 1:32 AM, Richard Biener <richard.guent...@gmail.com>
> wrote:
>
> On Tue, Nov 24, 2020 at 12:05 AM Qing Zhao via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Hi,
>>
>> Does gcc provide an iterator to traverse all the local variables that are
>> declared in the current routine?
>>
>> If not, what’s the best way to traverse the local variables?
>
> Depends on what for. There's the source level view you get by walking
> BLOCK_VARS of the
> scope tree, theres cfun->local_variables (FOR_EACH_LOCAL_DECL) and
> there's SSA names
> (FOR_EACH_SSA_NAME).
I am planing to add a new phase immediately after
“pass_late_warn_uninitialized” to initialize all auto-variables that are
not explicitly initialized in the declaration, the basic idea is following:
** The proposal:
A. add a new GCC option: (same name and meaning as CLANG)
-ftrivial-auto-var-init=[pattern|zero], similar pattern init as CLANG;
B. add a new attribute for variable:
__attribute((uninitialized)
the marked variable is uninitialized intentionaly for performance purpose.
C. The implementation needs to keep the current static warning on uninitialized
variables untouched in order to avoid "forking the language".
** The implementation:
There are two major requirements for the implementation:
1. all auto-variables that do not have an explicit initializer should be
initialized to
zero by this option. (Same behavior as CLANG)
2. keep the current static warning on uninitialized variables untouched.
In order to satisfy 1, we should check whether an auto-variable has initializer
or not;
In order to satisfy 2, we should add this new transformation after
"pass_late_warn_uninitialized".
So, we should be able to check whether an auto-variable has initializer or not
after “pass_late_warn_uninitialized”,
If Not, then insert an initialization for it.
For this purpose, I guess that “FOR_EACH_LOCAL_DECL” might be better?
Another issue is, in order to check whether an auto-variable has initializer, I
plan to add a new bit in “decl_common” as:
/* In a VAR_DECL, this is DECL_IS_INITIALIZED. */
unsigned decl_is_initialized :1;
/* IN VAR_DECL, set when the decl is initialized at the declaration. */
#define DECL_IS_INITIALIZED(NODE) \
(DECL_COMMON_CHECK (NODE)->decl_common.decl_is_initialized)
set this bit when setting DECL_INITIAL for the variables in FE. then keep it
even though DECL_INITIAL might be NULLed.
Do you have any comment and suggestions?
Thanks a lot for the help.
Qing
> Richard.
>
>>
>> Thanks.
>>
>> Qing
