Re: Improve optimization of some builtins

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

On Mon, Nov 8, 2021 at 8:04 AM Jan Hubicka via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
> for nested functions we output call to builtin_dwarf_cfa which
> initializes frame entry used only for debugging.  This however
> prevents us from detecting functions containing nested functions
> as const/pure or analyze side effects in modref.
>
> builtin_dwarf_cfa is not documented and I wonder if it should be turned to
> internal function. But I think we could consider functions using it const even
> if in theory one can do things like test the return address and see the
> difference between different frame addreses.
>
> While doing so I also noticed that special_buitin_state handles quite few
> builtins that are not special cased by ipa-modref.  They do not make
> user visible loads/stores and thus I think they shoul dbe annotated by
> ".c" to make this explicit for both modref and PTA.
>
> Finally I aded dwarf_cfa and similar return_address to list of simple
> bulitins since it compiles to simple stack frame load and we consider
> several other builtins doing so simple.
>
> lto-bootstrapped/regtested all languages on x86_64-linux, seems sane?

LGTM.

> Honza
>
>         * builtins.c (is_simple_builtin): Add builitin_dwarf_cfa
>         and builtin_return_address.
>         (builtin_fnspec): Annotate builtin_return,
>         bulitin_eh_pointer, builtin_eh_filter, builtin_unwind_resume,
>         builtin_cxa_end_cleanup, builtin_eh_copy_values,
>         builtin_frame_address, builtin_apply_args,
>         builtin_asan_before_dynamic_init, builtin_asan_after_dynamic_init,
>         builtin_prefetch, builtin_dwarf_cfa, builtin_return_addrss
>         as ".c"
>         * ipa-pure-const.c (special_builtin_state): Add builtin_dwarf_cfa
>         and builtin_return_address.
> diff --git a/gcc/builtins.c b/gcc/builtins.c
> index 7d0f61fc98b..43433e8d6ce 100644
> --- a/gcc/builtins.c
> +++ b/gcc/builtins.c
> @@ -10711,6 +10711,8 @@ is_simple_builtin (tree decl)
>        case BUILT_IN_VA_END:
>        case BUILT_IN_STACK_SAVE:
>        case BUILT_IN_STACK_RESTORE:
> +      case BUILT_IN_DWARF_CFA:
> +      case BUILT_IN_RETURN_ADDRESS:
>         /* Exception state returns or moves registers around.  */
>        case BUILT_IN_EH_FILTER:
>        case BUILT_IN_EH_POINTER:
> @@ -11099,6 +11099,19 @@ builtin_fnspec (tree callee)
>        CASE_BUILT_IN_TM_STORE (M256):
>         return ".cO ";
>        case BUILT_IN_STACK_SAVE:
> +      case BUILT_IN_RETURN:
> +      case BUILT_IN_EH_POINTER:
> +      case BUILT_IN_EH_FILTER:
> +      case BUILT_IN_UNWIND_RESUME:
> +      case BUILT_IN_CXA_END_CLEANUP:
> +      case BUILT_IN_EH_COPY_VALUES:
> +      case BUILT_IN_FRAME_ADDRESS:
> +      case BUILT_IN_APPLY_ARGS:
> +      case BUILT_IN_ASAN_BEFORE_DYNAMIC_INIT:
> +      case BUILT_IN_ASAN_AFTER_DYNAMIC_INIT:
> +      case BUILT_IN_PREFETCH:
> +      case BUILT_IN_DWARF_CFA:
> +      case BUILT_IN_RETURN_ADDRESS:
>         return ".c";
>        case BUILT_IN_ASSUME_ALIGNED:
>         return "1cX ";
> diff --git a/gcc/ipa-pure-const.c b/gcc/ipa-pure-const.c
> index a84a4eb7ac0..e5048092939 100644
> --- a/gcc/ipa-pure-const.c
> +++ b/gcc/ipa-pure-const.c
> @@ -529,6 +529,8 @@ special_builtin_state (enum pure_const_state_e *state, bool *looping,
>        case BUILT_IN_APPLY_ARGS:
>        case BUILT_IN_ASAN_BEFORE_DYNAMIC_INIT:
>        case BUILT_IN_ASAN_AFTER_DYNAMIC_INIT:
> +      case BUILT_IN_DWARF_CFA:
> +      case BUILT_IN_RETURN_ADDRESS:
>         *looping = false;
>         *state = IPA_CONST;
>         return true;