[Bug target/121319] New: Why is global_options.x_flag_pcc_struct_return cleared?

[hjl.tools at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121319

            Bug ID: 121319
           Summary: Why is global_options.x_flag_pcc_struct_return
                    cleared?
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                CC: crazylht at gmail dot com, ubizjak at gmail dot com
  Target Milestone: ---
            Target: x86_64

i386 has

gnu-user-common.h:#undef DEFAULT_PCC_STRUCT_RETURN
gnu-user-common.h:#define DEFAULT_PCC_STRUCT_RETURN 1

But there are:

/* Implement TARGET_OPTION_INIT_STRUCT.  */

static void 
ix86_option_init_struct (struct gcc_options *opts)
{
  if (TARGET_MACHO)
    /* The Darwin libraries never set errno, so we might as well
       avoid calling them when that's the only reason we would.  */
    opts->x_flag_errno_math = 0; 

  opts->x_flag_pcc_struct_return = 2; 
  opts->x_flag_asynchronous_unwind_tables = 2; 
}

static void 
ix86_recompute_optlev_based_flags (struct gcc_options *opts,
                                   struct gcc_options *opts_set)
{
  /* Set the default values for switches whose default depends on TARGET_64BIT
     in case they weren't overwritten by command line options.  */
  if (TARGET_64BIT_P (opts->x_ix86_isa_flags))
    {  
      if (opts->x_optimize >= 1)
        SET_OPTION_IF_UNSET (opts, opts_set, flag_omit_frame_pointer,
                             !USE_IX86_FRAME_POINTER);
      if (opts->x_flag_asynchronous_unwind_tables
          && TARGET_64BIT_MS_ABI)
        SET_OPTION_IF_UNSET (opts, opts_set, flag_unwind_tables, 1);
      if (opts->x_flag_asynchronous_unwind_tables == 2)
        opts->x_flag_unwind_tables
          = opts->x_flag_asynchronous_unwind_tables = 1;
      if (opts->x_flag_pcc_struct_return == 2)
        opts->x_flag_pcc_struct_return = 0;
    }
  else   
    {  
      if (opts->x_optimize >= 1)
          SET_OPTION_IF_UNSET (opts, opts_set, flag_omit_frame_pointer,
                               !(USE_IX86_FRAME_POINTER ||
opts->x_optimize_size));
      if (opts->x_flag_asynchronous_unwind_tables == 2)
        opts->x_flag_asynchronous_unwind_tables = !USE_IX86_FRAME_POINTER;
      if (opts->x_flag_pcc_struct_return == 2)
        {  
          /* Intel MCU psABI specifies that -freg-struct-return should
             be on.  Instead of setting DEFAULT_PCC_STRUCT_RETURN to 0,
             we check -miamcu so that -freg-struct-return is always
             turned on if -miamcu is used.  */
          if (TARGET_IAMCU_P (opts->x_target_flags))
            opts->x_flag_pcc_struct_return = 0;
          else
            opts->x_flag_pcc_struct_return = DEFAULT_PCC_STRUCT_RETURN;
        }
    }

  /* Keep nonleaf frame pointers.  */
  if (opts->x_flag_omit_frame_pointer)
    opts->x_target_flags &= ~MASK_OMIT_LEAF_FRAME_POINTER;
  else if (TARGET_OMIT_LEAF_FRAME_POINTER_P (opts->x_target_flags))
    opts->x_flag_omit_frame_pointer = 1;
}

For x86-64, global_options.x_flag_pcc_struct_return is always 0 and
DEFAULT_PCC_STRUCT_RETURN is ignored.