Re: status of current_pass (notably in gates) .... [possible bug in 4.9]

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Mar 10, 2014 at 1:30 PM, Basile Starynkevitch
<basile@starynkevitch.net> wrote:
> Hello All,
>
>
> I am a bit confused (or unhappy) about the current_pass variable
> (in GCC 4.9 svn rev.208447); I believe we have some incoherency about it.
>
> It is generally (as it used to be in previous versions of GCC)
> a global pointer to some opt_pass, declared in gcc/tree-pass.h line 590.
>
> It is also (and independently), a local integer in function
> connect_traces file gcc/bb-reorder.c line 1042. I feel that
> for readability reasons the local current_pass should be renamed
> current_pass_num in the function connect_traces.
>
> But most importantly, I find confusing the way current_pass pointer is
> globally set (and reset). The obvious policy seems to set current_pass to
> "this" before calling any virtual methods on it (notably the gate and
> the exec functions).
>
> However, if one use -fdump-passes program argument to gcc (i.e. to cc1), then
> dump_passes (from gcc/passes.c line 892) gets called. It then calls function
> dump_one_pass (from gcc/passes.c line 851) which does line 857
>
>   is_on = pass->has_gate ? pass->gate () : true;
>
> But in other occasions, notably in function execute_one_pass
> (starting at gcc/passes.c line 2153) the global current_pass is
> set (line 2166) before calling its gate function line 2170
>
>   gate_status = pass->has_gate ? pass->gate () : true;
>
> I believe something should be done about this, since it seems to confuse
> plugins (like MELT). Either we decide that current_pass is always set
> before calling any virtual function on it (notably the gate) or we
> decide that current_pass global should disappear (but then, what
> about the curr_statistics_hash function from gcc/statistics.c line 93
> which uses it line 98)?
>
>
> Comments are welcome. I think we should do something about this before
> releasing GCC 4.9...
>
> The simplest thing would be to set current_pass in dump_one_pass....

current_pass is not supposed to be accessed outside of pass
management.  It may or may not vanish in future and it may or
may not be set to random values.

Do not consider it part of the plugin API (what "API" ...).  Heh,
we could start marking certain decls with local visibility...

Richard.

> Regards.
> --
> Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
> email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
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