[erlang-bugs] Use a set to store ref registers in beam_receive

[Anthony Ramine]

Hello,

In some circumstances, as when inlining code, when some optimization passes are disabled or with hand-written but semantically correct Core Erlang or BEAM assembly, a fresh reference may be live in more than one register:

        ...
        {allocate_zero,2,2}.
        ...
        {call_ext,0,{extfunc,erlang,make_ref,0}}. % Ref in [x0]
        ...
        {move,{x,0},{y,0}}. % Ref in [x0,y0]
        {move,{y,1},{x,0}}. % Ref in [y0]
        ...
        {move,{y,0},{x,0}}. % Ref in [x0,y0]
        {move,{x,0},{y,1}}. % Ref in [x0,y0,y1]
      {label,5}.
        {loop_rec,{f,6},{x,0}}. % Ref in [y0,y1]
        ...
        {loop_rec_end,{f,5}}.
      {label,6}.
        {wait,{f,5}}.
        ...

Pass beam_receive expects a single live register for the ref when it encounters the loop_rec instruction and crashes with the following reason:

    $ erlc t.S
    ...
    crash reason: {{case_clause,
                       {'EXIT',
                           {{case_clause,[{y,1},{y,0}]},
                            [{beam_receive,opt_recv,5,
                                 [{file,"beam_receive.erl"},{line,154}]},
                             ...]}}},
                   ...}

This patch teaches beam_receive how to use a set of registers instead of a single one when tracking fresh references, thus avoiding the crash.

	git fetch https://github.com/nox/otp.git fix-multiple-ref-regs

	https://github.com/nox/otp/compare/erlang:maint...fix-multiple-ref-regs
	https://github.com/nox/otp/compare/erlang:maint...fix-multiple-ref-regs.patch

This is yet again something that I encountered while working on the file optimization branch file-receive-optim:

	https://gist.github.com/nox/2e33fe9a85e035caadda#file-t-codegen

Regards,

-- 
Anthony Ramine