Re: make FOR_EACH_IMM_USE_STMT safe for early exits (was: Re: move sincos after pre)

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Dec 22, 2020 at 11:03 PM Alexandre Oliva <oliva@adacore.com> wrote:
>
> On Oct 28, 2020, Richard Biener <richard.guenther@gmail.com> wrote:
>
> >> BTW, any reason why we are not (yet?) using something like:
> >>
> >> #define FOR_EACH_IMM_USE_STMT(STMT, ITER, SSAVAR)               \
> >> for (auto_end_imm_use_stmt_traverse auto_end                  \
> >> ((((STMT) = first_imm_use_stmt (&(ITER), (SSAVAR))),     \
> >> &(ITER)));                                             \
> >> !end_imm_use_stmt_p (&(ITER));                           \
> >> (void) ((STMT) = next_imm_use_stmt (&(ITER))))
>
> > Just laziness.  Or rather last time I remembered this I tried to do it
> > more fancy via range-for but didn't get very far due to the nested
> > iteration ...
>
> Use a dtor to automatically remove ITER from IMM_USE list in
> FOR_EACH_IMM_USE_STMT.
>
> Regstrapped on x86_64-linux-gnu.  Ok to install?

Hmm - while the change looks good, doesn't it end up
calling end_imm_use_stmt_tranverse twice for those
uses still calling BREAK_FROM_IMM_USE_STMT?

Thus, please remove uses of BREAK_FROM_IMM_USE_STMT
together with this patch.

Thanks,
Richard.

>
> for  gcc/ChangeLog
>
>         * ssa-iterators.h (end_imm_use_stmt_traverse): Forward
>         declare.
>         (auto_end_imm_use_stmt_traverse): New struct.
>         (FOR_EACH_IMM_USE_STMT): Use it.
> ---
>  gcc/ssa-iterators.h |   29 ++++++++++++++++++++++++-----
>  1 file changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/gcc/ssa-iterators.h b/gcc/ssa-iterators.h
> index 98724da14522d..817997aa952d4 100644
> --- a/gcc/ssa-iterators.h
> +++ b/gcc/ssa-iterators.h
> @@ -77,16 +77,35 @@ struct imm_use_iterator
>         !end_readonly_imm_use_p (&(ITER));                      \
>         (void) ((DEST) = next_readonly_imm_use (&(ITER))))
>
> -/* Use this iterator to visit each stmt which has a use of SSAVAR.  */
> +/* Forward declare for use in the class below.  */
> +static inline void end_imm_use_stmt_traverse (imm_use_iterator *);
> +
> +/* arrange to automatically call, upon descruction, end_imm_use_stmt_traverse
> +   with a given pointer to imm_use_iterator.  */
> +struct auto_end_imm_use_stmt_traverse
> +{
> +  imm_use_iterator *imm;
> +  auto_end_imm_use_stmt_traverse (imm_use_iterator *imm)
> +  : imm (imm) {}
> +  ~auto_end_imm_use_stmt_traverse ()
> +  { end_imm_use_stmt_traverse (imm); }
> +};
> +
> +/* Use this iterator to visit each stmt which has a use of SSAVAR.  The
> +   destructor of the auto_end_imm_use_stmt_traverse object deals with removing
> +   ITER from SSAVAR's IMM_USE list even when leaving the scope early.  */
>
>  #define FOR_EACH_IMM_USE_STMT(STMT, ITER, SSAVAR)              \
> -  for ((STMT) = first_imm_use_stmt (&(ITER), (SSAVAR));                \
> +  for (struct auto_end_imm_use_stmt_traverse                   \
> +         auto_end_imm_use_stmt_traverse                                \
> +          ((((STMT) = first_imm_use_stmt (&(ITER), (SSAVAR))), \
> +            &(ITER)));                                         \
>         !end_imm_use_stmt_p (&(ITER));                          \
>         (void) ((STMT) = next_imm_use_stmt (&(ITER))))
>
> -/* Use this to terminate the FOR_EACH_IMM_USE_STMT loop early.  Failure to
> -   do so will result in leaving a iterator marker node in the immediate
> -   use list, and nothing good will come from that.   */
> +/* These used to be needed to exit FOR_EACH_IMM_USE_STMT early, without leaving
> +   ITER behind in the stmt lists.  This is now taken care of automatically, but
> +   it doesn't hurt to use the macros for documentation purposes.  */
>  #define BREAK_FROM_IMM_USE_STMT(ITER)                          \
>     {                                                           \
>       end_imm_use_stmt_traverse (&(ITER));                      \
>
> --
> Alexandre Oliva, happy hacker  https://FSFLA.org/blogs/lxo/
>    Free Software Activist         GNU Toolchain Engineer
>         Vim, Vi, Voltei pro Emacs -- GNUlius Caesar