[Bug other/82880] New: [6/7/8 Regression] gcc --help=target --help=optimizers hangs on mips

[jcowgill+gcc at jcowgill dot uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82880

            Bug ID: 82880
           Summary: [6/7/8 Regression] gcc --help=target --help=optimizers
                    hangs on mips
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jcowgill+gcc at jcowgill dot uk
  Target Milestone: ---

Created attachment 42555
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42555&action=edit
mips workaround

From Debian: https://bugs.debian.org/880962

As the title says, running "gcc --help=target --help=optimizers" on mips
(including cross compilers targeting mips) hangs. The bug only occurs on
gcc-7-branch and not in any released version of gcc 7.

Bisected (on gcc-7-branch) to:
> 4972d77dcbe0c4186dabc67a0edb7f3f2df4e646 is the first bad commit
> commit 4972d77dcbe0c4186dabc67a0edb7f3f2df4e646
> Author: marxin <marxin@138bc75d-0d04-0410-961f-82ee72b054a4>
> Date:   Fri Sep 15 08:18:34 2017 +0000
> 
>     Subject: Backport r251400
>     
>     2017-09-15  Martin Liska  <mliska@suse.cz>
>     
>             Backport from mainline
>             2017-08-29  Martin Liska  <mliska@suse.cz>
>     
>             PR other/39851
[...]
>     git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-7-branch@252787 138bc75d-0d04-0410-961f-82ee72b054a4
> 
> :040000 040000 435ac2ed3f121183790fa89d3120400725e3c6a0 424643290a7f6c41e0abe05fb6c596113ed6e611 M	gcc

After this commit, mips_option_override is called twice (once for each --help
option). This results in a pass being registered twice
(mips_register_frame_header_opt) which causes register_pass to hang in an
infinite loop inside position_pass. The reason the same pass is registered
twice is becaise the register_pass_info struct in
mips_register_frame_header_opt is declared static and is therefore only
initialized once. Having said that, the documentation of TARGET_OPTION_OVERRIDE
seems to imply this hook should only ever be executed once, so I think the
actual bug is in the generic code which calls the hook more than once.

Hanging backtrace for reference:
> (gdb) bt
> #0  position_pass (new_pass_info=0x1cd3780 <mips_register_frame_header_opt()::f>, pass_list=0x1e4d048) at ../../gcc/gcc/passes.c:1325
> #1  0x0000000000c1385e in gcc::pass_manager::register_pass (this=0x1e4d030, pass_info=0x1cd3780 <mips_register_frame_header_opt()::f>) at ../../gcc/gcc/passes.c:1463
> #2  0x0000000000c136ea in register_pass (pass_info=0x1cd3780 <mips_register_frame_header_opt()::f>) at ../../gcc/gcc/passes.c:1418
> #3  0x00000000010b38f9 in mips_register_frame_header_opt () at ../../gcc/gcc/config/mips/frame-header-opt.c:103
> #4  0x00000000010aa8b1 in mips_option_override () at ../../gcc/gcc/config/mips/mips.c:20171
> #5  0x0000000001486ee3 in common_handle_option (opts=0x1e131e0 <global_options>, opts_set=0x1e14000 <global_options_set>, decoded=0x1e632e0, lang_mask=16, kind=0, loc=0, handlers=0x7fffffffdd70, 
>     dc=0x1e14ee0 <global_diagnostic_context>, target_option_override_hook=0x10a91ef <mips_option_override()>) at ../../gcc/gcc/opts.c:1857
> #6  0x000000000148b23c in handle_option (opts=0x1e131e0 <global_options>, opts_set=0x1e14000 <global_options_set>, decoded=0x1e632e0, lang_mask=16, kind=0, loc=0, handlers=0x7fffffffdd70, generated_p=false, 
>     dc=0x1e14ee0 <global_diagnostic_context>) at ../../gcc/gcc/opts-common.c:989
> #7  0x000000000148b990 in read_cmdline_option (opts=0x1e131e0 <global_options>, opts_set=0x1e14000 <global_options_set>, decoded=0x1e632e0, loc=0, lang_mask=16, handlers=0x7fffffffdd70, 
>     dc=0x1e14ee0 <global_diagnostic_context>) at ../../gcc/gcc/opts-common.c:1218
> #8  0x0000000000c10a91 in read_cmdline_options (opts=0x1e131e0 <global_options>, opts_set=0x1e14000 <global_options_set>, decoded_options=0x1e63240, decoded_options_count=3, loc=0, lang_mask=16, 
>     handlers=0x7fffffffdd70, dc=0x1e14ee0 <global_diagnostic_context>) at ../../gcc/gcc/opts-global.c:228
> #9  0x0000000000c10c3e in decode_options (opts=0x1e131e0 <global_options>, opts_set=0x1e14000 <global_options_set>, decoded_options=0x1e63240, decoded_options_count=3, loc=0, 
>     dc=0x1e14ee0 <global_diagnostic_context>, target_option_override_hook=0x10a91ef <mips_option_override()>) at ../../gcc/gcc/opts-global.c:309
> #10 0x0000000000d35574 in toplev::main (this=0x7fffffffde7e, argc=3, argv=0x7fffffffdf78) at ../../gcc/gcc/toplev.c:2116
> #11 0x00000000014828f3 in main (argc=3, argv=0x7fffffffdf78) at ../../gcc/gcc/main.c:39
Note the current and next passes are identical:
> (gdb) p pass
> $28 = (opt_pass *) 0x1e2a360
> (gdb) p pass->next
> $29 = (opt_pass *) 0x1e2a360
The attached patch works around this in the mips code, although as I said
above, I don't think this is the correct fix.