Re: [PATCH] lto: pass through -funwind-tables and -fasynchronous-unwind-tables

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

On Wed, Jan 18, 2023 at 11:17 AM Andreas Schwab via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> The -funwind-tables and -fasynchronous-unwind-tables options are relevant
> for the output pass, thus they need to be passed through by the lto
> wrapper.
>
> gcc/
>         * lto-wrapper.cc (merge_and_complain): Pass through
>         -funwind-tables and -fasynchronous-unwind-tables.
>         (append_compiler_options): Likewise.
> ---
>  gcc/lto-wrapper.cc | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/gcc/lto-wrapper.cc b/gcc/lto-wrapper.cc
> index 11c4d1b38a4..627e8238606 100644
> --- a/gcc/lto-wrapper.cc
> +++ b/gcc/lto-wrapper.cc
> @@ -314,6 +314,8 @@ merge_and_complain (vec<cl_decoded_option> &decoded_options,
>         case OPT_fshow_column:
>         case OPT_fcommon:
>         case OPT_fgnu_tm:
> +       case OPT_funwind_tables:
> +       case OPT_fasynchronous_unwind_tables:
>         case OPT_g:
>           /* Do what the old LTO code did - collect exactly one option
>              setting per OPT code, we pick the first we encounter.

A better place is

        case OPT_fopenmp:
        case OPT_fopenacc:
          /* For selected options we can merge conservatively.  */
          if (existing_opt == -1)
            decoded_options.safe_push (*foption);
          /* -fopenmp > -fno-openmp,
             -fopenacc > -fno-openacc  */
          else if (foption->value > decoded_options[existing_opt].value)
            decoded_options[existing_opt] = *foption;
          break;

where we'd prefer -funwind-tables over -fno-unwind-tables when the
options do not match
across TUs.  Note that you likely want to add
-f[asynchronous-]unwind-tables handling
in lto-options.cc:lto_write_options as well so the default is streamed
as explicit option.
Otherwise a single TU with -fno-unwind-tables on x86-64 would cause
the whole LTO
compilation to be built without.

> @@ -737,6 +739,8 @@ append_compiler_options (obstack *argv_obstack, vec<cl_decoded_option> opts)
>         case OPT_fopenacc_dim_:
>         case OPT_foffload_abi_:
>         case OPT_fcf_protection_:
> +       case OPT_funwind_tables:
> +       case OPT_fasynchronous_unwind_tables:
>         case OPT_g:
>         case OPT_O:
>         case OPT_Ofast:
> --
> 2.39.1
>
>
> --
> Andreas Schwab, SUSE Labs, schwab@suse.de
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."